The Influence Of Carbon Atom And The Substitution Of Rare-earth On The Structure And Magnetic Properties Of NaZn₁₃-type LaFe_13-xAl_x Compounds

Room-temperature magnetic refrigeration research has attracted much attention due to its higher energy efficiency and environment safety. NaZn₁₃-type La(Fe,Al)₁₃ compounds were promising candidate for magnetic refrigeration due to their low cost and large magnetocaloric effect. The magnetic properties of La(Fe,Al)₁₃ compounds were complicated. The research on the fundamental magnetic properties of these compounds is useful for the development of the magnetic refrigeration. Magnetic properties, magntetocaloric effect and magnetic phase transition in NaZn₁₃-type compounds La(Fe,Al)₁₃ were investigated by introducing interstitial atoms and substituting other atoms for the rare earth.NaZn₁₃-type LaFe_13-xAl)xC)y (x=1.6,1.8) and R_xLa_1-xFe_11.4Al_1.6C_y(R=Ce,Pr,Nd)compounds were prepared by arc melting in a high purity argon atmosphere and were vacuum annealed for ₁₃ days at 1223 K. The main results were as follows:The effects of carbon atoms on the magnetic properties and magnetic entropy change in compounds LaFe_13-xAl_x and the type of magnetic phase transition in LaFe_13-xAl_xC0.1 were studied. The volume expansion played a major role in determining its magnetic properties. Complicated magnetic phase transitions induced by external magnetic field were found in carbonization of LaFe_11.4Al_1.6 compound with low carbon concentration. And the temperature of phase transition depends on magnetic field strongly. The magnetic ground state of LaFe_11.4Al_1.6Cx compound changes from antiferromagnetic to ferromagnetic for x>0.06 and the Curie temperature increased monotonously with the increase of carbon content. A large magnetic entropy change was obtained near the phase transition temperature and the refrigerant capacity is good. The type of phase transition of LaFe_13-xAl_xC0.1 changed from first order to second order with Al content increased from 1.6 to 1.8. As a consequence, the magnetic entropy change decreased.The effect caused by the substitution of Pr for La on the magnetic properties and magnetocaloric effect in LaFe_13-xAl_x compounds were discussed. It was shown that the lattice parameter contraction and the R-Fe coupling resulted in complex magnetic properties in Pr_0.2La_0.8Fe_11.4Al₁.6 and Pr_0.3La_0.7Fe_11.4Al_1.6, which are similar to that of LaFe_11.4Al_1.6C0.02 and LaFe_11.4Al_1.6C_0.04 respectively. It shows that in these compounds the magnetic properties rely on both the lattice parameter and Pr-Fe interaction.The magnetic properties and magnetocaloric effect in Nd_0.1La_0.9Fe_11.4Al_1.6C_x compounds have been investigated. Although the Nd-Fe coupling and volume contraction enhance the positive Fe-Fe interaction, the volume expansion caused by carbon atoms weakens the ferromagnetic interaction. So the saturated magnetization of Nd_0.1La_0.9Fe_11.4Al_1.6C_x decreased and the entropy change is smaller than LaFe_11.4Al_1.6C_x.In conclusion, the lattice parameter, magnetic entropy change and magnetic phase transition of these compounds are accord with the previous results. It is worth noting that some significant...