Abstract :
Magnetoresistive La0.67−yYyBa0.33MnO3/LaAlO3 thin films were prepared by the sol–gel spin-coating method. Our resistivity and the electron spin resonance (ESR) measurements indicate that the main factor determining the metal-insulator transition temperature Tm is the cation disorder represented by the cation radii variance σ2, and that ferromagnetic insulating regions coexist in the ferromagnetic metallic phase. In the paramagnetic phase, the dissociation energy of spin clusters and the polaron hopping energy obtained from the ESR intensity and linewidth also displayed a prominent dependence on σ2. Polaron localization due to Jahn–Teller distortions appears to be responsible simultaneously for the decrease in the ferromagnetic order and for the increase in the orbital order.
