Charge disordering induced by electron irradiation in colossal magnetoresistant manganites

The electron microscopy investigation of Pr0.7Ca0.3MnO3 shows that a complete charge disordering is induced in this phase by electron irradiation at 92 K, the disordered state remaining stable at this temperature, even in the absence of irradiation. A model is proposed for this transition, according to which an electron jumping into the manganite matrix creates a local charge disordered state and extends to the whole matrix through a chain mechanism, leading to a ferromagnetic metallic state. This model is supported by the fact that the charge ordered state (evidenced by the doubling of the a parameter) is restored by heating the material above 120 K (similar to T-C) and then disappears above 150 K (similar to T-CO). Similar results are obtained for Nd0.7Ca0.3MnO3, whereas Pr0.5Ca0.5MnO3 is not sensitive to electron exposure, in agreement with the larger stability of its 1:1 Mn3+/Mn4+ charge ordering.