Neutron-diffraction magnetic scattering in ordered and disordered Sr2FeMoO6

Cationic antisite disorder in Sr2FeMoO6 has been shown to be an essential variable to understand the magnetotransport properties in this double perovskite. However, its effect on the electronic and magnetic properties of the system is still controversial. We have performed temperature-dependent neutron powder diffraction (NPD) experiments and high-temperature magnetic measurements in two Sr2FeMoO6 samples with a very different degree of cationic order, 70% for the so-called ordered sample and 18% for the disordered sample. Although X-ray diffraction and low-temperature magnetic measurements show clear differences between both samples, that is, the absence of a low-angle superstructure peak, lower saturation magnetization and smoother decay of the magnetization around the ferromagnetic transition temperature in the disordered sample, the NPD patterns are surprisingly similar. We propose that this unexpected strong magnetic scattering in the disordered sample arises from antiferromagnetically ordered Fe-rich patches in which strong antiferromagnetic Fe3+-O-Fe3+ superexchange interactions are promoted. This hypothesis is validated with the observation of the Neel peak in the disordered sample at around 770 K. (orig.)