Hyperfine Magnetic Fields for Os, Ir and Pt in Iron: Pre-equilibrium Effects, Domain Rotation and the Aharoni Effect

Hyperfine fields acting on subnanosecond excited states of impurity nuclei recoil-implanted into ferromagnetic hosts are being studied. These measurements are sensitive to effects 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 field at low recoil velocities, (ii) the dependence (magnitude and direction) of the hyperfine field on the applied field, (iii) the site distribution of the implanted nuclei, and (iv) the time the static field takes to reach equilibrium after implantation. It is found that the static hyperfine field takes about 10 ps after implantation to reach equilibrium. Once equilibrium is established the internal fields may be misaligned with respect to the direction of the external field, but this is associated with domain rotation in an incompletely saturated sample rather than with the 'Aharoni effect'.