The effect of clustering on the Hall and magnetoresistance coefficients in very dilute Al-Ti alloys

Abstract

A study has been made of the residual resistivity and magnetoresistivity at 4.2K, the Hall coefficient between 4.2 and 77K and the deviation from Matthiessen's rule at 77K in Al-210 PPM Ti and Al-522 PPM Ti in both the slow-cooled condition and when quenched from the melt. It is shown that in the slow-cooled state, clustering/precipitation of solute atoms occurs creating electron scattering entities which, while appearing to behave like point defects, nevertheless possess a scattering anisotropy entirely different from conventional point defects. As a result these clusters produce considerably enhanced deviations from Matthiessen's rule, Hall and magnetoresistance coefficients. Values of the anisotropy in the mean free paths are calculated using a three-group model and a simple clustering model is invoked which demonstrates why the scattering becomes more 'interstitial' in the clustered alloys. This leads to a scattering anisotropy for which the mean free path of electrons in the third zone becomes greater than that for holes in the corners of the second zone.