Fundamental Curie temperature limit in ferromagnetic GaMnAs
Abstract
We provide experimental evidence that the upper limit of ~110 K commonly observed for the Curie temperature TC of Ga(1-x)Mn(x)As is caused by the Fermi-level-induced hole saturation. Ion channeling, electrical and magnetization measurements on a series of Ga(1-x-y)Mn(x)Be(y)As layers show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of TC with increasing Be concentration, while the free hole concentration remains relatively constant at ~5x1020 cm-3. These results indicate that the concentrations of free holes and ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors.
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