Growth and Characterization of Mn2–xCoGe, Mn2–xRhGe and Mn2–xCoGe Thin Films

Abstract

Skyrmions are the smallest possible thermodynamically stable magnetic state, and are therefore promising objects for information storage. New tetragonal structures within the vast Heusler family of compounds are predicted by density functional theory (DFT) to be skyrmion hosting candidates. This work explores the crystal structure and magnetic properties of sputtered thin-films of Mn1≤α≤2{Co,Rh,Ir}Ge ternary compounds. These ternary compounds predominantly formed two hexagonal (P63/mmc and P-62m) structures. MnαCoGe films formed a Ni2In-type (P63/mmc) structure which had not been previously observed. The saturation magnetization, Msat, for Co and Rh variants are 20%–30% lower than MnCoGe bulk of Msat=2.78 µB per formula unit (f.u.). However, the Msat for Mn2.0IrGe was significantly lower. The Curie temperatures, TC, for Co variants were comparable to bulk MnCoGe at TC=260 K. The larger spin-orbit interaction in Ir and Rh compounds resulted in an increase in coercive field: In the case of Mn2.0IrGe of µ0HC=4.84 T at a temperature of 5 K. For MnRhGe and Mn1.5RhGe films, a hexagonal Fe2P-type (P-62m) structure was identified as the stable phase. However, the Fe2P-type structures have a much smaller magnetocrystalline anisotropy, with a coercive field that is up to 55 times smaller than found in the Ni2In-type structure. None of the thin-films studied in this dissertation demonstrate the DFT calculated Heusler structures. This indicates that the hexagonal phases must be considered when predicting the stable structure of the intermetallic germanides.