Kjetil Magne Dørheim Hals

Professor Department of Engineering Sciences

Email: kjetil.hals@uia.no
Phone: +47 37 23 31 06
Mobile phone: +47 97 09 57 84
Office: C5100 (Jon Lilletuns vei 9, 4879 Grimstad, Norway)

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Background and experience

Professor of Physics | Theoretical Quantum Spintronics and Quantum Materials

Research-group leader · Principal investigator · Quantum transport · Hybrid quantum materials · Scientific computing

I am a theoretical and computational condensed-matter physicist working at the interface of quantum materials, spintronics, and quantum technology. My research combines analytical theory and numerical modelling of quantum transport and spin dynamics, with particular emphasis on antiferromagnetic and altermagnetic materials, superconducting spintronics, and hybrid superconductor–magnet platforms for topological quantum computation. I lead the Physics and Applied Mathematics research group at UiA and am principal investigator of two Research Council of Norway projects with total funding of NOK 20 million.

Research highlights:

Research leadership: Principal investigator of FRIPRO and Young Research Talents projects, total funding NOK 20 million.
Scientific impact: two Nature Nanotechnology articles and eight Physical Review Letters articles; one Physical Review Letters cover.
Innovation: co-inventor of a patent family in topological quantum computation.
Supervision: five completed or current main-supervised PhD projects.

Academic and Research Positions:

2018 – present: Professor at University of Agder, Norway.
2017 – 2018: Associate Professor at Western Norway University of Applied Sciences, Norway.
2017: Postdoctoral researcher at Johannes Gutenberg Universität Mainz, Germany.
2014 – 2016: Niels Bohr Postdoctoral Fellow at the Niels Bohr International Academy, Denmark.
2013 – 2013: Postdoctoral Fellow at NTNU, Trondheim, Norway.
2011 – 2012: Researcher at Christian Michelsen Research, Bergen, Norway.

Education:

2011: NTNU, Ph.D. in theoretical physics. Supervisor: Prof. Arne Brataas.
2007: NTNU, Master of Science in physics (Siv.ing Teknisk Fysikk).

Awards & Fellowships:

Sørlandet Kompetansefonds Reseach Award 2024, Agder Academy of Sciences and Letters.
2019-2023: Young Research Talent Grant, The Research Council of Norway.
2014-2016: Niels Bohr Postdoctoral Prize Fellowship, Niels Bohr International Academy, Denmark.
2013-2014: Postdoctoral Fellowship in Material Science, Department of Physics, Norwegian University of Science and Technology (NTNU), Norway.
2012: ExxonMobil Researcher Prize for the best Ph. D. at NTNU within basic research.
2012: Prize for Best Ph.D. degree at the Faculty of Natural Science and Technology, NTNU.

Areas of responsibility

Projects:

2023-2028: The Research Council of Norway, The FriPro program, 12 000 000 NOK, Grant No. 334202 ”Ultra-Efficient Energy Harvesting with Antiferromagnetic Thermoelectrics”. Role: Principal Investigator. See the Project Webpage for details.
2019-2023: The Research Council of Norway, Young Research Talents Grant, 8 000 000 NOK, Grant No. 286889 ”Antiferromagnetic Spinmechatronics”. Role: Principal Investigator.

Research group:

Former members: Feodor S. Konomaev (PhD); Mike Alexander Lund (PhD); Akshaykumar Salimath (Post. Doc.); Jonas Nothhelfer (Ph.D., co-supervisor), TWIST group, Johannes Gutenberg Universität Mainz, Germany.

Teaching

FYS 701-G Mathematical Approximation Techniques in Physics and Engineering Sciences, part 1

FYS 701-G Mathematical Approximation Techniques in Physics and Engineering Sciences, part 2

ENE 113 Thermodynamics

Research

Research Interests

Quantum Spintronics in Noncollinear Magnets: I study spin transport and dynamics in antiferromagnets and altermagnets, with emphasis on chirality, topology, spin caloritronics, magnonics, spin pumping, and terahertz-frequency phenomena.
Superconductor–Magnet Hybrid Quantum Materials: I develop theories of how superconducting condensates couple to magnetic order through spin-triplet correlations, magnetoelectric interactions, magnetic textures, and hybrid collective modes, with the aim of enabling low-dissipation quantum spin transport and dynamics.
Topological Quantum Technology: I investigate composite topological excitations in superconductor–magnet heterostructures, including skyrmion–vortex pairs and their use for controlling and braiding Majorana bound states. This work underpins a granted patent family and numerical modelling of topological quantum-computing operations.

Selected publications

Chiara Ciccarelli, Kjetil M. D. Hals, Andrew Irvine, Vit Novak, Yaroslav Tserkovnyak,Hidekazu Kurebayashi, Arne Brataas, and Andrew Ferguson, ”Magnonic charge pumping via spin-orbit coupling”, Nature Nanotechnology 10, 50 (2015).
Arne Brataas and Kjetil M. D. Hals, “Spin-orbit torques in action”, Nature Nanotechnology 9, 86 (2014).
Kjetil M. D. Hals, Yaroslav Tserkovnyak and Arne Brataas, ”Phenomenology of current-induced dynamics in antiferromagnets”, Physical Review Letters 106, 107206 (2011).
Kjetil M. D. Hals, Michael Schecter and Mark S. Rudner, “Composite topological excitations in ferromagnet-superconductor heterostructures”, Physical Review Letters 117, 017001 (2016).
Kjetil M. D. Hals and Karin Everschor-Sitte, ”New Boundary-Driven Twist States in Systems with Broken Spatial Inversion Symmetry ”, Physical Review Letters 119, 127203 (2017).
Davi R. Rodrigues, Akshaykumar Salimath, Karin Everschor-Sitte, and Kjetil M. D. Hals, "Spin-Wave Driven Bidirectional Domain Wall Motion in Kagome Antiferromagnets", Physical Review Letters 127, 157203 (2021).
Mike A. Lund and Kjetil M. D. Hals, Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets, Physical Review Letters 131, 156704 (2023).

PATENTS:
Granted patent in the field of topological quantum computation (2020): “Method and device for providing anyons, use of the device”, J. Nothhelfer, K. M. D. Hals, K. Everschor-Sitte, and M. Rizzi – European Patent Application EP3751472A1/ International Patent Application WO2020EP66120 / JP2022536714A / US20220261678A1 / CN114008639A.

