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Aurélien Manchon, KAUST, Saudi Arabia

Antiferromagnetic spin-orbitronics


Antiferromagnets (AF) have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties considered as fundamental condensed matter physics. A conceptual breakthrough was achieved less than ten years ago with the proposal that spin transfer torque could be used to electrically control the direction of the order parameter of AF spin valves, henceforth making these materials potential candidates for low energy spin devices [1]. In spite of substantial theoretical efforts and experimental attempts to observe such a torque, the difficulty to independently detect the direction of the AF order parameter has remained a major obstacle. The paradigm has changed radically in the past few years with the discovery of antiferromagnetic anisotropic (tunneling) magnetoresistance [2], demonstrating that spin-orbit coupled AF might well be the next frontier in applied spintronics, combining the promises of spin-orbitronics and the richness of antiferromagnets.

 

In this seminar, I will first introduce the original concept of spin transfer torque in AF spin-valves, demonstrating that it is strongly limited by the spin decoherence and dramatically vanishes in the presence of disorder [3], leaving little hope to observe this effect experimentally. Then, I will present the newly proposed concept of spin-orbit torque that utilizes bulk or interfacial the spin-orbit coupling in non-centrosymmetric magnets to directly generate a torque on the AF order parameter, without needed an external polarizer [4]. This torque being local is much more robust against impurities, as will be demonstrated for the specific case of interfacial Rashba spin-orbit coupling as well as in Mn2Au a centrosymmetric antiferromagnetic with a hidden symmetry breaking. In both cases, intrinsic contributions to the torque play a dominant role as it allows the coherent control of the order parameter. Finally, I will conclude by outlining a few perspectives in the development of antiferromagnetic spin-orbitronics.

 

[1] A. S. Núñez, R. A. Duine, Paul Haney, and A. H. MacDonald§ Phys. Rev. B 73, 214426 (2006).

[2] Park et al., Nature Materials 10, 347 (2011).

[3] H. B. M. Saidaoui, A. Manchon, and X. Waintal, Phys. Rev. B 89, 174430 (2014)

[4] J. Železný, H. Gao, K. Výborný, J. Zemen,4J. Mašek, Aurélien Manchon, J. Wunderlich,
Jairo Sinova, and T. Jungwirth, Phys. Rev. Lett. 113, 157201 (2014).