Ion-beam modification of the magnetic properties ofGa1−xMnxAsepilayers

Abstract

We study the controlled introduction of defects in GaMnAs by irradiating the samples with energetic ion beams, which modify the magnetic properties of the DMS. Our study focuses on the low-carrier-density regime, starting with as-grown GaMnAs films and decreasing even further the number of carriers, through a sequence of irradiation doses. We did a systematic study of magnetization as a function of temperature and of the irradiation ion dose. We also performed insitu room temperature resistivity measurements as a function of the ion dose. We observe that both magnetic and transport properties of the samples can be experimentally manipulated by controlling the ion-beam parameters. For highly irradiated samples, the magnetic measurements indicate the formation of magnetic clusters together with a transition to an insulating state. The experimental data are compared with mean-field calculations for magnetization. The independent control of disorder and carrier density in the calculations allows further insight on the individual role of this two factors in the ion-beam-induced modification of GaMnAs.

β-detected NMR of Li in Ga1−xMnxAs

“…Comparison with the effects of much higher energy ions indicates we can expect little or no net effect of the implantation on the macroscopic properties of the sample. 28 This is confirmed by the fact that we found no time dependence in the results over the course of the experiment and between runs on the same sample.…”

Charge Carrier Dynamics in Ga1-xMnxAs Studied by Resistance Noise Spectroscopy

“…The film with a high irradiation dose shows a pronounced maximum at E 180 meV, which can presumably be explained by the high density of intentionally introduced defects due to the heavy irradiation with ions, causing trapping and detrapping processes of charge carriers with this particular energy. An alternative explanation is the spin-dependent scattering from weakly interacting nanoscale magnetic clusters with fluctuating spin orientation, which form after the irradiation process due to the increased disorder [9]. However, we do not find a systematic magnetic field dependence of the resistance noise.…”

“…While for the non-irradiated sample a monotonic increase in DpEq can be observed, a high fluence of ions yields a distinct peak at 180 meV. This can be explained by capture and emission processes of charge carriers or alternatively by spin-dependent scattering from magnetic clusters with fluctuating spin orientation [9]. Samples with a higher Mn content (x 7%) exhibit dominating two-level processes superimposed on the 1{f -type signal, possibly due to a higher density of substitutional and interstitial Mn atoms.…”

“…In detail, the main effect of ion * corresponding author; e-mail: lonsky@physik.uni-frankfurt.de irradiation is the compensation of holes by introducing deep traps and thereby enhancing disorder, while both the concentration of substitutional Mn atoms and Mn interstitials remain unaltered [8]. A majority of the induced defects reside in the As sublattice [9].…”

Switching the uniaxial magnetic anisotropy by ion irradiation induced compensation

“…One of the alternative approaches to tune the hole concentration in semiconductors is ion irradiation [14][15][16][17]. After irradiation, some deep-level trapping centers are generated in the irradiated region, compensating free carriers.…”