Structural and Magnetic Properties of MnFe₁ - rm xCoᵣm xGe Compounds

The structural and magnetic properties of MnFe₁ - xCo_ xGe compounds with$ x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9,$and$1.0$were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD shows that the MnFe₁ - xCo_ xGe compounds crystallize in the hexagonal Ni₂In-type crystal structure for$ x le 0.8$and in the orthorhombic NiTiSi-type structure for$x ≫ 0.8$. The magnetization measurements show that the MnFe₁ - xCo_ xGe compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni₂In type structure increase with increasing of x and the saturation of the magnetization in the NiTiSi-type structure also increases with increasing x. We investigated the magnetocaloric effects in these compounds by means of magnetization measurements. The maximum magnetic-entropy change observed in these compounds reaches 9 J/kgK for$ x = 0.8$in a field change from 0 to 5 T at around 289 K.