For a complete overview of the research, please visit the Google Scholar page:

https://scholar.google.com/citations?user=-IK94JYAAAAJ&hl=en

Projects

Ultra-efficient energy harvesting with antiferromagnetic thermoelectrics

Research groups

Physics and applied mathematics

Konomaev, Feodor Svetlanov; Tharmalingam, Mithuss & Hals, Kjetil M. D. (2026). Spin-Seebeck signatures of spin chirality in kagome antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 113(1). doi: 10.1103/g31w-32n6. Full text in Research Archive Show summary
Noncollinear antiferromagnets (NCAFMs) are appealing for antiferromagnetic spintronics, as they combine the advantages of collinear antiferromagnets with novel emergent phenomena stemming from their complex spin structures. These phenomena are often associated with the intrinsic spin chirality, which characterizes the handedness of the ground-state spin configuration. Here, we investigate a kagome NCAFM interfaced with a normal metal and demonstrate that the ground-state vector spin chirality can be probed through measurements of the spin Seebeck effect (SSE). Starting from a microscopic spin Hamiltonian, we derive the corresponding bosonic Bogoliubov–de Gennes Hamiltonians for the two chiral configurations. Using linear response theory, we obtain a general expression for the spin current thermally pumped into the normal metal by the SSE. We show that a sizable in-plane spin current emerges exclusively in the negative-chiral state, providing a direct signature for real-time detection of chirality switching in kagome NCAFMs. In addition, we find a field-dependent out-of-plane spin current whose magnitude differs between the two chiralities by about 81%, reflecting their distinct magnon band structures.
Tharmalingam, Mithuss; Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Strain-induced manipulation of noncollinear antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 112(10). doi: 10.1103/62np-6zjt. Full text in Research Archive Show summary
In recent years, there has been growing interest in harnessing noncollinear antiferromagnets (NCAFMs) for applications in antiferromagnetic spintronics. A key requirement for their practical use is the ability to control the spin order in a reliable and tunable manner. In this work, we investigate how the spin order in kagome antiferromagnets—an important class of NCAFMs—can be manipulated via strain. Starting from a microscopic spin Hamiltonian, we derive an effective action for the kagome antiferromagnet that captures the coupling between the spin order and the system's strain tensor. At the microscopic level, this coupling arises from strain-induced modifications of the Dzyaloshinskii-Moriya and exchange interactions. Using this effective description, we explore two strain-driven phenomena: (1) strain-induced switching of the antiferromagnetic spin order and (2) the piezomagnetic response. We numerically show that strain facilitates thermally assisted switching between spin configurations of opposite chirality. Specifically, we find that uniform tensile and compressive strain govern both the average switching time and the preferred switching direction between chiral states. Furthermore, we demonstrate that strain induces a net magnetization and provide an experimentally testable prediction of this effect for a typical NCAFM. Our results provide a theoretical framework for modeling strain-induced manipulation of kagome antiferromagnets, underscoring strain as a promising route for functional control of NCAFMs.
Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Amplifying the antiferromagnetic spin Seebeck effect through topological magnons. Physical review B (PRB). ISSN 2469-9950. 111(2). doi: 10.1103/PhysRevB.111.024403. Full text in Research Archive Show summary
Topological magnons emerge as topologically protected spin wave states at the edges of magnets. Here, we theoretically explore how these surface states can be harnessed to amplify the spin Seebeck effect (SSE) in antiferromagnets (AFMs) interfaced with normal metals (NMs). Based on a microscopic model of a kagome AFM, we demonstrate that broken mirror symmetry, combined with the Dzyaloshinskii-Moriya interaction (DMI), drives the system into a topological phase hosting spin-polarized magnons at the boundaries. Notably, linear response calculations reveal that in AFM/NM heterostructures the topological magnons exhibit strong coupling to the metal's charge carriers, resulting in a substantial enhancement of the SSE. The relative contribution of the topological magnons is found to be 4–5 times greater than that of the trivial magnon bands. Moreover, our results show that this enhancement is highly sensitive to the strength of the DMI.
Díaz, Sebastián A.; Nothhelfer, Jonas; Hals, Kjetil Magne Dørheim & Everschor-Sitte, Karin (2024). Manipulating vortices with domain walls in superconductor-ferromagnet heterostructures. Physical review B (PRB). ISSN 2469-9950. 109(20). doi: 10.1103/PhysRevB.109.L201110. Full text in Research Archive Show summary
Vortices are pointlike topological defects in superconductors whose motion dictates superconducting properties and controls device performance. In superconductor-ferromagnet heterostructures, vortices interact with topological defects in the ferromagnet such as linelike domain walls. While in previous heterostructure generations, vortex-domain wall interactions were mediated by stray fields; in new heterostructure families, more important become exchange fields and spin-orbit coupling. However, spin-orbit coupling's role in vortex-domain wall interactions remains unexplored. Here we uncover, via numerical simulations and Ginzburg-Landau theory, that Rashba spin-orbit coupling induces magnetoelectric interactions between vortices and domain walls that crucially depend on the wall's winding direction—its helicity. The wall's helicity controls whether vortices are pushed or dragged by Néel walls, and their gliding direction along Bloch walls. Our work capitalizes on interactions between topological defects from different order parameters and of different dimensionality to engineer enhanced functionality.
Lund, Mike Alexander; Rodrigues, Davi R.; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2023). Voltage-Controlled High-Bandwidth Terahertz Oscillators Based on Antiferromagnets. Physical Review Letters. ISSN 0031-9007. 131(15). doi: 10.1103/PhysRevLett.131.156704. Full text in Research Archive Show summary
Producing compact voltage-controlled frequency generators and sensors operating in the terahertz (THz) regime represents a major technological challenge. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome structure host gapless self-oscillations whose frequencies are tunable from 0 Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The auto-oscillations' initiation, bandwidth, and amplitude are investigated by deriving an effective theory, which captures the reactive and dissipative SOTs. We find that the dynamics strongly depends on the ground state's chirality, with one chirality having gapped excitations, whereas the opposite chirality provides gapless self-oscillations. Our results reveal that NCAFMs offer unique THz functional components, which could play a significant role in filling the THz technology gap.
