Magnetotransport of lanthanum doped RuSr<Subscript>2</Subscript>GdCu<Subscript>2</Subscript>O<Subscript>8</Subscript> – the role of gadolinium

Strongly underdoped RuSr<Subscript>1.9</Subscript>La<Subscript>0.1</Subscript>GdCu<Subscript>2 </Subscript>O<Subscript>8</Subscript> has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO<Subscript>2</Subscript> planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K in low applied magnetic fields, and the gadolinium sublattice orders antiferromagnetically at 2.8 K. The magnetoresistivity in this compound exhibits a complicated temperature dependence due to the occurence of the two magnetic orders and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO<Subscript>2</Subscript> layers while the gadolinium magnetism influences the conductivity in the CuO<Subscript>2</Subscript> layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic close to the gadolinium antiferromagnetic order temperature. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007