Design And Fabrication Of A Measuring Instrument Of Magnetocaloric Effect And Study On Magnetic Properties Of High Pressure And High Temperature Sintered Mn_1.28Fe_0.68P_0.46Si_0.58Compound

Magnetic refrigeration is a kind of refrigeration which works base on the magnetocalric effect (MCE) of magnetic materials. Magnetic refrigeration is more efficiency and environment-friendly than normal refrigeration. And this makes the research of magnetic refrigeration draws worldwide attention. In this thesis, we report the design and fabrication of a measuring instrument of magnetocaloric effect, and the magnetic properties of MnFePSi compound sintered at different temperatures and under different pressures.The magnetocaloric effect of magnetic materials can be characterized by adiabatic temperature change or isothermal magnetic entropy change. Since the mature of magnetic measurements, the method of magnetic entropy change is often used. But in magnetic refrigeration cycle, the adiabatic temperature change ΔTad is more practical parameter.Therefore, we designed and fabricated a measuring instrument of magnetocaloric effect. This measurement system consists of magnetic field section, temperature-varying-control section and data acquisition section. The maximum field intensity of magnetic field is1.2T. Temperature-varying-control section includes the drive system, the sample isulation part and the environment temperature control part. The temperature-varying-control system and the data acquisition hardware and software were made by ourselve. This measuring instrument can test the adiabatic temperature change of magnetic materials in the temperature range from-253K to303K under1.2T.In order to calibrate the device, we take Gd as standard sample to get the data of adiabatic temperature change in1.2T. The data are consistent with the literature’s data, that means the device has high accuracy. This measuring instrument has become a common device for measuring magnetocaloric effect, due to the simple operation, high measurement speed and high accuracy.In recent years, the first-order phase transition material MnFePSi compounds attracted much attention as a room-temperature magnetic refrigerant. In order to further study the magnetic refrigeration performance of MnFePSi, we studied the influence of different sintered temperature and different pressure on to the magnetic properties of MnFePSi compounds.First, the samples were sintered at temperature of1373K under different pressures,2,3and4GPa. All of the sintered compounds crystallize in Fe2P-type hexagonal structure. With the increasing pressure, the thermal hysteresis has a maximum at2GPa, but the Curie temperature decreases. The magnetic entropy change decreased strongly when pressure increased to4GPa.Then, at a fixed pressure2GPa, sinterd the samples at different temperatures,1273K,1373K and1473K. The result shows that the compounds crystallization Fe2P-type hexagonal, structure. Higher or lower sintering temperature will lead to the decrease of magnetic entropy change.1373K is the most suitable sintering temperature, same as ambient pressure.In summary, the Curie temperature TC, MCE and the lattice parameters decrease with applied pressure. The density and mechanical properties of the compounds can be adjusted by sintering temperature and pressure.