Anisotropy of the size effect in the electrical resistivity of high-purity Al single crystals

To clarify the anisotropy of the de size effect in Al, measurements have been made of the electrical resistivity rho(4.2) (K) of high-purity Al single crystals (RRR similar or equal to 50 000) at 4.2 K. The specimen surfaces were set parallel to each of three crystallographic planes, {100}, {111} and {110}, and the axis orientations were parallel to [100], [111] and [110]. The main results were the following. (1) The size effect increased in the following order of the surface orientations: {110}, {111}, {100}. (2) For the size effect due to a {110} surface, the Fuchs-Sondheimer theory with rho(b)l(b) = 0.82 f Omega m(2) gave a good description, while, for the size effect due to {100} and {111} surfaces, substantial disagreement with the theory was suggested for the very thick specimens. (3) For each surface orientation, rho(4.2 K) for sufficiently thin specimens was independent of the axis orientation within the experimental error; i.e. the size effect was independent of the direction of current flow. (4) However, as the specimen thickness increased, strong anisotropy of rho(4.2) (K) with respect to the current direction appeared: rho(4.2 K) increased in the following order of directions: [110], [111], [100]. Results (3) and (4) suggest an anisotropy effect of the bulk resistivity rho(b) in high-purity Al.