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Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures

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posted on 03.06.2019 by Lina G. Johnsen, Niladri Banerjee, Jacob Linder
© 2019 American Physical Society. UK. Recent theoretical and experimental work has demonstrated how the superconducting critical temperature (Tc) can be modified by rotating the magnetization of a single homogeneous ferromagnet proximity-coupled to the superconducting layer. This occurs when the superconductor and ferromagnet are separated by a thin heavy normal metal that provides an enhanced interfacial Rashba spin-orbit interaction. In the present work, we consider the reciprocal effect: magnetization reorientation driven by the superconducting phase transition. We solve the tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and compute the free energy of the system. We find that the relative angle between the spin-orbit field and the magnetization gives rise to a contribution in the free energy even in the normal state, T>Tc, due to band-structure effects. For temperatures below Tc, superconductivity gives rise to a competing contribution. We demonstrate that by lowering the temperature, in addition to reorientation of the favored magnetization direction from in-plane to out-of-plane, a π/4 in-plane rotation for thicker ferromagnetic layers is possible. Furthermore, computation of Tc of the structure in the ballistic limit shows a dependence on the in-plane orientation of the magnetization, in contrast to our previous result on the diffusive limit. This finding is relevant with respect to thin-film heterostructures since these are likely to be in the ballistic regime of transport rather than in the diffusive regime. Finally, we discuss the experimental feasibility of observing the magnetic anisotropy induced by the superconducting transition when other magnetic anisotropies, such as the shape anisotropy for a ferromagnetic film, are taken into account. Our work suggests that the superconducting condensation energy in principle can trigger a reorientation of the magnetization of a thin-film ferromagnet upon lowering the temperature below Tc, in particular for ferromagnets with weak magnetic anisotropies.

Funding

This work was supported by the Research Council of Norway through its Centres of Excellence funding scheme grant 262633 QuSpin. N.B. was supported by the UKIERI grant from the British Council.

History

School

  • Science

Department

  • Physics

Published in

Physical Review B

Volume

99

Issue

13

Citation

JOHNSEN, L.G., BANERJEE, N. and LINDER, J., 2019. Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures. Physical Review B, 99: 134516.

Publisher

© American Physical Society

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2019-04-23

Notes

This paper was accepted for publication in the journal Physical Review B and the definitive published version is available at https://doi.org/10.1103/PhysRevB.99.134516

ISSN

2469-9950

eISSN

2469-9969

Language

en

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