Direct imaging of the ac component of the pumped spin polarization with element specificity

TL;DR

This study directly images the ac spin polarization generated by spin pumping in a heterostructure, revealing its spatial distribution, phase relationship, and lateral propagation beyond the ferromagnetic region using element-specific, time-resolved microscopy.

Contribution

It provides the first direct, spatially resolved imaging of ac spin polarization with element specificity in a heterostructure, highlighting complex distribution and lateral propagation effects.

Findings

Ac spin polarization is generated by spin pumping from permalloy.

The ac spin polarization in Co-doped ZnO is antiphase with the magnetization.

Lateral propagation of spin polarization extends beyond the ferromagnetic region.

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.