| Condensed matter physics has been the subdiscipline of the most important in contemporary physics. The unique physical properties and potential application prospect of perovskite manganites has been one of the hotspots in Condensed matter physics strong correlation electronic system. In the decades of researching perovskite manganese oxide, researchers established different models, such as, double Exchange and polaron model and so on. However, due to the strong interaction of charge, spin, orbital and lattice degrees of freedom exist in the system which can produce some novel physical phenomenon, it is difficult to completely explain clearly with the existing model. Therefore, the research of perovskite manganese oxide plays an important role in the development throughout the many related areas of condensed matter physics.In this dissertation, based on the preparation of single-phase polycrystalline sample series Nd0.5Ca0.5Mn1-xFexO3(0≤x≤0.30) by solid phase reaction. The structure of a series of samples is determined by X-ray diffraction (XRD). The PPMS (physics properties measurement system) was used for measuring M-T, M-H, p-T, p-H curves.X-ray diffraction patterns show that the series of samples are single-phase orthorhombic structure and the position of the diffraction peaks with no significant increase in the amount of Fe-doped.The M-T curves show that with the increasing of Fe doped the charge ordering peak was not clearly which is indicated that Fe doping damage the ordered between Mn3+and Mn4+. Zero field cooling (ZFC) and field cooling (FC) curves are bifurcate at low temperatures, indicating that Mn3+and Mn4+coexist in the parent phase, the mutual competition between the double exchange interaction (Mn3+and Mn4+) with the super-exchange interaction (Mn3+and Mn3+) makes coexistence of ferromagnetic and antiferromagnetic clusters.The isothermal magnetic hysteresis loops of all the samples are measured at2K, It can be seen that no magnetization step is observed for the undoped sample and the saturation is not reached at applied field of9T. This is attributed to the stronger charge ordered (CO) state of Nd0.5Ca0.5MnO3. x=0.025and x=0.05sample show magnetization step, because of the system is phase separation state at low temperatures, the antiferromagnetic (AFM) phase to a ferromagnetic (FM) phase under the external magnetic field. The interfacial strain can be destroyed drastically when the field is up to the critical field He, the ferromagnetic fraction increases dramatically, resulting in the existence of magnetization step. For the samples x≥0.10there is no magnetization step, it indicates that the high doped at low temperatures, the short-range charge/orbital ordering would be suppressed, therefore, the antiferromagnetism begins to be reinforced and the ferromagnetic (FM) fraction is decreased.Nd0.5Ca0.5Mn0.95Fe0.05O3sample carried out a detailed study, the hysteresis loops were measured at different temperatures. It can be seen no magnetization step at5K, because of not all antiferromagnetic phase transformation to ferromagnetic phase. When the temperature is raised to44K, obvious hysteresis can be observed. With the temperature increasing and more than166K, the magnetization of the sample show a linear relationship with the magnetic field, showed that the sample is in the paramagnetic state. Furthermore, the sample was measured repeatedly at the same temperature makes the state of sample changed and this phenomenon reflects the irreversibility. Different samples of the same doping amount also showed difference.The study of resistivity show that the series of samples are insulating state below50K and the insulator-metal transition has not been observed under the absence of magnetic field in the entire temperature range. For x=0.05sample, the obvious colossal magnetoresistance (CMR) effect is observed. |
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