Theory of spin Hall magnetoresistance (SMR) and related phenomena

A new anisotropic magnetoresistance effect has recently been found for a Pt film on top of the insulating ferrimagnet Yttrium-Iron-Garnet (YIG) [1-6]. We interpret this effect by the simultaneous action of spin Hall and inverse spin Hall effects as a non-equilibrium proximity phenomenon dubbed spin Hall magnetoresistance (SMR). This mechanism does not require the equilibrium proximity magnetization in Pt, which was assumed in [5]. We computed the SMR in F\textbar N and F\textbar N\textbar F layered systems, where F is a magnetic insulator, treating the normal metal N by spin-diffusion theory with quantum mechanical boundary conditions at the interfaces in terms of the spin-mixing conductance [7]. Our results explain the experimentally observed spin Hall magnetoresistance in F\textbar N bilayers. An analysis of the Hall effect when magnetization is normal to the plane allowed the experimental observation of the imaginary part of the mixing conductance [4]. For F\textbar N\textbar F spin valves we predict enhanced SMR amplitudes when magnetizations are collinear. In this talk I review the state of the art and discuss recent extensions of the SMR theory. \\[4pt] [1] H. Nakayama et al., Phys. Rev. Lett. 110, 206601 (2013).\\[0pt] [2] C. Hahn, Phys. Rev. B 87, 174417 (2013).\\[0pt] [3] M. Althammer et al., Phys. Rev. B 87, 224401 (2013).\\[0pt] [4] N. Vlietstra, et al., Appl. Phys. Lett. 103, 032401 (2013).\\[0pt] [5] Y. M. Lu et al., Phys. Rev. B 87, 220409 (2013).\\[0pt] [6] M. Isasa et al., arXiv:1307.1267\\[0pt] [7] Y. Chen et al., Phys. Rev. B 87, 144411 (2013).