Investigation on the intergranular magnetoresistance of polycrystalline Sr₂FeMoO₆

In this paper, the temperature dependence of the magnetoresistance (MR) of Sr₂FeMoO₆ powder compacts, whose interfacial state was modulated by mechanical ball milling, has been investigated. At low temperatures, the MR is enhanced by the improvement of the spin-dependent intergranular tunneling across insulating tunneling barriers at grain boundaries, which are mostly the SrMoO₄ impurity phase introduced by ball milling. This tunneling conductance is found to be proportional to exp[-(Δ/T)^1/2], and the MR at low temperatures is mainly determined by variation of Δ under magnetic field. However, at high temperatures, the MR decreases rapidly since the inelastic spin-independent hopping that follows the power law T^r dominates the conductance. The enhancement of this inelastic hopping, which is associated with the defects induced by mechanical ball milling, makes the MR show strong temperature dependence with the increase in milling time.