Studies On The Magnetocaloric And Electrical Transport Properties Of MnFe(P,Si)Compounds

Compared comprehensively with various room-temperature magnetic refrigerant materials, the series of MnFe(P,Si) compounds stand out for its environment-friendly and superior performance, low cost, and simple and mature preparation process. In. order to further enhance the value of its commercial applications, the researchers have been carrying out a large number of in-depth and meticulous research. Through the experiment, the author of this paper did some research and exploration on the phase structure, magnetocaloric effect and electronic transport properties of the series of Mn2-xFexP0.48Si0.56(x=0.55,0.60,0.65,0.70) compounds.The research course of magnetic refrigerant technology as well as the research progress of magnetic refrigerant materials was briefly summarized in the first chapter. The choice and its application prospect of room-temperature magnetic refrigerant materials were summed up.The experimental apparatus and equipment, and some software used in the process of the preparation and the measurement of the series of Mn2-xFexP0.48Si0.56(x=0.55,0.60,0.65,0.70) compounds were briefly introduced, and test process is given in the second chapter.The research of the phase structure and energy dispersive spectrum analysis of Mn2-xFexP0.48Si0.56(x=0.55,0.60,0.65,0.70) series compounds was discussed in the third chapter. Experimental results show that the series compounds are characterized with Fe2P-type hexagonal structure, space group P-62m, the lattice constants (a,c) change regularly with the change of Fe content. By SEM, the accuracy of XRD pattern analysis results is further confirmed. The energy dispersive spectrum shows that this series of compounds are into uniform phase and the single structure;there is no impurity. The research of the magnetism and magnetocaloric effect of Mn2-xFexP0.48Si0.56(x=0-55,0.60,0.65,0.70) series compounds was discussed in the fourth chapter. The experimental results show that with the increase of the content of Fe, the magnetism of the compound enhances; Curie temperature and maximal isothermal magnetic entropy change are growing; thermal hysteresis has no obvious change rule. When x=0.70, the Curie temperature increases to286.6K; when field change is1.5T, the maximal isothermal magnetic entropy change to7.79J/kgK. Along with the rise of temperature, materials undergo a first-order phase transition of ferromagnetic phase to the paramagnetic phase; The field-induced PM-FM transition was not observed near the Curie temperature; to view comprehensively, this series of materials has good magnetocaloric performance.The research of the electronic transport properties of the series of Mn2-xFexP0.48Si0.56(x=0-55,0.60,0.65,0.70) compounds was discussed in the fifth chapter. Experimental results show that the resistivity of the material with doped semiconductor element rises apparently. With different doping ratio, the resistivity changes differ. Under the condition of300K and the zero field, the resistivity of this series of compounds changes between (7.19～71.63)μmΩ. The resistivity will also rise obviously with increasing field. The resistivity within the zone lower than Curie temperature presents a typical metal electrical conductivity. When temperature increases, abnormal behavior of resistivity takes place. When it is over the Curie temperature, the resistivity decreases sharply. The mutations of resistivity reflect that magnetic phase changes. When field change is1.5T, the magnetoresistance effect of the material changes between4.86%～30%with hysteresis in the process; hysteresis has no obvious change rule.