Preparation And Rotating Magnetocaloric Effect Of RB₂（R=Er,Ho） Polycrystal Alloy

Magnetic refrigeration technology is a powerful candidate for traditional gas compression refrigeration due to its advantages of environmentfriendly and high efficiency.But so far,its practical application is limited because the magnetic refrigeration equipment is bulky and the external magnetic field device is too expensive.Compared with ordinary refrigerators,the new magnetic refrigerator based on rotating magnetocaloric effect has simpler structure and higher refrigeration efficiency,which can effectively solve the volume problem of magnetic refrigeration equipment.Many magnetic refrigeration materials have excellent refrigeration capacity only under high magnetic field,but the magnetic field provided by permanent magnets is hardly more than 2 T,which means that these materials need expensive electromagnets to realize refrigeration.Compared with polycrystalline materials,the preparation cost of single crystal materials is higher and the preparation process is more complex.Therefore,it is of great significance to exploit polycrystalline materials with large rotating magnetocaloric effect under low magnetic field to promote the practical application of magnetic refrigeration technology.In this thesis,ErB₂,Ho B~2 and Ho_0.6Dy_0.4B₂polycrystalline alloys were prepared by arc melting.Their composition,morphology and magnetic performance were tested,and some valuable research results have been obtained.The main conclusions are as follows:（1）Rotating magnetocaloric effect was observed in ErB₂ polycrystalline alloy,H=1 T,T=15.5 K,-?S_R=5.46 J/kg K,which indicated that ferromagnetic RB₂polycrystalline alloy prepared by arc melting could produce rotating magnetocaloric effect under low magnetic field.（2）Compared with ErB₂ alloy,the rotating magnetocaloric effect of Ho B₂polycrystalline alloy under low magnetic field is obviously improved:the cooling temperature zone is 2-3 times of ErB₂ alloy,and the refrigeration capacity is more than doubled,RC=74.3 J/kg.（3）The reason why RB₂（R=Er,Ho）polycrystalline alloy can produce rotating magnetocaloric effect under low magnetic field is found.The texture structure of the alloy is formed by arc melting,which makes its magnetization mechanism along the parallel and perpendicular directions different under low magnetic field.The mechanisms along the parallel and perpendicular directions are magnetic domain wall shift and magnetic domain rotation,respectively,which leads to great differences in magnetic susceptibility in different directions,and then the rotating magnetocaloric effect is observed in the alloy.（4）A slight decrease in the-ΔS_R can be observed after considering the demagnetization correction.A maximum-ΔS_R of 6.27 J/kg K,which is 6.33 J/kg K without correction,can be obtained the magnetic field change ofΔH=1T,which shows that demagnetization effect has little effect on RMCE of the alloy.（5）The refrigeration capacity of Ho_0.6Dy_0.4B₂ alloy under low magnetic field is lower than that of Ho B₂ alloy,the rotating magnetocaloric effect with a wide temperature range can be obtained only under high magnetic field（over 3 T）,and the refrigeration capacity of 5 T magnetic field is obviously improved compared with that of Ho B₂ alloy:δT_FWHM=23 K,RC=100.84 J/kg.