Rodrigues, Davi R.; Salimath, Akshaykumar; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2022). Dzyaloshinskii-Moriya induced spin-transfer torques in kagome antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 105(17). doi: 10.1103/PhysRevB.105.174401. Full text in Research Archive Show summary
In recent years antiferromagnets (AFMs) have become very promising for nanoscale spintronic applications due to their unique properties, such as THz dynamics and the absence of stray fields. Manipulating antiferromagnetic textures is currently, however, limited to very few exceptional material symmetry classes allowing for staggered torques on the magnetic sublattices. In this work, we predict for kagome AFMs with broken mirror symmetry a new coupling mechanism between antiferromagnetic domain walls (DWs) and spin currents, produced by the relativistic Dzyaloshinskii-Moriya interaction (DMI). We microscopically derive the DMI's free-energy contribution for the kagome AFMs. Unlike ferromagnets and collinear AFMs, the DMI does not lead to terms linear in the spatial derivatives, but instead renormalizes the spin-wave stiffness and anisotropy energies. Importantly, we show that the DMI induces a highly nontrivial, twisted DW profile that is controllable via two linearly independent components of the spin accumulation. This texture manipulation mechanism goes beyond the concept of staggered torques and implies a higher degree of tunability for the current-driven DW motion compared to conventional ferromagnets and collinear AFMs.
Nothhelfer, Jonas; Díaz, Sebastián A.; Kessler, Stephan; Meng, Tobias; Rizzi, Matteo & Hals, Kjetil Magne Dørheim [Show all 7 contributors for this article] (2022). Steering Majorana braiding via skyrmion-vortex pairs: A scalable platform. Physical review B (PRB). ISSN 2469-9950. 105(22). doi: 10.1103/PhysRevB.105.224509. Full text in Research Archive Show summary
Majorana zero modes are quasiparticles that hold promise as building blocks for topological quantum computing. However, the litmus test for their detection, the observation of exotic non- abelian statistics revealed by braiding, has so far eluded experimental efforts. Here we take advantage of the fact that skyrmion-vortex pairs in superconductor-ferromagnet heterostructures harboring Majorana zero modes can be easily manipulated in two spatial dimensions. We adiabatically braid the hybrid topological structures and explicitly confirm the non-abelian statistics of the Majorana zero modes numerically using a self-consistent calculation of the superconducting order parameter. Our proposal of controlling skyrmion-vortex pairs provides the necessary leeway toward a scalable topological quantum computing platform.
Rodrigues, Davi; Salimath, Akshaykumar; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2021). Spin-Wave Driven Bidirectional Domain Wall Motion in Kagome Antiferromagnets. Physical Review Letters. ISSN 0031-9007. 127(15). doi: 10.1103/PhysRevLett.127.157203. Full text in Research Archive Show summary
We predict a mechanism to controllably manipulate domain walls in kagome antiferromagnets via a single linearly polarized spin-wave source. We show by means of atomistic spin dynamics simulations of antiferromagnets with kagome structure that the speed and direction of the domain wall motion can be regulated by only tuning the frequency of the applied spin-wave. Starting from microscopics, we establish an effective action and derive the corresponding equations of motion for the spin-wave-driven domain wall. Our analytical calculations reveal that the coupling of two spin-wave modes inside the domain wall explains the frequency-dependent velocity of the spin texture. Such a highly tunable spin-wave-induced domain wall motion provides a key component toward next-generation fast, energy-efficient, and Joule-heating-free antiferromagnetic insulator devices.
Lund, Mike Alexander; Salimath, Akshaykumar & Hals, Kjetil Magne Dørheim (2021). Spin pumping in noncollinear antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 104(17). doi: 10.1103/PhysRevB.104.174424. Full text in Research Archive Show summary
The ac spin pumping of noncollinear antiferromagnets is theoretically investigated. Starting from an effective action description of the spin system, we derive the Onsager coefficients connecting the spin pumping and spin-transfer torque associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome antiferromagnet resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) spin-transfer torque parameter can be extracted from the pumped ac spin current in-phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AF generate spin currents with mutually orthogonal polarization directions. This offers a unique way of controlling the spin orientation of the pumped spin current by exciting different spin-wave modes.
Lund, Mike Alexander; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2020). Large surface magnetization in noncentrosymmetric antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 102(18). doi: 10.1103/PhysRevB.102.180412. Full text in Research Archive Show summary
Thin-film antiferromagnets (AFs) with Rashba spin-orbit coupling are theoretically investigated. We demonstrate that the relativistic Dzyaloshinskii-Moriya interaction (DMI) produces a large surface magnetization and a boundary-driven twist state in the antiferromagnetic Néel vector. We predict a magnetization on the order of 2.3×10^4 A/m, which is comparable to the magnetization of ferromagnetic semiconductors. Importantly, the magnetization is characterized by ultrafast terahertz dynamics and provides different approaches for efficiently probing and controlling the spin dynamics of AFs as well as detecting the antiferromagnetic DMI. Notably, the magnetization does not lead to any stray magnetic fields except at the corners where weak magnetic monopole fields appear
Hals, Kjetil Magne Dørheim & Everschor-Sitte, Karin (2019). Twists in ferromagnetic monolayers with trigonal prismatic symmetry. Physical review B (PRB). ISSN 2469-9950. 99(10). doi: 10.1103/PhysRevB.99.104422. Full text in Research Archive
Mulkers, Jeroen; Hals, Kjetil Magne Dørheim; Leliaert, Jonathan; Milosevic, Milorad V; Waeyenberge, Bartel Van & Everschor-Sitte, Karin (2018). Effect of boundary-induced chirality on magnetic textures in thin films. Physical review B (PRB). ISSN 2469-9950. 98(6). doi: 10.1103/PhysRevB.98.064429. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Everschor-Sitte, Karin (2017). New Boundary-Driven Twist States in Systems with Broken Spatial Inversion Symmetry. Physical Review Letters. ISSN 0031-9007. 119(127203). doi: 10.1103/PhysRevLett.119.127203. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Brataas, Arne (2015). Spin-motive forces and current-induced torques in ferromagnets. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 91(21). doi: 10.1103/PhysRevB.91.214401. Full text in Research Archive
