A comparative study of the circular polarization degree dependences on external magnetic field was carried out in spin light-emitting diodes including semiconductor InGaAs/GaAs heterostructure and a magnetic CoPt contact and in control non-magnetic structures with an Au contact. In a weak magnetic field, the magnetic field dependence of electroluminescence circular polarization degree is similar to the magnetic field dependence of magnetization: it represents a hysteresis loop with saturation in a field of ~0.3 T. In a strong magnetic field, an additional linear contribution to the circular polarization degree is detected. This contribution is associated with the Zeeman splitting of energy levels. The magnitude of the linear contribution depends on the position of the quantum well relative to the ferromagnet/semiconductor interface. The obtained dependence is associated with the influence of the magnetic field of the inhomogeneously magnetized CoPt electrode on the spin relaxation time of carriers. Keywords: spin injection, quantum well, Zeeman splitting.

A weak magnetic field is used to study the effect voltage has on the circular polarization of light in light-emitting diode structures with InGaAs/GaAs/δ-Mn quantum wells and remote δ layers of Mn magnetic impurities (spacers with thickness dS = 2−5 nm). The weakening of circular polarization upon raising the applied voltage testifies to the strong contribution from the stationary mechanism of carrier polarization by the exchange field of the δ-Mn layer.

A detailed study of the coherent spin dynamics of photoexcited carriers in a heterostructure with an InGaAs/GaAs quantum well and a δ-Mn-layer separated from the quantum well by a 3–10 nm-thick GaAs spacer indicates its strong non-uniformity in the plane and mesoscopic separation to the regions of carrier localization. Mesoscopic separation with a characteristic scale of 100–200 nm is also observed using magnetic force microscopy below the Curie temperature of the δ-Mn-layer.

The changes in the substituted La0.5Sr0.5FeO3_ & gamma; orthoferrite under vacuum annealing in the temperature range of 200-650 degrees C have been studied by X-ray diffraction analysis, as well as Mo & BULL;ssbauer and Raman spectroscopy. Annealing of the as-prepared ferrite with the rhombohedral structure (R 3 c) resulted in its transition to the cubic one (Pm 3 m) at 650 degrees C. In the as-prepared ferrite being paramagnetic at room temperature, Fe ions were detected in an averaged-valence state between Fe3+ and Fe4+, which was not revealed with a decrease in the temperature down to 85 K. Gradual oxygen loss and an increase in the number of oxygen vacancies took place with an increase in the vacuum annealing temperature. Only Fe3+ ions were present in the ferrite at a vacuum annealing temperature above 500 degrees C. Several Zeeman sextets in the Mo & BULL;ssbauer spectra associated with Fe3+ ions were resulted from the presence of oxygen vacancies and Fe4+ ions in the local environment of Fe3+ ions. The variations in the ratio of the valence states of Fe ions obtained from Mo & BULL;ssbauer data depending on a vacuum annealing temperature allowed determining the content of oxygen in all the investigated samples. The contri-bution of Fe3+ ions that did not have Fe4+ ions and oxygen vacancies in their local environment was shown to increase with a vacuum annealing temperature from 12% (for the as-prepared sample) to 60% (for the sample annealed at 650 degrees C). On a whole, the process taking place under vacuum annealing can be characterized as a variation of the local environment of Fe3+ ions towards a decrease in its distortion. It was found that the width of the peaks of the Raman spectra decreased and their amplitude increased with an increase in the vacuum annealing temperature, which also demonstrated the improvement of the structural perfection of the samples.

The luminescence kinetics of the electron transition 5D0 → 7F2 (~613 nm) of Eu3+ ions has been studied in tungstates (Lu1 – xEux)2(WO4)3 and molybdates (Lu1 – xEux)2(MoO4)3. Luminescence decay times are very close in both compounds at x ≥ 0.2, while a significant difference is observed at x 0.1. Observed behavior is attributed to the difference in electronic structure of compounds.

The luminescence kinetics of electron transition 5D0 → 7F2 (~613 nm) of Eu3+ ions is studied in (Lu1 − xEux)2(WO4)3 tungstates and (Lu1 − xEux)2(MoO4)3 molybdates. Luminescence decay times are very close in both compounds at x ≥ 0.2, while a considerable difference is observed when x < 0.1. This behavior is attributed to difference in the electron structure of the compounds.

The ferromagnetic influence of a thin (~8 nm) surface CoPt layer on the circular polarization of the InGaAs/GaAs quantum well photoluminescence is observed in the structure of GaAs/InGaAs/GaAs/Al2O3(1 nm)/CoPt with narrow GaAs spacer ds = 5 nm, while electroluminescence is polarized throughout the range of ds = 5–100 nm. It is suggested that the short-range proximity effect is due to the overlap of electron wavefunctions and the nearby ferromagnetic CoPt film.

