| In the past half a century’s development, great progress has been achieved in Condensed matter physics, which has been the most important branch of physics. Among them, Strongly-Correlated electrons system physics remains to be a puzzling problem which needs solving. Due to the Strongly-Correlated electrons system, perovskite manganites attract more and more attention in physicists. Since the1980s, the specific study of perovskite manganites created quite a stir. Various types of models have been set by researchers, such as double exchange models and polaron models to analysis the complex effects among them. In the meantime, considering the complex inner structure, charge, spin orbital, crystal latticeand the interactions of Strongly-Correlated electrons system, some new phenomenon still remains to be explained. In this way, it is essential to continue the deep study in perovskite manganites.In this dissertation, Ndo.5Cao.5Mn1-xGaxO3(0≤x≤0.15) has been prepared using solid phase reaction. Serious of single phase samples and polycrystal samples have been chosen, whose resultant temperature can be as high as1300℃for twenty-four hours. Through X-ray diffraction, the results of samples have been represented. With the help of Physical Property Measurement System, the magnetization, magnetic hysteresis loop, resistivity of the samples has been measured. After analyzing diffractions and patterns of XRD, it turns out that all of the samples have single-phase orthorhombic structures, whose space groups are pnma and the maximum diffraction peak are about33.30°. With the doping of Gallium, no obvious changes in the location of the diffraction peak can be detected.On the light of M-T curves of the series of samples, we can draw a conclusion that the doping of Gallium has an obvious influence on the magnetization of the samples. The temperature of charge ordering in Nd0.5C0.5MnO3is248K. When x turns to be equal or greater than0.02, a sharp peak of ZFC can be observed at the temperature of nearly50K, which means the freezing temperature. Under the temperature of2K, the magnetization of samples’ FC curve strengthen with the doped increasing in amount, which means that the doping of Gallium may have an inhibiting effect the order of anti-ferromagnetic, and in this way samples’ ferromagnetism can be strengthened.When the temperature is2K, analyze the magnetic hysteresis loop of all the samples. The field scan from-9T～9T. The five samples which doping2%,3%,4%,5%,7%of the Ga, show the step-like magnetic phase transition in first loop of the samples. Especially for the x=0.05sample, there is two step in the first loop. We thought that the AFM and FM coexistence in the sample. Due to external field, AFM transition to FM. The samples’ferromagnetism is strengthened. Analyzing the magnetic hysteresis loop x=0.05sample at different temperature, the result show that upon160K sample shows paramagnetism. While the temperature below120K, the sample happened the magnetic phase transition under the high-intensity magnetic field. But there is no step-like magnetic phase transition.All the samples’ resistivity increases with decreasing temperature, at the external magnetic field are0T and1T. All the samples showed the semiconductor properties. There is no the peak of the transition of insulator to conductor. While the external magnetic field is5T, the samples x<0.07show the peak of the transition of insulator to conductor.The samples x<0.07show colossal magnetoresistance effect. The x=0.03sample under the external magnetic field of5T, show the most MR is326000%. There is no CMR effect in the large doped sample. |
PDF Full Text Request