Ciccarelli, Chiara; Hals, Kjetil Magne Dørheim; Irvine, Andrew; Novak, Vit; Tserkovnyak, Y & Kurebayashi, Hidekazu [Show all 8 contributors for this article] (2015). Magnonic charge pumping via spin-orbit coupling. Nature Nanotechnology. ISSN 1748-3387. 10, p. 50–54. doi: 10.1038/nnano.2014.252. Full text in Research Archive
Shulz, Thomek; Alejos, Oscar; Martinez, Eduardo; Hals, Kjetil Magne Dørheim; Garcia, Karin & Vila, Laurent [Show all 14 contributors for this article] (2015). Spin-orbit torques for current parallel and perpendicular to a domain wall. Applied Physics Letters. ISSN 0003-6951. 107(12). doi: 10.1063/1.4931429. Full text in Research Archive Show summary
We report field- and current-induced domain wall (DW) depinning experiments in Ta/Co20Fe60B20/MgO nanowires through a Hall cross geometry. While purely field-induced depinning shows no angular dependence on in-plane fields, the effect of the current depends crucially on the internal DW structure, which we manipulate by an external magnetic in-plane field. We show for the first time depinning measurements for a current sent parallel to the DW and compare its depinning efficiency with the conventional case of current flowing perpendicularly to the DW. We find that the maximum efficiency is similar for both current directions within the error bars, which is in line with a dominating damping-like spin-orbit torque (SOT) and indicates that no large additional torques arise for currents parallel to the DW. Finally, we find a varying dependence of the maximum depinning efficiency angle for different DWs and pinning levels. This emphasizes the importance of our full angular scans compared to previously used measurements for just two field directions (parallel and perpendicular to the DW) and shows the sensitivity of the spin-orbit torque to the precise DW structure and pinning sites.
Hals, Kjetil Magne Dørheim & Brataas, Arne (2014). Spin-orbit torques and anisotropic magnetization damping in skyrmion crystals. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 89(6). doi: 10.1103/PhysRevB.89.064426. Full text in Research Archive
Yuan, Zhe; Hals, Kjetil Magne Dørheim; Liu, Yi; Starikov, Anton A.; Brataas, Arne & Kelly, Paul K. (2014). Gilbert Damping in Noncollinear Ferromagnets. Physical Review Letters. ISSN 0031-9007. 113(26). doi: 10.1103/PhysRevLett.113.266603. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Berre, Inga (2013). Thermal fracturing of geothermal wells and effects of borehole orientation. In Horne, Roland (Eds.), Proceedings of the 38th Workshop on Geothermal Reservoir Engineering 2013. Curran Associates, Inc.. ISSN 9781627485708. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Brataas, Arne (2013). Spin-transfer torques in helimagnets. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 87(17:174409). doi: 10.1103/PhysRevB.87.174409. Full text in Research Archive Show summary
We theoretically investigate current-induced magnetization dynamics in chiral-lattice helimagnets. Spin-orbit coupling in noncentrosymmetric crystals induces a reactive spin-transfer torque that has not been previously considered. We demonstrate how the torque is governed by the crystal symmetry and acts as an effective magnetic field along the current direction in cubic B20-type crystals. The effects of the new torque are computed for current-induced dynamics of spin spirals and the Doppler shift of spin waves. In current-induced spin-spiral motion, the new torque tilts the spiral structure. The spin waves of the spiral structure are initially displaced by the new torque, while the dispersion relation is unaffected.
Hals, Kjetil Magne Dørheim & Brataas, Arne (2013). Phenomenology of current-induced spin-orbit torques. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 88(8). doi: 10.1103/PhysRevB.88.085423. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Berre, Inga (2012). Interaction between injection points during hydraulic fracturing. Water Resources Research. ISSN 0043-1397. 48. doi: 10.1029/2012WR012265. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Tserkovnyak, Yaroslav & Brataas, Arne (2011). Phenomenology of Current-Induced Dynamics in Antiferromagnets. Physical Review Letters. ISSN 0031-9007. 106(10). doi: 10.1103/PhysRevLett.106.107206. Full text in Research Archive
Hals, Kjetil Magne Dørheim & Brataas, Arne (2011). Magnetization dissipation in the ferromagnetic semiconductor (Ga,Mn)As. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 84(10). doi: 10.1103/PhysRevB.84.104404. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Nguyen, Kiet Anh; Waintal, Xavier & Brataas, Arne (2010). Effective Magnetic Monopoles and Universal Conductance Fluctuations. Physical Review Letters. ISSN 0031-9007. 105(20). doi: 10.1103/PhysRevLett.105.207204. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Brataas, Arne & Bauer, Gerrit E. W. (2010). Thermopower and thermally induced domain wall motion in (Ga, Mn)As. Solid State Communications. ISSN 0038-1098. 150(11-12), p. 461–465. doi: 10.1016/j.ssc.2010.01.023. Full text in Research Archive Show summary
We study two reciprocal thermal effects in the ferromagnetic semiconductor (Ga, Mn)As by scattering theory: domain wall motion induced by a temperature gradient and heat currents pumped by a moving domain wall. The effective out-of-plane thermal spin transfer torque parameter PQβQ, which governs the coupling between heat currents and a magnetic texture, is found to be of the order of unity. Unpinned domain walls are predicted to move at speed 10 m/s in temperature gradients of the order 10 K/μm. The cooling power of a moving domain wall only compensates the heating due to friction losses at ultra-low domain wall velocities of about 0.07 m/s. The Seebeck coefficient is found to be of the order 100–500 μV/K at View the MathML source, in good agreement with recent experiments.
Hals, Kjetil Magne Dørheim; Brataas, Arne & Tserkovnyak, Y (2010). Scattering theory of charge-current-induced magnetization dynamics. Europhysics letters. ISSN 0295-5075. 90(4). doi: 10.1209/0295-5075/90/47002. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Nguyen, Kiet Anh & Brataas, Arne (2009). Intrinsic Coupling between Current and Domain Wall Motion in (Ga,Mn)As. Physical Review Letters. ISSN 0031-9007. 102(25). doi: 10.1103/PhysRevLett.102.256601. Full text in Research Archive Show summary
We consider current-induced domain wall motion and, the reciprocal process, moving domain wall-induced current. The associated Onsager coefficients are expressed in terms of scattering matrices. Uncommonly, in (Ga,Mn)As, the effective Gilbert damping coefficient αw and the effective out-of-plane spin-transfer torque parameter βw are dominated by spin-orbit interaction in combination with scattering off the domain wall, and not scattering off extrinsic impurities. Numerical calculations give αw∼0.01 and βw∼1 in dirty (Ga,Mn)As. The extraordinarily large βw parameter allows experimental detection of current or voltage induced by domain wall motion in (Ga,Mn)As.

