Magnetic Properties And Magnetocaloric Effect In NaZn₁₃-type LaFe_11.6-xCo_xSi_1.4 And LaY_0.1Fe_11.4T_0.1Si_1.5 Alloys

NaZn13-type La(Fe,Si)13 compounds are one of the promising candidates for magnetic refrigerant due to their large magnetocaloric effect, low cost and friendly environment. However, the disadvantages of the compounds are lower Curie temperature and the unstable phase structure. In order to improve these disadvantages, we have systematically investigated the magnetic properties and magnetcaloric effect in (LaR)(Fe,T,Si)13 alloys by the substitution for La site and substitution for Fe site. LaFe11.6-xCoxSi1.4(x=0, 0.1,0.2,0.3,0.4,0.5,0.6)and LaY0.1Fe11.4T0.1Si1.5(T=Cr, Mn, Fe, Co, Ni) were successfully prepared by arc melting the raw material with low purity. The structure, magnetic properties and magnetocaloric effect have been investigated by means of x-ray diffraction, Scanning electron microscopy (SEM), magnetic measurements and the direct measurement of the adiabatic temperature change. The main results are as follows:The structural and magnetic properties of LaFe11.6-xCoxSi1.4(x=0,0.1,0.2, 0.3,0.4,0.5,0.6)compounds have been investigated by means of X-ray diffraction and magnetic measurements. The XRD results show that all the compounds crystallize in the NaZn13-type structure (space group Fm-3c). The Curie temperature increases with increasing Co content. The Curie temperature is about 188 K and the maximum value of the magnetic entropy change is found to be 18.2J/(kg.K) for LaFe11.5Co0.1Si1.4 compound for a field change from 0 to 1.5 T. The large magnetic entropy change is attributed to the sharp change of the magnetization in the vicinity of Curie temperature and the field-induced transition.The LaYo.1Fe11.4To.1Si1.5(T=Cr, Mn, Fe, Co, Ni) compounds were prepared by arc melting. XRD analysis and SEM component analysis show that the LaYo.1Fe11.4T0.1Si1.5(T=Cr, Mn, Fe, Co, Ni) compounds of the NaZn13-type cubic phase, La rich phase (P4/nmn) andα-Fe phase, the lattice parameters keep a constant almost due to the similar atom radii of Cr, Mn, Fe, Co.Magnetic measurement indicates that the Curie temperature of the compounds increase with decreasing atom radius of substitution atom T (except for T=Mn). Magnetic entropy changes-△Sm are calculated from the isothermal magnetizations by using the Maxwell relation,the maximum values of the magnetic entropy change are 5.1,13.0,20.7,12.7 and 7.4 J·kg-1·K-1, respectively. It should be noticed that the alloy has the largest magnetic entropy change for T=Fe. The largest value of magnetic entropy change extends to the high temperature zone when increasing the external fields, which is due to the IEMT above Criue Temperature.