Anomalous temperature behavior of resistance in C1-xCox thin films grown by pulsed laser deposition technique

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Writers: S. Sergeenkov and C. Córdova and L. Cichetto Jr. and O.F. de Lima and E. Longo and F.M. Araújo-Moreira

Keywords: Carbon-cobalt nanocomposite; Thin films; Resistance; Polaron hopping; Magnetic scattering

Abstract: We study the transport properties of C_1−xCo_x thin films (with x = 0.1, 0.15 and 0.2) grown on Si substrate by pulsed laser deposition technique. The results demonstrate some anomalous effects in the behavior of the measured resistance R(T,x). More specifically, for 0 < T < T^∗ range (with T^∗ ≃ 220 K  ), the resistance is shown to be well fitted by a small polaron hopping scenario with and a characteristic temperature T₀(x)≃T₀(0)(1−x) (with T₀(0) = 120 K). While for higher temperatures T^∗ < T < T_C(x), the resistance is found to be linearly dependent on spontaneous magnetization M(T,x), viz. R_M(T,x)∝M(T,x), following the pattern dictated by electron scattering on cobalt atoms formed robust ferromagnetic structure with the Curie temperature T_C(x  ) obeying a percolation like law T_C(x)≃T_C(x_m)(x/x_m)^0.15 with T_C(x_m) = 295 K   and the maximum zero-temperature magnetization reaching M(0,x_m)≃0.5μ_B per Co atom for x_m = 0.2.