Hyperflne Magnetic Fields for Os, Ir and Pt in Iron: Pre-equilibrium Efiects, Domain Rotation and the Aharoni Efiect⁄

Hyperflne flelds acting on subnanosecond excited states of impurity nuclei recoil-implanted into ferromagnetic hosts are being studied. These measurements are sensitive to efiects on the picosecond time-scale that accompany implantation as well as to phenomena of longer duration. We review our recent work, mainly on 5d impurities implanted into iron, which has concerned: (i) the behaviour of the transient fleld at low recoil velocities, (ii) the dependence (magnitude and direction) of the hyperflne fleld on the applied fleld, (iii) the site distribution of the implanted nuclei, and (iv) the time the static fleld takes to reach equilibrium after implantation. It is found that the static hyperflne fleld takes about 10 ps after implantation to reach equilibrium. Once equilibrium is established the internal flelds may be misaligned with respect to the direction of the external fleld, but this is associated with domain rotation in an incompletely saturated sample rather than with the ‘Aharoni efiect’. 1