Structure And Magnetic Properties Of GdTbHoErRE(RE=La,Pr,Y)rare Earth High Entropy Alloy

In this work,the rare earth high-entropy alloys（HEAs）Gd Tb Ho Er,GdTbHoErY,Gd Tb Ho Er La,Gd Tb Ho Er Pr and Gd Tb Ho Er La Y with hexagonal close-packed（HCP）structure were prepared by arc smelting and ribbon spinning.Three aspects of work have been done on these HEAs:1.XRD,SEM and TEM have proved that the rare earth HEA GdTbHoErY has a single phase HCP structure,and its magnetic phase diagram was drawn.The types of phase transition and magnetocaloric effect（MCE）were studied.2.On the basis of the rare earth HEA Gd Tb Ho Er,the non-magnetic elements La,Y and the magnetic element Pr are added respectively to explore the relationship between the"entropy"in the HEAs and the"entropy"in the magnetic entropy（?S_M）.3.The effect of rapid cooling treatment on the structure and MCE of rare earth HEA was investigated.Based on research on the rare earth HEA GdTbHoErY,it is found that the alloy is a single-phase HCP structure.Under a magnetic field of 5 T,the refrigerant capacity（RC）and?S_Mof GdTbHoErY reaches 341 J·kg^-1and 5.4 J·kg^-1K^-1,respectively.The high RC is caused by the larger operating temperature range.With the increase of the external magnetic field,the peak near the magnetic transition temperature combines with the peak below the magnetic transition temperature,which makes the operating temperature region larger,thereby increasing the RC value.In addition,because the atoms are randomly distributed on the crystal lattice,the complex magnetic structure and exchange coupling make the magnetic sequence gradually change,which leads to the enhancement of the MCE.On the basis of the rare earth HEA Gd Tb Ho Er,by the addition of non-magnetic elements La and Y,it is found that these HEAs all have a single-phase HCP structure.As the configuration entropy increases,the?S_M(from 8.64 to 5.85 J·kg^-1K^-1)decreases instead.For the HEAs Gd Tb Ho Er,Gd Tb Ho Er La and Gd Tb Ho Er La Y,the RC values under an applied magnetic field of 5 T are 924.48,390.72 and 245.70 J·kg^-1,respectively.In order to verify whether the dilution effect of non-magnetic La and Y reduces the magnetization of these HEAs,magnetic Pr is added to the HEA Gd Tb Ho Er,and it is found that it is still decreasing.According to experimental results and related literature,the magnetic properties of HEAs depend on the intrinsic magnetic properties of rare earth 4f,and the configuration entropy seems to have almost nothing to do with the?S_M.In addition,it is also found that these HEAs show very high saturation magnetization at low temperatures,especially the HEA Gd Tb Ho Er,which exhibit a saturation magnetization of 291.3 emu/g.The study found that the rare earth HEAs Gd Tb Ho Er,Gd Tb Ho Er La and Gd Tb Ho Er La Y after rapid cooling（29 m/s）still maintained the HCP structure with the space group P63/mmc.In addition,the magnetic transition temperatures of the HEAs Gd Tb Ho Er,Gd Tb Ho Er La and Gd Tb Ho Er La Y are 190 K,117 K and 120 K,respectively.Under a 5 T magnetic field,their?S_Mare 7.43,6.83 and 6.37 J·kg^-1k^-1,and the corresponding RC values are 420,306 and 249 J·kg^-1,respectively.In summary,the?S_Mand RC of the HEAs after the rapid cooling still maintain the law of decreasing with the increase of configuration entropy.This shows that the method of preparing or processing the sample will not affect the relationship between configuration entropy and magnetic entropy.Rare earth HEAs exhibit excellent magnetic properties,which provides ideas for the development of new refrigeration materials.