Evidence for Mn2+ fine structure in CdMnSe/ZnSe quantum dots caused by their low dimensionality

JETP Letters - The axial fine structure with strong positive zero-field splitting for Mn2+ ions in CdMnSe/ZnSe quantum dots caused by their low dimensionality was revealed. Magnetic resonance was...     

Suppression of electron spin relaxation in Mn-doped GaAs

We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.     

Nuclear Spin relaxation mediated by Fermi-edge electrons in n-type GaAs

A method based on the optical orientation technique was developed to measure the nuclear-spin lattice relaxation time T ₁ in semiconductors. It was applied to bulk n-type GaAs, where T ₁ was measured after switching off the optical excitation in magnetic fields from 400 to 1200 G at low (< 30 K) temperatures. The spin-lattice relaxation of nuclei in the studied sample with n _D = 9 × 10¹⁶ cm^?3 was found to be determined by hyperfine scattering of itinerant electrons (Korringa mechanism) which predicts invariability of T ₁ with the change in magnetic field and linear dependence of the relaxation rate on temperature. This result extends the experimentally verified applicability of the Korringa relaxation law in degenerate semiconductors, previously studied in strong magnetic fields (several Tesla), to the moderate field range.     

Optical orientation of Mn2+ ions in GaAs in weak longitudinal magnetic fields

We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100 mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.     

Interfacial Ferromagnetism in a Co/CdTe Ferromagnet/Semiconductor Quantum Well Hybrid Structure

The magnetization properties of a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure are investigated by several techniques. Exploiting the proximity effect between acceptor bound holes and magnetic ions we detect the magnetization curves by measuring the circular polarization of photoluminescence in an out-of-plane magnetic field. We show that magnetization originates from interfacial ferromagnet on Co-CdMgTe interface and the proximity effect is caused by magnetization of interfacial Co-CdMgTe ferromagnetic layer whose magnetic properties are very different from Co.     

Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn²⁺ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.     

Spectroscopy of polarized luminescence of nanostructures

The effect of different distortions arising in nanostructures and of external fields on polarization of radiation has been studied. Occurrence of linear polarization of photoluminescence in a magnetic field applied in the plane of a structure containing a CdTe/CdMnTe quantum well has been considered. The influence of a magnetic field on the effects of optical orientation and optical alignment of excitons and trions in self-assembled CdSe/ZnSe quantum dots has been investigated. Analysis of the experimental data reveals low symmetry of the structures studied. It is shown that the distribution of the anisotropy axes in the plane of nanostructures is nearly random.     

Evidence for Mn<Superscript>2+</Superscript> fine structure in CdMnSe/ZnSe quantum dots caused by their low dimensionality

The axial fine structure with strong positive zero-field splitting for Mn²⁺ ions in CdMnSe/ZnSe quantum dots caused by their low dimensionality was revealed. Magnetic resonance was measured as a variation of photoluminescence intensity. In spite of isotropic g factor of Mn²⁺ ions, the anisotropic behavior of the center of gravity of the resonance has been observed because of the high Boltzmann factor at 35 GHz and 2 K. The article is published in the original.