Sr2FeMoO6+x: Magnetic and electrical property dependence on thickness and substrate type

We have produced a series of Sr2FeMoO6+x films from 15 to 240 nm thick on MgO, LaAlO3, Sr0.5Ba0.5TiO3, and SrTiO3 substrates and measured their electrical and magnetic properties. It is clear that as the nominal lattice mismatch increases the magnetisation decreases and when the mismatch is small there is no dependence of the magnetisation on the film thickness for films above 30 nm thick. Evidence for a thin antiferromagnetic (AF) rich interface layer in the thinner films on Sr0.5Ba0.5TiO3 and SrTiO3 comes from the magnetisation data, but a clear influence is seen in the electrical dependence on temperature. However, for the 120 and 240 nm thick films there is little evidence of this AF layer, and an almost universal conduction mechanism is seen. This mechanism applies also to the 240 nm thick films on LaAlO3 and can also explain the observed magnetoresistance. Films on MgO show evidence of the often seen re-organised layer at the film/substrate interface.