The magnetic properties of a 180-nm-thick epitaxial film of the dilute magnetic semiconductor Ga${}_{1-x}$Mn${}_x$As with $x=0.054$ are investigated using beta-detected NMR of low-energy implanted ${}^8$Li${}^{+}$. There is a broad distribution of local magnetic fields in the Ga${}_{1-x}$Mn${}_x$As layer, reflecting the magnetic inhomogeneity of the system. The resonance (representing the local magnetic field distribution) is followed as a function of temperature through the ferromagnetic transition. The average hyperfine field at the ${}^8$Li nucleus is measured to be positive and on the order of 150 G at low temperature, implying a negative hyperfine coupling of the ${}^8$Li to the delocalized holes and suggesting that the holes are better described by an Mn–derived impurity band. The spin–lattice relaxation of ${}^8$Li shows a remarkably weak feature at the phase transition and no Korringa behavior despite metallic conductivity. No evidence is found of the microscopic magnetic phase separation that has been suggested by some low-energy muon spin-rotation measurements.

• Received 21 March 2011
• Corrected 5 December 2011

DOI:https://doi.org/10.1103/PhysRevB.84.054414