Spin-orbit coupling enables charge currents to give rise to spin currents and vice versa, which has applications in non-volatile magnetic memories, miniature microwave oscillators, thermoelectric converters and Terahertz devices. In the past two decades, a considerable amount of research has focused on electrical spin current generation in different types of nonmagnetic materials. However, electrical spin current generation in ferromagnetic materials has only recently been actively investigated. Due to the additional symmetry breaking by the magnetization, ferromagnetic materials generate spin currents with different orientations of spin direction from those observed in nonmagnetic materials. Studies centered on ferromagnets where spin-orbit coupling plays an important role in transport open new possibilities to generate and detect spin currents. We summarize recent developments on this subject and discuss unanswered questions in this emerging field. paul.haney@nist.gov xin.fan@du.edu * These two authors contributed equally to the manuscript.1 Note that the physical mechanisms required to generate spin polarized current can depend on boundary conditions. If the boundary condition is that the current entering the system is unpolarized, then spin-flip scattering is necessary for polarizing the current. If the boundary condition only specifies the electric field at the system edge, then spin-dependent conductivities are sufficient to obtain spin-polarized current.

Spin-orbit coupling near the surface of a ferromagnetic metal gives rises to spin-to-charge conversion with symmetry different from the conventional inverse spin Hall effect. We have previously observed this spin galvanic effect with spin rotation symmetry (SGE-SR) in a spin valve under a temperature gradient. Here we show there are two processes that contribute to the SGE-SR, one of which is sensitive to the free magnetic layer thickness, while the other only depends on the interface of the free layer. Based on the free-layerthickness-dependent study, we extrapolate the spin diffusion length of Py to be 3.9 ± 0.2 nm. We also propose that the SGE-SR can help to quantitatively study the spin Seebeck effect in metallic magnetic films.

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