Diffusive and ballistic current spin-polarization in magnetron-sputtered L1o-ordered epitaxial FePt

TL;DR

This study investigates the structural, magnetic, and electron transport properties of epitaxial FePt films, revealing high diffusive spin current polarization and moderate ballistic spin polarization, with implications for spintronic applications.

Contribution

It provides the first detailed comparison of diffusive and ballistic spin current polarization in epitaxial FePt films, highlighting the impact of scattering times on spin polarization.

Findings

Diffusive spin current polarization exceeds 80% across temperatures 2-258 K.

Ballistic spin polarization measured at ~42% at 4.2 K.

Strong perpendicular magnetic anisotropy with S~0.90 in FePt films.

Abstract

We report on the structural, magnetic, and electron transport properties of a L1o-ordered epitaxial iron-platinum alloy layer fabricated by magnetron-sputtering on a MgO(001) substrate. The film studied displayed a long range chemical order parameter of S~0.90, and hence has a very strong perpendicular magnetic anisotropy. In the diffusive electron transport regime, for temperatures ranging from 2 K to 258 K, we found hysteresis in the magnetoresistance mainly due to electron scattering from magnetic domain walls. At 2 K, we observed an overall domain wall magnetoresistance of about 0.5 %. By evaluating the spin current asymmetry alpha = sigma_up / sigma_down, we were able to estimate the diffusive spin current polarization. At all temperatures ranging from 2 K to 258 K, we found a diffusive spin current polarization of > 80%. To study the ballistic transport regime, we have performed point-contact Andreev-reflection measurements at 4.2 K. We obtained a value for the ballistic current spin polarization of ~42% (which compares very well with that of a polycrystalline thin film of elemental Fe). We attribute the discrepancy to a difference in the characteristic scattering times for oppositely spin-polarized electrons, such scattering times influencing the diffusive but not the ballistic current spin polarization.