Study On Magnetic And Magnetocaloric Effect Of ABO₃ Type Oxide Materials

ABO₃ type rare earth oxides have been widely studied for their rich physical properties,especially Mn and Fe based rare earth composite oxides.By doping ions with different radii in A or B position,the crystal structure changes,and then shows different physical properties.In this paper,the influence of doping A or B sites on the magnetic and magnetocaloric effects of ABO₃ type Mn and Fe based rare earth composite oxides is studied.The traditional solid-state reaction method is used for sample preparation.The main contents and results are as follows:?1?ABO₃ type Mn-based rare earth oxide La_0.775Eu_0.025Sr_0.2MnO₃ was used as the research object?A-site doping?.The magnetic and magnetocaloric effects of the samples were studied.The crystal structure of the sample is orthogonal structure,and its space group is Pbnm.The sample exhibited ferromagnetic characteristics in the 15—340 K temperature region,the Griffiths phase in the 340—364 K temperature region,and the paramagnetic characteristics in the 364—400 K temperature region.Under the external field of 7 T,the maximum magnetic entropy change of the sample is 2.60 J/?kg·K?,and the magnetic refrigeration efficiency is 439.40 J/kg.?2?ABO₃ type Mn-based rare earth series oxide La_0.9-xEu_xSr_0.1MnO₃?x=0.000,0.025?was used as the research object?A-site doping?.The effects of cationic Eu³⁺and Sr²⁺double doping on the preformed clusters,critical behavior and magnetic entropy of LaMnO₃ were studied.The results show the samples are orthogonal structures,and the space group is Pbnm.As the measurement temperature increases,they appear as cluster spin glass characteristics,ferromagnetic phase characteristics,preformed cluster phase characteristics and paramagnetic phase characteristics;The critical index of the sample fits the Mean-field model best,and the critical index of the doped sample best fits the 3D-Ising model;At 7 T,the maximum magnetic entropy changes of the two samples are 2.76 and 2.81 J/?kg·K?,and the maximum cooling capacity is 436.01 and 438.09 J/kg respectively.?3?ABO₃ type Fe-based rare earth series oxide DyFe_1-xMn_xO₃?x=0,0.025,0.075,0.15?was used as the research object?B-site doping?.The structure,magnetic and magnetocaloric properties of these samples were studied.The experimental results show that the series of samples are all orthogonal structures and the space group is Pbnm.After doping,the average size decreases.The maximum magnetic entropy change,occurring near the Curie temperature,obtained at a magnetic-field span of 7 T,was 18.2 J/?kg·K?.The maximum cooling capacity was 441 J/kg.?4?ABO₃ type Fe-based rare earth series oxide Tb_1-xTm_xFeO₃?x=0.0,0.2?was used as the research object?B-site doping?.The effects of doping Tm on the magnetic and magnetocaloric effect on ferrite TbFeO₃ were systematically investigated.The results showed that both samples are orthogonal structures and the space group is D-Pbnm.After doping,the spin-flip phenomenon of the doped sample is weakened,the antiferromagneticity is almost disappeared,and the magnetization and magnetocaloric effect are reduced.Under the field of 7 T,the maximum magnetic entropy change?S_M of the two samples was-13.78 and-11.59 J/?kg·K?respectively,and the refrigeration capacity?RC?was 316.85 and 312.89 J/kg respectively.