Structure And Magnetic Properties Of RNi_4-xCo_xCu（R=Nd,Gd） Compounds

With the development of magnetic refrigeration technology,magnetic refrigeration prototype,magnetic refrigerant and magnetic refrigeration theory have made great progress,because of its environmental protection and high efficiency.Rare earth intermetallic compounds are selected as magnetic refrigerants because of their high magnetic moment,adjustable Curie temperature and large magnetocaloric effect.Among them,RTM₅rare earth compound is an important kind of magnetic material.In this paper,the crystal structure and magnetic properties of RTM₅ rare earth compounds have been systematically studied.The main findings are as follows:NdNi_4-xCo_xCu（x=0,1,1.5,1.7,1.9,2,2.1,2.3,2.5,3.0,4.0）series compound samples were prepared by using arc-melting method.The results of XRD analysis show that the samples annealed at 1423 K are all single-phase Ca Cu₅ hexagonal structure with space group P6/mmm,the lattice parameter a increases,the lattice parameter c decreases and the volume V increases.The results of magnetic measurements show that spin reorientation occurs when x≥1.9,Curie temperature increases with the increase of Co content,and the Arrott curves show that the series of compounds undergo a second-order phase transition.Using Maxwell relation,the isothermal magnetic entropy change of the samples with temperature and magnetic field change was obtained from the isothermal M-B curves.The results show that the relatively large cooling power can be obtained.GdNi_4-xCo_xCu（x=1.5,1.7,1.9,2.1,2.3,2.5）samples were prepared by using arc-melting method.The samples were annealed at 1423 K.The main phase of GdNi_4-xCo_xCu was Ca Cu₅ hexagonal structure（space group P6/mmm）,there is a small amount of impurity phase with GdNi₃-type hexagonal structure（R3m）,The change of lattice parameters is the same as that of Nd-series.The results of magnetic measurement show that there is no spin reorientation phenomenon in GdNi_4-xCo_xCu series,and the Curie temperature increases with the increase of Co content.Based on the isothermal M-B curve data,the isothermal magnetic entropy changes of the samples were derived in different temperatures and magnetic field changes.Only the sample with x=1 show large magnetocaloric effect,but the working temperature of it is low.