Sintering Effects on Fe/Mo Ordering and Magnetoresistance in Double Perovskite Sr₂FeMoO₆

Abstract

We have investigated sintering effects on Fe/Mo ordering and magnetoresistance (MR) in double perovskite Sr₂FeMoO_6 (SFMO). Polycrystalline samples have been prepared by the conventional solid-state reaction by sintering in a stream of 5% H₂/Ar gas. All samples are single phase and exhibit a series of superstructure -reflection lines due to cation ordering at Fe and Mo sites. As sintering temperature increases from 900 to 1300 ℃, the degree of Fe/Mo ordering increases from 82 to 92%, magnetization (15 K, 7 kOe) increases from 1.6 to 2.7 μ_B/f.u., and Curie temperature increases at a rate of 4.3 K/% with the increase of Fe/Mo ordering ratio. The magnitude of MR measured at 5 K is 19% for sample prepared at 1000 ℃ with magnetic fields of 7 kOe. The observed MR is proportional to the square of magnetization indicating that the MR feature in SFMO is explained by the spin-polarized tunneling at grain boundaries.