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How to make GaMnAs with high ferromagnetic phase transition temperature?

100%

Sadowski J. , Domagała J. Z. , Kanski J. , Rodriguez C. H. , Terki F. , Charar S. , Maude D.

Materials Science Poland

2006

tom Vol. 24, No. 3

617--625

We analyze the role of structural defects in GaMnAs and demonstrate how their density can be drastically reduced by in situ post-growth annealing under As capping. Modifications of the magnetic, transport and structural properties of the annealed GaMnAs layers are presented. The main result is that the Curie temperatures are strongly increased relative those of the as-grown layers, from typically 70 - 80 K to 150 - 160 K. The annealed layers exhibit well-ordered smooth surfaces, suitable for further epitaxial overgrowth.

Quantum oscillation measurements on the organic superconductor ?-(BEDT-TTF)2I3

84%

Nothardt A. , Balthes E. , Salameh B. , Schmidt W. , Schweitzer D. , Strempfer J. , Keimer D. , Maude D.

tom Vol. 22, No. 4

299--305

Quantum oscillation experiments were performed on high quality single crystals of ?-(BEDT-TTF)2I3. Their electronic properties are similar to those of crystals of ?-(BEDT-TTF)2(I3)1-x(AuI2)x (x < 0.02). Nevertheless, in the neat crystals used here, quantum oscillations for the a-orbit (Fa?= 780 T) are observed already at a field of 2 T, and the magnetic breakdown of the a-orbit (Fa= 4200 T) occurs at 3 T. In the large magnetic field range, in which quantum oscillations are observed, the warping of the Fermi surface of the a-orbit and a-orbit could be determined to be aFa?= 6.6 T and aFa?= 16.6 T, respectively. At high magnetic fields, the de Haas-van Alphen signal consists of pronounced inverse saw-tooth oscillations, and the Shubnikov-de Haas signal has a peaked structure. This behaviour is interpreted in terms of magnetic interaction.