Substitution effects of cr or fe on the curie temperature for Mn-based layered compounds MnAlGe and MnGaGe with Cu₂Sb-type structure

Structure, lattice parameters, spontaneous magnetization (I_s), and the Curie temperature (T_C) of MnAlGe and MnGaGe compounds with the Cu2 Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced Is and T_C, whereas Fe substitution for Mn degraded them. These behaviors are in accord with the previously reported results, and are also common to the MnGaGe compound series. For MnAlGe, lattice parameter a increases by 0.2% and 0.4% for Cr and Fe substitution, while c changes by +0.1% and -1.3%, respectively. For MnGaGe, a decreases by 0.08% for Cr and increases by 0.2% for Fe substitution, while c changes by +0.5% and -1.0%, respectively. T_C tended to increase with increasing length of c, suggesting that the interlayer distance between Mn layers is a key factor related to the height of T_C, i.e., the strength of the magnetic exchange interaction.