Systematic Studies of Electron Transport in Amorphous Alloys

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We have proposed to classify amorphous alloys in five groups in terms of magnetic states, to facilitate the discussion of the electron transport mechanism in a disordered system. Among them, non-magnetic alloys are grouped into groups (5) and (4), depending on the location of the Fermi level in the sp-band and d-band, respectively. They are considered to be of fundamental importance in understanding the scattering mechanism.Major conclusions are summarized here.(1) The electron transport in group (5) is found to be dominated by sp-electrons at the Fermi level, whereas that in group (4) by d-electrons. We found that the difference in the character of the carriers at the Fermi level yields unique electron transport features in the respective group alloys.(2) The scattering mechanism in group (5),where only sp-electrons are reaponsible for the transport, changes with increasing resistivity. In the low-resistivity regime of less than 200 <mu><omega> -cm, where the electron mean free path is longer than the average atomic distance, the normal scattering mechanism described by the Boltzmann equation, is found to be valid. The mobility of conduction electrons is greatly lowered as the resistivity exceeds about 500 <mu><omega>-cm. In such high- resistivity regime, the electron-electron correlation and quantum interference effect becomes substantial and yield unique temperature dependence of resistivity over a wide temperature range below 300 K. (3) We demonstrated that the electron transport mechanism in group (4),where d-electronconduction is significant, is essintially the same as that in high-resistivity group (5) having resistivities above about 500 <mu><omega>-cm. From this we concluded that the electron transport in non-magnetic amorphous alloys including both group (4) and (5) can be understood on the same footing, regardless of the difference in the electronic structure at the Fermi level.