Static magnetic proximity effect in Pt/NiFe2O4 and Pt/Fe bilayers investigated by x-ray resonant magnetic reflectivity

TL;DR

This study uses x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects in Pt/NiFe2O4 and Pt/Fe bilayers, revealing significant proximity-induced magnetization in Pt/Fe but not in Pt/NiFe2O4.

Contribution

It provides quantitative measurements of induced magnetic moments in Pt at interfaces, demonstrating the presence in Pt/Fe and the absence in Pt/NiFe2O4, clarifying the origin of spin Seebeck effects.

Findings

Induced magnetic moment in Pt/Fe is approximately 0.6 μB per atom.

No detectable magnetic proximity effect in Pt/NiFe2O4.

Proximity effects do not influence the spin Seebeck effect in Pt/NiFe2O4.

Abstract

The spin polarization of Pt in Pt/NiFe2O4 and Pt/Fe bilayers is studied by interface-sensitive x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects. The asymmetry ratio of the reflectivity was measured at the Pt L3 absorption edge using circular polarized x-rays for opposite directions of the magnetization at room temperature. The results of the 2% asymmetry ratio for Pt/Fe bilayers are independent of the Pt thickness between 1.8 and 20 nm. By comparison with ab initio calculations, the maximum magnetic moment per spin polarized Pt atom at the interface is determined to be $(0.6\pm0.1)\,\mu_{B}$ for Pt/Fe. For Pt/NiFe2O4 the asymmetry ratio drops below the sensitivity limit of $0.02\,\mu_{B}$ per Pt atom. Therefore, we conclude, that the longitudinal spin Seebeck effect recently observed in Pt/NiFe2O4 is not influenced by a proximity induced anomalous Nernst effect.