Abstract :
The electrical conductivity and magnetoresistance property of the bulk sample La 0.67 Ca 0.33 Mn 0.99 Fe 0.01 O 3 has been reported, between the magnetic fields 0 and 5 T and in temperature range 10–300 K. Ferromagnetic metallic resistivity ρ F M ( T ) = ρ 0 + ρ 1 T n is observed well below the metal insulator (MI) transition temperature T < T MI . Above the metal insulator transition T > T M I the electrical conductivity is dominated by the Shklovskii–Efros variable-range hopping mechanism (SE-VRH), giving ρ P M ( T ) = ρ o h e x p [ ( T 0 / T ) 1 / 2 ] . Based on the scenario that the doped manganites consists of phase separated ferromagnetic metallic and paramagnetic insulating regions, a good fit of ρ(T) is well described by combining the contribution of ρ F M ( T ) and ρ P M ( T ) by the single expression between the temperature region 33 and 300 K. Above T M I the ρ(T) also gives satisfactory fit and is well described using the small polaronic model (SPC) and Mottʹs VRH. At T ≥ T M I , a critical behavior of ρ(T) obeys the scaling law ρ − 1 ( T ) ∼ ( 1 − ( T / T M I ) ) v . Investigations of magnetoresistance (MR) using magnetic field up to 5 T shows two kinds of contribution: one is intrinsic MR and the other is extrinsic MR, which has been accounted fairly well by a phenomenological model based on spin polarized tunneling.
