Study On The Magnetocaloric Effect Of Lanthanide Perovskite Manganese Oxide Substitution With Rare Earth Elements Eu

In the optical fiber communication technology,the heat dissipation problem of various optical communication devices such as fiber amplifiers,fiber lasers,and fiber light sources can be solved to achieve the miniaturization of the equipment to a greater extent.It is of great practical significance to study and improve the cooling efficiency and improve the cooling capacity of miniaturized equipment for improving the overall performance of the device and reducing the cost.With the development of refrigeration technology,more and more attention has been paid to magnetic refrigeration technology and magnetic refrigeration materials,and magnetic refrigeration materials are developing in the direction of large magnetic entropy change and low cost.Perovskite oxides have been widely studied because of their unique crystal structure and easy doping properties,which enable controllable regulation of the physicochemical properties of materials.In the field of magnetic refrigeration,perovskite manganese oxides have the advantages of large magnetic entropy change,strong chemical stability,low cost,non-toxicity,and easy miniaturization.Its maximum magnetic entropy change is close to Gd,and the Curie temperature of perovskite manganese can be precisely regulated by ion doping,enabling it to work in the low temperature region（below 77 K）to the high temperature region（above 350 K）.At present,the problems faced by perovskite manganese oxides in the field of magnetic refrigeration are:compared with magnetic refrigeration materials of other alloy systems,the magnetic entropy change is still small,and for some manganese oxides with large magnetic entropy changes,the working temperature is difficult controlled.This paper intends to dope the A-site ions of perovskite manganese oxides with rare earth elements.The structure,magnetic and magnetocaloric properties of the doped rare-earth element material are studied,so that it can have a large magnetic entropy change in a wide temperature range to meet the needs of practical applications.The main research contents of this paper are:（1）In this paper,the La_2/3Ca_1/3MnO₃ samples with large magnetic entropy change were doped with rare earth ions at the A site,and the changes of the structure,magnetic and magnetocaloric properties of the samples doped with rare earth elements Eu and Yb were studied.The changes of the lattice structure and Mn-O-Mnbond angle of La_2/3Ca_1/3MnO₃ after doping with two elements were systematically studied by Rietveld refinement.Further research found that the doping of Eu element can effectively change the Curie temperature of the material,and can maintain a high magnetic entropy change.In addition,we use the Arrott diagram and the general curve model to determine that the magnetic phase transition type of all samples is the second-order phase transition,and the Yb element doping has little effect on the material structure,Curie temperature and magnetocaloric properties.We also studied the effect of other rare earth elements such as Dy,Tb and Er.However,some of these rare earth elements cannot enter the crystal structure,such as Er,Tm,etc.,which form impurity phases.Other rare earth elements such as Yb,Tb,etc.have little effect on the magnetic and magnetocaloric properties.So this part only studies the changes of Curie temperature and magnetic properties of two typical rare earth elements Eu and Yb doped.By comparing the sample data of Eu³⁺and Yb³⁺doping,we are full of interest in the doping of Eu element,and continue the doping of Eu element in the A-site La ion of lanthanide perovskite manganese oxide.（2）On the basis of the above research,we determined that the Eu rare earth element can regulate the Curie temperature and has a large magnetocaloric effect.Therefore,we further studied the effect of Eu element doping on the structure,magnetic and magnetocaloric properties of La0.7-x Eux Sr0.3MnO3,La0.7-x Eux Ba0.3MnO3 and La0.7-x Eux Ba0.15Ca0.15MnO3（x=0,0.02,0.04,0.06 and 0.08）.The Curie temperatures of La_0.7Sr_0.3MnO₃ and La_0.7Ba_0.3MnO₃in these three substrates are higher than room temperature.We hope to adjust the Curie temperature of materials to around room temperature through Eu doping.We found that under a small amount of Eu doping,the effect on different bases is different.In La_0.7Sr_0.3MnO₃,the doping of Eu does not change the magnetic entropy change of the material,but the Curie temperature increases with the increase of the doping amount.We analyze the possible causes from the changes in the material’s structure and magnetic properties.After the La_0.7Ba_0.3MnO₃ and La_0.7Ba_0.15Ca_0.15MnO₃ samples are doped with Eu element,the magnetocaloric effect of both materials is increased by about 20%,and the Curie temperature of the materials decreases with the increase of doping amount.The Curie temperature of La_0.7Ba_0.3MnO₃ is close to room temperature.We also further studied the phase transition types of the materials,and made in-depth analyses of their ferromagnetic and magnetocaloric properties using Landau theory.Overall,our research has achieved the expected goal,and found that the rare earth element Eu can be used to tune the operating temperature of perovskite manganese oxides without reducing the magnetocaloric properties of the material.For some manganese oxides,the magnetocaloric properties of the materials can be improved at the same time,which provides a reference value for the research of other magnetic refrigeration systems.