Semimagnetic Cd Research Articles

Optically induced magnetization in diluted magnetic quantum dots

We report the effect of intense laser field on donor impurities in a semimagnetic Cd 1 - x in Mn x in Te / Cd 1 - x out Mn x out Te quantum dot. The spin polaronic energy of different Mn 2+ is evaluated for different dot radii using a mean field theory in the presence of laser field. Magnetization is calculated for various concentrations of Mn 2+ ions with different dot sizes. Significant magnetization of Mn spins can be obtained through the formation of polarized exciton magnetic polarons (EMPs). A rapid decrease of the laser dressed donor ionization energy for different values of dot sizes with increasing field intensity is predicted. Also, it is found that the polarization of EMPs increases rapidly at higher excitation energies.

Spin excitations of the spin-polarized electron gas in semimagnetic quantum wells.

Collective and single-particle spin-flip excitations of a two-dimensional electron gas in a semimagnetic Cd(1-x)Mn(x)Te quantum well are observed by resonant Raman scattering. Application of a magnetic field splits the spin subbands and a spin polarization is induced in the electron gas. Above 1 T the collective modes, which disperse with the in-plane wave vector, dominate the spectra. The local spin-density approximation provides a good description of our results and enables us to confirm that the energy of the low wave vector collective mode is given by the bare Zeeman energy.

Exciton magnetic polarons in semimagnetic quantum wells with nonmagnetic and semimagnetic barriers

We report on the optical study of exciton magnetic polarons in structures with semimagnetic Cd 1− y Mn y Te quantum wells sandwiched between nonmagnetic Cd 1− x Mg x Te or semimagnetic Cd 1− x Mn x Te barriers. We have found magnetic polarons with energy of 9 meV formed from quasi-two-dimensional excitons in Cd 0.9Mn 0.1Te/Cd 0.7Mg 0.3Te quantum wells with thicknesses varying from 18 to 100 Å, but no polaron formation has been found for quasi-three-dimensional excitons situated in quantum wells thicker than 300 Å. The experimentally established effect of the dimensionality of the system on the stability of exciton magnetic polarons is in qualitative agreement with theoretical predictions. In Cd 1− y Mn y Te/Cd 1− x Mn x Te structures contributions of the carrier exchange with Mn spins located in the well and in the barrier layers are responsible for the process of magnetic polaron formation. Relation of these contributions has been demonstrated to be controlled by the quantum well width.

Excitons as intermediate states in spin-flip Raman scattering of electrons bound to donors in Cd1-xMnxTe epilayers.

The resonance behavior of the spin-flip Raman scattering in semimagnetic Cd 1-x Mn x Te epilayers has been used to investigate the scattering process itself as well as to identify the state of the carrier that changes its spin. The characteristic variation of the Stokes shift with magnetic field, a magnetic polaron effect for vanishing magnetic field, and the independence of the scattering efficiency of laser power indicate that a donor-bound electron changes its spin orientation. According to magnetic dipole selection rules of electrons for the spin-flip scattering, the Raman signal shows resonances with excitonic transitions involving the m j =±1/2 hole states as they can be characterised by luminescence and photoluminescence excitation spectroscopy

Electronic structure of semimagnetic semiconductor heterostructures

An extended k.p model for zincblende semiconductor heterostructures is used to calculate the sub-band structure as a function of the parallel momentum and the Landau levels as a function of applied magnetic field, of semimagnetic Cd(Mn)Te-CdTe quantum wells. The model takes into account the full degeneracy, conduction-valence band coupling, valence band mixing, warping and anisotropy, and effective mass discontinuities at each heterointerface. The effect of sample magnetisation on Landau levels is discussed.

Bound magnetic polaron in semimagnetic semiconductor heterostructures

The binding energy of the magnetic polaron, in semimagnetic Cd(Mn)Te/CdTe quantum wells, is calculated within a 6 × 6 k. p Hamiltonian. Local magnetic field effects and Coulomb interaction between electrons and holes with hydrogenic impurities are treated exactly.