Hopping Transport and Spin-Polarized Tunneling Mechanism in Cr-Doped Gd0.7Ca0.3Mn1−x Cr x O3 (x = 0.0–0.5)

Abstract

Temperature-dependent DC electrical resistivity of polycrystalline samples with orthorhombic perovskite structure Gd0.7Ca0.3Mn1−x Cr x O3 (x = 0.0–0.5) has been reported. The samples were prepared by the solid-state reaction method. The resistivity of all the samples indicates a semiconducting nature. In the high-temperature region, the electrical conduction process follows the small polaron hopping (SPH) mechanism showing exponential variation of resistivity with temperature. The activation energy increases with Cr concentration. The low-temperature resistivity data follows Mott’s ln(ρT −1/2)∼T −1/4 law of variable-range hopping (VRH) conduction mechanism. The estimated values of hopping distances (R) and hopping energies (W) of the samples start to increase with increasing Cr concentrations from and above x = 0.5 and satisfy essential conditions of the Mott VRH, i.e., αR>> 1 (α = inverse localization length) and W/ K B T>> 1. This signifies that evaluation of these parameters being logical and the effect can be attributed to high density of doping which introduces simultaneously potential disorder and localized states. The magnetic field-dependent magnetoresistance has been explained by a phenomenological model considering spin-polarized tunneling at grain boundaries in the samples.