Surface effects in Mn L3,2 x-ray absorption spectra from (Ga,Mn)As

Abstract

We have identified a Mn-rich layer on the surface on (Ga,Mn)As thin films which significantly influences soft x-ray absorption measurements. The Mn L3,2 x-ray absorption spectra of the untreated films show a strong multiplet structure, consistent with earlier observations and characteristic of MnO. After removal of the surface layer, the multiplet structure is less pronounced and the spectrum is shifted to ∼0.5 eV lower photon energy. Comparison with calculated spectra imply a localized Mn ground state for the untreated sample and a hybridized ground state after etching. In addition, a large x-ray magnetic circular dichroism is observed at the Mn L3,2 edge in the etched film. These results may explain several peculiarities of previously reported x-ray absorption studies from (Ga,Mn)As.

Surface treatments and magnetic properties of Ga1−xMnxAs thin films

“…The XAS spectrum of sample S2, chemically etched, has the L 3 threshold at 637.6 eV, namely 0.4 eV below the L 3 of S1. Its lineshape does not have clear structures, and can be simulated with a mixed state of d4-d5-d6 atomic configurations [14], due to the hybridization of the Mn 3d electrons with As valence band. The shape of the XMCD difference spectrum of S2, and its energy position, correspond the one of the S1 sample.…”

“…2, has two strong features at 1.4 and 3.6 eV above the L 3 edge (638 eV). These structures can be well simulated starting from an atomic d5 electronic configuration [14], typical of Mn oxides. The XMCD main peak centre is 0.4 eV below the L 3 XAS edge.…”

“…Chemical etching is a very efficient way to remove the surface Mn oxide layer [14]. Samples S2, S3 and Sb3 were treated by etching the epitaxial film in pure HCl for one minute, then rinsed in de-ionised water up to the insertion in UHV environment (base pressure P = 4 · 10 À10 mbar).…”

“…To our knowledge the only examples of XAS measurements which reflected lineshape of the Mn embedded in GaAs matrix before 2004, were made by Rader et al [10], on a sputtered and annealed surface, and by Soo et al [13] on a GaAs capped sample. In 2004 the group of Edmonds [14] showed that HCl etching, followed by rinsing in de-ionized water, can efficiently remove the Mn oxidized layer, allowing the measurement of the Mn embedded in GaAs bulk, leaving the magnetic properties of the surface unaffected.…”

Identifying the character of ferromagnetic Mn in epitaxial Fe/(Ga,Mn)As heterostructures

“…The latter configuration has a more structured XAS spectrum, located at higher BE with respect to the d 4 -d 5 -d 6 one. [19][20][21][22] A recent detailed study on the depth concentration of Mn in ͑Ga,Mn͒As reveals the presence of Mn with d 5 configuration up to 6 nm from the interface, coexisting with Mn Ga and not related to oxide. 23 Results in Fig.…”