| Perovskite structure manganese oxide has been attracted by extensive attention due to the colossal magnetoresistance (CMR) and electrical pulse induced resistance (EPIR) effect, which makes it becomes an important material in spintronic field and the promising candidate for the next generation of non-volatile memory. There are several models proposed to understand the physical and mechanism and origin of EPIR since the year of2000the EPIR effect firstly found by American scientists in manganites. However, no mater what mode proposed previously can explain all the features of EPIR for manganese oxides and it is still considerable worthy of studying.In this thesis, Ndo.7Sro.3MnO3(NSMO) ceramic polycrystalline samples were synthetized by solid-state reaction and the samples with different oxygen concentration were produced by annealing in different kinds of atmospheres and oxygen pressure. The physical properties of samples, including crystallographic structure and electrical transport, especially the EPIR, were investigated by powder X-ray, Vibrating sample magnetometer and the variable temperatures measuring system combined with the software of Lab view. According to the experimental data, the conclusions are as following:1. After analysizing on the grain boundary resistance by equivalent circus simulating the network resistances connecting in series or parallel, it confirms that the EPIR cannot occur in the grain boundary or phase boundary even though the Ⅰ-Ⅴ shows nonlinearity and non-ohm characteristic in the case measured by four-wire mode. The reason is that only so small voltage is uploaded upon each boundary that is not enough to excite the EPIR effect since there are numerous grain boundaries in the sample. At the same time, it shows that the EPIR effect of NSMO can only occur at the contact interface between the electrode and the surface of sample.2. The EPIR effect of NSMO fatigued with the number of test frequency and measurement time increased, and the degree of fatigue was related to stimulating voltage and stimulation time. The larger pulse amplitude can cause a stronger EPIR value, but at the same time samples are also easier to fatigue. The Experiments show that pulse width can also cause the fatigue of the EPIR, as similar to the effect of amplitude.3. Temperature and oxygen pressure has a significant effect on the EPIR effect of NSMO. Near the Curie temperature, the sample resistance is high, and the EPIR effect is more remarkable than those at other temperatures. In different oxygen pressure, the results show that oxygen is very associated with the EPIR effect and it becomes stronger if the sample was annealed under a lower oxygen pressure.4. The oxygen content has important influence on the EPIR of NSMO. If annealed in the atmosphere of oxygen, there is little oxygen vacancy left in NSMO samples. Therefore the sample shows a small resistance, linear Ⅰ-Ⅴ and almost undetectable EPIR effect. However, after annealed in oxygen-poor condition or vacuum, the sample has a higher resistance, nonlinear Ⅰ-Ⅴ characteristic, more significant and stable EPIR effect since the oxygen escapes from the sample and then produces a lot of vacancies. These results indicate that oxygen vacancies are the key factors for the EPIR effect in NSMO. |
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