Multi-frequency ESR study on the charge-ordered manganite Nd0.5Ca0.5MnO3: phase separation effects?

In Nd0.5Ca0.5Mn0.3, Mn3+ and Mn4+ ions become ordered below T-co = 250 K. A t 160 K, a long-range antiferromagnetic order is established. The ESR spect ra have revealed that, for T-N < T < T-CO, this phase is non magnetic but p resents strong antiferromagnetic fluctuations. No evidence of a separated f erromagnetic phase was detected in this temperature range. Below T-N, macro scopic antiferromagnetic modes are observed which depend on whether the mag netic field is swept upward or downward. Besides, both charge-ordered phase s are unstable against magnetic field: a first-order, strongly hysteretic t ransition towards a ferromagnetic state occurs. This high-field phase order s ferromagnetically below T-C = 270 K. For a given temperature, mixing of t he charge ordered and the ferromagnetic phases occur in a restricted magnet ic field ranged. (C) 2001 Elsevier Science B.V. All rights reserved.