(Ga,Mn)As is one of the most intensively investigated magnetic semiconductors due to its high Curie temperature and compatibility with the GaAs technology. While annealing at about 200 C results in a substantial improvement of its properties [1], annealing at higher tempera-tures leads to the formation of inclusions. Depending on the annealing conditions, inclusions consist in smaller zinc-blende Mn-rich (Ga,Mn)As nanoclusters, or larger clusters of MnAs in the NiAs phase [2].

To understand structural stability of (Ga,Mn)As we performed first principles calculations using the local spin density approximation, and we generalized the definition of the mixing enthalpy to the case of alloys with a varying crystalline structure. We find that the stability of the zinc blende phase persists up to about x=0.75, while for higher Mn contents the equilib-rium structure is the NiAs phase. Moreover, due to the lattice mismatch, cubic GaMnAs is intrinsically unstable with respect to the segregation into pure end compounds. This suggests that formation of MnAs inclusions occurs in two steps. First, intrinsic instability results in fluctuations of the alloy composition, i.e., formation of Mn-rich clusters. In the second step, the clusters undergo a structural transformation from the metastable zinc blende to the stable NiAs structure.

Finally, we extend the analysis to (Cd,Mn)Te. The phase diagrams of both (Ga,Mn)As and (Cd,Mn)Te are similar, exhibiting a transition from the cubic to the NiAs phase with the in-creasing Mn content. For both systems we discuss magnetic ordering (which is ferromagnetic for (Ga,Mn)As, and antiferromagnetic for (Cd,Mn)Te), and its contribution to the structural stability.

The work has been supported by grant PBZ-KBN-044/P03/2001.

[1] K. Edmonds et al., Phys. Rev. Lett. 92, 37201 (2004).

[2] M. Moreno et al., Phys. Rev. B 67, 235206 (2003); J. Appl. Phys. 92, 4672 (2002).

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/3921 must be provided.

1. Innowacyjne technologie wielofunkcyjnych materiałów i struktur dla nanoelektroniki, fotoniki, spintroniki i technik sensorowych (InTechFun).
2. Transparent p-type ZnO obtained by Ag doping
3. Magnetism of CaAs and CaP half-metals
4. Structural properties of MnTe, ZnTe, and ZnO, and phase stability of Mn_xZn_1-xTe alloy