View all works in NVA

Konomaev, Feodor Svetlanov; Tharmalingam, Mithuss & Hals, Kjetil Magne Dørheim (2026). Spin-Seebeck Signatures of Spin Chirality in Kagome Antiferromagnets. Full text in Research Archive Show summary
Non-collinear antiferromagnets (NCAFMs) are appealing for antiferromagnetic spintronics, as they combine the advantages of collinear antiferromagnets with novel emergent phenomena stemming from their complex spin structures. These phenomena are often associated with the intrinsic spin chirality, which characterizes the handedness of the ground-state spin configuration. Non-collinear antiferromagnets (NCAFMs) are appealing for antiferromagnetic spintronics, as they combine the advantages of collinear antiferromagnets with novel emergent phenomena stemming from their complex spin structures. These phenomena are often associated with the intrinsic spin chirality, which characterizes the handedness of the ground-state spin configuration. Here, we investigate a kagome NCAFM interfaced with a normal metal and demonstrate that the ground-state vector spin chirality can be probed through measurements of the spin Seebeck effect (SSE). Starting from a microscopic spin Hamiltonian, we derive the corresponding bosonic Bogoliubov-de Gennes Hamiltonians for the two chiral configurations. Using linear response theory, we obtain a general expression for the spin current thermally pumped into the normal metal by the SSE. We show that a sizable in-plane spin current emerges exclusively in the negative-chiral state, providing a direct signature for real-time detection of chirality switching in kagome NCAFMs. In addition, we find a field-dependent out-of-plane spin current whose magnitude differs between the two chiralities by about 81%, reflecting their distinct magnon band structures.
Helene, Ursin Sofie; Klaui, Mathias Michael & Hals, Kjetil Magne Dørheim (2026). Tunable Phonon-Driven Magnon Spin Currents in Altermagnets. Full text in Research Archive Show summary
Altermagnets have recently attracted considerable interest due to their unique symmetry-governed spintronic properties. Here, we investigate phonon-induced magnon spin currents in a two-dimensional altermagnet. Starting from a microscopic theory of the coupled magnon-phonon system, we derive the nonequilibrium magnon distribution generated by selective phonon excitations. We show that the resulting spin currents exhibit a pronounced d-wave symmetry with respect to the phonon momentum. Moreover, the spin current along the altermagnetic directions can be completely reversed by tuning the phonon frequency. These findings establish altermagnets as promising platforms for realizing highly tunable, phonon-driven coherent terahertz magnon spin currents.
Hals, Kjetil Magne Dørheim (2026). Spinntronikk: Hvordan kan elektronets spinnegenskaper benyttes i fremtidens kvanteteknologi? Agder Vitenskapsakademi Årbok. ISSN 0809-7283. Full text in Research Archive Show summary
Kvanteteknologi har potensial til å initiere en av de største teknologiske revolusjonene i vår tid ved å muliggjøre løsning av problemer som er uoverkommelig selv for de mest avanserte klassiske superdatamaskiner. Samtidig har spinntronikk vokst frem som en videreutvikling av tradisjonell elektronikk. I denne artikkelen ser vi på hvordan disse to fagfeltene, som lenge har utviklet seg hver for seg, nå møtes i arbeidet med å realisere robuste og skalerbare kvantedatamaskiner.
Konomaev, Feodor Svetlanov; Tharmalingam, Mithuss & Hals, Kjetil Magne Dørheim (2026). Spin-Seebeck signatures of spin chirality in kagome antiferromagnets. Full text in Research Archive Show summary
Non-collinear antiferromagnets (NCAFMs) are appealing for antiferromagnetic spintronics, as they combine the advantages of collinear antiferromagnets with novel emergent phenomena stemming from their complex spin structures. These phenomena are often associated with the intrinsic spin chirality, which characterizes the handedness of the ground-state spin configuration. Here, we investigate a kagome NCAFM interfaced with a normal metal and demonstrate that the groundstate vector spin chirality can be probed through measurements of the spin Seebeck effect (SSE). Starting from a microscopic spin Hamiltonian, we derive the corresponding bosonic Bogoliubov-de-Gennes Hamiltonians for the two chiral configurations. Using linear response theory, we obtain a general expression for the spin current thermally pumped into the normal metal by the SSE. We show that a sizable in-plane spin current emerges exclusively in the negative-chiral state, providing a direct signature for real-time detection of chirality switching in kagome NCAFMs. In addition, we find a field-dependent out-of-plane spin current whose magnitude differs between the two chiralities, reflecting their distinct magnon band structures
Tharmalingam, Mithuss; Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2026). Strain-induced manipulation of noncollinear antiferromagnets. Full text in Research Archive Show summary
Recently, interest has grown in harnessing noncollinear antiferromagnets (NCAFMs) for applications in antiferromagnetic spintronics. A key requirement for their practical use is the ability to control the spin order in a reliable and tunable manner. We investigate how the spin order in kagome antiferromagnets—an important class of NCAFMs—can be manipulated via strain. Starting from a microscopic spin Hamiltonian, we derive an effective action that captures the coupling between the spin order and the system's strain tensor. Microscopically, this coupling arises from strain-induced modifications of the Dzyaloshinskii-Moriya and exchange interactions. Using this effective description, we explore two strain-driven phenomena: (1) the piezomagnetic response and (2) strain-induced switching of the antiferromagnetic spin order. We show that strain linearly induces a net magnetization and provide an experimentally testable prediction in Mn3Sn. Moreover, we numerically show that strain can facilitate thermally assisted chirality switching of the spin order. In particular, we find that strain governs both the average switching time and direction between chiral states. Our results provide a general theoretical framework for modeling strain-induced manipulations of kagome antiferromagnets, underscoring strain as a promising route for functional control of NCAFMs in antiferromagnetic spintronic devices.
Hals, Kjetil Magne Dørheim (2026). Spinntronikk: Hvordan kan elektronets spinnegenskaper benyttes i fremtidens kvanteteknologi? Full text in Research Archive Show summary
Spinntronikk representerer et forskningsfelt innen faststoffysikk, der elektronets spinnegenskaper, i tillegg til ladningen, benyttes til å utvikle ny elektronikk. Dette foredraget tar sikte på å belyse hvordan denne fagretningen kan anvendes til å utvikle nye metoder for å utføre kvanteberegninger i fremtidens kvanteteknologi.
Tharmalingam, Mithuss; Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Replication Data for: Strain-induced manipulation of non-collinear antiferromagnets. doi: 10.18710/NSF2KN. Full text in Research Archive Show summary
Replication Data for the article "Strain-induced manipulation of non-collinear antiferromagnets" published in Physical Review B (2025). The files ‘Fig4a_S1’, ‘Fig4a_S2’ and ‘Fig4a_S3’ contain the x, y and z coordinate of the macrospins S1, S2 and S3, respectively, in Figure 4a. The files ‘Fig4b_Phitrajectory’, ‘Fig4b_Psitrajectory’and ‘Fig4b_Thetatrajectory’ contain the evolution of the nautical angles Phi, Psi and Theta, respectively, in Figure 4b. The files ‘Fig5_Output10’, ‘Fig5_Output15’ and ‘Fig5_Output20’ contain the switching times for strains of 1.0%, 1.5% and 2.0% respectively, in Figure 5. In each file from left to right, the columns represent the Temperature, Switching Time, Standard Deviation, and the Standard Error.
