Low-temperature resistivity minimum and weak spin disorder of polycrystalline La2/3Ca1/3MnO3 in a magnetic field

Low-temperature transport properties were systemically studied for the optimal magnetic coupled polycrystalline La2/3Ca1/3MnO3 system under an applied magnetic field from 0 to 8.0 T. The temperature dependence of resistivity shows a generally minimum behavior at low temperatures (T < 30 K) under various applied fields. For the low fields of H < 1.0 T, best fittings were made by considering both the electron-electron (e-e) interactions in terms of T-1/2 dependence and the Kondo-like spin dependent scattering in terms of ln T dependence. But for the high fields, at the low-temperature region of T < 15 K, accompanying a disappearance of Kondo term ln T, the electronic resistivity only follows T-1/2 dependence, which is a characteristic of enhanced e-e interactions in three dimension (3D) disorder system, and is also confirmed by the specific-heat measurement. It is found that the ln T dependence of resistivity under low fields could be attributed to the weak spin disorder scattering including both spin polarization and grain boundary (GB) tunneling, which are the typical characteristics of the polycrystalline sample. The suppression of resistivity upturn under low fields may result from the increase of the conduction electrons tunneling and the decrease of the resistivity by the applied magnetic field. The existence of e-e interaction should be a general characteristic and reflect the strong correlated interaction between electrons in the mixed-valent manganites.