The Magnetocaloric Effect Of Transition Metal Based Bulk Metallic Glasses

Magnetic refrigeration based on the magnetocaloric effect?MCE?of magnetic materials has attracted more and more attention.Compared with conventional gas compression refrigeration,magnetic refrigeration has many merits,such as high refrigeration efficient,environmentally friendly,broad operating temperature,low noise,wide application fields and so on.The transition-metal?TM?-based soft magnetic amorphous alloys,which exhibit negligible hysteresis,good corrosion resistance and low cost,are potential candidate magnetic refrigeration materials.In this thesis,the MCE of TM-based bulk metal glasses?BMGs?are studied.The main work includes the following three parts.?1?The MCE of Co₇₁Mo₉P₁₄B₆ BMG has been investigated.The results shows that the peak values of the isothermal magnetic entropy change(|?_M^peak|)and refrigerant capacity?RC?of the Co₇₁Mo₉P₁₄B₆ BMG are 0.96 J kg^-11 K^-1 and 70.5 J kg^-1,respectively,under a maximum magnetic field of 5 T.The magnetocaloric properties of the Co₇₁Mo₉P₁₄B₆ BMG are not good,which may be caused by the antiferromagnetic coupling between Co and Mo atoms.However,it is of significance that this BMG exhibits a Curie temperature of 317 K,which is near room temperature,and thus the present BMG is adapted to room-temperature magnetic refrigeration.?2?The effect of preparation cooling rate on the MCE of Fe₈₀P₁₃C₇ amorphous alloy is studied.The Fe₈₀P₁₃C₇ glassy rod and amorphous ribbon are prepared by J-quenching and melt-spinning techniques,respectively,and a comparative study on the MCE of the two samples with different preparation cooling rates is performed.The value of peak of isothermal magnetic entropy change(|?_M^peak|)and refrigerant capacity(RC_FWHM)for the Fe₈₀P₁₃C₇ amorphous ribbon is larger than those of the glassy rod under varies applied field.Hence,we consider that the demagnetization field effect may have a significant influence on the MCE measurement results of the Fe₈₀P₁₃C₇ glassy rod.After the demagnetization field correction,the values of|?_M^peak|and RC_FWHM for the Fe₈₀P₁₃C₇ glassy rod are close or even superior to those of the amorphous ribbon.Further,it is indicated from the|?_M^peak|?ⁿ relationship that the glassy rod has more homogeneous internal atomic structure compared with the amorphous ribbon.It has been proposed that more homogeneous structure could lead to greater magnetocaloric properties,and therefore we suggest that the i ntrinsic MCE performance of the Fe₈₀P₁₃C₇ glassy rod should be better than that of the amorphous ribbon.?3?The MCE of TM-based high entropy bulk metallic glass?HE-BMG?has been studied.In this part of work,?FeCoNi?₇₅Cr₅(P_0.5B_0.5)₂₀ HE-BMG is prepared by combing fluxing and J-quenching techniques.It is shown that the Curie temperature of the?Fe CoNi?₇₅Cr₅(P_0.5B_0.5)₂₀ HE-BMG is 572 K.The values of|?_M^peak|and RC_FWHM of the present TM-based HE-BMG are 0.66 J kg^-11 K^-1 and 42.9 J kg^-1,respectively,for the applied magnetic field of 1.5 T,and 1.88 J kg^-11 K^-1 and 136.1 J kg^-1,respectively,for the applied magnetic field of 5 T.The value of|?_M^peak|for the present TM-based HE-BMG is higher than that of Co-based amorphous alloys but lower than that of Fe-based and Ni-based amorphous alloys.It indicates that the high entropy effect seem have little effect on the MCE of TM-based amorphous alloys.