Structural Evolution Under Pressure And Magnetic Properties Of Rare Earth-Based High Entropy Alloys

High-entropy alloys(multi-principal-element alloys)overturned the traditional alloy design concept.The alloy design is based on equal-atomic ratio and high mixing entropy,etc.,and the formation of multi-principal-element single-phase solid solution structure has attracted widespread attention.Investigating the stability of the structure and other properties of material along with its composition has the significant guidance for the practical values of new alloys in the future.Moreover that is the critical point in this research field.In this paper,we investigate the rare earth-based high entropy alloy.The evolution of the structure under pressure and the change of its structure and magnetic properties with its composition are studied detailedly.The vacuum arc furnace was used to prepare the La Pr Nd YDy high-entropy alloy which has a double close-packed hexagonal(d HCP)structure.We used the in-situ high-pressure synchrotron radiation X-ray diffraction technology to study the structure of materials and focused on the structural evolution under pressure.The measurement turns out,during the compressing process,the La Pr Nd YDy high-entropy alloy undergoes a phase transition of d HCP?FCC(face centered cubic)?d FCC(disordered face centered cubic),and the phase change pressure is about 4.3 GPa and 13.2 GPa,respectively;In decompressing process,the alloy structure gradually changed from d FCC back to d HCP,indicating that this pressure-induced structural phase is a one.Through the analysis of the average atomic volume during the experiment,it was found that no obvious volume collapse occurred in the experiment,which indicating that the experimental pressure has no effect on the delocalized electrons in 4f band.The phase transition is mainly caused from the changed electron density in the d band.Five kinds of high-entropy alloys with different light and heavy rare earth components,including YTb Dy Ho Er,YPr Dy Ho Er,La Nd Dy Ho Tb,La Pr Nd Dy Ho and YDy Pr Nd La,were prepared by electric arc furnace,and we detailedly discuss the evolution of their structure with composition.From the result of X-ray diffraction(XRD),the structure of the high-entropy alloy sample undergoes a structural transformation of HCP?Sm-type?d HCP,with the increase of the composition of light rare earth elements.This is corresponding to the variation of the rare earth elements structure when decrease the atomic number,and it shows the typical cocktail effect of high-entropy alloys.The magnetic properties of the three rare earth-based high-entropy alloys,YPr Gd Tb Dy,YDy Ho Pr Nd and YTb Dy Ho Er were studied.Experimental studies have found that the magnetic change trajectories of these three high-entropy alloys are similar.First,the magnetic properites of the alloys gradually change from antiferromagnetic(AFM)to paramagnetic(PM)near the Neel temperature(T_N).And second,the corresponding saturated magnetization(M_S)is gradually decreased which is directly due to thermal movement in the systems.In addition,according to the specific experimental data,the T_N of the YDy Ho Pr Nd high-entropy alloy is about 54 K,the M_S(unified statistics 10 K)is 83.41 emu/g,the T_N of the YPr Gd Tb Dy high-entropy alloy is about 134.6 K,and the M_S is 157.33 emu/g,The T_N of the high-entropy alloy YTb Dy Ho Er is about 142.5K,and the M_S is 231.38 emu/g,indicating that with the decrease of the atomic proportion of the heavy rare earth element,the T_N gradually shifts to low temperature,and the M_S gradually decreases accordingly.That shows although rare earth elements have significant chemical similarities and almost complete mutual solubility,due to their different magnetic characteristics,random mixing will cause high-entropy alloys to exhibit different magnetic behaviors.