Thermodynamic limits to the maximum Curie temperaturein GaGa1-x 1-xMn MnxAs As

摘要

Using the ion channeling techniques we find that a substantial fraction (upto 15%) of the Mn atoms reside in interstitial sites in GaGa1-x 1-xMn MnxAs alloys (with xranging from 0.02 to 0.09). Moreover, the TAs TC of Ga Ga1-x 1-xMn MnxAs is found to be verysensitive to annealing at temperatures close to the growth temperature of 265oC. Ionchanneling results demonstrate that the increase of TAs TC after annealing at 282℃ can beattributed to a relocation of Mn atoms from interstitial sites to form random clusters.A series of GaGa1-x-y 1-yMn MnxBe BeyAs layers, in which the magnetic moments and free holesare independently controlled by the Mn and Be contents, respectively, are alsoinvestigated. A dramatic increase of the concentration of Mn interstitials and areduction of TAs TC are observed as the Be concentration increases, while the free holeconcentration stays relatively constant at ~5x105x1020 20cm cm-3 -3. These results demonstrate thatthe concentrations of free holes as well as uncompensated Mn spins are governed bythe position of the Fermi level, which controls the formation energy of compensatinginterstitial Mn acceptors. This Fermi-level-induced hole saturation is responsible forthe commonly observed upper limit of 110 K for the Curie temperature of thismaterial system.