Variable-Range Hopping Conduction in LaMnO₃₊δ

Abstract

The temperature dependence of the electrical resistivity ρ(T) for ceramic samples of LaMnO₃₊δ (δ = 0.100-0.154) are studied in the temperature range T = 15-350 K, in magnetic fields of 0-10 T, and under hydrostatic pressures P of up to 11 kbar. It is shown that, above the ferromagnet-paramagnet transition temperature of LaMnO₃₊δ, the dependence p(T) of this compound obeys the Shklovskii–Efros variable-range hopping conduction: ρ(T) = ρ₀(T)exp[(T₀/ T½ ], where ρ₀(T) = AT 9/2 ( A is a constant). The density of localized states g (ε) near the Fermi level is found to have a Coulomb gap Δ and a rigid gap γ(T). The Coulomb gap Δ assumes values of 0.43, 0.46, and 0.48 eV, and the rigid gap satisfies the relationship γ(T) =γ(Tv )(T/Tv)½ , where Tv is the temperature of the onset of variable-range hopping conduction and γ(Tv ) = 0.13, 0.16, and 0.17 eV for δ = 0.100, 0.125, and 0.154, respectively. The carrier localization lengths a = 1.7, 1.4, and 1.2 A are determined for the same values of δ. The effect of hydrostatic pressure on the variable-range hopping conduction in LaMnO₃₊δ with δ = 0.154 is analyzed, and the deendences Δ (P) and γv(P) are obtained