Magnetic Investigations on the MnNiSi1−xGex Compounds Crystallizing in the Co2P Type Structure

$\mathrm{MnNiSi}$ crystallizes in the orthorhombic ${\mathrm{Co}}_2\mathrm{P}$ type structure with a Curie temperature of 616 K and saturation magnetic moment of 2.51 μ_B. Ge was substituted for silicon to increase the Mn‐Mn distance, the magnetic moment, and Curie temperatures. It was possible to obtain single phase materials of ${\mathrm{MnNiSi}}_{\text{1−}\mathrm{x}}{\mathrm{Ge}}_{\mathrm{x}}$ up to $\mathrm{x}\text{\hspace{0.17em}=\hspace{0.17em}0.8}$ . As $\mathrm{x}$ is increased the magnetic moment increases from 2.51 μB to a maximum of 2.90 but the Curie temperature decreases continuously as $\mathrm{x}$ increases. Magnetization versus field measurements at 4.2 K and room temperature show a normal ferromagnetic behavior for all the compounds investigated except for ${\mathrm{MnNiSi}}_{\text{.2}}{\mathrm{Ge}}_{\text{.8}}$ . This compound has a metamagnetic behavior at room temperature and magnetization versus temperature at 6 kOe indicates a sharp peak in the magnetization at 370 K. This anomalous behavior is absent in ${\mathrm{MnNiSi}}_{\text{.3}}{\mathrm{Ge}}_{\text{.7}}$ .