Magnetoresistance and magnetothermopower in the rhodium misfit oxide [Bi1.95Ba1.95Rh0.1O4][RhO2]1.8

The magnetotransport properties of the Rh-based [Bi1.95Ba1.95Rh0.1O4][RhO2](1.8) misfit oxide have been investigated. A metallic behavior is observed, coexisting with a large thermopower S of +95 mu V/K at room temperature, similar to what is observed in cobalt based misfit oxides. This S value can be explained by the coexistence of Rh3+(4d(6)) and Rh4+(4d(5)) in the RhO2 layers, suggesting that they have the same influence as isoelectronic low spin state t(2g)(6) S=0 Co3+ (3d(6)) and t(2g)(5) S=1/2 Co4+ (3d(5)) in cobalt misfit oxides. From the specific heat measurements, the coefficient gamma=38 mJ K-2 mol(Rh)(-1) shows that electron correlations are moderately strong. A small magnetoresistance is observed at low T, with two contributions, first negative up to 7 T, and positive for mu H-0 > 7 T, reaching +5% at 14 T and T=2.5 K. This is a unique example of magnetoresistance in rhodium oxides, emphasizing the peculiarity of the transport properties arising from these CdI2 type layers. The thermopower depends also strongly on field, with a magnetothermopower reaching -50% in 9 T at 2.5 K.