Study On Structure And Magnetic Related Properties Of R_1-xR’_xCo₂ Compounds Mixed With Light And Heavy Rare Earths

Rare earth-transition metal compounds with Laves phase exhibit excellent magnetocaloric and magnetostrictive properties.In this paper,the compounds of Pr_1-xDy_xCo₂,Nd_1-xGd_xCo₂,Sm_1-xDy_xCo₂,Nd_1-xDy_xCo₂ containing both light and heavy rare earths were mainly studied,and compared with the compounds of Dy Co_2-xCr_xand Pr_1-xDy_xNi₂,respectively.The above samples were prepared by strip quenching and argon arc melting respectively.The crystal structures,phases and magnetic properties of the above compounds were characterized by some modern advanced technology and methods.In the study of Pr_1-xDy_xCo₂ compounds,the substitution of Dy for Pr results in the shift of diffraction peak angle to high angle and the increase of Curie temperature.In addition,the mutual substitution of Pr and Dy leads to many anomalous physical phenomena in the compound:large hard magnetic properties are found in the RCo₂ compounds,which are considered to be soft magnetic materials;the isothermal magnetization curves of the compounds show a crossover phenomenon,which leads to positive and negative sudden changes and double peaks in the magnetic entropy curve of the compounds.However,when the two samples of Pr_0.6Dy_0.4Co₂ and Pr_0.7Dy_0.3Co₂ were characterized by variable temperature XRD,no structural transformation of the compounds was found,but the lattice expanded with the increase of temperature.In addition,the Pr_1-xDy_xNi₂ compounds in the comparative experiment did not exhibit low temperature hard magnetic properties.In the study of Nd_1-xGd_xCo₂ compounds,it was found that the substitution of heavy rare earth Gd for light rare earth Nd also led to the decrease of lattice constant and the linear increase of Curie temperature.At the critical point x=0.4,the magnetic properties of the compound changed abruptly and the coercivity was 2200 Oe at 10 K.The overall magnetocaloric properties of the compounds are not very excellent,because the mutual substitution of Nd and Gd does not change the order of the magnetic transition of the compounds,and the compounds are still second order magnetic transition materials.However,the Curie temperature of the compounds increase from 156.2 K at x=0.2 to 340.1K at x=0.8,and the compounds have a wide working temperature range.In the study of Sm_1-xDy_xCo₂ compounds,it was found that the mutual substitution of Sm and Dy can greatly enhance the hard magnetic properties of the compounds.Sm_0.45Dy_0.55Co₂ has the largest coercivity,while Sm_0.3Dy_0.7Co₂ has the largest magnetic energy product.In addition,the hysteresis loops of the compound have good squareness and the maximum remanence ratio is 0.97.In addition,the magnetocaloric effect of Sm_0.4Dy_0.6Co₂ compound was characterized,and the compound had first-order phase transition with a maximum magnetic entropy change of 4.75 J/kg K and a relative cooling capacity RCP of 143.69 J/kg under a magnetic field of 5 T.The study on Nd_1-xDy_xCo₂ also found that the mutual substitution of light and heavy rare earths could also increase the coercivity of the compounds.It was found that the coercivity of the compounds had the maximum coercivity at x=0.4.In addition,the magnetic remanence ratios of the compounds were all above 0.6.In contrast,the improvement of the coercivity of the Dy Co_2-xCr_x compound was not obvious,and the highest magnetic remanence ratio of this series of compounds was only 0.53.This study provides detailed experimental data and theoretical basis for the development of hard magnetic properties and magnetocaloric properties of RCo₂ rare earth-transition group intermetallic compounds.