Spin-dependent and spin-independent channels of electrical transport in perovskite manganites

Abstract

A model with two channels of electrical transport (TCET) for perovskite manganites is proposed, and it is described by an equivalent device with two current-carrier channels. In one channel, there is a spin-independent resistor (R₃) with an equivalent resistivity of ρ₃. In the other channel, there are two spin-dependent resistors in series (R₁ and R₂) with an equivalent resistivity of ρ₁ + ρ₂. The component ρ₁ includes residual resistivity and the resistivity contributed by crystal-lattice scattering. The other component of the equivalent resistivity, ρ₂, originates from the spin orientations of the itinerant electrons and the local electrons of the outer O 2p and Mn 3d orbits that deviate from the orientation of their ground states when the test temperature is close to the Curie temperature. Using this model, we fitted the experimental curves of the resistivity versus test temperature for single-crystalline La_1−xSr_xMnO₃ (0.00 ≤ x ≤ 0.40) and polycrystalline La_0.6Sr_0.4Mn_1−xFe_xO₃ (0.00 ≤ x ≤ 0.30). In addition, we investigated the effects of the fraction of the antiferromagnetic phase, scattering at the crystallite interfaces, and the crystal-cell constants on the samples' resistivity. The physical mechanism of the TCET model was explained using an O 2p itinerant-electron model, which has been used in other studies to explain the magnetic ordering of several series of spinel ferrites and perovskite manganites.