Study On Glass Forming Ability And Magnetocaloric Properties Of Rare Earth-based High Entropy Amorphous Alloys

The magnetic refrigeration material is new refrigeration material with high energy efficiency,low energy consumption,and environmental friendliness,which has large potential value in industrial applications.As a new type of amorphous magnetic refrigerant,the rare earth-based(RE-based)high entropy(HE)amorphous alloy has the charaacteristics of complex electrionic structure and second-order magnetic phase transition,thereby exhibits excellent magnetocaloric performances such as a high peak value of magnetic entropy change(|?_M⁶)|),adjustable Curie temperature(T_C)and a wide range of magnetic transition temperature(₍₂₎.However,it is difficult to synthesize the bulk RE-based HE amorphous alloy with large size till now.In addition,the RE-based HE amorphous alloy is expensive because it contains a large amount of heavy RE elements as raw materials.How to improve the glass forming ability(GFA)and develop a RE-based HE amorphous alloy system with low price and excellent magnetocaloric performance is an urgent issue.This is the primary problem that must be solved for the industrial application of amorphous magnetic refrigerants.Previous studies have indicated that Y element with cheap price,as a substitute element for precious REs,can not only improve the GFA of amorphous alloy systems,but also maintain excellent magnetocaloric properties.Based on this context,the effects of the Y content and the types of lanthanide heavy RE elements as well as the configuration entropy on the GFA and magnetocaloric properties of RE-based HE amorphous alloy was systematically investigated in this work.Firstly,to reduce the cost of RE-based HE amorphous alloy,the Gd₂₅Co₂₅Al₂₅Ho_25-xY_x(x=1,5,10,15,25)amorphous alloys samples were fabricated by replacing Ho by Y element based on the composition of Gd₂₅Co₂₅Al₂₅Ho₂₅ alloy.It can be seen that the T_C of the alloy decreases from 51 to 39 K with the increase of Y element.The Gd₂₅Co₂₅Al₂₅Ho₂₀Y₅amorphous alloy exhibits the largest GFA and the|?_M⁶)|,and the values of the|?_M⁶)|and corresponding RC reach 8.79 Jkg^-1K^-1and 547 Jkg^-1.This phenomenon may be attributed to the HE and magnetic effects in these alloys.Our study shows that the cheaper Y element can effectively manipulate the GFA,|?_M⁶)|and RC of RE-based HE amorphous alloy without significantly deteriorating the magnetocaloric properties.Secondly,the Gd₂₅Co₂₅Al₂₅Y₁₅RE₁₀(RE=Dy,Ho,Er)amorphous alloys were designed and prepared by replacing Ho with Dy or Er element to explore the effect of RE elements on Y-containing RE-based HE amorphous alloys.It is found that with the increase of the atomic number of RE elements,T_C do not show a general changing trend with the order of de Gennes factors(G)based on the Rudermann-Kittel-Kasuya-Yosida theory.Due to the fact that the Y element don't have 4f electrons,the abnormal trend of T_C can be attributed to the weakened f-f exchange interaction caused by the lack of lanthanide RE elements.This work indicate that the presence of Y element can reduce the sensitivity of T_C on heavy RE elements,which can be used to vary the|?_M⁶)|and RC without changing the working temperature of magnetic refrigeration.Finally,we design the compositions of the medium entropy Gd_27.5Tb_27.5Co_17.5Al_27.5 and high entropy Gd_18.34Tb_18.33Dy_18.33Co_17.5Al_27.5 amorphous alloys based on the low entropy RE₅₅Co_17.5Al_27.5(RE=Gd,Tb,Dy)amorphous alloy with the critical diameters of 8 mm to explore the effect of configuration entropy on the GFA and magnetocaloric properties.It can be seen that the high configuration entropy reduces the critical diameters of the amorphous alloys.It may be attributed to the disordered structure of HE system,which reduce the influence of the element types and atomic size on the formation of amorphous phase during solidification process.Based on the magnetocaloric properties,we found that the variation of TC and|?_M⁶)|of the alloys is mostly affected by the types of heavy RE elements rather than the configuration entropy.In a conclusion,we found that high configuration etropy is one of the underneath reasons that causes the low GFA of the RE-based HE amorphous alloys in general.On the other hand,the addition of Y element can reduce the cost and improve the GFA of the RE-based HE amorphous alloy obviously,and effectively changes the magnetocaloric properties around a specific T_C at the same time.This work provides some novel ideas for the desigin of RE-based HE amorphous alloys with low cost,high GFA and excellent magnetocaloric properties.