  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.
