Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs

Abstract

The recently reported Rutherford backscattering and particle-induced X-ray emission experiments 1 have revealed that in low-temperature MBE grown Ga1−xMnxAs a significant part of the incorporated Mn atoms occupies tetrahedral interstitial sites in the lattice. Here we study the magnetic properties of these interstitial (MnI) ions. We show that they do not participate in the hole-induced ferromagnetism. Moreover, MnI double donors may form pairs with the nearest substitutional (MnGa) acceptors -our calculations evidence that the spins in such pairs are antiferromagnetically coupled by the superexchange. We also show that for the Mn ion in the other, hexagonal, interstitial position (which seems to be the case in the Ga1−x−yMnxBeyAs samples) the p-d interactions with the holes, responsible for the ferromagnetism, are very much suppressed.

Prospects for high temperature ferromagnetism in (Ga,Mn)As semiconductors

“…In real ͑Ga,Mn͒As materials a fraction of Mn is incorporated during the growth in interstitial positions. These donor impurities are likely to form pairs with Mn Ga acceptors in as-grown systems with approximately zero net moment, 8,37,38 resulting in an effective free local-moment doping x ef f = x s − x i . Here x s and x i are partial concentrations of substitutional and interstitial Mn, respectively.…”

“…Arsenic antisites ͑As Ga ͒ and interstitial manganese ͑Mn I ͒ represent two major sources of charge compensation in ͑Ga,Mn͒As grown by low-temperature molecular beam epitaxy ͑LT-MBE͒, both acting as double-donors. 35,36 A Mn I cation when attracted to a Mn Ga anion compensates also the Mn Ga local moment as the two species are expected to couple antiferromagnetically 8,37,38 due to superexchange over the whole range from strong to weak charge compensation.…”

Annealing-dependent magnetic depth profile inGa1−xMnxAs

“…10 This is at least partially due to Mn I aligning antiferromagnetically with Mn Ga , effectively canceling their moments. 11 It has been well established that low temperature post-growth annealing of films can serve to significantly raise T , As Mn Ga -1 x x C 12 and increase the magnetization. 9, 13 Yu et al 8,9 present evidence to suggest that this phenomenon is in large part due to the redistribution of Mn I during annealing.…”

Mn3delectronic configurations in(Ga1−xMnx)Kronast1, Ovsyannikov2, Vollmer3 et al. 2006Phys. Rev. B120110View full textAdd to dashboardCite

“…This is an indication that substitutional and interstitial Mn occupy neighbor sites and form magnetic clusters. 10,8 The bulk XAS line shape changes significantly with increasing Mn concentrations ͓see Fig. 5͑A͔͒.…”

“…7 Furthermore, it was proposed that interstitial Mn tends to align antiferromagnetically with substitutional Mn effectively canceling their moments. 8 The presence of Mn interstitials close to clusters of substitutional Mn was also predicted to strongly modify the exchange coupling between the latter as well as their charge state. 9,10 Finally, in contrast to II-VI-based magnetic semiconductors no antiferromagnetic exchange between Mn-Mn nearest neighbors has been considered for ͑GaMn͒As due to a lack of experimental evidence despite its possibly adverse effect on a high ferromagnetic T c ͑Ref.…”