Spin-transfer torque and magnetoresistance in superconducting spin valves

Jacob Linder; Takehito Yokoyama; Asle Sudbø

doi:10.1103/PhysRevB.79.224504

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Spin-transfer torque and magnetoresistance in superconducting spin valves

Jacob Linder, Takehito Yokoyama, Asle Sudbø

DOI 10.1103/PhysRevB.79.224504 · Physical Review B

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Abstract

We study the spin-transfer torque and magnetoresistance of a ferromagnet∣superconductor∣ferromagnet spin valve, allowing for an arbitrary magnetization misorientation and treating both s-wave and d-wave symmetries of the superconductor. We take fully into account Andreev reflection and also the spin-triplet correlations that are generated when the magnetizations are noncollinear. It is found that the torque and magnetoresistance are both strongly enhanced when topological zero-energy states are present at the interfaces, which is the case for d-wave superconductors with a crystallographic orientation of [110] relative to the interface (dxy-wave symmetry). Moreover, we find that the magnetoresistance displays a strong oscillatory and nonmonotonous behavior as a function of dS/ξ where dS and ξ are the interlayer width of the superconducting region and the superconducting coherence length, respectively. This feature is also attributed to the crossover from layers of size dS∼2ξ to layers of size dS⪢2ξ, where the contribution to transport from zero-energy states gradually vanishes.