Study On Electromagnetic Characteristics Of Perovskite Manganese Oxides Pr_0.87Ca_0.13MnO₃ Doped With Dy And Gd

In this paper,Pr_（0.87-x）Dy/Gd_xCa_0.13Mn O₃（x=0,0.05,0.1,0.15）series polycrystalline samples were produced by high temperature solid phase reaction method.The effects of doping amounts of Dy³⁺and Gd³⁺on the structure,magnetic properties and electric transport properties of parent Pr_0.87Ca_0.13Mn O₃ samples were investigated.The results are as follows:The XRD patterns of Pr_（0.87-x）Dy_xCa_0.13Mn O₃（x=0,0.05,0.1,0.15）series polycrystalline samples show that the samples have good crystallinity and single-phase property,and high purity.The spatial point group of the polycrystalline samples is orthogonal crystal system Pnma.The samples with doping amount of 0,0.05 and 0.1 meet the typical characteristics of preformed cluster phase,while the samples with doping amount of 0.15may meet the typical characteristics of class Griffiths phase.The negative values of the maximum magnetic entropy change were 4.60770 J·kg^-1·K^-1（x=0）、4.11222 J·kg^-1·K^-1（x=0.05）、3.87818 J·kg^-1·K^-1（x=0.1）、3.84890 J·kg^-1·K^-1（x=0.15）,respectively.The RC values of Pr_0.82Dy_0.05Ca_0.13Mn O₃ are 114.73J·kg^-1（0-3T）、222.92J·kg^-1（0-5T）、351.88J·kg^-1（0-7T）,and Pr_0.82Dy_0.05Ca_0.13Mn O₃ may be an excellent magnetic refrigeration material.The RCP values were 468.79308 J·kg^-1（0-7T）,and the adiabatic temperatures(ΔT_ad)were 4.21K,4.30K,4.51K and 4.96K,respectively.The parent phase Pr_0.87Ca_0.13Mn O₃ sample and Pr_0.82Dy_0.05Ca_0.13Mn O₃ sample undergo second-order phase transition,while Pr_0.77Dy_0.1Ca_0.13Mn O₃ sample and Pr_0.72Dy_0.15Ca_0.13Mn O₃ sample undergo first-order phase transition.By using different models to fit the samples and Kouvel-Fisher（K-F）method to calculate the critical index,it is concluded that the critical behavior of this group of samples is the mean field model.All the samples showed great magnetic anisotropy and antiferromagnetic composition.The samples in this group belong to semiconductor materials.The sample x=0 follows the conduction mode of variable range jump in the measuring temperature zone,the sample x=0.05 follows the conduction mode of small polaron in the measuring temperature zone,and the sample x=0.1 and 0.15 follow the conduction mode of thermal activation in the measuring temperature zone.The spatial point group of Pr_（0.87-x）Gd_xCa_0.13Mn O₃（x=0,0.05,0.1,0.15）series polycrystalline samples is the orthorhombic system Pnma,which all meet the typical characteristics of preformed cluster phase.The negative values of the maximum magnetic entropy change were 4.26962 J·kg^-1·K^-1（x=0）、4.89822 J·kg^-1·K^-1（x=0.05）、6.26870 J·kg^-1·K^-1（x=0.1）、5.92600 J·kg^-1·K^-1（x=0.15）,respectively.The adiabatic temperatures(ΔT_ad)were 3.76K,4.49K,6.52K,and 6.39K,respectively.The paramagnetic-ferromagnetic transition modes were all second-order phase transitions.The results show that the critical behavior of Pr_0.87 Ca_0.13Mn O₃ and Pr_0.72Gd_0.15Ca_0.13Mn O₃ samples is more similar to the mean field model,and the critical behavior of Pr_0.82Gd_0.05Ca_0.13Mn O₃ samples is more similar to the 3D Heisenberg model.The phase transition critical behavior of Pr_0.77Gd_0.1Ca_0.13Mn O₃ samples is more similar to the three-critical model.The Dy³⁺-doped Pr_0.87Ca_0.13Mn O₃ parent phase sample shows a Griffiths-like phase with both second and first-order phase transitions in the paramagnetic-ferromagnetic transition;while the Gd³⁺-doped Pr_0.87Ca_0.13Mn O₃ parent phase sample has a better magnetic entropy change and adiabatic temperature,and the sample with Gd doping of 0.1 is more suitable to be an excellent magnetically refrigeration material.