High-temperature metal–insulator transition in YxCa1−xMnO3 (0.05⩽x⩽0.12): An electron-spin resonance study

Abstract

Abstract Electron-spin resonance (ESR) studies have been performed on Y x Ca 1− x MnO 3 (0.05 ⩽ x ⩽ 0.12) compounds in the temperature range from 140 K to 470 K. It is found that with the temperature increasing, the ESR linewidth increases to the maximum at T max (=200 K, 220 K, and 270 K for x = 0.08, 0.10, and 0.12, respectively), and then decreases for all the compounds except that with x = 0.05 which shows a continuous decrease in the whole temperature range. For x ⩾ 0.08, the change of the ESR linewidth can be described very well by the adiabatic small polaron hopping model in the temperature range from 140 K to T max . The ESR intensity decreases with temperature increasing for all the compounds between 140 K and 470 K except 300 K ⩽ T ⩽ 330 K in which it increases with temperature increasing. Meanwhile, the g -factor reaches the minimum at about T = 300 K. The characteristics of the ESR linewidth and intensity indicate the appearance of the short-range magnetic correlations and that the spin–lattice relaxation plays an important role for x ⩾ 0.08. In addition, the electronic transport properties of Y x Ca 1− x MnO 3 compounds reveal a metal–insulator transition at T MI which varies from 254 K to 293 K with Y content increasing. The resistivity versus temperature between 140 K and T MI can be fitted well by the adiabatic small polaron hopping model. It is suggested that the metal–insulator transition in Y x Ca 1− x MnO 3 compounds is correlated with the variation of the magnetism under high temperature.