Magnetic and structural properties of Fe-substituted MnCoGe with Ni2In-type structure

Abstract

Site occupation of Fe atoms, magnetic and structural properties in MnCo1-xFexGe (x = 0.2, 0.5, 0.7 and 1.0) were investigated. Two phase co-existence of the hexagonal Ni2In-type structure (P-phase) and the orthorhombic TiNiSi-type structure was observed at room temperature for x = 0.2. For x = 0.5, 0.7 and 1.0, MnCo1-xFexGe was confirmed to be the P-phase. With increasing x from 0.2 to 1.0 for the P-phase, the lattice parameter ap slightly increased by only 0.14%, but cp decreased by 2.1%. As a result, when x was increased from 0.2 to 1.0, the unit cell volume of the P-phase decreased monotonously by 1.8%. The saturation magnetic moment and Curie temperature of MnCo0.5Fe0.5Ge were 2.16 μB/f.u. and 205 K, respectively, which decreased monotonically with increasing x. 57Fe Mössbauer spectroscopy indicated that 90–94% of the substituted Fe atoms occupied the Co-site but 10–6% of the Fe also occupied the Mn-site in the P-phase. For x = 0.5, 0.7 and 1.0, the hyperfine field at the Co-site was 8.29–9.44 T, which was larger than that at the Mn-site. The sign of quadruple splitting at the Co-sites changed from positive to negative with the increase of x, suggesting that the electric field gradients at Co-sites changed.