Enhanced low field magnetoresistance in Sr2Fe1-xAgxMoO6 double perovskite system

Abstract

Polycrystalline samples of Sr2Fe1-xAgxMoO6 (x = 0, 0.05, 0.10 and 0.20) have been prepared by solid state sintering. Single phase nature of the samples has been confirmed by the XRD analysis for the samples up to an Ag content of 0.10. SEM analysis shows that Ag enhances the grain growth and coarsening of the system. Though the saturation magnetisation and Curie temperature decreases, the Fe-Mo ordering as well as spin polarization enhances with respect to Ag substitution. All the samples except for the x = 0.20, shows the LFMR hysteresis nature at 20 K indicative of the tunnelling magneto-resistance behaviour. The magneto-resistance values were found to increase with respect to Ag content up to a limit of x = 0.10. The enhancement of LFMR behaviour and the tunnelling magnet-resistance is explained in terms of the formation of the non magnetic patches like Mo-O-Ag-O-Mo-O within the grain which acts as insulating tunnel barrier between the ferromagnetic regions of Fe-O-Mo-O-Fe-O due to the substitution of Ag in place of Fe. The striking feature of our finding is that the LFMR nature of the double perovskite increases with respect to the enhancement in the grain size which is contrary to the reported results wherein LFMR is found to increase with respect to a decrease in the grain size. So it is proposed that the LFMR nature and magnetoresistance of double perovskite systems in general and Sr2FeMoO6 in particular depend on intra-grain properties also.