A Study Of Preparation And Properties Of The La_2/3Ca_1/3MnO₃ Coating System

The discovery of colossal magnetoresistance (CMR) in perovskite manganites has attracted great interest. It is generally thought that the CMR effect should be closely related to the field-induced alignment of Mn spins, which belongs to the intrinsic MR effect. Unfortunately, the CMR phenomenon becomes observable only on a magnetic field of several Teslas, which is far away from applications. Towards this end, another property of perovskite manganites, extrinsic MR effect, can be utilized in the form of the MM/ML/MM structure,which is just like sandwich structure, there MM means magnetic material and ML means middle layer. In our work, we take the La2/3Ca1/3MnO3, which are prepared with low sintering temperature, as MM. And the Cu dependent material (CuDM) becomes the ML, and more, we also use Zn dependent material (ZnDM) and Fe dependent material (FeDM) as ML. We find that these systems have special features in transport properties. Specially, we find the great low-field magnetoresistance (LFMR) of the CuDM-coated system. In this thesis, the main investigation including: 1. A summary about the structure, properties and magnetoresistance effect of the perovskite manganites has been given. We summarize the research work related to the LFMR effect, and then give major studies of the thesis. 2. We introduce the different preparation procedures about perovskite manganites, and use the sol-gel method to produce the La2/3Ca1/3MnO3 material. We give the preparation process of the systems in this thesis. 3. The electrical and magnetic transport properties of (1-x)La2/3Ca1/3MnO3 /xCu(NO3)2 system have been given. We find that there are many differences with that in the La2/3Ca1/3MnO3 system. And more, we find the great LFMR effect for low applied magnetic field in this system. 4. The thermal and magnetic hysteresis is observed in the (1-x)La2/3Ca1/3MnO3/ xCu(NO3)2 system. Using the assumption of the "MM/ML/MM"structure, we give the qualitative indicant about these phenomena and the LFMR effect. 5. The electrical transport properties in the zero magnetic field about the (1 -x) La2/3Ca1/3MnO3/xZn(NO3)2 system and the (1-x)La2/3Ca1/3MnO3/xFe(NO3)3 system have been given. We compare these results in three systems and simply give the qualitative indicant.