High-T _C ferromagnetic semiconductor-like behavior and unusual electrical properties in compounds with a 2× 2× 2 superstructure of the half-heusler phase

Heusler phases, including the full- and half-Heusler families, represent an outstanding class of multifunctional materials on account of their great tunability in compositions, valence electron counts (VEC), and properties. Here we demonstrate a systematic design of a series of new compounds with a 2× 2× 2 superstructure of the half-Heusler unit cell in X-Y-Z (X=Fe, Ru, Co, Rh, Ir; Y=Zn, Mn; Z=Sn, Sb) systems. Their structures were solved by using both powder and single-crystal X-ray diffraction, and also directly observed by using high-angle annular dark-field imaging in a scanning transmission electron microscope (HAADF-STEM). The VEC values of these new compounds span a wide and continuous range comparable to those for the full- and half-Heusler families, thereby implying tunability in compositions and physical properties in the superstructure. In fact, we observed abnormal electrical properties and a ferromagnetic semiconductor-like behavior with a high and tunable Curie temperature in these superstructures. Doing things by halves: A series of new compounds that crystallize in the 2× 2× 2 superstructure of the half-Heusler phase have been obtained (see figure). In these new compounds, abnormal electrical properties and a ferromagnetic semiconductor-like behavior above room temperature have been observed.