Structure and magnetic properties in the compounds of Sr2FeMo1−xNbxO6

The series of the Sr2FeMo1−xNbxO6 compounds have been synthesized throughout the range of 0≤x≤1 using conventional solid-state reaction method. The compounds show a tetragonal structure in the range of 0≤x≤0.4 while showing an orthorhombic structure in the range of 0.5≤x≤1. Magnetic and electrical properties of the compounds have been studied in order to investigate the effect of the substitution of non-magnetic Nb5+ ion for Mo5+ (or Mo6+) ion in the double perovskite compound. The magnetization (M) values are found to decrease slowly with increasing x in all compounds with 0≤x≤0.75 due to less correlation among the magnetic ions induced by the non-magnetic Nb5+ ions. The measurements of magnetic susceptibilities at zero-field-cooled and field-cooled conditions show that a transition from a ferromagnetic (FM) to a ferro-cluster glass state gradually transforms from a paramagnetic (PM) to a spin-glass state with increasing Nb5+ content. With increasing x, the conductivity decreases. Meanwhile, the compounds lose the ferromagnetic component. The compounds have good conductivity from 10−3 to 10 Ω cm with x in the range of 0≤x≤0.3, though they show insulator behavior. While those with x in the range of 0.6≤x≤0.75 show poor transport property. All samples with x≥0.25 show large negative magnetoresistances (MRs), similar to that observed in Sr2FeMoO6.