Investigation Of The Magnetic Properties And Magnetocaloric Effect In Rare-Earth Based Intermetallic Compounds

In recent years,magnetic refrigeration technology has been recognized as a promising new type of refrigeration technology due to its advantages of energy conservation,efficiency,and environmental protection,and is also a potential alternative to gas compression refrigeration.The key to the development of magnetic refrigeration technology is to explore giant magnetothermal materials that can meet the requirements of working at suitable temperatures.In this thesis,RE_1-xRE’_xCo Ni（RE,RE’=Dy,Ho,Er,x=0,0.25,0.5,0.75,1）,Er Co₂B_x（x=0,0.025,0.05,0.075,0.1）and RE₆Ni_2.3In_0.7（RE=Ho,Er,Tm）intermetallic compounds were prepared by arc melting,and their structures,magnetism and magnetocaloric effects were systematically researched,and the following research results were obtained.The RE_1-xRE’_xCo Ni（RE,RE’=Dy,Ho,Er,x=0,0.25,0.5,0.75,1）compounds are Mg Cu₂（C15）cubic structure,and the space group are Fd3m.With the increase of temperature,the compound will undergo a secondary magnetic phase transition from ferromagnetic state to paramagnetic state,with almost no hysteresis and thermal hysteresis.Moreover,with the increase of x,the Curie temperature T_Cof Dy_1-xHo_xCo Ni compounds linearly decreased from 67.0 K to 41.0 K,and the T_Cvalue of Ho_1-xEr_xCo Ni linearly decreased from 41.0 K to 23.0 K,basically covering the entire cooling range in the mid-temperature region.WhenΔH=5 T,the maximum magnetic entropy change-ΔS_Mof RE_1-xRE’_xCo Ni compounds varies from 9.87 to 18.80 J/kg K;The average temperature magnetic entropy change TEC（5 K）varies from 9.79 to18.29 J/kg K;The refrigerant capacity RC varies from 330.23 to 433.27 J/kg;The relative cooling power RCP varies from 427.51 to 586.97 J/kg.It has been proved that RE_1-xRE’_xCo Ni material is a medium temperature magnetic refrigeration material with good application potential.The main phase of Er Co₂B_x（x=0,0.025,0.05,0.075,0.1）doped with trace boron element is Mg Cu₂type Laves phase structure,and the space group is Fd3m.The doping of trace boron will make the lattice constant decrease first and then increase,but the Curie temperature T_Cdoes not change significantly.The ferromagnetic-paramagnetic phase transition occurs with the increase of temperature.Although all compounds are first-order magnetic phase transitions,the doping of B element can effectively reduce the thermal hysteresis of the compounds.Er Co₂B_xcompounds in external magnetic field change ofΔH=5 T,the maximum magnetic entropy change-ΔS_Mcan reach 28.10,30.07,26.78,27.71 and 25.62 J/kg K respectively;The average temperature magnetic entropy change TEC（5 K）is 26.62,28.17,24.94,26.36 and24.86 J/kg K respectively;TEC（10 K）is 22.09,24.98,20.97,24.07 and 21.99 J/kg K respectively.The refrigerant capacity RC is 204.98,258.76,205.02,265.95 and235.40 J/kg respectively;The relative cooling power RCP is 245.84,298.70,257.62,322.53 and 285.40 J/kg respectively.It is proved that B element doping can regulate the magnetic and magnetothermal properties of Er Co₂,which makes Er Co₂B_x（x=0,0.025,0.05,0.075,0.1）material have certain research value in the field of mid-temperature magnetic refrigeration.The ternary intermetallic compounds RE₆Ni_2.3In_0.7（RE=Ho,Er,Tm）belong to Ho₆Co₂Ga type structure,and the space group is Immm.The three samples undergo continuous and complex magnetic phase transitions as the temperature increases.When external magnetic field changeΔH=2,5 and 7 T,the maximum magnetic entropy change-ΔS_Mof RE₆Ni_2.3In_0.7（RE=Ho,Er,Tm）compounds can reach 1.27,5.97and 9.66 J/kg K,2.12,9.09 and 13.93 J/kg K,6.54,14.49 and 17.59 J/kg K respectively.In addition,whenΔH=5 T,the average temperature magnetic entropy change TEC（5K）and TEC（10 K）of RE₆Ni_2.3In_0.7（RE=Ho,Er,Tm）compounds can reach 5.84 and5.70 J/kg K,8.78 and 8.48 J/kg K,13.90 and 12.79 J/kg K respectively.The RC and RCP can reach 140.24 J/kg and 179.75 J/kg,171.79 J/kg and 220.70 J/kg;182.86 J/kg and 234.45 J/kg,respectively.Among them,Tm₆Ni_2.3In_0.7material not only has good refrigeration capacity,but also has a relatively wide refrigeration temperature range,which has potential application prospects in the field of magnetic refrigeration.