Study On The Magnetic And Magnetocaloric Effect Of The NaZn₁₃ Type Rare Earth-Transition Compounds

With people's widespread attentions on environmental and energy problems,people pay more and more attention to and explore more reasonable and effective cooling way,to replace the traditional gas compression expansion refrigeration technology in order to avoid the damage to the environment.The magnetic refrigeration technology based on the magnetocaloric effect?MCE?,with its green environmental protection,energy saving and efficient significant advantage,becoming one of the most potential of application of refrigeration technology.Recently,NaZn₁₃-type La?Fe,M?₁₃?M=Si,Al?compounds have attracted highly attentions on account of their low cost,toxin-free,tunable Curie temperature?T_C?and giant magnetocaloric effect?GMCE?.TheLa?Fe,M?₁₃?M=Si,Al?-based compounds were prepared by smelting,annealing,quenching and hydrogen absorption and then being detected.X-Ray Powder Diffraction?XRD?,vibrating sample magnetometer?VSM?were used to investigate the phase structure,the magnetic transition and MCE.1.The effects of different hydrogen pressure on the hydrogen absorption process of LaFe_11.5Al_1.5.5 compound were studied.The hydrogen content and the lattice constant of LaFe_11.5Al_1.5.5 compound increase with enhance the hydrogen pressure.Nevertheless,when the pressure achieves to 15MPa,hydrogen content and lattice constant decline appreciably because of the decline of lattice radius under high pressure.Moreover,hydrogenation treatment to the LaFe_11.5Al_1.5.5 compound remarkably lessen the thermal hysteresis and keep the-?S_M at high value.2.The magnetic properties and the magnetocaloric effect?MCE?of LaFe_11.5Al_1.5alloy introduced into the small radius of atoms?H,B,C?have been studied.Introduction of small radius atoms?H,B,C?as interstitial atoms makes the magnetic ground state has changed from the anti-ferromagnetic?AFM?to the ferromagnetic?FM?state at the same time with T_C and Ms significantly enhanced with adding the content of interstitial atoms?H,B or C?.Interestingly,the magnetic transition changed from the second-order to the weakly first-order with adding hydrogen contents.On the contrary,the magnetic transition from the weakly first-order to the second-order with adding boron or carbon contents.All the compounds of LaFe_11.5Al_1.5.5 hydrides,borides and carbides present a largish magnetic entropy change.The maximum magnetic entropy change?-?S_M?attains to 12.3J/kg·K for LaFe_11.5Al_1.5H_1.3,10.8J/kg·K for LaFe_11.5Al_1.5B_0.1.1 and 9.6J/kg·K for LaFe_11.5Al_1.5C_0.2.2 under 0-5T magnetic field change.The value of refrigerant capacity?RC?attains to 259.2 J/kg for LaFe_11.5Al_1.5H_0.6,230.4 J/kg for LaFe_11.5Al_1.5B_0.1.1 and116.4 J/kg for LaFe_11.5Al_1.5C_0.1.3.The magnetic properties and the magnetocaloric effect?MCE?of La(Fe_1-x-x Al_x)_11.4Si_1.6compounds and La(Fe_1-y-y Mn_y)_11.4Si_1.6.6 compounds have been studied.?-Fe phase has been found in La(Fe_1-yMn_y)_11.4Si_1.6?x=o.o4,0.06?compounds,indicating Mn atoms is go against to form 1:13 phase.By replacing Fe sites with Al atoms,the magnetic ground state is changed from an AFM to a FM state,accompanied by significant rises in the Curie temperature?T_C?with increasing Al atoms.The random substitution of Mn for Fe lead to the competition between the FM and AFM interactions will cause the frustration generating the spin-glass behavior.With increasing Mn content,the Curie temperature?T_C?decline.And with increasing the content of substituent atoms?Al/Mn?,the large magnetic entropy change?-?S_M?decrease linearly.