Study On Magnetocaloric Properties Of Double Perovskite Sr_2-xA_xFeMoO₆?A=Al?Gd/Ba?Ga?

Since the last century,double perovskite materials have been extensively studied due to their rich physical properties,especially their magnetoelectric content is the most interesting.In 1998,Japanese physicist Kobayashi et al.made a series of research results in the study of the double perovskite Sr₂FeMoO₆,which triggered a great response from the academic community.According to the density functional theory,by calculating the energy band structure of Sr₂FeMoO₆ and other double perovskite materials,it is found that the double perovskite Sr₂FeMoO₆ exhibits a spin polarization of 100%near the Fermi level.This result indicates that this type of material has great application potential in spintronic devices,and the resulting research boom in academic world for several years.In recent years,many reseachers have tried to discover the possibility of applying this system material in other fields.It is well known that the double perovskite oxide Sr₂FeMoO₆ has an easily adjustable near-temperature magnetic phase transition point and a second-order magnetic phase transition characteristic,which satisfies some basic requirements for room temperature magnetic refrigeration materials.Therefore,it is neccesary to carry out the magnetocaloric properties of this materials.This paper provides an in-depth analysis of the magnetocaloric properties of the double perovskite oxide Sr₂FeMoO₆ and controlled the magnetocaloric properties of the material by means of ion substitution.The crystal structure,micromorphology,ion valence and magnetocaloric properties of the materials were characterized to analyze the effect of ion substitution on the magnetocaloric properties of the materials.The specific work content is as follows:?1?The double perovskite oxide Sr₂FeMoO₆ was successfully prepared by the sol-gel method,and ion doping was performed using a trace amount of Al³⁺.The effects of ion doping on the magnetocaloric properties of the materials were investigated by comparing the physical properties of the maternal and doped samples.In this experiment,the effect of ion doping on the crystal structure of the sample were first explored.Secondly,the grain size of the sample and the valence state of the ion were observed.The results showed that the doping caused a significant change in the grain size and ion valence of the sample.The saturation magnetization of the sample was observed at a very low temperature of 5 K,and the Curie temperature of the sample was determined by the field cooling curve.The results showed that the doping caused the magnetization and Curie temperature of the sample to decrease.Finally,the maximum magnetic entropy change of the parent sample and the doped sample is calculated by the isothermal magnetization curve and the corresponding relationship.The introduction of aluminum ions was found to help improve the magnetocaloric properties of the samples.?2?The magnetocaloric properties of the co-doped double perovskite system (Sr_2-3xGd_xBa_2x)FeMoO₆?SGBFMO?were characterized.The samples were prepared by a solid state reaction method,and the X-ray diffraction patterns of the samples were first refined.Secondly,the valence state of Fe/Mo ions in the samples was measured to reveal the influence of the electronic arrangement on the order degree of the sample.Finally,by measuring the magnetic properties of the sample,it was found that as the doping amount increases,the magnetic transition region of the sample broadens significantly,the Curie temperature decreases,and the maximum magnetic entropy change and relative cooling power of the sample decrease significantly.?3?Finally,the sample preparation process was improved,and the magnetocaloric properties of the double perovskite ceramic material under Gd³⁺doping were briefly analyzed.The effects of doping on the magnetization and Curie temperature of the sample were investigated,and the magnetocaloric properties of the sample were calculated.The results show that the improved preparation process can effectively improve the magnetocaloric properties of the material.