Magnetti Properties And Magnetocaloric Effect In La_0.8Ce_0.2 (Fe_1-xCo_x)_11.4Si_1.6, La_0.5Pr_0.5 (Fe_1-xCo_x)_11.4Si_1.6, La_0.8

Room-temperature magnetic refrigeration research has attracted much attention due to its higher energy efficiency and environment safety. Because of low cost and large magnetocaloric effect, the Cubic NaZn₁₃-type compounds La(Fe_xM_1-x)₁₃ (M=A1, Si) were promising candidate for magnetic refrigerant materials at room temperature. The LaFe_11.4Si_1.6 compound exhibits the itenerant-electron metamagnetic (IEM) transition and large magnetovolume effect, so that it has giant magnetocaloric effect (MCE). It has been reported that the isothermal entropy change AS could be greatly increased by the substitution of Ce or Pr for part of La in the LaFe_11.4Si_1.6 compound. However, after substitution, the Curie temperature of compound is too low. So in order to increase the Curie temperature, the compound has been studied further by the way of experimentation. The main results were as follows:(1) The crystal structure, itinerant-electron metamagnetic transition (IEMT)and magnetocaloric effects (MCE) in the compounds La_0.8Ce_0.2 (Fe_1-xCo_x) _11.4Si_1.6(x=0.02, 0.04, 0.06 ) have been investigated . The powder X-ray diffractionrevealed that the La_0.8Ce_0.2 (Fe_1-xCo_x ) _11.4Si_1.6(x=0.02, 0.04, 0.06 ) annealed at 1373 K in vacuum for only 7days could be crystallized in the cubic NaZn-type structure. The Curie temperature T_C is tunable from 207K to 277 K with Co doping from x=0.02 to 0.06. The maximum value of |â–³S_M(T)| for x=0.02, 0.04, 0.06 are 40.17, 12.60 and 7.65J/kg·K under a field of 1.5T. Therefore the compounds exhibited giant values of entropy change. The Curie temperature of x=0.06 is 277 K which has been reached to room-temperature and the maximum value of |â–³S_M(T)| is 7.65J/kg·K under a field of 1.5T which is much larger than that of Gd. These properties make it as a promising candidate of magnetic refrigerant material.(2) La_0.5Pr_0.5 (Fe_1-xCo_x ) _11.4Si_1.6(x=0, 0.02., 0.04, 0.06,0.08) compounds were prepared by arc melting and their magnetic properties have been studied. The powder X-ray diffraction revealed that the compounds annealed at 1373 K in vacuum for only 7days could be crystallized in the cubic NaZn-type structure. The Curie temperature increases from 185K to 296 K with Co doping from x=0 to 0.08. Under a field of 1.5T,the maximum value of |â–³S_M(T)| for x=0, 0.02, 0.04, 0.06,0.08 are 28.92,14.72 12.10,7.12,4.22J/kg·K respectively.(3) The effect which caused by the substitution of Co for Fe on the Curie temperature in the La_0.8Ce_0.2 (Fe_1-xCo_x )_11.4Si_1.6(x=0.02, 0.04, 0.06 ) compounds and La_0.5Pr_0.5 (Fe_1-xCo_x ) _11.4Si_1.6(x=0, 0.02, 0.04, 0.06,0.08) compounds has been discussed. It is conclude that the changes of lattice parameter contraction and the reciprocity between various atoms after substitution of Co are the main reason of increasing the Curie temperature.(4) The structural and magnetic properties of La_0.8Ce_0.2Fe_11.1-xCo_0.8Si_1.1B_x (x=0,0.3,0.6) compound have been investigated by means of X-ray diffraction and magnetization measurements. Our results demonstrate that the addition of element B 3could help to be crystallized in the cubic NaZn₁₃-type structure for the compound. With increasing B content, the Curie temperature T_C increase from 278K for x=0.3 to 286K for x =0.6. Simultaneity, the magnetic entropy change |â–³S_M(T)| increase from 6.364J/kg·K for x=0.3 to 10.23J/kg·K for x =0. 6 under a field of 1.5T .