The effects of Al substitution on the magnetic and electronic properties of Sr2Fe1−xAlxMoO6

We report the results from magnetic, transport and Mo zero field nuclear magnetic resonance measurements on polycrystalline Sr2Fe1−xAlxMoO6. We find that there is a small electron-doping effect induced by Al3+ substitution for Fe, which suggests that Fe is not in the 3+ state assumed in some theoretical models. We show that the decrease in the Curie temperature, Tc, with increasing Al concentration can be interpreted in terms of 3D random site dilution. The saturation moment per formula unit, as determined from magnetization measurements, decreases with increasing x but the Mo moment shows a very small increase. The spin-wave dispersion is complicated in this compound and the temperature-dependent Mo moment does not follow the Bloch T3/2 law. There is no correlation between the resistivity or the magneto-resistance at 77 K with the Al concentration, which may be due to different grain boundary properties in each sample.