Ab initiotheoretical study of magnetization and phase stability of the(Fe,Co,Ni)23B6and(Fe,Co,Ni)23Zr6structures ofCr23C6andMn23Th6prototypes

Abstract

We present an ab initio theoretical investigation of the magnetization and phase stability of two different complex cubic structures of prototype Cr23C6 and Mn23Th6, with an emphasis on the Fe,Co,Ni23B6 and Fe,Co,Ni23Zr6 compositions. These phases have recently been observed as secondary or even primary crystallization products of Fe,Co,Ni-Zr-B and related metallic glasses that have been studied for applications as soft magnets with nanocrystalline grain size. We first demonstrate the validity of the theoretical technique employed through a detailed comparison between the predictions of the calculations for the Co-Zr binary system and the experimentally stable phases. We then investigate the magnetization and stability of the binary phases. While the Fe-based binary Fe23Zr6 and Fe23B6 phases are expected to have the highest magnetization, the Co-based binary Co23Zr6 and Co23B6 structures are predicted to be the most stable of each prototype. The Co23Zr6 structure is the only binary 23:6 structure predicted to be a stable phase for the Fe,Co,Ni23B6 and Fe,Co,Ni23Zr6 systems investigated here. Small additions of Zr atoms to the Fe,Co,Ni23B6 phases tend to substitutionally occupy the 8c Wykoff site and stabilize these structures. In contrast, small additions of B to the Fe,Co,Ni23Zr6 phases have a much weaker site preference and tend to destabilize these structures. As a result, Fe,Co,Ni23B6 structures are stabilized in Fe,Co,Ni-Zr-B systems relative to the binary Fe,Co,Ni23B6 systems while the Fe,Co,Ni23Zr6 phases are not. The results presented in this work are in good qualitative agreement with experimental observations of the compositional modifications tending to promote formation of the 23:6 phases in Fe-Co-Zr-B and related metallic glasses.