Study On Physical Characteristic Of La_1-xAg_xMnO₃

The discovery of the colossal magnetoresistance (CMR) in hole-doped perovskite manganites Ra1-xMxMnO3 (Ra is a trivalent rare-earth ion and M is a metal ion) has attracted much attention since 1989 due to not only its technological applications in magnetic recording and sensor, but also the effect of the strong correlation concerning metal-insulator transition in the field of basic research.Since then, several physics models have been suggested to explain the mechanism of CMR. However, the exact mechanism of CMR remains to be done. The double exchange interaction founded by Zener in early 1950's, and developed by Anderson and de Gennes later is a better theory in describing the conductive behavior in the compounds. It provides us a correct route to make clear the origin of CMR. Since 1995, Millis et al. have made a lot of wok, respectively, in order to interpret a lot to experimental facts, of which the research about lattice effect is of great importance. It should be point out there are some shortcoming of early double exchange model in manganites and there are much more works to be done on the interaction between electron and phonon, charge and orbital, spin and orbital and the tendency to phase separation.In this paper, the primary content is the study on physical characteristic of La1-xAgxMnO3. It covered tow aspects: the one is the study of phase formation of the polycrystalline La1-xAgxMnO3, and point out its distinct characteristic; the other is the study on magnetoresistance of La1-xAgxMnO3 at room temperature. Our main work includes:1. The study of phase formation of the polycrystalline La1-xAgxMnOA series of polycrystalline La1-xAgxMnO3 samples with x range nominally from 0.05 to 0.45 were investigated, and found that the critical phase temperature has close relation with the content of silver in the sample. And pointed out in the case of Agl+ doped in LaMnO3, when x achieved a fixed value(x=0.15), Ag would separate out, Ag-rich phase appeared, samples became compound phase. Then analyzed the cause of these.2. The study on magnetoresistance of La1-xAgxMnO3 at room temperature.By way of doping excessive Ag1+ ion in LaMnO3, we found that the sample's magnetoresistances have appeared two peaks when so-called x=0.3 and x=0.65 at roomtemperature. At H=1.8T the sample's MR ( R/R=(R(H) -R(0)/R(0)) ) respectivelyachieved -23.0% and -22.7%. But something must be point out that the true contents of Ag are less than the calculated contents, because Ag will separate out from samples. By way of analyzing, we think that this kind of huge magnetoresistances effect in the sample of x=0.3 is independent of Ag-rich phase. But the huge magnetoresistances effect in the sample of x-=0.65 has close correlation with Ag-rich phase. In this sample Ag, perovskite and hole have achieve optimum ratio, and lead to a strong field-induced enhancement in percolation.