Effects of high magnetic fields on the spin-glass states in disordered manganites

Magnetization and magnetoresistance were measured in single crystals of random alloys RE$_{1-x}$AE$_{x}$MnO$_{3}$ (RE and AE denote the rare-earth and alkaline-earth ions at the perovskite A-site) in pulsed high magnetic fields up to 50 T with a long time duration ($\sim $10 ms) and up to 140 T with a short time duration ($\sim \mu $s). The crystals exhibit the spin glass behaviors at low temperatures in zero field. In high magnetic fields, Sm$_{1-x}$(Ba$_{1-y}$Sr$_{y})_{x}$MnO$_{3}$ showed prominent metamagnetic transitions, whereas RE$_{1-x}$Ba$_{x}$MnO$_{3}$ (RE=Sm, Eu, Gd) showed a smooth magnetization saturation with just kinks in the derivative of the magnetization. Moreover, in the metamagnetic phase transitions, peculiar time dependence and the pre-history dependence were found in the hysteresis of the magnetization. It was also found that the magnetization is accompanied with a colossal magnetoresistance. These behaviors were interpreted in terms of the developments of the clusters and the orbital orders by magnetic fields, which are dependent on the average A-site ionic radius and the randomness.