Investigation Of The Magnetic Properties And Magnetocaloric Effect In Rare Earth-Co Based Ternary Intermetallics

Magnetic refrigeration is considered to be one of the most promising cooling method in the future.Compared with traditional gas compression/expansion-based cooling technique,it has many advantages like high efficiency,non-polluting refrigerant and more reliable.Magnetic refrigeration is based on magnetocaloric effect?MCE?which usually manifest as isothermal magnetic entropy change??SM?and adiabatic temperature change??Tad?.Searching new materials with large value of MCE is considered to be the main work in the research field of magnetic refrigeration.In this thesis,we synthesis the single phases RECoC₂?RE = Gd,Ho,Er?,RECoC?RE = Gd,Tb,Er?and RE₂CoAl₃?RE = Gd,Tb,Dy,Ho?compounds and investigate their crystal structure,magnetic properties and magnetocaloric effect,the relevant results are as followes.RECoC₂?RE = Gd,Ho,Er?are crystallized in CeNiC₂-type structure with space group of Ammm2.All the compounds undergo a second-order PM-FM transition around Tc = 15 K,11 K,14 K.The large MCE appears around its own transition temperature.For the magnetic field change of 0-5 T,the values of-?SMmax reach 28.4 J/kg K,15.6 J/kg,17.2 J/kg K,the values of RCP are 566 J/kg,242 J/kg,378 J/kg and the values of RC are 369 J/kg,183 J/kg,243 J/kg for RECoC₂?RE-Gd,Ho,Er?,respectively.RECoC?RE = Gd,Tb,Er?are crystallized in YCoC-type structure with space group of P4/mmm.GdCoC and TbCoC undergo a second-order PM-FM transition around Tc ?14 K,22 K.ErCoC undergo a PM-AFM transition around TN =10 K and a field induced AFM-FM metamagnetic phase transition occured.The large MCE appears around the transition temperature.For the magnetic field change of 0-5 T,the values of-?SMmax reach 13.2 J/kg K,8.6 J/kg K,7.7 J/kg K,14.1 J/kg K,the values of RCP are 602 J/kg,368 J/kg,340 J/kg,382 J/kg and the values of RC are 450 J/kg,285 J/kg,268 J/kg,294 J/kg for RECoC?RE = Gd,Tb,Er?,respectively.RE₂CoAl₃?RE = Gd,Tb,Ho,Er?are 'crystallized in MgCu₂ structure with space group of Fd-3m.All the compounds undergo a second-order PM-FM transition around TC 70 K,47 K.33 K,20 K.The considerable MCE appears around the transition temperature.For the magnetic field change of 0-5 T,the values of-?SMmax reach 28.4 J/kg K,15.6 J/kg,17.2 J/kg K,the values of RCP are 566 J/kg,242 J/kg,378 J/kg and the values of RC are 369 J/kg,183 J/kg,243 J/kg,respectively.