T. Wojtowicz

Perpendicular magnetization reversal, magnetic anisotropy, multistep spin switching, and domain nucleation and expansion in Ga1−xMnxAs films

We present a comprehensive study of the reversal process of perpendicular magnetization in thin layers of the ferromagnetic semiconductor Ga1−xMnxAs. For this investigation we have purposely chosen Ga1−xMnxAs with a low Mn concentration (x≈0.02), since in such specimens contributions of cubic and uniaxial anisotropy parameters are comparable, allowing us to identify the role of both types of anisotropy in the magnetic reversal process. As a first step we have systematically mapped out the angular dependence of ferromagnetic resonance in thin Ga1−xMnxAs layers, which is a highly effective tool for obtaining the magnetic anisotropy parameters of the material. The process of perpendicular magnetization reversal was then studied by magnetotransport (i.e., Hall effect and planar Hall-effect measurements). These measurements enable us to observe coherent spin rotation and noncoherent spin switching between the (100) and (010) planes. A model is proposed to explain the observed multistep spin switching. The agreement of the model with experiment indicates that it can be reliably used for determining magnetic anisotropy parameters from magnetotransport data. An interesting characteristic of perpendicular magnetization reversal in Ga1−xMnxAs with low x is the appearance of double hysteresis loops in the magnetization data. This double-loop behavior can be understood by generalizing the proposed model to include the processes of domain nucleation and expansion.We present a comprehensive study of the reversal process of perpendicular magnetization in thin layers of the ferromagnetic semiconductor Ga1−xMnxAs. For this investigation we have purposely chosen Ga1−xMnxAs with a low Mn concentration (x≈0.02), since in such specimens contributions of cubic and uniaxial anisotropy parameters are comparable, allowing us to identify the role of both types of anisotropy in the magnetic reversal process. As a first step we have systematically mapped out the angular dependence of ferromagnetic resonance in thin Ga1−xMnxAs layers, which is a highly effective tool for obtaining the magnetic anisotropy parameters of the material. The process of perpendicular magnetization reversal was then studied by magnetotransport (i.e., Hall effect and planar Hall-effect measurements). These measurements enable us to observe coherent spin rotation and noncoherent spin switching between the (100) and (010) planes. A model is proposed to explain the observed multistep spin switching. The agre...

Spin coherence of a two-dimensional electron gas induced by resonant excitation of trions and excitons in Cd Te ∕ ( Cd , Mg ) Te quantum wells

The mechanisms for generation of long-lived spin coherence in a two-dimensional electron gas (2DEG) have been studied experimentally by means of a picosecond pump-probe Kerr rotation technique.

Size control and midinfrared emission of epitaxial PbTe∕CdTe quantum dot precipitates grown by molecular beam epitaxy

\mathrm{Cd}\mathrm{Te}∕(\mathrm{Cd},\mathrm{Mg})\mathrm{Te}

Determination of free hole concentration in ferromagnetic Ga1−xMnxAs using electrochemical capacitance–voltage profiling

quantum wells with a diluted 2DEG were investigated. The strong Coulomb interaction between electrons and holes, which results in large binding energies of neutral excitons and negatively charged excitons (trions), allows one to address selectively the exciton or trion states by resonant optical excitation. Different scenarios of spin coherence generation were analyzed theoretically, among them the direct trion photocreation, the formation of trions from photogenerated excitons, and the electron-exciton exchange scattering. Good agreement between experiment and theory is found.

Ferromagnetic resonance study of the free-hole contribution to magnetization and magnetic anisotropy in modulation-doped Ga 1 − x Mn x As ∕ Ga 1 − y Al y As : Be

Epitaxial quantum dots with symmetric and highly facetted shapes are fabricated by thermal annealing of two-dimensional (2D) PbTe epilayers embedded in a CdTe matrix. By varying the thickness of the initial 2D layers, the dot size can be effectively controlled between 5 and 25nm, and areal densities as high as 3×1011cm−2 can be achieved. The size control allows the tuning of the quantum dot luminescence over a wide spectral range between 2.2 and 3.7μm. As a result, ultrabroadband emission from a multilayered quantum dot stack is demonstrated, which is a precondition for the development of superluminescent diodes operating in the near infrared and midinfrared.

Magnetic polaron formation and exciton spin relaxation in single Cd1-xMnxTe quantum dots

We demonstrate that electrochemical capacitance–voltage profiling can be used to determine the free hole concentration in heavily p-type doped low-temperature-grown GaAs films. This provides a simple and reliable method for measuring the hole concentration in ferromagnetic Ga1−xMnxAs semiconductor alloys. The method overcomes the complications that arise from the anomalous Hall effect term which affects standard transport studies of carrier concentration in conducting ferromagnetic materials. Specifically, we find that the maximum Curie temperature of about 111 K found for our Ga0.91Mn0.09As samples corresponds to a hole concentration of 1021 cm−3.

Origin of Magnetic Circular Dichroism in GaMnAs: Giant Zeeman Splitting versus Spin Dependent Density of States

Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs in a series of Ga

Common origin of ferromagnetism and band edge Zeeman splitting in GaMnAs at low Mn concentrations

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Temperature variation of the luminescence spectra in crystals

Mn

Pressure effect on magneto-optical properties in CdTe/(Cd, Mn)Te single quantum wells with high Mn concentration

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