Interaction of localized spins in low-temperature-grown GaAs layers

Localized spins are associated with anti-site arsenic (AsGa+)ions in a GaAs layer grown at a low temperature by molecular-beam epitaxy (LT-GaAs). In order to investigate possible interactions among these localized spins, magnetic properties of Be-doped LT-GaAs layers were studied by electron spin resonance (ESR) spectroscopy and super-conducting quantum interference device (SQUID) measurements, for the latter of which single crystalline LT-GaAs layers with thicknesses up to 20 μm were grown. In the SQUID measurements at strong fields, thick LT-GaAs layers show the Curie-type paramagnetism. At weak fields, a spin-glass like transition occurs; the temperature dependence of the magnetization under the zero-field cooling exhibits a peak, and the field dependence of the magnetization has a significant hysteresis at temperatures lower than the peak temperature. The peak temperature varies among samples, ranging from 2.7 to 5.5 K, depending on their growth temperatures and Be concentrations. Measured line-widths of ESR spectra have a close correlation with the results of SQUID measurements; a sample in which more significant effects of interactions among localized spins occur in the SQUID results exhibits a narrower ESR line and a larger increase in the line-width with a decrease in temperature.