Study On Magnetostriction And Phase Separation Of Perovskite Manganites

The discovery of the giant magnetoresistance (CMR) in hole- doped perovskite manganites R1-xAxMnO3 (R is a trivalent rare-earth ion and A is a divalent alkali earth 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. In recent years, a lot of new physical phenomena have also been observed in these compounds, for example, large magnetostriction, structural phase transition driven by an external field, and anomalous thermal expansion, etc.Since then, several models or physical pictures 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. and Xing et al. have made a lot of work, respectively, in order to interpret a lot of experimental facts, of which the research about lattice effect is of great importance. It should be pointed out that there are some shortcomings of early double exchange model in manganites and there are much more works to be be done on the interaction between electron and phonon, charge and orbital, spin and orbital and the tendency to phase separation.Our works in this paper covered some aspects of the above contents of which a part concentrated on the magnetostriction of La2/3Sr1/3MnO3 with the substitution of the other rare-earth ions such as Pr, Sm, and Tb for La. We want to understand the information of the interaction between magnetism and lattice by these works. On the other hand, we have found the evidence for phase separation in Sm1/2Sr1/2MnO3 at low temperature induced by the difference in microstruture leading to a distinct difference of magneto-transport...