In recent years a rapid development of the field of research called spintronics is observed. The goal of the studies is to create conceptually new devices which will utilize spin of electron. To achieve this goal it is necessary to fabricate effective injectors of polarized spins and to learn how to manipulate and detect spin polarization. On the other hand the integration of magnetic materials with conventional semiconductor technology should be also possible to achieve. All of these imply the fabrication of suitable materials with appropriate properties at room temperature and manufacturing the reliable spin based device.
As suitable candidates for these studies GaMnAs structures were chosen being a composite multiphase material, after high temperature post-growth annealing, with small ferromagnetic nanoparticles of MnAs immersed in the semiconductor host lattice. Changes of the local structure around Mn atoms in (Ga,Mn)As layers after high temperature annealing were determined by an X-Ray absorption spectroscopy (namely EXAFS) and high resolution X-Ray diffraction (HRXRD) measurements, and were compared with their magnetic properties. The X-Ray absorption is sensitive enough to detect crystalline structure changes around Mn atoms in consequence of annealing at the temperatures of 500 and 600 ºC. The qualitative and the quantitative analysis of EXAFS spectra gives unambiguously evidence of transition of the local structure around Mn atoms from cubic to hexagonal (i.e. new phase formation, namely hexagonal inclusions of MnAs). The sample with MnAs hexagonal inclusions exhibits ferromagnetic properties up to room temperature with almost all Mn atoms being in ferromagnetic phase.

ACKNOWLEDGMENTS
This work was partially supported by national grant of Ministry of Science and High Education N202-052-32/1189 and by DESY and the European Community under Contract RII3-CT-2004-506008 (IA-SFS).

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