Abstract
Spin pumping in a ferromagnet/nonferromagnet heterostructure is directly imaged with spatial resolution as well as element selectivity. The time-resolved detection in scanning transmission x-ray microscopy allows to directly probe the spatial extent of the ac spin polarization in Co-doped ZnO which is generated by spin pumping from an adjacent permalloy microstrip. Comparing the relative phases of the dynamic magnetization component of the two constituents is possible and found to be antiphase. The correlation between the distribution of the magnetic excitation in the permalloy and the Co-doped ZnO reveals that laterally there is no one-to-one correlation. The observed distribution is rather complex, but integrating over larger areas clearly demonstrates that the spin polarization in the nonferromagnet extends laterally beyond the region of the ferromagnetic microstrip. Therefore the observations are better explained by a local spin pumping efficieny and a lateral propagation of the ac spin polarization in the nonferromagnet over the range of a few micrometers.
Highlights
In spintronics the generation and manipulation of pure spin currents is in the focus of research activities
Amongst the utilized fundamental effects is spin pumping where a precessing magnetization of a ferromagnet being at ferromagnetic resonance (FMR) transfers angular momentum to an adjacent nonferromagnetic layer [1]
Spin pumping is electrically detected via the inverse spin Hall effect (ISHE) inside the nonferromagnetic layer that makes conducting high-Z materials such as Pt advisable for easy detection [3,5,6]; for few other materials like semiconducting Ge [7], conducting SrRuO3 [8] and ZnO [9] spin pumping could be detected via the ISHE as well
Summary
In spintronics the generation and manipulation of pure spin currents is in the focus of research activities. From the perspective of suitable materials, a more versatile approach is to detect the presence of spin pumping via the increased FMR linewidth [4,10,11]. It is nowadays consensus between experiment and theory that the flow of angular momentum from the ferromagnet into the nonferromagnet represents another Gilbert-like damping mechanism. Such spin pumping heterostructures allow different nonferromagnetic materials to be used without the restriction of the ISHE as the detection channel. Insulating nonferromagnets have the advantage that the increased magnetic damping is less influenced by other mechanisms like eddy-current damping; see Ref. [4] for a recent overview
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