Electronic structure, magnetism, and disorder in the Heusler compound Co$_2$TiSn

TL;DR

This study investigates how disorder affects the electronic structure and magnetism of Co$_2$TiSn Heusler compounds using experimental techniques and density functional theory, revealing that moderate antisite disorder does not eliminate half-metallicity.

Contribution

It combines bulk and local spectroscopic methods with advanced DFT calculations to quantify disorder effects and establish spectroscopic probes for local ion ordering in Co$_2$TiSn.

Findings

Up to 10% antisite disorder can exist without detection by X-ray diffraction.

12.5% antisite disorder does not destroy half-metallicity.

Proper DFT level of theory is essential for accurate predictions.

Abstract

Polycrystalline samples of the half-metallic ferromagnet Heusler compound Co$_2$TiSn have been prepared and studied using bulk techniques (X-ray diffraction and magnetization) as well as local probes ($^{119}$Sn M\"ossbauer spectroscopy and $^{59}$Co nuclear magnetic resonance spectroscopy) in order to determine how disorder affects half-metallic behavior and also, to establish the joint use of M\"ossbauer and NMR spectroscopies as a quantitative probe of local ion ordering in these compounds. Additionally, density functional electronic structure calculations on ordered and partially disordered Co$_2$TiSn compounds have been carried out at a number of different levels of theory in order to simultaneously understand how the particular choice of DFT scheme as well as disorder affect the computed magnetization. Our studies suggest that a sample which seems well-ordered by X-ray diffraction and magnetization measurements can possess up to 10% of antisite (Co/Ti) disordering. Computations similarly suggest that even 12.5% antisite Co/Ti disorder does not destroy the half-metallic character of this material. However, the use of an appropriate level of non-local DFT is crucial.