Beta-detected NMR study of the local magnetic field in epitaxial GaAs:Mn

A low energy beam of spin polarized 8Li+ has been employed to study the magnetic field distribution in an epitaxial thin film of 5.4% Mn doped GaAs(180 nm) on a (1 0 0) GaAs substrate via beta-detected NMR. The spectrum is a strong function of the implantation energy in the range 28-3 keV. In the magnetic layer, there is no indication of a missing fraction, and even more remarkable, there is a broad negatively shifted resonance. The spin lattice relaxation rate is, however, much faster in the Mn doped layer than in the substrate. A sharp peak characteristic of nonmagnetic GaAs is observed down to the lowest implantation energy, for which none of the Li should reach the substrate. This unexpected depth dependence is discussed.