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Ferromagnetic Resonance Study of Exchange Coupled (Ga,Mn)As/GaAs/(Ga,Mn)As Heterostructures

100%

Dziatkowski K. , Ge Z. , Liu X. , Furdyna J. , Clerjaud B. , Twardowski A.

nr 2

227-232

Ferromagnetic resonance study of the exchange coupled (Ga,Mn)As/ GaAs/(Ga,Mn)As heterostructures is reported. The measurements were performed on the series of samples with varying thicknesses d_{GaAs} of nonmagnetic GaAs spacer, established d_{GaAs}-dependent extent of weak and strong interlayer exchange coupling, judging on the observation of one or two ferromagnetic resonance modes.

Transport and Magnetic Properties of Low Temperature Annealed Ga_{1-x}Mn_xAs

84%

Kuryliszyn I. , Wojtowicz T. , Liu X. , Furdyna J. , Dobrowolski W. , Broto J. , Goiran M. , Portugall O. , Rakoto H. , Raquet B.

nr 4-5

659-665

We present the results of low temperature annealing studies of Ga_{1-x}Mn_xAs epilayers grown by low temperature molecular beam epitaxy in a wide range of Mn concentrations (0.01

Sputtered n-type Bi2Te3/ (Bi,Sb)2Te3superlattice systems

84%

Winkler M. , Liu X. , Hansen A.-L. , König J. D. , Bensch W. , Kienle L. , Böttner H. , Bartholomé K.

tom 1

1-9

Bi2Te3, (Bi1−xSbx )2Te3 and layered Bi2Te3/(Bi1−xSbx)2Te3 superlattices fabricated by nanoalloying. Our approach is based on the sequential sputtering of nanoscale layers of the elements and subsequent annealing in order to induce a solid state reaction. While conventionally Bi2(SexTe1−x )3 compounds are used as n-type V2VI3 material system, the deposition of Se proves to be problematic especially for sputtering deposition and is therefore replaced by (Bi1−xSbx )2Te3. A superlattice consisting of 25 nm Bi2Te3/25 nm (Bi0:9Sb0:1)2Te3 – ML (periodicity of 50 nm) was synthesized and annealed at temperatures of 150, 200, 225, and 250°C. The layers are slightly rough and polycrystalline, and the grain sizes increase with increasing annealing temperature. The XRD analysis shows a pronounced (00l) texture of the sputtered layers. SIMS depth profiles reveal that the chemical separation into layers is present, yet smeared out to some degree after annealing at 200°C. High Seebeck coefficients of up to ~−190 μV/K were achieved. A high maximum power factor of 22 μW/cmK2 can be attained after annealing at 250 °C for 12 h. The superlattice system Bi2Te3 / (Bi1−xSbx )2Te3 can compete with Bi2Te3 / Bi2(SexTe1−x )3 in terms of electrical properties while representing a good practical alternative for the sputter deposition due to the substitution of problematic Se with Sb. Cross-plane thermal conductivities are in the range of 0.55 to 0.6 W/mK. The thermal conductivity is generally reduced due to the nanocrystallinity of the material, however, there seems to be no measurable reduction of the thermal conductivity by the superlattice-type 2D nanostructuring.