An investigation of low-field magnetoresistance in the double perovskitesSr2Fe1−xZnxMoO6,x = 0, 0.05, 0.15 and 0.25

Abstract

The electrical, magnetic and transport properties of Zn doped polycrystalline samples ofSr2Fe1−xZnxMoO6 (x = 0,0.05,0.15 and 0.25) with the double perovskite structure have been investigated. The subtle replacement ofFe3+ ionsby Zn2+ ions facilitates the formation of a more ordered structure, while further substitution leadsto disordered structure because of the presence of a striped phase. Analysis of the x-raypowder diffraction patterns based on Rietveld analysis indicates that the replacement ofFe3+ byZn2+ ions favoursthe formation of Mo6+ ions. The spin-glass behaviour can be explained on the basis of the competitionbetween the antiferromagnetic superexchange and the ferromagnetic double-exchangeinteraction. The low-field magnetoresistance was moderately enhanced atx = 0.05, and its origin was found to be the competition between the decrease of the concentrationof the itinerant electrons and the weaker antiferromagnetic superexchange in the antiphaseboundaries. An almost linear negative magnetoresistance in moderate field has been observed forx = 0.25. A possibledouble-exchange mechanism is proposed for elucidating the observations; it also suggests a coexistenceof (Fe3+,Mo5+)and (Zn2+,Mo6+) valence pairs.