Structural insight using anomalous XRD into Mn2CoAl Heusler alloy films grown by magnetron sputtering, IBAS and MBE techniques

TL;DR

This study uses anomalous XRD to analyze the atomic structures of Mn2CoAl Heusler alloy films grown by different methods, revealing structural details crucial for understanding their spin-gapless semiconductor properties.

Contribution

It provides the first detailed atomic-level structural analysis of Mn2CoAl films grown by various techniques using anomalous XRD, highlighting discrepancies from expected structures.

Findings

None of the films form the expected XA-type structure.

All films exhibit spin-gapless semiconductor characteristics.

Microstructure and atomic-scale defects influence SGS properties.

Abstract

Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless semiconductor (SGS), grown by three different methods: ultra-high vacuum magnetron spattering, Ar-ion beam assisted sputtering, and molecular beam epitaxy, are investigated by comparing their electric transport properties, microstructures and atomic-level structures. Of the samples, the Mn2CoAl thin film grown by MBE consists of Mn- and Co-rich phases, the structures of which are determined to be the L21B-type and disordered L21-type, respectively, according to anomalous XRD analysis. None of them forms the XA-type structure expected for SGS Heusler alloy, although they all show SGS characteristics. We suggest, to validate SGS characteristics, it is necessary to extract not only magnetic and electric transport properties but also information about microstructures and atomic-scale structures of the films including defects such as atomic swap.