Anomalous magnetoresistance in [ Sr<Subscript>2</Subscript>Bi<Subscript>2-x</Subscript>Pb<Subscript>x</Subscript>O<Subscript>4</Subscript>] <Superscript>RS</Superscript>[ CoO<Subscript>2</Subscript>] <Subscript>y</Subscript> (x=0, 0.3, and 0.4; y ≈ 1.85) single crystals

Magnetoresistance (MR) of the [ Sr<Subscript>2</Subscript>Bi<Subscript>2-x</Subscript>Pb<Subscript>x</Subs cript>O<Subscript>4</Subscript>] <Superscript> RS</Superscript>[ CoO<Subscript>2</Subscript>] <Subscript>y</Subscript> (x=0, 0.3, and 0.4; y ≈ 1.85; RS is referred to rocksalt block) single crystals is investigated systematically. A nonmonotonic variation of the isothermal in-plane and out-of-plane MR with the field is observed. The out-of-plane MR is positive at high temperatures and increases with decreasing T, and exhibits a pronounced hump, then changes the sign from positive to negative at a certain temperature. These results strongly suggest that the observed MR consists of two contributions: one negative and one positive component. The isothermal MR in high magnetic fields follows a H<Superscript>2</Superscript> law. The negative contribution comes from spin scattering of carriers by localized-magnetic-moments based on the Khosla-Fischer model. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006