Fully-Compensated Ferrimagnetic Spin Filter Materials within the Cr$\textit{M}\textit{N}$Al Equiatomic Quaternary Heusler Alloys

TL;DR

This study uses advanced density functional theory to identify new fully-compensated ferrimagnetic spin filter materials within CrMNAl Heusler alloys, highlighting their electronic properties and stability under stress for spintronic applications.

Contribution

The paper predicts novel fully-compensated ferrimagnetic spin filter materials with small gaps and large exchange splitting, and analyzes their stability and electronic phase tunability under hydrostatic stress.

Findings

CrVZrAl, CrVHfAl, CrTiNbAl, CrTiTaAl are robust spin filter candidates.

CrTiNbAl and CrTiTaAl have very small band gaps (~0.10 eV).

Certain compounds exhibit phase transitions under hydrostatic stress.

Abstract

XX'YZ equiatomic quaternary Heusler alloys (EQHA's) containing Cr, Al, and select Group IVB elements ($\textit{M}$ = Ti, Zr, Hf) and Group VB elements ($\textit{N}$ = V, Nb, Ta) were studied using state-of-the-art density functional theory to determine their effectiveness in spintronic applications. Each alloy is classified based on their spin-dependent electronic structure as a half-metal, a spin gapless semiconductor, or a spin filter material. We predict several new fully-compensated ferrimagnetic spin filter materials with small electronic gaps and large exchange splitting allowing for robust spin polarization with small resistance. CrVZrAl, CrVHfAl, CrTiNbAl, and CrTiTaAl are identified as particularly robust spin filter candidates with an exchange splitting of $\sim 0.20$ eV. In particular, CrTiNbAl and CrTiTaAl have exceptionally small band gaps of $\sim 0.10$ eV. Moreover, in these compounds, a spin asymmetric electronic band gap is maintained in 2 of 3 possible atomic arrangements they can take, making the electronic properties less susceptible to random site disorder. In addition, hydrostatic stress is applied to a subset of the studied compounds in order to determine the stability and tunability of the various electronic phases. Specifically, we find the CrAlV$\textit{M}$ subfamily of compounds to be exceptionally sensitive to hydrostatic stress, yielding transitions between all spin-dependent electronic phases.