Polycrystalline Sr <sub> 2 </ Sub> The Femoo <sub> 6 </ Sub> Grain Boundary Magnetoresistance Effect

Sr2FeMoO6 polycrystalline bulk material was synthesized by traditional solid state reaction technique. And then the interfacial state was modulated by using mechanical ball milling method. The effects of such modulating interfacial state on the magnetoresistance, together with the mechanism of grain boundary magnetoresistance are investigated.From X-ray diffraction data, it is found that the crystal structure of polycrystalline Sr2FeMoO6 is not changed, but SrMoO4 phase is introduced and its quantity increases with the increase of the milling time. X-photon spectroscopy analysis makes evidence that this SrMoC>4 phase exists at grain boundaries further. The results of magnetoresistance measurements under different magnetic fields show that at low temperatures, the magetoresistance is enhanced by the reinforcement of the tunneling barriers at the grain boundaries. This behavior is related to the existence of the SrMoO4 insulating phase, which improves the spin-polarized electron inter-granular tunneling. However, as the temperature increases, due to the increasing intensity of the inelastic hopping through localized states at grain boundaries, the magnetoresistance has stronger temperature dependence. Our study shows that the interfacial state plays an important role in the transport properties of Sr2FeMoO6 grain boundary magnetoresistance.Based on the theory of conduction in the ferromagnetic metal-insulating granular system, the experimental phenomena we observed can be explained by two conductance-channel model, i.e. spin-dependent tunneling and spin-independent hopping, in the Sr2FeMoO6 granular system. Both have different temperature dependence so as to lead to different temperature dependence of magnetoresistance. It is also suggested that in order to improve magnetoresistance properties, both sides need to be done as follows:On one hand, reinforce the tunneling barrier, to enhance the spin-polarized electron tunneling. On the other hand, consider reducing the spin-independent hopping channel, for example, reducing the disorder, defects, and etc in the grain boundary region.