Quantitative determination of the Pt magnetic moment in proximity to ferromagnetic material

Abstract

The magnetic proximity effect (MPE) enhances the exchange interaction of nominally non-ferromagnetic materials overcoming the Stoner limit in close contact to ferromagnetic (FM) materials. The paramagnet Pt is a famous example and gets spin polarized by the MPE in Pt/FM bilayers which is of huge importance when studying spin transport phenomena at interfaces such as for the spin Seebeck effect [1], the spin Hall magnetoresistance [2], or spin-orbit torque effects [3]. However, the exact quantitative values for the induced magnetic moment per Pt atom cannot be determined by standard x-ray magnetic circular dichroism (XMCD) experiments on a single thin-film system due to the depth-insensitivity of the XMCD technique at buried interfaces of the sample. Within this contribution, we present the quantitative determination of the Pt magnetic moment induced by the MPE utilizing x-ray resonant magnetic reflectivity (XRMR) [4-6], a favored synchrotron-based technique for spin-depth profiling. Thus, element selectivity and depth resolution can be combined. A detailed data analysis based on asymmetry ratio fits and mapping the goodness of fit parameter Χ2 (see Fig. 1) [3,7] together with an ab-initio factor (conversion from magnetooptic constant Δβ to Pt magnetic moment) [4] provides quantitative reliable results. The obtained quantitative XRMR values are in very good agreement to vibrating sample magnetometry results [3] and XMCD analyses [8] which take the effective magnetic Pt thickness determined by XRMR into account. Therefore, XRMR is a powerful technique to study spin distributions with depth resolution, element selectively and quantitative reliability.