Study On The Magnetic And Magnetocaloric Properties Of Dy₃Al₅O₁₂ And PrNi₅

Magnetic refrigeration based on magnetocaloric effect（MCE）has attracted a great deal of attention due to its high energy efficiency and eco-friendly characters in the refrigeration area.The key to develop this technology is to search for materials that show giant MCE.Dy₃Al₅O₁₂（DyAG）and PrNi₅ crystals have been regarded as Kano-type magnetic refrigerants because of their excellent magnetic and magnetocaloric properties.The main purpose of this article is to explain the magnetic and magnetocaloric properties of DyAG and PrNi₅ crystals at a micro lever and to provide theoretical help for the technical applications of the materials.The main studied results are presented as follows:The first accomplished work is the investigation of magnetic and magnetocaloric properties of DyAG.On the condition of ignoring the exchange interaction between the magnetic ions in DyAG,the crystal field and external magnetic field-split ground state of Dy³⁺ in DyAG,the magnetic moments,the total entropy and the magnetic entropy changes of DyAG have been calculated in the temperature ranges of 3<T<42K and magnetic field ranges of 0<He<9T.The calculated results are in good agreement with the measured data.The study indicates that the exchange interaction between the magnetic ions in DyAG is so weak that it may be neglected.Besides,the variation of the adiabatic temperature change ?T with T is theoretically anticipated and the anticipated results are compared with that of Gd3Ga5O12（GdGG）.It is found that there are differences between the refrigerative properties of DyAG and GdGG when they are in different external magnetic fields and different temperature regions.At low temperature（T <10 K）,the DyAG is a good magnetic refrigerative material in the lower external magnetic field.However,When He is higher,GdGG is a good selection.This study is helpful to select suitable materials for the magnetic refrigeration technology.The second accomplished work is to study magnetic and magnetocaloric properties of PrNi₅ crystal under strong magnetic field and at low temperature.Based on the law of approach to saturation and the experimental results of magnetic moments of PrNi₅,the exchange interaction-effective field in PrNi₅ is given under a strong magnetic field and at low temperature,which is shown al in .By using the exchange interaction-effective field,the Zeeman Hamiltonian can be calculated directly without using the self-consistent method.Furthermore,the magnetic moment,the magnetic entropy and the magnetic entropy changes of PrNi₅ are calculated in the ranges of 0 < He < 20 T and 2 < T < 60 K.The obtained results are in good agreement with the experimental data.The investigation indicates that the exchange interaction-effective field in PrNi₅,under the strong magnetic field and at low temperature,is only a function of the applied field.In this work,the corrections of the effective field set up by us is proven by the good agreement of the theoretical with the experiment data.