Influences of interstitial atoms H, B and C on magnetic properties and magnetocaloric effect in LaFe11.5Al1.5 compound

Abstract

Magnetic refrigeration materials based on magnetocaloric effect (MCE) attract wide attention.In the past decades, magnetic materials with MCE have been extensively studied due to their enormous potential applications in magnetic refrigeration fields.Among these materials,La (Fe,Al)13 compound is perceived to be one of the promising candidates as high-performance magnetic refrigerant because of its giant magnetic entropy change,tunable Curie temperature,low cost and toxin-free.For LaFe13-xAlx compounds,previous studies showed that the TC can increase by substituting Co for Fe,which leads to the value of maximum magnetic entropy change (-△SM) decreasing.In addition,the interstitial atom (N,H,C and B) can cause the lattice to expand,which shifts the anti-ferromagnetic (AFM) ground state to the ferromagnetic (FM) state.The TC increases with doping the interstitial atoms,accompanied by a remarkable change in the magnetic properties related to the magneto-volume effect.In this paper,the magnetic properties and the magnetocaloric effects of LaFe11.5Al1.5Hx(x=0,0.12,0.6 and 1.3), LaFe11.5Al1.5By(y=0.1,0.2 and 0.3) and LaFe11.5Al1.5Cz(z=0.1,0.2,0.3,0.4 and 0.5) intermetallic compounds are studied.The H,B or C atoms are inserted into the LaFe11.5Al1.5 compounds by gas-solid or solid-solid reaction.All the compounds crystallize into the cubic NaZn13-type structure.The magnetic ground state changes from the AFM to the FM state due to the introduction of interstitial atoms.Unlike the patent compound LaFe11.5Al1.5,all of the hydrides,borides and carbides display a typical FM state,which easily reach saturation under a magnetic field of 1 T.In addition,the saturation magnetization (MS) slightly increases and the Curie temperature (TC) significantly is enhanced with increasing the interstitial atom (H,B or C) content.It is attractive that the magnetic transition changes from the second-order to the weakly first-order with increasing hydrogen content,which is in contrast with the magnetic transition from the weakly first-order to the second-order with increasing boron or carbon content.All the compounds of LaFe11.5Al1.5 hydrides, borides and carbides exhibit a considerable magnetic entropy change.The values of maximum magnetic entropy change (-△SM) reach 12.3 J/kg·K for LaFe11.5Al1.5H1.3,9.6 J/kg·K for LaFe11.5Al1.5B0.1 and 10.8 J/kg·K for LaFe11.5Al1.5C0.2 under a magnetic field change of 0-5 T,respectively.And the values of refrigerant capacity (RC) reach 259.2 J/kg for LaFe11.5Al1.5H0.6,116.4 J/kg for LaFe11.5Al1.5B0.1,and 230.4 J/kg for LaFe11.5Al1.5C0.1 under a magnetic field change of 0-5 T,respectively,indicating that LaFe11.5Al1.5H0.6 compound is a promising candidate for magnetic refrigerants.