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

In Nd 0.5 Ca 0.5 MnO 3 , Mn 3+ and Mn 4+ ions become ordered below T co = 250K. At 160 K, a long-range antiferromagnetic order is established. The ESR spectra have revealed that, for T N < T < T co , this phase is non magnetic but presents strong antiferromagnetic fluctuations. No evidence of a separated ferromagnetic phase was detected in this temperature range. Below T N , macroscopic antiferromagnetic modes are observed which depend on whether the magnetic field is swept upward or downward. Besides, both charge-ordered phases are unstable against magnetic field: a first-order, strongly hysteretic transition towards a ferromagnetic state occurs. This high-field phase orders ferromagnetically below T C = 270 K. For a given temperature, mixing of the charge ordered and the ferromagnetic phases occur in a restricted magnetic field range.