Direct evidence for minority spin gap in the Co2MnSi Heusler alloy

TL;DR

This study provides direct experimental evidence of a minority spin gap in Co2MnSi Heusler alloy, demonstrating how surface modifications can restore the gap at the Fermi level, leading to highly efficient spintronic properties.

Contribution

The paper presents the first direct observation of the minority spin gap at the Fermi level in Co2MnSi and shows how surface treatments can recover this gap for improved spin polarization.

Findings

Minority spin gap observed at the surface of Co2MnSi.

Surface modifications can restore the spin gap at the Fermi level.

Achieved very low damping coefficients (~7x10^-4) with surface treatments.

Abstract

Half Metal Magnets are of great interest in the field of spintronics because of their potential full spin-polarization at the Fermi level and low magnetization damping. The high Curie temperature and predicted 0.7eV minority spin gap make the Heusler alloy Co2MnSi very promising for applications.We investigated the half-metallic magnetic character of this alloy using spin-resolved photoemission, ab initio calculation and ferromagnetic resonance. At the surface of Co2MnSi, a gap in the minority spin channel is observed, leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi level and a minority spin state is observed at the Fermi level. We show that a minority spin gap at the Fermi energy can nevertheless be recovered either by changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi or MgO. This results in extremely small damping coefficients reaching values as low as 7x 10-4.