  Measurements of the low frequency electrical noise in the ferromagnetic
semiconductor (Ga,Mn)As reveal an enhanced integrated noise at low temperature.
For moderate localization, we find a 1/f normalized power spectrum density over
the entire range of temperatures studied (4.2K < T < 70K). However, for
stronger localization and a high density of Mn interstitials, we observe
Lorentzian noise spectra accompanied by random telegraph noise. Magnetic field
dependence and annealing studies suggest that interstitial Mn defects couple
with substitutional Mn atoms to form nanoscale magnetic clusters characterized
by a net moment of about 20 Bohr magnetons whose fluctuations modulate hole
transport.
