The Research On Magnetic Properties And Magnetocaloric Effect Of Mn₅Ge_3-xIn_x And Mn₅Ge_3-xSn_x Compounds

The technique of magnetic refrigeration is a new type of refrigeration technology with energy saving and environmental protection. It has a bright prospect in replacing the conventional vapor compression technology. Magnetic material is a key factor for the development of room temperature magnetic refrigeration technology. So we have studied two different materials in this thesis:one is Mn5Ge3-xSnx(x= 0,0.05,0.1,0.15,0.2) compounds and the other is Mn5Ge3-xnx (x= 0,0.05,0.1,0.15,0.2) compounds. The structure, magnetic properties and magnetocaloric effect of Mn5Ge3 compounds were studied by the substitution of Sn and In for Ge sites. The main results and conclusions of works are as follows:Mn5Ge3-xSnx(x= 0,0.05,0.1,0.15,0.2) and Mn5Ge3-xInx(x= 0,0.05,0.1, 0.15,0.2) compounds were prepared by arc-melting and High-Temperature Furnaces. X-ray diffraction analysis reveals that the above compounds all have the Mn5Si3-type orthorhombic structure (space group:P63/mcm). The magnetic measurements show that there is no thermal hysteresis effect in Mn5Ge3-xSnx(x= 0,0.05,0.1,0.15,0.2) compounds and Mn5Ge3-xnx (x= 0, 0.05,0.1,0.15,0.2) compounds, behaving ferro-paramagnetic second-order phase transition. The Curie temperature of the above compounds are between 300 K and 305 K. The isothermal magnetic entropy change of Mn5Ge3-xSnx (x = 0,0.05,0.1,0.15,0.2) are 2.81 J/kg·K,2.85 J/kg·K,2.03 J/kg·K,2.5 J/kg·K, 2.33 J/kg·K and the isothermal magnetic entropy change of Mn5Ge3-xInx(x= 0, 0.05,0.1,0.15,0.2) are 2.81 J/kg·K,2.74 J/kg·K,2.73 J/kg·K,2.03 J/kg·K, 2.42 J/kg·K, which can both compare the isothermal magnetic entropy change of Gd, in the low magnetic field 1.5 T.