Coexistence of intrinsic and extrinsic magnetoresistance in the double-perovskite Sr2Fe(Mo1-xWx)O6-w system

In a recent study, it was shown that by partially substituting Mo with W in the double-perovskite Sr2FeMoO6-w system, the magnetoresistivity can be en hanced. [K.-I. Kobayashi, T. Okuda, Y. Tomioka, T. Kimura, and Y. Tokura, J . Magn. Magn. Mater. 218, 17 (2000).] In order to explain the increase in t he magnetoresistivity a series of W-substituted Sr2Fe(Mo1-xWx)O6-w samples with 0 less than or equal tox less than or equal to1 was synthesized. Upon increasing the W content, the samples began to exhibit coexistence of param agnetism and ferrimagnetism at 300 K. Signatures of antiferromagnetic order ing appeared around T(N)approximate to 50 K for x greater than or equal to0 .6. In samples with 0.7 less than or equal tox less than or equal to0.8 a b road peak was observed in the magnetoresistance data at temperatures corres ponding to the Neel temperature. The peak was found to have its origin in t he colossal magnetoresistance effect. The W-substituted samples were partia lly ferrimagnetic and therefore also exhibited the tunneling-type magnetore sistance, which is characteristic of pure Sr2FeMoO6-w. The coexistence of t he two types of magnetoresistance effect is responsible for the enhancement of the overall magnetoresistance value. A slight enhancement in the magnet oresistance values around 300 K for the strongly W-substituted samples was found to be related to a second colossal magnetoresistance peak related to the para- to ferrimagnetic transition at T-c. (C) 2001 American Institute o f Physics.