The interest for metal deposition on GaAs has been driven by the technology of metal contacts and, more recently, by the interest in the preparation of magnetic interfaces for the development of innovative spintronic devices. Two-dimensional systems, such as ultrathin epitaxial films, exhibit magnetic properties distinct from bulk materials. Despite the extensive research on the magnetic properties of metal nano-structures and, more recently, of metal oxide interfaces containing magnetic ions, the investigation of magnetic semiconductors with reduced dimensions is still an open research field boosted by the foreseen development of spintronics devices.
Epitaxially grown Mn based alloys have been studied as elements for spin injection in the semiconductor. In particular the Mn/GaAs(001) interface has been experimentally and theoretically studied by several research groups in the recent years. [1-4] These studies have shown that Mn induces a strong rearrangement of the GaAs surface even at low coverage and low temperature. The surface rearrangement is a complex process involving two or even three crystallographic layers and it is controlled by kinetic effects. 
Here we report on a combined investigation by scanning tunneling microscopy (STM), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) of the magnetic and structural characteristic of the Mn sites in the Mn/GaAs(001) surface as a function of the Mn coverage.
The Mn/GaAs(001) system exhibits a strong dependence of the surface reconstruction on the preparation method. Further, the surface reconstruction undergoes a phase transition from (2×1) to (2×2) when increasing the Mn coverage on a pre-heated substrate (390°C) up to 1/2 monolayer (ML). 
The combination of XAS and XMCD investigation has allowed obtaining information on the local atomic coordination around the Mn sites and its influence on the surface magnetic properties.  In order to study the magnetic anisotropy of the atomic rows at the surface, XMCD and XAS measurements have been performed for different orientations of the magnetic field B with respect to the sample surface.
 A. Ohtake et al. J. Phys. Chem. C 120 (2016) 6050
 S. Colonna et al. Journal of Applied Physics 109 (2011) 123522
 S. D. Thorpe et al. Superlattices and Microstructures 46 (2009) 258
 S.B. Zhang et al. Phys. Rev. B 69 (2004) 121308(R)
 S. Colonna et al. J. Phys.: Condens. Matter (submitted)