The influence of structural disorder on the magnetic properties of Sr₂Fe₁ - _xGa_xTaO₆ (0 ≤ x ≤ 1)

Powder samples of the magnetically diluted cubic perovskite phases Sr₂Fe₁ - _xGa_xTaO₆ have been prepared by high temperature ceramic methods. X-Ray powder diffraction data show that the cations occupying the 6-coordinate site are chemically disordered in the range 0.10 ≤ x ≤ 0.40 and that increasing the Ga³⁺ concentration above this value leads to partial cation ordering between Ga³⁺ and Ta⁵⁺. Magnetic susceptibility data collected irom these compounds can be fitted to the Curie-Weiss law, resulting in estimates of the magnetic moment per Fe³⁺ cation of between 4.57(1) (x = 0.20) and 6.37(1) μ_B (x = 0.90). The cause of the unexpectedly low paramagnetic moment observed in most of these compositions is ascribed to the effect of superexchange interactions extending beyond the adjacent 6-coordinate sites in the simple cubic lattice.