We report a strong correlation between the location of Mn sites in ferromagnetic Ga1xMnxAs measured by combined channeling Rutherford backscattering and by particle-induced x-ray emission experiments and its Curie temperature. The concentrations of free holes determined by electrochemical capacitance-voltage profiling and of uncompensated Mn2+ spins determined from superconducting quantum-interference device magnetization measurements are found to depend on the concentration of unstable defects involving highly mobile Mn interstitials. This leads to large variations in TC of Ga1xMnxAs when it is annealed at different temperatures in a narrow temperature range. The fact that annealing under various conditions has failed to produce Curie temperatures above ∼110 K is attributed to the existence of an upper limit on the free hole concentration in low-temperature-grown Ga1xMnxAs.

  • Received 22 January 2002


©2002 American Physical Society