[Zurück]

V. Drchal, J. Kudrnovsky, F. Maca, J. Masek, I. Turek, P. Weinberger:
"Phase Stability and Ordering in (Ga,Mn)As Alloys";
in: "Complex Inorganic Solids: Structural, Stability, and Magnetic Properties of Alloys", Springer-Verlag, 2005, ISBN: 0-387-24811-0, S. 87 - 98.

One of the key aspects of this volume is to cut across the traditional taxonomy of disciplines in the study of alloys. Hence there has been a deliberate attempt to integrate the different approaches taken towards alloys as a class of materials in different fields, ranging from geology to metallurgical engineering. The emphasis of this book is to highlight commonalities between different fields with respect to how alloys are studied. The topics in this book fall into several themes, which suggest a number of different classification schemes. We have chosen a scheme that classifies the papers in the volume into the categories Microstructural Considerations, Ordering, Kinetics and Diffusion, Magnetic Considerations and Elastic Considerations. The book has juxtaposed apparently disparate approaches to similar physical processes, in the hope of revealing a more dynamic character of the processes under consideration. This monograph will invigorate new kinds of discussion and reveal challenges and new avenues to the description and prediction of properties of materials in the solid state and the conditions that produce them.

Diluted magnetic III V semiconductors DMS such asGa􀀀􀀀xMnxAs alloys repre
sent a new class of promising materials with potential applications in spin electronics􀀀
The samples are usually prepared by molecular beam epitaxy MBE on GaAs sub
strates at temperatures ranging from C to C Higher temperatures or a
Mn content higher than at can lead to precipitation of MnAs According to the
measurements 􀀀 of Hall resistivities in strong magnetic elds the conductivity is of
p type Extended X ray absorption ne structure EXAFS studies have shown that
Mn is substitutionally incorporated into the Ga sublattice and acts as acceptor These
materials are highly compensated i e the experimentally observed number of holes
in the valence band is considerably smaller than the concentration of Mn impurities
This indicates the presence of other lattice defects acting as donors
The most probable candidate for such a compensation are As antisites but also
other possibilities e g Mn interstitials 􀀀 are conceivable The highest Curie temper
ature reported 􀀀 for Ga􀀀􀀀xMnxAs alloys is K while for Ga􀀀􀀀xMnxN alloys it is

K
It is often assumed that the defects are randomly distributed however experi
ments suggest that impurities can di use rapidly at
C which is a typical growth
and annealing temperature for Ga􀀀􀀀xMnxAs samples prepared by MBA In such a case
the spatial distribution of impurities is not random any more but it becomes at least
partially correlated􀀀 These correlations can substantially modify the transport and
magnetic properties of the DMSs

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