Effects Of B, Cr, V Doping On The Structural And Magnetocaloric Effect Of MnFe (P, Si) Compounds

In recent years, studies on room-temperature magnetic refrigerant materials have become the hot research topic for new type of refrigeration. Among the room temperature magnetic refrigerant materials, Mn-Fe-based magnetic refrigerant materials have been investigated intensively, due to their large magnetocaloric effect, simple preparation process, low cost of materials. In order to obtain the excellent room-temperature magnetocaloric material, this work studies the effects of doping on the performance of MnFe(P, Si) compound, and further tuning the microstructure and magnetic properties.The first chapter introduces the research background of magnetic refrigeration materials, the principle of magnetic refrigeration, the development in room temperature magnetic refrigeration materials and theories.The second chapter describes the sample preparation methods and measurement equipments.The third chapter studies using non-poisonous Si element instead of As elements, MnFe (P, Si) compound is formed, Mn1.25FexP0.5Si0.5 compounds were prepared by mechanical alloying followed by solid state sintering method and their structure and magnetic properties were investigated. The results show that the compounds crystallize in a main phase of Fe2P-type hexagonal structure with space group P 6 2m; With the increase of the Fe content, the thermal hysteresis decreases first and then increases.The fourth chapter studies the incorporation of interstitial atom B, using B instead of Si, to study the structure and magnetic properties of Mn1.25Fe0.65P0.5Si0.5-xBx compounds. The XRD results show that the main phase of the compounds is Fe2P-type hexagonal structure with space group P6 2m. With the increase of the content of B, the Curie temperature increases. With the increase of the content of B, the maximum magnetic entropy decreases.The fifth chapter reports the study of the structure and magnetic properties of Mni.oFeo.9-xCrxP0.5Si0.5 and Mn1.0-xCrxFeo.9Po.5Sio.5 compounds. The results show that:(1) Mn1.0Fe0.9xCrxP0.5Si0.5 the main phase of the compounds is Fe2P-type hexagonal structure with space group P 6 2m.With the increase of the content of Cr, the Curie temperature decreases. With the increase of the content of Cr, the maximum magnetic entropy decreases. (2) Mn1.0-xCrxFeo.9Po.5Sio.5 the main phase of the compounds is Fe2P-type hexagonal structure with space group P 6 2m. With the increase of the content of Cr, the Curie temperature decreases. With the increase of the content of Cr, the maximum magnetic entropy decreases.The chapter 6 studies using V instead of Mn and Fe, to study the structure and magnetic properties of Mni.oFe0.9-xVxPo.5Sio.5 and Mn1.0-xVxFeo.9Po.5Sio.5 compounds. The results show that:(1) Mn1.0Fe0.9-xVxPo.5Sio.5 the main phase of the compounds is Fe2P-type hexagonal structure with space group P 6 2m.With the increase of the content of V, the Curie temperature decreases. With the increase of the content of V, the maximum magnetic entropy decreases. (2) Mn1.0-xVxFeo.9Po.5Sio.5 the main phase of the compounds is Fe2P-type hexagonal structure with space group P62m.With the increase of the content of V, the Curie temperature decreases. With the increase of the content of V, the maximum magnetic entropy decreases.