Systematic search for new Co2YZ and Rh2YZ Heusler alloys based on theoretical calculations

Abstract

A systematic structural and magnetic study of an extensive list of Co2YZ and Rh2YZ alloys (Y = d-elements, Z = p-elements) has been performed to identify new materials structurally related to the Ni2MnGa alloys. The target compositions were selected according to theoretical predictions of a tetragonal distortion of an ideally Heusler lattice. Based on the X-ray diffraction, microprobe, and differential scanning calorimetry results, the quality of individual samples was determined and 11 systems, including the novel Co3Sn, Co2NiSn, Co2NiSi, Co2CuGa, and Co2RhGe alloys, were found to be phase-pure or containing only a minor fraction of any secondary phases. The analysis of X-ray diffraction patterns confirmed the tetragonal structure of the Rh2YZ alloys, space group P 42/n c m, as predicted by DFT calculations. However, the crystal structure of Co2YZ is not consistent with the predicted tetragonal structure. Instead, a hexagonal structure, space group P 6/m m m, was determined. Magnetization measurements revealed that all the Rh- and Co-based alloys order ferromagnetically below 450 K and 1000 K, respectively. Additional anomalies of Co3Sn and Co2NiSn in the magnetization data and the peaks in differential scanning calorimetry profiles evidence the respective phases are metastable below ~900 K and transform to equilibrate phases above this temperature. The experimental results, both structural and magnetic properties, are discussed in the framework of previous experimental and theoretical studies.