| The material studied in this paper is double perovskite oxide ceramic samples.All samples are prepared by traditional high-temperature solid-state reaction method.The X-ray diffraction?XRD?is used to check whether the phase formation of the series of samples is good.The electromagnetic properties of the samples are measured by PPMS.The specific analysis results are as follows:?1?The effects of Tb doping on Curie temperature,magnetic entropy change and magnetic phase transition of Pr2CoMnO6 were studied.The results show that the spatial point group of Pr?2-x?TbxCoMnO6?x=0,0.05,0.1,0.15?is monoclinic P21/n,which has good single-phase property;There are two magnetic transition points(TC1 and TC2)in this group of samples;TC1 and TC2 decrease with the increase of Tb doping amount;in the temperature range of measurement,four samples successively experience the paramagnetic and paramagnetic ferromagnetic coexistence states with the decrease of temperature;the maximum change value of magnetic entropy?SM of this group of samples in 7 T external magnetic field is-1.862 J·kg-1·K-1?-1.779 J·kg-1·K-1?-1.768J·kg-1·K-11 and-1.766 J·kg-1·K-1.Doping Tb makes the maximum magnetic entropy smaller,but widens the half high and wide temperature range.According to the RCP value,Pr1.9Tb0.1CoMnO6 has more potential as a magnetic refrigeration material in the high temperature region than the other three samples.According to the analysis of Arrott curve,recalibration curve and Loop curve,this group of samples experienced a first-order phase transition at this stage.All the samples belong to semiconductor materials,and all the four samples follow the conduction mode of range hopping in the temperature measurement area.?2?The electromagnetic properties of double perovskite oxide Gd?2-x?CexNiMnO6?x=0,0.1,0.2,0.3?were studied.The results show that all the four samples show good single-phase,the spatial point group is monoclinic P21/n,T>TG is paramagnetic,TC<T<TG is paramagnetic ferromagnetic coexistence,in this temperature region,the samples show Griffiths like phase,in the lower temperature region?T<TN?ferromagnetic antiferromagnetic competition,When the applied magnetic field is 7T,When the applied magnetic field is 7 T,the maximum entropy value?SM of these samples is-4.248J·kg-1·K-1?-3.850 J·kg-1·K-1?-3.123 J·kg-1·K-1?-2.376 J·kg-1·K-1;the calculated magnetic refrigeration efficiency?RCP?is 301.60 J/kg,265.60 J/kg,249.84 J/kg,213.88J/kg,respectively.Compared with the doped samples,Gd2NiMnO6 has more potential as magnetic refrigeration material in high temperature region.Through the analysis of Arrott curve,recalibration curve and Loop curve,it can be seen that the ferromagnetic paramagnetic transition of the samples is a second-order phase transition.The samples belong to semiconductors.Ce doping changes the conduction mode.x=0,0.1 samples follow the conduction mode of range hopping in the temperature measurement area,and x=0.2,0.3 samples follow the conduction mode of thermal activation in the temperature measurement area. |
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