Konomaev, Feodor Svetlanov; Tharmalingam, Mithuss & Hals, Kjetil Magne Dørheim (2025). Replication Data for: Spin-Seebeck Signatures of Spin Chirality in Kagome Antiferromagnets. doi: 10.18710/CN2VGX. Full text in Research Archive Show summary
Replication Data for the article "Spin-Seebeck Signatures of Spin Chirality in Kagome Antiferromagnets" published in Physical Review B (2026). The file ‘Fig2.txt’ contains the energy of the three spin-wave bands of the kagome antiferromagnet when it is in the (+)- and (-)-chiral state as a function of the momentum along the x- and y-directions, which is plotted in Figure 2 in the paper. The file ‘Fig3b.txt’ contains the z-component of the spin current in the (+) chiral state, the z-component of the spin current in the (-)-chiral state, as well as the y-component of the spin current in the (+)-chiral state, normalized by the constant y-component of the spin current in the (-)-chiral state, as a function of the applied magnetic field in the z-direction. The data is plotted in Figure 3b in the paper.
Hals, Kjetil Magne Dørheim (2025). Unconventional spin phenomena in noncollinear antiferromagnets. Full text in Research Archive Show summary
In recent years, noncollinear antiferromagnets (NCAFMs) have attracted growing interest for spintronic applications. These materials are characterized by an SO(3)-valued order parameter field, which gives rise to richer and more complex spintronic behavior compared to conventional ferromagnets and collinear antiferromagnetic. In this talk, we explore two distinct spin phenomena in NCAFMs with a kagome lattice structure: spin-wave-driven domain wall motion [1], and voltage-controlled terahertz (THz) self-oscillations [2]. Notably, we propose a novel mechanism to manipulate domain walls in kagome antiferromagnets using a single linearly polarized spin-wave source. Through atomistic spin dynamics simulations and an effective action description, we demonstrate that both the velocity and direction of domain wall motion can be precisely controlled by tuning the spin-wave frequency. Furthermore, we show that kagome antiferromagnets support gapless self-oscillations, with frequencies continuously tunable from 0 Hz to the THz regime via electrically induced spin-orbit torques (SOTs). Using an effective theory that accounts for both reactive and dissipative SOTs, we analyze the onset, bandwidth, and amplitude of these auto-oscillations. Remarkably, the dynamics are highly sensitive to the chirality of the ground state, with one chirality having gapped excitations, whereas the opposite chirality supports gapless self-oscillations. [1] D. R. Rodrigues, A. Salimath, K. Everschor-Sitte, K. M. D. Hals, Phys. Rev. Lett. 127, 157203 (2021). [2] M. A. Lund, D. R. Rodrigues, K. Everschor-Sitte, and K. M. D. Hals, Phys. Rev. Lett. 131, 156704 (2023).
Tharmalingam, Mithuss & Hals, Kjetil Magne Dørheim (2025). Strain-induced manipulation of non-collinear antiferromagnets. Full text in Research Archive Show summary
In recent years, there has been growing interest in harnessing non-collinear antiferromagnets (NCAFMs) for applications in antiferromagnetic spintronics. A key requirement for their practical use is the ability to control the spin order in a reliable and tunable manner. In this work, we investigate how the spin order in kagome antiferromagnets—an important class of NCAFMs—can be manipulated via strain. Starting from a microscopic spin Hamiltonian, we derive an effective action for the kagome antiferromagnet that captures the coupling between the spin order and the system’s strain tensor. At the microscopic level, this coupling arises from strain-induced modifications of the Dzyaloshinskii–Moriya and exchange interactions. Using this effective description, we explore two strain-driven phenomena: (1) strain-induced switching of the antiferromagnetic spin order and (2) the piezomagnetic response. We numerically show that strain facilitates thermally assisted switch- ing between spin configurations of opposite chirality. Specifically, we find that uniform tensile and compressive strain govern both the average switching time and the preferred switching direction between chiral states. Furthermore, we demonstrate that strain induces a net magnetization and provide an experimentally testable prediction of this effect for a typical NCAFM. Our results provide a theoretical framework for modeling strain-induced manipulation of kagome antiferromagnets, underscoring strain as a promising route for functional control of NCAFMs.
Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Amplifying the antiferromagnetic spin Seebeck effect through topological magnons. Full text in Research Archive Show summary
Topological magnons emerge as topologically protected spin wave states at the edges of magnets. Here, we theoretically explore how these surface states can be harnessed to amplify the spin Seebeck effect (SSE) in antiferromagnets (AFMs) interfaced with normal metals (NMs). Based on a microscopic model of a kagome AFM, we demonstrate that broken mirror symmetry, combined with the Dzyaloshinskii-Moriya interaction (DMI), drives the system into a topological phase hosting spin-polarized magnons at the boundaries. Notably, linear response calculations reveal that in AFM/NM heterostructures, the topological magnons exhibit strong coupling to the metal’s charge carriers, resulting in a substantial enhancement of the SSE. The relative contribution of the topo- logical magnons is found to be 4-5 times greater than that of the trivial magnon bands. Moreover, our results show that this enhancement is highly sensitive to the strength of the DMI.
Tharmalingam, Mithuss & Hals, Kjetil Magne Dørheim (2025). Strain-induced manipulation of non-collinear antiferromagnets. Full text in Research Archive Show summary
In recent years, there has been growing interest in harnessing non-collinear antiferromagnets (NCAFMs) for applications in antiferromagnetic spintronics. A key requirement for their practical use is the ability to control the spin order in a reliable and tunable manner. In this work, we investigate how the spin order in kagome antiferromagnets—an important class of NCAFMs—can be manipulated via strain. Starting from a microscopic spin Hamiltonian, we derive an effective action for the kagome antiferromagnet that captures the coupling between the spin order and the system’s strain tensor. At the microscopic level, this coupling arises from strain-induced modifications of the Dzyaloshinskii–Moriya and exchange interactions. Using this effective description, we explore two strain-driven phenomena: (1) strain-induced switching of the antiferromagnetic spin order and (2) the piezomagnetic response. We numerically show that strain facilitates thermally assisted switch- ing between spin configurations of opposite chirality. Specifically, we find that uniform tensile and compressive strain govern both the average switching time and the preferred switching direction between chiral states. Furthermore, we demonstrate that strain induces a net magnetization and provide an experimentally testable prediction of this effect for a typical NCAFM. Our results provide a theoretical framework for modeling strain-induced manipulation of kagome antiferromagnets, underscoring strain as a promising route for functional control of NCAFMs.
Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Amplifying the antiferromagnetic spin Seebeck effect through topological magnons. Full text in Research Archive Show summary
