Synthesis, Characterization, and First-Principles Analysis of the MAB-Like Ternary Transition-Metal Boride Fe(MoB)2.

Abstract

Novel transition-metal borides have attracted considerable attention because they exhibit high stability under extreme conditions. Compared with binary borides, ternary transition-metal borides (TTMBs) exhibit novel boron substructures and diverse properties, which result in excellent designability. In this study, we synthesized the MAB-like (where M = iron, A = molybdenum, and B = boron) phase Fe(MoB)2 using a high-pressure and high-temperature method. Fe(MoB)2 exhibited ferromagnetic metastable characteristics with a saturation magnetization of 8.35 emu/g at room temperature. Microhardness measurement revealed an indentation hardness of 10.72 GPa, which was higher than those of conventional magnetic materials. First-principles calculations revealed excellent mechanical properties, which mainly originated from the strong covalent short B2 chains. Furthermore, magnetism was attributed to the Fe 3d electrons. Numerous d-d hybridizations existed between the Fe 3d eg and Mo 4d orbitals, and the antibonding/nonbonding state difference for up/down-spin electrons in the hybridization orbitals led to the local magnetic moment of Fe(MoB)2. The magnetic anisotropy energy analyses reveal that Fe(MoB)2 prefers the easy magnetization axis along the z direction, and Mo atom acts as a medium to realize the exchange action between two Fe atoms. The B-B and Fe-B bonds were considerably stronger than the Fe-Mo and Mo-B bonds, and Fe(MoB)2 exhibited a class of atomically laminate composed of FeB2 and Mo layers. These results may provide guidance for the design of novel multifunctional TTMBs by adjusting the interactions between binary metal components.