Evidence of hopping of charge carriers in the clustered state of manganites

The electrical resistivity and magnetization measurements as a function of both temperature and magnetic field provide clear evidence for three temperature intervals in which the magnetic and transport properties are altered in the La0.55Y0.15Ca0.3MnO3 compound. The intermediated-T regime, called clustered state, involves the presence of both ferromagnetic and paramagnetic phases and is shown to be closely related to the colossal magnetoresistivity effect. An extra hopping conducting process is proposed to exist in this clustered state. We use both the Abeles' model and microstructural parameters to estimate the hopping activation energy between ferromagnetic clusters. The size (density) temperature dependence and the shape of the ferromagnetic metallic clusters are revealed to play a major role in the clustered state of this manganite.