Hall effect and magnetoresistance in SrxNbO3 (x=0.80, 0.85, and 0.90).

Abstract

Both the Hall coefficient and the magnetoresistance have been measured for polycrystalline samples of ${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NbO}}_{3}$ (x=0.80, 0.85, and 0.90). The Hall coefficient is found to be negative and weakly dependent on temperature for every sample. The carrier concentration (n) is comparable with that for a conventional metallic conductor, i.e., n\ensuremath{\sim}${10}^{22}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at 5 K. The effective mass (${\mathit{m}}^{\mathrm{*}}$) is estimated to be ${\mathit{m}}^{\mathrm{*}}$\ensuremath{\sim}3${\mathit{m}}_{0}$ using the free-electron model (where ${\mathit{m}}_{0}$ is the free-electron mass). The metallic parameter ${\mathit{k}}_{\mathit{F}}$${\mathit{l}}_{\mathrm{tr}}$ (in which ${\mathit{k}}_{\mathit{F}}$ is the Fermi wave number and ${\mathit{l}}_{\mathrm{tr}}$ is the transport mean free path) is rather small being approximately unity, though the typical value for a metal is ${\mathit{k}}_{\mathit{F}}$${\mathit{l}}_{\mathrm{tr}}$\ensuremath{\gg}1. The increase in magnetoresistance (\ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}) at H=6 T, \ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}={\ensuremath{\rho}(H)-\ensuremath{\rho}(0)}/\ensuremath{\rho}(0), is estimated at 1.5--3 %. As H increases, \ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho} increases in proportion to ${\mathit{H}}^{2}$ up to H\ensuremath{\sim}3 T, and then linearly with H. In order to explain this result we discuss the transport property of ${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NbO}}_{3}$ in terms of quantum-interference phenomena such as weak localization or electron-electron interaction effects.