Ion-beam mixing of Al-V films: Structure and Hall effect

Icosahedral and amorphous structures have been produced in multilayered Al-V by ion-beam mixing. In contrast to the possibilities with the Al-Mn alloy system, we find that the formation of ``single-phase'' icosahedral Al-V at higher temperatures is inhibited by a coexisting, as yet unreported, bcc phase (a=3.82 A{}). When the mixing is performed with 500-keV Xe⁺, transmission-electron-microscopy (TEM) --amorphous structures have been obtained at liquid-nitrogen temperature in an extended concentration regime (15--26 at. % V). Electrical resistivity data for all the alloys studied show a negative temperature dependence which cannot be explained quantitatively in the framework of current theories. The Hall coefficient in glassy Al-V is found to change sign and become positive above 16 at. % V. This fact is discussed in the context of existing theories for the sign of the Hall coefficient. As far as we know, this is the first time such a change of sign has been observed for a nonmagnetic glassy metallic system which is not of the ``early-late'' transition-metal type.