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

Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless semiconductor (SGS), grown by three different methods—ultra-high vacuum magnetron sputtering, 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 molecular beam epitaxy 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 X-ray diffraction analysis. None of them forms the XA-type structure expected for SGS Heusler alloy, although they all exhibit SGS characteristics. To validate the SGS characteristics, it is necessary to extract not only the magnetic and electric transport properties but also information about microstructures and atomic-scale structures of the films including defects such as atomic swap.