Spin Dependent Transport And Magnetic Properties Of Nanosize Films

Film materials with magnetoresistance (MR) effects have both important theoretic and practical value. In this dissertation, we investigate mainly two types of film materials with magnetoresistance effects: the manganese perovskites oxide sandwich films and metal granular films. We focus on the preparation technique of the two types of films, microstructure of the two types of films, electrotransport and magnetotransport properties of the two types of films. The major studies and some of the important conclusions are listed below: (1) The advances in the study of film materials with magnetoresistance effects have been summarized. More attentions have been paid to the study of the manganese perovskites oxide sandwich films and granular metal films.(2) A magnetron sputtering method was used to fabricate the sandwich films and granular films. We introduce the theory and technique of magnetron sputtering method, the measurement method of film thickness, the X-ray analysis technique, the scan tunneling microscopy technique, and the four-probe technique for measurement of the resistance versus temperature.(3) High quality La0.67Ca0.33MnO3-(/ La0.67Sr0.33MnO3-(/ La0.67Ca0.33MnO3-( (LC/LS/LC) sandwich multilayer films have been achieved on LaAlO3 (100) substrates by means of dc magnetron sputtering technique. The electrical resistivities versus temperature of the films were measured with a standard four-probe method. Results show that, for a given LC, with increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (TP) increases; for a given LS, with the increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (TP ) increase also. Base on the double-exchange (DE) mechanism, the effects of interaction between layers on the electrical transport was interpreted.(4) Granular Fe films were deposited on insulating glass substrate and (100) silicon wafer with a 2nm native SiO2 surface respectively. The temperature coefficient of resistance of the granular Fe films on insulating glass substrate will change its sign from negative to positive with deposition time in a wide temperature range. A very interesting switching effect of conducting channel and magnetoresistance has been found in granular Fe films on (100) silicon wafer with a 2nm native SiO2 surface. The electron transport between the upper metal Fe and the Si wafer has been found to cause the switching effect. The switching effect can be heavily influenced by the two factors: the deposition time of the granular Fe films and the temperature range measured for transport properties. The electron on upper metal Fe can be emitted into the Si layer by thermal excitation when the temperature is higher than 250K.