Element Substitution And Doping Effect On The Magnetic Properties And Magnetocaloric Effect Of Mn(Fe,Co)Ge-based Alloy

Room temperature magnetic refrigeration materials are updated refrigeration materials that changes temperature under the alternating magnetic field. There are several advantages of nontoxic, high efficiency, long life etc. The based Mn Co Ge magnetic refrigeration materials which have structure of XMM ′ —type Martensitic phase transition have characteristics of second-order phase transition of FM-PM, and its phase transition at low temperature, thermal hysteresis and hysteresis-free, simple preparation and cooling capacity.In recent years, cooling materials researchers attention to and research this material because of the great potential and excellent performance on magnetocaloric.Using powder x-ray diffractometer and vibrating sample magnetometer system research and analysis the crystal structure of alloys and magnetocaloric effect.This paper present to reveal the impact on material critical structures changing alloy chemical ratios with Structure of martensite phase transition Mn Co Ge alloy as research object.The first three chapters are introduced research status of Magnetic refrigeration materials and Materials for magnetic refrigeration at room temperature and Structure of martensite phase transition Mn Co Ge alloy respectively, and describes the instruments and equipment required for the preparation and measurement.The fourth chapter(introduces the experimental method and principles that)a large amounts of lower price Si elements replace expensive Ge elements of Mn Co Ge alloy, and Mn Fe0.3Co0.7Ge1-xSix(0.00,0.10,0.20,0.30,0.40,0.50,0.60,0.70)series alloys is prepared by means of the natural cooling way in the resistance furnace.the alloy structure turned from Ni2 In Hexagon structure to Ti Ni Si orthogonal structure with the addition of elements. Based M-T curve find that Curie temperature increases from 234.3 K to 288.6 K.And the property of this series alloys is Second-order phase transition in the room temperature environment conditions. The M-B curves data measured by VSM calculated magnetic entropy change by maxwell relationship, and obtained that m?S minimize to 1.23 1K)(kg J-?? from 1.461K)(kg J-?? under the 0~1.5 T external magnetic field. Si elements replacement Ge elements achieved the purpose of reducing the cost, and get the half-peak widths second phase materials, and lay a good foundation for further research.The fifth chapter, in order to further improve the magneto-thermal properties of the series alloy, micro adjust Fe/Co ratio and prepared Mn FexCo1-xGe0.5Si0.5(0.20,0.22,0.24,0.26, 0.30) series alloy with Curie temperature room-span temperature. And measure magnetic properties of the alloy and analysis phase. Phase analysis with X-ray diffractometer indicate that this series alloys for Ti Ni Si-phase structure. X,pert Plus Fitting software found that Lattice parameters a have no significant variation, but b and c decreased linear, and cell volume also has a decreasing trend. Constant magnetic field magnetization curve(M-T) measured by vibrating sample magnetometer find that curie temperature room-span temperature gradually from 322.5 K down to 287.4 K. Isothermal magnetization curve(M-B)data made Arrott curve and can be seen that is the second order phase transition materials not the first phase transition materials,and sure phase transition temperature of the window has been closed. By Fe/Co micro adjust under0~1.5 T enhanced alloy magnetic entropy from 1.201K)(kg J-?? to 1.421K)(kg J-??. So get the half-peak widths and lower price and curie temperature room-span temperature alloy.In the sixth chapter, structural phase transition temperature decreased between Ti Ni Si phase Ni2 In phase FM-PM phase by put interstitial atom B and prepared Mn Fe0.22Co0.78Ge0.5Si0.5Bx(x=0.01,0.04,0.05,0.06)series alloy. Phase analysis with powder x-ray diffractometer and measured magnetic properties of the alloy of VSM indicate that alloy structure turned into hexagonal structure(Ni2In type)from orthogonal structure(Ti Ni Si type). We can see from M-T curve that CT decreased linear of this series alloys with the increase of B element until FM-PM no happened first phase transition under the first curie temperature(265K). Arrott curve of Mn Fe0.22Co0.78Ge0.5Si0.5B0.05 alloys indicate that this series alloys happened second-order phase transition.M?S increased slightly from 1.22 to 1.521K)(kg J-?? witch calculated under 0~1.5 T.