Possible Half-Metallic Behavior of Co2-xCrxFeGe Heusler Alloys: Theory and Experiment

Abstract

Co2- based intermetallic Heusler alloys are among the most attractive half-metallic systems due to their high Curie temperatures, high spin polarization and the structural similarity to binary semiconductors [1,2]. The Co2FeGe system is one such candidate of interest for spintronic applications, but experimentally it does not form a single phase in bulk form [3,4,5]. In this work, we have introduced Cr doping to stabilize the Co2FeGe system, and examined the structural, magnetic, transport, and mechanical properties of quaternary Heusler alloys Co2-xCrxFeGe with 0 ≤ x ≤ 1, both experimentally and theoretically. Single phase microstructures are observed for Cr compositions from x = 0.25 to x = 1. The samples with Cr concentrations below x = 0.25 are multi-phase. XRD patterns at room temperature show the presence of ordered Y structure (space group F-43m, # 216) for all single-phase samples. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a noted prerequisite for half metallicity. The Density functional theory calculations performed using VASP code with projector augmented wave method (PAW) and the Perdew-Burke-Enzerhof (PBE) functional predict half-metallic character in the alloys after Cr substitution. All alloys are observed to have high Curie temperatures, and show a linear dependence with the saturation magnetic moment which is expected in half metallic Co-based Heusler alloys [6]. Transport measurements were performed to explain the electronic structure of the alloys. High mechanical hardness values are also observed which makes these materials suitable for industrial applications requiring repetitive thermal cycling and resist cracking from vibrations.