Transport spin polarization of Ni_xFe_{1-x}: electronic kinematics and band structure

TL;DR

This study measures and calculates the transport spin polarization of Ni_xFe_{1-x} alloys, revealing its surprising independence from composition and highlighting the complex relationship between spin polarization and electronic band structure.

Contribution

It provides the first combined experimental and theoretical analysis of spin polarization across the Ni-Fe alloy system, uncovering composition-independent behavior.

Findings

Spin polarization is nearly constant across compositions.

Sign of spin polarization does not match the density of states difference.

Compensation of DOS and Fermi velocity explains the observed behavior.

Abstract

We present measurements of the transport spin polarization of Ni_xFe_{1-x} (0<x<1) using the recently-developed Point Contact Andreev Reflection technique, and compare them with our first principles calculations of the spin polarization for this system. Surpisingly, the measured spin polarization is almost composition-independent. The results clearly demonstrate that the sign of the transport spin polarization does not coincide with that of the difference of the densities of states at the Fermi level. Calculations indicate that the independence of the spin polarization of the composition is due to compensation of density of states and Fermi velocity in the s- and d- bands.