Phase Separation And Magnetocaloric Effect Of Perovskite Manganites

Perovskite manganese oxides has many interesting physical phenomena.The interaction between charge-orbit spin and lattice degrees of freedom renders them unique.Including paramagnetic ferro-magnetic phase change accompanied by metal insulation phase transition,phase separation phenol-menon,giant magnetoresistance effect,magnetocaloric effect and other special physical phenomen-a.All these properties make this kind of material has the very high potential value in industrial applic-ation,and become the hotest issue in the research of condensed matter physicists today.In this paper,two samples of perovskite manganese oxides La_0.6Er_0.1Sr_0.3MnO₃ and(La_0.5Pr_0.5)-_0.67Ca_0.33MnO₃ were prepared.With the material La_0.6Er_0.1Sr_0.3MnO₃ we studied the magnetic phase transition,electron transport and phase separation and with the material(La_0.5Pr_0.5)_0.67Ca_0.33MnO₃,we studied the short-range antiferromagnetic interaction and magnetocaloric effect and the phase separate-on of spin-lattice relaxation and spin-relaxation coexistence.These phenomena are widely used to explain interesting physical phenomena such as giant magnetoresistance and have special significance for actual production activities.1.The effect of micro doping of Er on the magnetoelectric properties of La_0.6Er_0.1Sr_0.3MnO₃perovskite manganese oxide material was investigated.Measurement of the applied magnetic field,the electron paramagnetic resonance spectrum,the temperature resistance,and the like demonstrated that there was a significant electron-phase separation?EPS?behavior in the sample.By analyzing the electron paramagnetic resonance spectrum,the magnetization and the resistivity change with the temperature,finally the model description system magnetic phase transition and electron-phase separation evolution are given.2.The phase separation behavior of(La_0.5Pr_0.5)_0.67Ca_0.33MnO₃ was studied by electron paramag-netic resonance spectroscopy?EPR?.The spin-lattice relaxation or spin-only relaxation mechanism can explain the change of the peak-to-peak width of the EPR spectrum,where the change in line width indicates that two types of spin relaxation mechanisms coexist.We propose that the intrinsic self-organizing processes form some inhomogeneous electronic phases which are responsible for different relaxation mechanism due to the appearance of multiple spin exchange interactions.This finding is possible to pave a new way for further investigating magnetic correlations and spin dyna-mics in the paramagnetic hole-doped manganites.3.The magnetic properties of(La_0.5Pr_0.5)_0.67Ca_0.33MnO₃ samples were further investigated.It shows an abnormal upturn deviation from the Curie-Weiss law on the inverse susceptibility curve.From isothermal magnetization curves,hysteresis loops and other measurements,we found some short-range charge-order-antiferromagnetic?CO-AFM?phases exist in the system.The upward devia-tion is due to the appearance of the short-range CO-AFM phase.The magnetic entropy change curve was drawn to find that the sample has a large magnetic entropy change.Arrott plots and the renormal-ized entropy curves demonstrate that the transition belongs to the first-order phase transition.The insignificant hysteresis loop indicate that the inevitable thermal hysteresis can be ignored in the present first-order material implying that it is a potential candidate for the cryogenic temperature magnetic refrigeration.