Topological magnons emerge as topologically protected spin wave states at the edges of mag- nets. Here, we theoretically explore how these surface states can be harnessed to amplify the spin Seebeck effect (SSE) in antiferromagnets (AFMs) interfaced with normal metals (NMs). Based on a microscopic model of a kagome AFM, we demonstrate that broken mirror symmetry, combined with the Dzyaloshinskii-Moriya interaction (DMI), drives the system into a topological phase hosting spin-polarized magnons at the boundaries. Notably, linear response calculations reveal that in AFM/NM heterostructures, the topological magnons exhibit strong coupling to the metal’s charge carriers, resulting in a substantial enhancement of the SSE. The relative contribution of the topological magnons is found to be 4-5 times greater than that of the trivial magnon bands. Moreover, our results show that this enhancement is highly sensitive to the strength of the DMI.
Konomaev, Feodor Svetlanov & Hals, Kjetil Magne Dørheim (2025). Amplifying the antiferromagnetic spin Seebeck effect through topological magnons. Full text in Research Archive Show summary
Topological magnons emerge as topologically protected spin wave states at the edges of magnets. Here, we theoretically explore how these surface states can be harnessed to amplify the spin Seebeck effect (SSE) in antiferromagnets (AFMs) interfaced with normal metals (NMs). Based on a microscopic model of a kagome AFM, we demonstrate that broken mirror symmetry, combined with the Dzyaloshinskii-Moriya interaction (DMI), drives the system into a topological phase hosting spin-polarized magnons at the boundaries. Notably, linear response calculations reveal that in AFM/NM heterostructures, the topological magnons exhibit strong coupling to the metal’s charge carriers, resulting in a substantial enhancement of the SSE. The relative contribution of the topological magnons is found to be 4-5 times greater than that of the trivial magnon bands. Moreover, our results show that this enhancement is highly sensitive to the strength of the DMI.
Nothhelfer, Jonas; Díaz, Sebastián A.; Kessler, Stephan; Meng, Tobias; Rizzi, Matteo & Hals, Kjetil Magne Dørheim [Show all 7 contributors for this article] (2024). Exploring Vortex Dynamics in Superconductor-Ferromagnet Heterostructures: From Domain Wall Interactions to Adiabatic Braiding of Majorana Modes. Full text in Research Archive Show summary
In superconductor-magnet heterostructures, interface-induced spin-orbit coupling can play a vital role in the dynamics of textures in the superconductor and the magnet. We show that magnetic textures like domain walls and skyrmions exhibit a rich interaction spectrum with superconducting vortices. We find that the Rashba spin-orbit coupling induces magnetoelectric interactions between vortices and domain walls, with the domain wall’s helicity determining the interaction: Néel walls push or pull the vortices, and vortices glide along Bloch walls. Furthermore, we show that hybrid excitations of superconducting vortices and magnetic skyrmions can bind Majorana modes that enable quantum computing. By adiabatically braiding these hybrid topological structures, we explicitly confirm the non-Abelian statistics of Majorana zero modes through self-consistent numerical simulations. Our findings provide a crucial basis for controlling superconducting vortices and using them for quantum computing. [1] Díaz et al. arXiv:2310.06866 [2] Nothhelfer et al. Phys. Rev. B 105 (2022) 224509
Lund, Mike Alexander; Rodrigues, Davi R.; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2024). Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets. Full text in Research Archive Show summary
The terahertz (THz) technology gap refers to a frequency range of electromagnetic radiation in the THz regime where current technologies are inefficient for generating and detecting radiation. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome structure host gapless self-oscillations whose frequencies are tunable from 0 Hz to the THz regime via electrically induced spin-orbit torques (SOTs) [1]. The auto-oscillations' initiation, bandwidth, and amplitude are investigated by deriving an effective theory, which captures the reactive and dissipative SOTs. We find that the dynamics strongly depends on the ground state's chirality, with one chirality having gapped excitations, whereas the opposite chirality provides gapless self-oscillations. Our results demonstrate that NCAFMs offer unique THz functional components, which could play a significant role in bridging the gap between technologies operating in the microwave and infrared regions. [1] M. A. Lund, D. R. Rodrigues, K. Everschor-Sitte, and K. M. D. Hals, Phys. Rev. Lett. 131, 156704 (2023).
Hals, Kjetil Magne Dørheim; Lund, Mike Alexander; Everschor-Sitte, Karin & Rodrigues, Davi R. (2023). Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets. Full text in Research Archive Show summary
The terahertz (THz) technology gap refers to a frequency range of electromagnetic radiation in the THz regime where current technologies are inefficient for generating and detecting radiation. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome structure host gapless self-oscillations whose frequencies are tunable from 0 Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The auto-oscillations' initiation, bandwidth, and amplitude are investigated by deriving an effective theory, which captures the reactive and dissipative SOTs. We find that the dynamics strongly depends on the ground state's chirality, with one chirality having gapped excitations, whereas the opposite chirality provides gapless self-oscillations. Our results demonstrate that NCAFMs offer unique THz functional components, which could play a significant role in bridging the gap between technologies operating in the microwave and infrared regions. *We acknowledge funding from the Research Council of Norway Project No. 286889, the German Research Foundation (DFG) Project No. 320163632 and the TRR 173 – 268565370 Spin + X (project B12).
Lund, Mike Alexander; Salimath, Akshaykumar & Hals, Kjetil Magne Dørheim (2023). Spin pumping in noncollinear antiferromagnets. Full text in Research Archive Show summary
The spin pumping and spin-transfer torque (STT) mechanisms in antiferromagnets have been theoretically and experimentally investigated in recent years. However, most of these works have concentrated on collinear antiferromagnets, leaving the spin dynamics of the more complex noncollinear antiferromagnets largely unexplored. In this talk, I will present our latest work [1] on ac spin pumping in non-collinear antiferromagnets. Starting from an effective theory of the spin system, we derive the Onsager coefficients connecting the spin pumping and STT associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome AFM resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) STT parameter can be extracted from the pumped ac spin-current in phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AFM generate spin currents with mutually orthogonal polarization directions. This offers a unique way of controlling the spin orientation of the pumped spin current by exciting different spin-wave modes. [1] M. A. Lund, A. Salimath, K. M. D. Hals, Phys. Rev. B 104, 174424 (2021). *We acknowledge funding from the Research Council of Norway Project No. 286889
Hals, Kjetil Magne Dørheim; Schecter, Michael & Rudner, Mark (2022). Composite topological excitations. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Salimath, Akshaykumar; Rodrigues, Davi R. & Everschor-Sitte, Karin (2022). Spin-wave driven bidirectional domain wall motion in kagome antiferromagnets. Full text in Research Archive Show summary
We predict a mechanism to controllably manipulate domain walls in kagome antiferromagnets via a single linearly polarized spin-wave source. We show by means of atomistic spin dynamics simulations of antiferromagnets with kagome structure that the speed and direction of the domain wall motion can be regulated by only tuning the frequency of the applied spin-wave. Starting from microscopics, we establish an effective action and derive the corresponding equations of motion for the spin-wave-driven domain wall. Our analytical calculations reveal that the coupling of two spin-wave modes inside the domain wall explains the frequency-dependent velocity of the spin texture. Such a highly tunable spin-wave-induced domain wall motion provides a key component toward next-generation fast, energy-efficient, and Joule-heating-free antiferromagnetic insulator devices.
