Random telegraph noise from magnetic nanoclusters in the ferromagnetic semiconductor (Ga,Mn)As

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.