Investigation Of The Magnetic Properties And Magnetocaloric Effect In The Material Of Rare Earth Transition Metal Boroncarbides Compounds

Magnetic refrigeration technology,because of its high efficiency,simple structure and environmental protection,is one of the most promising refrigeration technology.The key of magnetic refrigeration technology is magnetic refrigeration materials.Magnetic refrigeration technology is based on the magnetocaloric effect(MCE)of magnetic refrigeration materials.MCE is characterized by isothermal magnetic entropy change(ΔSM)and adiabatic temperature change(ΔTad).It is the most urgent requirement for the development of magnetic refrigeration technology to find magnetic refrigeration materials with large MCE and wide cooling temperature range.In this thesis,the crystal structure,magnetic properties and magnetocaloric properties of the three systems,the rare earth boron-carbon intermetallic compounds La1-xPrxFe12B6(x=0,0.05,0.1,0.15 and 0.2),RE2Cr2C3(RE=Tb,Dy,Ho and Er)and RECo2B2C(RE=Gd,Tb and Dy),were systematically studied.The conclusions are as follows:The structure of the intermetallic compounds of La1-xPrxFe12B6(x=0,0.05,0.1,0.15 and 0.2)is a trigonal system of the SrNii2B6-type,and the space group is R-3m.With the increase of the temperature,the La1-xPrxFe12B6 compounds undergo the first-order magnetic phase transition of AFM-FM and FM-PM magnetic transition,and the TC of FM-PM magnetic transition increases with the increase of Pr(wt.%),changing between 52～82K.There is a obvious jump and an initial effect in the magnetization process at 3 K.the addition of Pr slow down the hysteresis of the LaFei2B6 compound.The maximum value of the entropy change-ΔSMmax of La1-xPrxFe12B6(x=0.05,0.1,0.15 and 0.2)compounds at the applied magnetic field of 0～5T is calculated to be 9.4,11.4,8.8 and 9.8 J/kg·K,respectively.Compared with the-ΔSMmax of LaFei2B6 compound at 0～5T,0.2J/kg·K,the magnetic entropy of the La1-xPrxFe12B6 compounds becomes very significant after the incorporation of Pr.The magnetic refrigeration capacity RC and the relative magnetic refrigeration capacity RCP of La1-xPrxFe12B6(x=0.05,0.1,0.15 and 0.2)compounds are 249.6,248.3,196.9 and 194.5J/kg;306.4,303.2,241.1 and 250.9J/kg,respectively.The structure of the intermetallic compounds of RE2Cr2C3(RE=Tb,Dy,Ho and Er)belongs to the monoclinic system with Ho2Cr2C3-type,the space group is C2/m.The compounds undergoe the first-order magnetic structure phase transition of PM-AFM magnetic transition.TN are 53.8,23,15,and 7K,respectively.The maximum values of the-ΔSMmax of RE2Cr2C3(RE=Tb,Dy,Ho and Er)at the applied magnetic field of 0-5T are 4.1,8.8,14.0 and 15.2J/kg·K,respectively.The magnetic refrigeration capacity RC and the relative magnetic refrigeration capacity RCP are 95.6,209.3,307.8 and 320.8J/kg;115.7,273.2,402.6 and 399.7J/kg under a magnetic field of 0-5T,respectively.It can be seen that the intermetallic compound of RE2Cr2C3(RE=Tb,Dy,Ho and Er)is a magnetic refrigeration material with great application potential.The RECo2B2C(RE=Gd,Tb and Dy)intermetallic compounds belongs to the tetragonal system of the LuNi2B2C-type,and the space group is I/4mmm.The secondary magnetic structure phase transition of PM-FM transition is verified,and the phase transition temperature TC is 11,5 and 8K,respectively.The maximum value of the entropy change of the intermetallic compounds of RECo2B2C(RE=Gd,Tb and Dy)at 0～5T is calculated to be 9.4,18.1 and 18.0J/kg·K,respectively.Magnetic refrigeration capacity RC and relative magnetic refrigeration capacity RCP are 169.0,350.0 and 380.4J/kg;215.7,441.4 and 485.6J/kg under a magnetic field of 0～5T,respectively.