Structure, lattice parameters, spontaneous magnetization (Is), and the Curie temperature (TC) of MnAlGe and MnGaGe compounds with the Cu2 Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced Is and TC, 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. TC 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 TC, i.e., the strength of the magnetic exchange interaction.
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