Magnetocaloric Effect In Perovskite Manganite Submicron Clusters

A series of Nd_1-xSr_xMnO₃ perovskite manganite materials were synthesized by sol-gel method.The effects of submicron size on the magnetic phase transition temperature and magnetocaloric properties of the materials were investigated.The magnetic entropy change and RCP value of these materials near the phase transition temperature are calculated,and the data is used to judge the potential of the material as a magnetic refrigeration material.The specific conclusions are summarized as follows:（1）The cluster NdMnO₃ with submicron particle size was successfully prepared by sol-gel method.The Curie temperature of the sample was near the 68 K by using the ZFC-FC curve,the Curie-Weiss law and the Arrott diagram.And it is calculated that the maximum magnetic entropy change is0.34 J/kg·K,0.69 J/kg·K,1.32 J/kg·K at T=68 K,ΔH=0.5 T,1.0 T,2.0 T,respectively.Besides,the value of RCP was 85.8 J/kg atΔH=2.0 T.There are indeed some improvements compared to bulk materials and small-sized nanomaterials.On this basis,this system still has great potential value in the application of magnetic refrigeration materials.（2）Similarly,the cluster of submicron particles Nd_0.67Sr_0.33MnO₃ was successfully prepared by sol-gel route.the Curie temperature of the sample was obtained around the 275 K by the ZFC-FC curve,the Curie-Weiss law and the Arrott diagram.And the maximum magnetic entropy change of the sample is 0.58 J/kg·K,1.09 J/kg·K,1.52 J/kg·K at T=275 K,ΔH=1.0 T,2.0T,3.0 T,respectively.In addition,the value of RCP was 88.0 J/kg atΔH=2.0 T.There is only a small increase in the RCP value comparing to the previous sample NdMnO₃,but the phase transition temperature rises to 275K which is near room temperature.In this system,controlling the suitable amount of Sr will improve extremely the performance of the magnetic refrigeration material.（3）Finally,the submicron cluster Nd_0.33Gd_0.33Sr_0.33MnO₃ particles was also successfully prepared by sol-gel method.Similarly,the phase transition of the sample was observed in the ZFC-FC curve,and the Curie temperature of the sample was obtained by Curie-Weiss’s law and Arrott diagram.However,it was found that the droping of Gd causes the phase change temperature becomes blurred which embodies a discrepancy on the phase transition temperature.And the maximum magnetic entropy change of the sample is 0.77 J/kg·K,1.58 J/kg·K,2.23 J/kg·K at T=123 K,ΔH=1.0 T,2.0T,3.0 T,respectively.Besides,the RCP value of the sample is 114.0 J/kg atΔH=2.0 T.Compared with the previous sample Nd_0.67Sr_0.33MnO₃,not only the maximum magnetic entropy change has improved,but also the value of RCP has increased.This confirms that the droping of Gd in this system can realize an improvement in the performance of the magnetocaloric effect.