Structural and Magnetic Properties of MnFe $_1 - rm x$ Co $_rm x$ Ge Compounds

The structural and magnetic properties of MnFe 1-x Co x Ge 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 MnFe 1-x Co x Ge compounds crystallize in the hexagonal Ni 2 In-type crystal structure for xles0.8 and in the orthorhombic NiTiSi-type structure for x>0.8. The magnetization measurements show that the MnFe 1-x Co x Ge compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni 2 In 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