Lund, Mike Alexander; Salimath, Akshaykumar & Hals, Kjetil Magne Dørheim (2022). Spin pumping in noncollinear antiferromagnets. Full text in Research Archive
Diaz, Sebastian A; Hals, Kjetil Magne Dørheim; Meng, Tobias; Rizzi, Matteo; Nothhelfer, Jonas & Everschor-Sitte, Karin [Show all 7 contributors for this article] (2022). Steering Majorana braiding via skyrmion-vortex pairs: a scalable platform. Full text in Research Archive Show summary
Majorana zero modes are quasiparticles that hold promise as building blocks for topological quantum computing. However, the litmus test for their detection, the observation of exotic non-abelian statistics revealed by braiding, has so far eluded experimental efforts. Here we take advantage of the fact that skyrmion-vortex pairs in superconductor-ferromagnet heterostructures harboring Majorana zero modes can be easily manipulated in two spatial dimensions. We adiabatically braid the hybrid topological structures and explicitly confirm the non-abelian statistics of the Majorana zero modes numerically using a self-consistent calculation of the superconducting order parameter. Our proposal of controlling skyrmion-vortex pairs provides the necessary leeway toward a scalable topological quantum computing platform. [1] J. Nothhelfer, K. M. D. Hals, K. Everschor-Sitte, and M. Rizzi, European Patent Application EP3751472A1 / International Patent Application WO2020EP66120 (2019).
Lund, Mike Alexander; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2021). Large Surface Magnetization in Noncentrosymmetric Antiferromagnets. Full text in Research Archive Show summary
Thin-film antiferromagnets (AFs) with Rashba spin-orbit coupling are theoretically investigated. We demonstrate that the relativistic Dzyaloshinskii-Moriya interaction (DMI) produces a large surface magnetization and a boundary-driven twist state in the antiferromagnetic N´eel vector. We predict a magnetization on the order of 2.3 · 10^4 A/m, which is comparable to the magnetization of ferromagnetic semiconductors. Importantly, the magnetization is characterized by ultra-fast terahertz dynamics and provides new approaches for efficiently probing and controlling the spin dynamics of AFs as well as detecting the antiferromagnetic DMI. Notably, the magnetization does not lead to any stray magnetic fields except at corners where weak magnetic monopole fields appear
Salimath, Akshaykumar; Rodrigues, David; Everschor-Sitte, Karin & Hals, Kjetil Magne Dørheim (2021). Magnon driven bidirectional domain wall motion in kagome antiferromagnets. Full text in Research Archive Show summary
We predict a mechanism to controllably manipulate domain walls in kagome antiferromagnets via a single linearly polarized spin-wave source. We show by means of atomistic spin dynamics simulations of antiferromagnets with kagome structure that the speed and direction of the domain wall motion can be regulated by only tuning the frequency of the applied spin wave. Starting from microscopics, we establish an effective action and derive the corresponding equations of motion for the spin-wave-driven domain wall. Our analytical calculations reveal that the coupling of two spin-wave modes inside the domain wall explains the frequency-dependent velocity of the spin texture. Such a highly tunable spin-wave-induced domain wall motion provides a key component toward next-generation fast, energy-efficient, and Joule-heating-free antiferromagnetic insulator devices.
Alexander, Lund Mike; Hals, Kjetil Magne Dørheim & Karin, Everschor-Sitte (2020). Large Surface Magnetization in Noncentrosymmetric Antiferromagnets. Full text in Research Archive
Hals, Kjetil Magne Dørheim (2018). s Composite topological excitations in superconductor-ferromagnet heterostructures. Full text in Research Archive
Hals, Kjetil Magne Dørheim (2018). Composite Topological Excitations in Ferromagnet-Superconductor Heterostructures. Full text in Research Archive
Brataas, Arne; Hals, Kjetil Magne Dørheim; Waintal, Xavier & Nguyen, Anh Kiet (2011). Magnetic Monopole Fingerprints. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Brataas, Arne & Tserkovnyak, Y (2011). Phenomenology of Current-Induced Dynamics in Antiferromagnets. Full text in Research Archive
Hals, Kjetil Magne Dørheim; Brataas, Arne & Tserkovnyak, Y (2011). Phenomenology of Current-Induced Dynamics in Antiferromagnets. Full text in Research Archive
Brataas, Arne; Hals, Kjetil Magne Dørheim; Waintal, Xavier & Nguyen, Anh Kiet (2011). Magnetic Monopole Fingerprints. Full text in Research Archive
Brataas, Arne; Hals, Kjetil Magne Dørheim; Waintal, Xavier & Nguyen, Anh Kiet (2011). Magnetic Monopole Fingerprints. Full text in Research Archive
Brataas, Arne; Hals, Kjetil Magne Dørheim; Waintal, Xavier & Nguyen, Anh Kiet (2011). Magnetic Monopole Fingerprints. Full text in Research Archive
Brataas, Arne; Hals, Kjetil Magne Dørheim; Waintal, Xavier & Nguyen, Anh Kiet (2011). Magnetic Monopole Fingerprints. Full text in Research Archive
Lund, Mike Alexander; Hals, Kjetil Magne Dørheim; Everschor-Sitte, Karin & Salimath, Akshaykumar (2025). Spin Dynamics in Antiferromagnetic Systems. Universitetet i Agder. ISSN 9788284272399. Full text in Research Archive Show summary
This dissertation presents three research papers on spintronics-related effects. Two of the papers discuss dynamic spin phenomena in noncollinear antiferromagnets (NCAFMs). The third paper investigates the equilibrium properties of collinear antiferromagnets (CAFMs) with broken spatial inversion symmetry. The most central part of the presented work discusses the spin dynamics of NCAFMs. To this end, we develop effective action descriptions that capture the dynamics of the SO(3)-valued antiferromagnetic order parameter in response to applied currents and magnetic fields. We first theoretically investigate the ac spin pumping of NCAFMs. Starting from an effective action description of the spin system, we derive the Onsager coefficients that represents the coupling between the NCAFM and spin currents. When our theory is applied to kagome AFMs, we show that the three spin-wave bands of the material can generate ac spin currents with mutually orthogonal polarization directions when driven into resonance by an external magnetic field. Additionally, we demonstrate that the reactive and dissipative STT parameters of the kagome AFM can be extracted from the spin signal measured via the Inverse spin-Hall effect. Second, we investigate magnetic self-oscillations driven by electrically induced spin-orbit torques in kagome AFMs with broken spatial inversion symmetry. We show that the chirality of the noncollinear antiferromagnetic ground state strongly influences the dynamics. One chirality displays gapped excitations, while the opposite chirality provides gapless self-oscillations whose frequencies can be tuned from 0 Hz to the terahertz regime. Thus, the NCAFMs offer unique chiral magnetic properties that makes them especially appealing for bridging the gap between technologies operating in the microwave and infrared regions. Motivated by recent observations of magnetic surface twist states induced by Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric ferromagnets, we study the effects of DMI at the boundaries of noncentrosymmetric CAFMs. We demonstrate that the DMI leads to a boundary-induced twist state in the antiferromagnetic order parameter and a large surface magnetization. The magnetization couples directly to the variation in the order parameter field. As a result, the surface magnetization demonstrates ultrafast THz dynamics and offers effective means to investigate and control the spin dynamics of AFMs and detect the antiferromagnetic DMI.