Spin pumping under magnetic field gradient

The spin pumping effect is the generation of a spin current by spin waves in a ferromagnet. Its properties have enthusiastically been investigated mainly in uniform magnetic fields, but they are yet to be explored well in nonuniform magnetic fields. Meanwhile, a recent study reported an interesting behavior of spin waves that the wave number of spin waves is converted to another value during its propagation under inhomogeneous magnetic fields. This fact indicates that spin current emission via the spin pumping effect can be spatially tuned taking advantage of the spin-wave wave number conversion in nonuniform magnetic fields. In this talk, we report spatially nonuniform spin current generation by the spin pumping effect under a magnetic field gradient in a Pt/Y₃Fe₅O₁₂ bilayer system. We found that a spin current generated by spin waves is nonlocally enhanced depending on the magnetic field gradient. We explain the result on the basis of the wave number conversion of spin waves, considering its dispersion relation spatially varying with the magnetic field gradient. Our results offer a new insight of spin current generation utilizing nonuniform magnetic fields.