Magnetic-thermal Properties Of Heterogeneous Structures Of La_1/3Sr_2/3MnO₃-LaMnO₃

Magnetic refrigeration technology can greatly reduce the energy consumption required for refrigeration,and avoid the current use of gas compression refrigeration working medium leakage caused by the harm to the environment,has a significant application value in environmental protection,energy saving.Finding suitable refrigeration working medium is a key link that affects the application of magnetic refrigeration technology.This study is based on the preparation of multilayer film composite structure by oxide material represented by LSMO and metal material represented by Gd,and explores a new way to use film composite material as magnetic refrigeration working medium.In this study,the magnetic and thermal properties of LSMO films,LSMO-LMO bilayer films,Gd films and thin strip materials prepared by pulsed laser deposition were studied.In this exercise,the work completed and the results obtained include:The first part of the study mainly takes LSMO thin film as an example,analyzes the effect of the inverse hysteresis loop phenomenon of LSMO thin film and the backbottom signal generated by substrate on the fitting value of magnetic entropy change,and determines the technical standards for the experimental work on the magnetic thermal properties and magnetic phase transformation of thin films.The results show that the magnetic phase transition of LSMO thin films conforms to the first-order phase transition characteristics.The Curie temperature is about 339K,and the magnetic entropy and RCP within the range of 10kOe magnetic field are 0.95 J/kg·K and 31.35J/kg,respectively.In the second part of the study,we analyzed the magnetic and magnetothermal properties of LSMO and LMO bilayer films grown in different sequences.The results show that both the LSMO/LMO bilayers with LMO film as the covering layer and the LMO/LSMO bilayers with LMO film as the buffer layer show "inverse hysteresis loop"phenomenon at room temperature,indicating that the hard magnetic interface layer is formed in the LSMO film layer.Compared with the LSMO monolayer,the peaks of magnetic entropy change of the two bilayer films decreased significantly,and the width of the half peaks of magnetic entropy change increased,and the RCP remained at the same level as that of the LSMO monolayer films.In the LSMO/LMO bilayer films,the Curie temperature of the LSMO films decreased significantly compared with that of the LSMO monolayer films,and the maximum value of magnetic entropy change appeared near room temperature.The results show that the interlayer coupling has a significant effect on the overall magnetothermal properties of the material.In the third part,we analyze the magnetic and magnetothermal properties of Gd film and strip samples.The results show that the properties of Gd films prepared by magnetron sputtering are similar to those of metal strips,and both have excellent magnetothermal properties.Considering that thin film,thin tape samples can greatly reduce the quality of the sample,thus can reduce the use of rare materials.Through this work,we determined that the interlayer interaction within thin film materials can affect the magnetothermal properties of the material within a large thickness range,and analyzed the magnetothermal properties of LSMO film,LSMO-LMO bilayer film,Gd film and thin strip samples.These work laid a foundation for further research on the magnetic and thermal properties of oxid-metal composites.