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High-resolution transmission electron microscopy and superconducting quantum interference device magnetometry shows that epitaxial CuMnSb films exhibit a coexistence of two magnetic phases, coherently intertwined in nanometric scales. The dominant ~phase is half-Heusler cubic antiferromagnet with the N\'eel temperature of 62~K, the equilibrium structure of bulk CuMnSb. The secondary phase is its ferromagnetic tetragonal polymorph with the Curie temperature of about 100~K. First principles calculations provide a consistent interpretation of experiment, since (i) total energy of --CuMnSb is higher than that of --CuMnSb only by 0. 12~eV per formula unit, which allows for epitaxial stabilization of this phase, (ii) the metallic character of --CuMnSb favors the Ruderman-Kittel-Kasuya-Yoshida ferromagnetic coupling, and (iii) the calculated effective Curie-Weiss magnetic moment of Mn ions in both phases is about 5. 5~B, favorably close to the measured value. Calculated properties of all point native defects indicate that the most likely to occur are MnCu antisites. They affect magnetic properties of epilayers, but they cannot induce the ferromagnetic order in CuMnSb. Combined, the findings highlight a practical route towards fabrication of functional materials in which coexisting polymorphs provide complementing functionalities in one host.
Ciechan et al. (Wed,) studied this question.