Muon hyperfine fields in Fe(Al) alloys

The hyperfine field on the muon, Bhf, at interstitial sites dilute Fe(Al) alloys has been measured for four different concentrations of and as a function of temp. by the muon-spin-rotation method. The magnitude of Bhf, which is negative, decreases at rates ranging from (0.09 plus/minus 0.03)%/at.-% Al at 200 deg K to an asymptotic limit of 0.35 plus/minus 0.03 far above 440 deg K. This behavior shows that sites near the impurity are weakly repulsive to the muon, with an interaction potential of 13 plus/minus 3 meV. To fit the temp. dependence of the hyperfine field, it is necessary to hypothesize the existence of a small concentration of unidentified defects, possibly dislocations, which are attractive to the muon. Although the Al impurity acts as a nonmagnetic hole in the Fe lattice, the observed decrease in Bhf is only 35% of the decrease in the bulk magnetization and Bhf is determined mainly by the enhanced screening of conduction electrons in Fe and Fe(Al). Since the influence of Al impurity on the neighboring Fe moments is very small, most of the change Bhf is therefore attributed to the increase in conduction-electron polarization at the Al impurity.47 refs.--AA