Ag-doped La <sub> 0.67 </ Sub> Ca <sub> 0.33 </ Sub> Of Mno <sub> 3 </ Sub> Thin-film Non-ohm Behavior

CMR materials is one of the materials being investigated widely in the world. Due to its complex phenomena with different temperature and its colossal negative magneto- resistance in the magnetic field, the CMR material is interested in either its theory or its application.The first and second chapter in the paper explain the former study of CMR materials and the related theory. In order to understand the paper better, the theory of preparation films with PLD(pulsed laser deposition) techniques and that of electron s' tunneling through the barriers are explained. But the most important part in the paper is the preparation of LCMO-Ag (short for La0.67Cao.33MnO3 doped with Ag 5%)films with PLD technique and studying their nonohmic behavior though the T-R curves measured by four probe method and the analysis of the cause of nonohmic behavior.In our experiment, LCMO-Ag films were prepared with PLD technique firstly. Secondly films were measured by four probe method with different biased currents. Joule heat effect is obvious when the biased current is large (10mA). It was found that the Rp(short for peak resistance) of R-T curves decreases with increasing the biased current by contrasting the curves with different biased current, which is contrary to the ohmic law. So we call this phenomenon nonohmic behavior in LCMO-Ag films. In order to systemic contrast the nonohmic behavior, the LCMO-Ag films grown on LaAlO3 substrates with different canted angle were studied. Besides the regulation former, the result shows that nonohmic behavior increases with canted angle of the substrate increasing and the behavior is different obviously in the canted and the other direction. Further more, the LCMO-Ag film grown on 20?canted substrate was treated in high temperature and O2 ambience. Contrasting with films without heat treatment, the nonohmic behavior of the film with heat treatment is much smaller. At last, the film grown on SrTiO3 substrate was studied. The result showed that Rp of the R-T curve with 10mA biased current didn't obey the former regulation and the nonohmic behavior with small current(0.01~lmA)was larger than that of films grown on LaAlO3 substrate.Form many reference, we analyze the method of films' preparation films' growth and factors affecting films growth. In most cases films prepared by PLD technique are polycrystal, but not epitaxial crystal films. Based on the tunneling knowledge, nonohmic behavior can be caused by the grain boundary and other defection in the films.Additional, the multi phenomena of CMR material give rise to the interest in application. In our group, small bulk of La0.67 Ca0.33 MnO3 target for film preparation was suggested as detector of thermometer. Now the experiment is carrying on.