Spin-wave excitations and low-temperature magnetization in the dilute magnetic semiconductor (Ga,Mn)As

The spontaneous magnetization as a function of temperature has been investigated for a number of (Ga,Mn)As layers grown on GaAs (001) using superconduction quantum interference device magnetometry. The measurements have been performed with a focus on the low-temperature behavior of the magnetization. The temperature dependence of the spontaneous magnetization MS for T=0.5TC is found to be well described by Bloch's T3∕2 law for all measured samples. However, we observe an extraordinary enhancement of the spin-wave parameter compared to conventional $3d$ ferromagnets such as Fe, which implies an enhanced low-temperature decay of the magnetic order. For a thorough understanding of this result, we have theoretically investigated the effect of dilution (disorder) on the finite-temperature spin dynamics and on the spin-wave parameter. It is shown that, due to the preferential accumulation of holes in spin clusters, which weakens the majority bulk spin coupling and results in low-energy magnon softening, there is a strong enhancement in the low-temperature decay of the magnetization with dilution. We find excellent agreement between the calculated and measured values for the spin-wave parameter.