The LaFe 11.4 Si 1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K(5 h) to 1623 K(2 h) . The powder X-ray diffraction(XRD) and microstructure observations show that large amount of 1:13 phase begins to appear in the LaFe 11.4 Si 1.6 compound annealed at 1423 K(5 h) . In the temperature range from 1423 K to 1523 K,the α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. The LaFeSi phase is rarely observed by XRD when the as-cast compound is annealed at 1523 K(5 h) . With annealing temperature increasing to 1573 K,LaFeSi phase is detected again in LaFe 11.4 Si 1.6 compound. In LaFe 11.4 Si 1.6 compounds annealed at 1523 K(5 h) ,at 1373 K(2 h) +1523 K(5 h) ,and 1523 K(7 h) +1373 K(2 h) ,the impurity phases including small amount of α-Fe and LaFeSi phase reduce in turn. The magnetic measurement shows that LaFe 11.4 Si 1.6 compounds annealed by above three processes keep the first-order of magnetic transition behavior,and T C are both at about 200 K. But the values of the maximal S M(T,H) of has large difference,they are 9.94,12.66,and 13.96 J/(kg·K) under a magnetic field of 0-2 T,respectively.
Magnetic properties and magnetocaloric effects(MCEs) of the HoPdAl compounds with the hexagonal ZrNiAl-type and the orthorhombic TiNiSi-type structures are investigated.Both the compounds are found to be antiferromagnet with the Néel temperature TN=12 and 10 K,respectively.A field-induced metamagnetic transition from antiferromagnetic(AFM) state to ferromagnetic(FM) state is observed below TN.For the hexagonal HoPdAl,a small magnetic field can induce an FM-like state due to a weak AFM coupling,which leads to a high saturation magnetization and gives rise to a large MCE around TN.The maximal value of magnetic entropy change(?SM) is-20.6 J/kg K with a refrigerant capacity(RC) value of 386 J/kg for a field change of 0-5 T.For the orthorhombic HoPdAl,the critical field required for metamagnetic transition is estimated to be about 1.5 T,showing a strong AFM coupling.However,the maximal SM value is still-13.7 J/kg K around TN for a field change of 0-5 T.The large reversible SM and considerable RC suggest that HoPdAl may be an appropriate candidate for magnetic refrigerant in a low temperature range.
Magnetic properties and magnetocaloric effects of La_(1-x)R_xFe_(1105) Si_9105)(R=Pr,(0≤x≤0.5);R = Ce and Nd, (0≤x≤0.3)) compounds are investigated.Partially replacing La with R = Ce,Pr and Nd in La_(1-x)R_xFe_(11.5)Si_(1.5) leads to a reduction in Curie temperature due to the lattice contraction.The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition,which leads to a remarkable increase in magnetic entropy change△S_m and also in hysteresis loss.However,a high effective refrigerant capacity RC_(eff) is still maintained in La_(1-x)R_xFe_(11.5)Si_(1.5).In the present samples,a large△S_m and a high RC_(eff) have been achieved simultaneously.
The magnetic and magnetocaloric properties of(Tb1-xDyx) 6 Co 1.67 Si 3(0 ≤ x ≤ 0.8) have been experimentally investigated.The compounds exhibit a Ce6Ni2Si3-type hexagonal structure and undergo a second-order magnetic transition.The Curie temperature decreases from ～ 187 K to 142 K as the content of Dy grows from 0 to 0.8.The maximal magnetic entropy change,for a field change of 0-5 T,varies between ～ 6.2 and ～ 7.4 J/kg.K,slightly decreasing when Dy is introduced.The substitution of Dy leads to a remarkable increase in refrigeration capacity(RC).A large RC value of ～ 626 J/kg is achieved for x = 0.4 under a field change of 0-5 T.
