Static magnetic proximity effect inPt/Ni1−xFexbilayers investigated by x-ray resonant magnetic reflectivity

Abstract

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/FM heterostructures. Different XRMR experiments are carried out and the results are evaluated for their dependence on the magneto-optical depth profile, the photon energy, the optical parameters, and the ferromagnetic material. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight into the spatial distribution of the spin polarization of a nonmagnetic 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. For a series with different ferromagnetic materials consisting of Pt/Fe, Pt/Ni 33 Fe 67 , Pt/Ni 81 Fe 19 (permalloy), and Pt/Ni bilayers 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 magneto-optical parameters and allow identifying the optical dispersion δ and absorption β across the Pt L 3 -absorption edge.

Quantitative Disentanglement of the Spin Seebeck, Proximity-Induced, and Ferromagnetic-Induced Anomalous Nernst Effect in Normal-Metal–Ferromagnet Bilayers

“…5(b) to ab initio calculations [28], we obtain a maximum Pt magnetic moment of (0.48 ± 0.08) µ B per spin polarized Pt atom, consistent with earlier results [41]. The effective spin polarized Pt thickness is calculated to be (1.0 ± 0.1) nm similar to our previous investigations [41].…”

Static Magnetic Proximity Effect inPt/NiFe2O4andKuschel1, Klewe2, Schmalhorst3 et al. 2015Phys. Rev. Lett.Self Cite70251141View full textAdd to dashboardCite

“…The asymmetry ratio of the Pt/Fe sample has its maximum near the absorption maximum of the Pt L 3 edge (11567.5 eV) and vanishes at energies of more than 30 eV below and above 40 . Therefore, influences from other absorption edges can be excluded.…”

“…1). The magnetooptic profile is generated by a Gaussian function at the Pt/Fe interface convoluted with the roughness profile of the layers 40 . We obtain a FWHM value of the magnetooptic profile of (1.1 ± 0.1) nm, which can be interpreted as the effective thickness of the spin polarized Pt layer at the interface to Fe.…”

Interface-induced phenomena in magnetism

“…An example phenomenon is proximity-induced magnetism at the interface between a non-magnet and a ferromagnet, in which ferromagnetic order in one layer induces a moment in the neighboring non-magnetic layer, which decays away from the interface. In non-magnetic materials that are already close to a ferromagnetic instability, like Pt or Pd, this induced moment can be substantial, although its magnitude is presently somewhat controversial [Wilhelm et al ., 2000; Wende, 2004; Huang et al ., 2012; Geprägs et al ., 2012; Zhang et al ., 2015a; Kuschel et al ., 2015; Klewe et al ., 2016]. This effect is related to the “giant moments” known to exist in Pt and Pd with very dilute Co or Fe substitution [Crangle and Scott 1965].…”