Magnetoresistance and Hall effect of the complex metal alloyMg2Al3

Abstract

Unusual electronic transport properties have been found in the rhombohedral ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase of the complex metallic alloy ${\text{Mg}}_{2}{\text{Al}}_{3}$. The magnetoresistance (MR) is 2 orders of magnitude larger than in the related cubic $\ensuremath{\beta}\ensuremath{-}{\text{Mg}}_{2}{\text{Al}}_{3}$-phase and Kohler's rule is strongly violated in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase at higher temperatures. Above about 100 K the Hall coefficient ${R}_{H}$ of the $\ensuremath{\beta}$- and ${\ensuremath{\beta}}^{\ensuremath{'}}$-phases are similar and free-electron-like, while in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase, ${R}_{H}$ changes sign with decreasing temperature at low fields. We have inquired into the sources of these transport anomalies, but have not been able to clearly identify the grounds. Several conventional mechanisms for a large magnetoresistance are discussed, and found not to be applicable. The different properties in the $\ensuremath{\beta}$- and the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phases are puzzling since the magnitudes of the electrical resistivities are similar and ${\ensuremath{\omega}}_{c}\ensuremath{\tau}$ (cyclotron $\text{frequency}\ifmmode\times\else\texttimes\fi{}\text{scattering}$ time) is equally small in both phases. The similar temperature range in which anomalies occur in the ${\ensuremath{\beta}}^{\ensuremath{'}}$-phase in the resistivity, the Hall effect, and the magnetoresistance indicates an electronic transition or a change of the electron structure in this phase below about 100 K.