Spin-orbitronics in epitaxial CuMnSb/NiMnSb half-Heusler heterostructures
Final Report Abstract
Spin-orbit torques (SOT) originate from charge currents that get spin polarized when passing through materials with strong spin-orbit coupling. Conceptually, SOT promises both energyefficient and fast manipulation of the magnetic order in spintronic devices. Goal of this project was to investigate spintronics and SOT related effects in antiferromagnetic/ferromagnetic heterostructures containing the half-Heusler alloys CuMnSb (AFM) and NiMnSb (FM). Heusler alloys play an important role in the growing field of antiferromagnetic spintronics. Their advantage compared to other materials is that they do not contain critical raw materials and they offer a wide tunability of their material parameters. One such example in the half-Heusler family is antiferromagnetic CuMnSb, which was so far synthetized only as bulk crystals. During this project, we developed a molecular beam epitaxy growth process for high crystal quality, thin layers of CuMnSb and we studied in detail the influence of molecular beam epitaxial growth conditions on its structural, magnetic, and electronic properties. We found that CuMnSb films containing stoichiometric composition exhibit a maximum value of the antiferromagnetic phase transition temperature (62 K). While this temperature is obviously too low for applications, it is convenient for standard laboratory equipment, which makes CuMnSb a particularly suitable model platform for studying effects near and above the antiferromagnetic transition temperature. Using microfabricated devices, we conducted electrical transport experiments to identify current induced (SOT) switching of the magnetic order parameter in CuMnSb. Although SOT switching was theoretically predicted for CuMnSb, we could not observe this effect unequivocally. Still, we identified an anisotropic magnetoresistance effect in the antiferromagnetic phase of CuMnSb which is a requirement for electrical read-out of the magnetic state. The samples had a low defect density, as confirmed by a minimum value of the residual resistance of 35 μΩcm which is lower than the lowest value reported for bulk CuMnSb to date. Via Hall measurements, we confirmed a hole dominated conduction in CuMnSb layers. In tunnel devices, we observed a tunneling anisotropic magneto resistance and a non-saturating magnetoresistance effect (up to 7 T). We also studied heterostructures consisting of CuMnSb and ferromagnetic layers and observed exchange coupling between the AFM and ferromagnets with in-plane magnetic anisotropy. Furthermore, fully epitaxial CuMnSb/NiMnSb heterostructures were grown by molecular beam epitaxy. We found that the realization of sharp interfaces between CuMnSb and NiMnSb is prevented by interdiffusion of Cu and Ni atoms between the two half-Heusler layers, even at very low growth temperatures. Still, we observe indications of the exchange bias effect for the CuMnSb/NiMnSb heterostructures.
Publications
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Magnetic properties and transport investigations of antiferromagnetic CuMnSb thin films, poster presentation at the workshop on Antiferromagnetic spintronics (from topology to neuromorphic computing) 2019, JGU MITP, Mainz, Germany
S. Banik, L. Scheffler, K. Gas, M. Kamp, J. Knobel, C. Schumacher, C. Gould, M. Sawicki, J. Kleinlein, L. W. Molenkamp
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Magnetic properties of antiferromagnetic CuMnSb epitaxial thin films investigated by SQUID magnetometry, poster presentation at the workshop on Antiferromagnetic spintronics (from topology to neuromorphic computing) 2019, JGU MITP, Mainz, Germany
K. Gas, L. Scheffler, S. Banik, J. Knobel, C. Schumacher, C. Gould, J. Kleinlein, L. W. Molenkamp, M. Sawicki
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Molecular beam epitaxy and characterization of the half-Heusler antiferromagnet CuMnSb, poster presentation at the 20th European Workshop on Molecular Beam Epitaxy – EuroMBE, Lenggries, Germany, 2019
L. Scheffler, C. Schumacher, C. Gould, J. Kleinlein, Laurens W. Molenkamp
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Molecular beam epitaxy of the half-Heusler antiferromagnet CuMnSb, poster presentation at the workshop on Antiferromagnetic spintronics (from topology to neuromorphic computing) 2019, JGU MITP, Mainz, Germany.
Lukas Scheffler; K. Gas; S. Banik; M. Kamp; J. Knobel; C. Schumacher; C. Gould; M. Sawicki; J. Kleinlein & L. W. Molenkamp
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Molecular beam epitaxy of the half-Heusler antiferromagnet CuMnSb. Physical Review Materials, 4(11).
Scheffler, L.; Gas, K.; Banik, S.; Kamp, M.; Knobel, J.; Lin, H.; Schumacher, C.; Gould, C.; Sawicki, M.; Kleinlein, J. & Molenkamp, L. W.
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Bulk-like magnetic properties in MBE-grown unstrained, antiferromagnetic CuMnSb. Applied Physics Letters, 121(1).
Scheffler, L.; Werther, J.; Gas, K.; Schumacher, C.; Gould, C.; Sawicki, M.; Kleinlein, J. & Molenkamp, L. W.
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Molecular beam epitaxy of the half-Heusler antiferromagnet CuMnSb, oral presentation at the 2022 Joint European Magnetic Symposia in Warsaw, Poland
L. Scheffler, K. Gas, M. Kamp, C. Schumacher, C. Gould, M. Sawicki, J. Kleinlein, and L. W. Molenkamp
