Study On The Magnetic Properties Of Double Perovskite Oxide La₂Co/NiMnO₆

The chemical general formula of double perovskite manganese oxides is A₂BB'O₆,which has become the research focus of functional materials of manganese oxides due to its wide range of physical properties and great application prospects in magnetic storage and magnetic refrigeration.Among them,La₂CoMnO₆ and La₂NiMnO₆ are the typical representatives.In this paper,La_(2-x)Ca_xCoMnO₆(x=0.6,0.75,0.9,1.0)and La_(2-x)Dy_xNiMnO₆(x=0,0.1,0.2,0.3)series samples were prepared by using the traditional high-temperature solid-state reaction method with different chemical elements doped at the A site,respectively.X-ray diffraction(XRD)showed that the samples showed good single-phase structure,and the structure and lattice parameters of the samples were further analyzed.The magnetic properties of the samples were measured by PPMS.The main research contents and conclusions are as follows:(1)La_2-xCa_xCoMnO₆(x=0.6,0.75,0.9,1.0)series samples belong to monoclinic system,P2₁/n space group.When x=0.75 in La_2-xCa_xCoMnO₆ sample,it can be seen from the observation of the FC curve under M-T that the magnetization intensity in the sample appears a negative magnetization phenomenon from positive to zero,and then from zero to negative.The product(?T)and temperature(T)curves of susceptibility and temperature determined the Neel temperature T_N of the two groups of samples.Further analysis showed that the cluster glass behavior appeared in the low temperature region of the two groups of samples.The inverse magnetic susceptibility(?^-1)and temperature(T)curves showed upward deviation from the Curie-Weiss(C-W)fitting line.(2)La_(2-x)Dy_xNiMnO₆(x=0,0.1,0.2,0.3)polycrystalline samples were analyzed by measuring the change curve of magnetization with temperature(M-T)and the change curve of magnetization with isothermal magnetization with applied magnetic field(M-H).The results show that when T>T_G,the four groups of samples show pure paramagnetic state.When T_G<T<T_C of paramagnetic-ferromagnetic coexistence,The?^-1-T curve showed a shift from downward deviation to upward slight deviation from the C-W fitting line,indicating that the antiposition defect gradually occupied the dominant position.As the doping of Dy element replaced a small amount of La ions,the T_C and T_N of the sample were reduced,which may be because the doping amount had a certain weakening effect on the interaction between ions.The slope of Arrott curve is positive which conforms to the characteristics of second-order phase transition,indicating that the paramagnetic-ferromagnetic transformation in the sample is a second-order phase transition.The change value of magnetic entropy increases with the increase of the outfield,and all appear the maximum value near T_C.Further calculation of the refrigeration capacity of the material,RCP value decreased after doping,but still within the ideal range,the sample has the potential to achieve magnetic refrigeration in high temperature region.