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= 0.5T(C) is found to be well described by Bloch's T-3/2 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.