Static magnetic proximity effect in Pt/Ni$_{1-x}$Fe$_x$ bilayers investigated by x-ray resonant magnetic reflectivity

TL;DR

This study uses x-ray resonant magnetic reflectivity to detect and analyze the magnetic proximity effect at interfaces between platinum and various ferromagnetic alloys, revealing the spatial distribution and magnitude of induced spin polarization.

Contribution

It demonstrates the effectiveness of XRMR in quantifying interface spin polarization and provides detailed insights into the energy dependence of magnetooptic parameters in Pt-based bilayers.

Findings

Largest spin polarization observed in Pt/Fe bilayers.

Smaller magnetic proximity effect in Pt/Ni bilayers.

Good agreement between experiments and ab initio calculations.

Abstract

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/Fe, Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight in the spatial distribution of the spin polarization of a non-magnetic metal across the interface to a ferromagnetic layer. The evaluation of the experimental results with simulations based on optical data from ab initio calculations provides the induced magnetic moment per Pt atom in the spin polarized volume adjacent to the ferromagnet. We find the largest spin polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni. Additional XRMR experiments with varying photon energy are in good agreement with the theoretical predictions for the energy dependence of the magnetooptic parameters and allow identifying the optical dispersion $\delta$ and absorption $\beta$ across the Pt L3-absorption edge.