The luminescence kinetics of electron transition 5 D 0 → 7 F 2 (~613 nm) of Eu 3+ ions is studied in (Lu 1 − x Eu x ) 2 (WO 4 ) 3 tungstates and (Lu 1 − x Eu x ) 2 (MoO 4 ) 3 molybdates. Luminescence decay times are very close in both compounds at x ≥ 0.2, while a considerable difference is observed when x < 0.1. This behavior is attributed to difference in the electron structure of the compounds.

Strong pulsed nonresonant photoexcitation is used to study the spectral and kinetic characteristics of the stimulated luminescence of red intracenter electronic transitions of the Eu3+ ion (580–650 nm) in densely packed nanopowders and nanospheres (diameter, 100–270 nm) of the composition Lu2O3:Eu (5–10 at %). The observed glow spot (~1 mm) is much larger than a laser spot focused on a powder sample (~100 μm). The recorded glow pulse slows upon an increase in the detected area, testifying to the inhomogeneity of luminescent radiation and its diffusion from the region of the photoexcitation spot.

Structures consisting of an InGaAs/GaAs quantum well and a ferromagnetic 〈Mn〉 δ layer separated by a narrow 3–10 nm spacer have been studied using the optically detected cyclotron resonance (ODCR). Despite strong disorder in these structures, the photoluminescence of charge carriers in the quantum well indicates ODCR upon absorption in the far infrared regions with the maximum in magnetic fields much lower than those expected for typical electron or hole cyclotron mass. The extraordinary manifestation of ODCR is due to dimensional magnetoplasma resonance of two-dimensional degenerate holes in submicron regions of the high-quality quantum well, which appear in the strong fluctuation Coulomb potential because of the mesoscopic separation of the high-density acceptor 〈Mn〉 δ layer. Magnetic force microscopy also indicates the inhomogeneity of the structure in the plane with a characteristic scale of ~100–200 nm below the Curie temperature of the 〈Mn〉 δ layer. At the same time, the resonance field of ODCR in a light-emitting diode structure on the n -GaAs substrate is noticeably lower than that in the structure on the insulating i -GaAs substrate, which is explained by resonance on donors in the doped substrate.

The substituted orthoferrite La0.67Sr0.33FeO3_gamma was studied using scanning electron microscopy, X-ray diffraction (XRD), and Mo center dot ssbauer and Raman spectroscopy. A series of vacuum annealing in the temperature range of 200-650 degrees C was performed, resulting in negligible changes in the crystal structure of samples. The volume of the pseudocubic unit cell increased continuously with raising temperature up to 450 degrees C. It follows from the Mo center dot ssbauer measurements that at room temperature Fe ions were characterized by an averaged-valence state. The vacuum annealing induced oxygen vacancies and changed the averaged-valence state of Fe ions. Sufficiently good correlations among the Mo center dot ssbauer, XRD, and Raman spectroscopy data were obtained.

Spontaneous luminescence of Eu ions is studied in Y2O3:Eu (5 at %) nanoparticles obtained via low temperature thermolysis from an amorphous precursor. Depending on details of the synthesis procedure, the nanoparticles have different morphology and structure that strongly affect such spectral and kinetic properties of doping Eu ions as the period of luminescence decay (which yields lines in the red range of the spectrum), its intensity, and the maximum of the charge transfer band.

A comparative study of the circular polarization degree dependences on external magnetic field was carried out in spin light-emitting diodes including semiconductor InGaAs/GaAs heterostructure and a magnetic CoPt contact and in control non-magnetic structures with an Au contact. In a weak magnetic field, the magnetic field dependence of electroluminescence circular polarization degree is similar to the magnetic field dependence of magnetization: it represents a hysteresis loop with saturation in a field of ~ 0.3 T. In a strong magnetic field, an additional linear contribution to the circular polarization degree is detected. This contribution is associated with the Zeeman splitting of energy levels. The magnitude of the linear contribution depends on the position of the quantum well relative to the ferromagnet/semiconductor interface. The obtained dependence is associated with the influence of the magnetic field of the inhomogeneously magnetized CoPt electrode on the spin relaxation time of carriers.

Crystal structure, short range order, lattice dynamics and valence state of polycrystalline single-phase strontium ferrites SrFeO3-delta (with 3-6 = 2.87 divided by 2.5) were studied by Raman and Mossbauer spectroscopy at normal conditions. Valence states of Fe ions and their fractions were determined from Mossbauer spectroscopy and concentrations of oxygen in all phases were estimated. For all studied SrFeO3-delta phases only five (or less) bands were observed above 200 cm(-1) in spite of numerous Raman active phonon modes predicted by a factor group analysis. For the antiferromagnetic Brownmillerite phase (3-delta = 2.5), a broad band observed at -1350-1400 cm(-1), was attributed to the two-magnon scattering. This band was found also for the SrFeO3-delta samples with 3-6 = 2.87 divided by 2.725 which are in paramagnetic state at room temperature. This fact indicates an existence of the unusual magnetic correlations in all SrFeO3-delta perovskites.

It is found that the degree of circular polarization of the photoluminescence of an InGaAs/GaAs/δ-〈Mn〉 quantum well with a ferromagnetic Mn δ-layer (a GaAs spacer with thickness ds = 2–10 nm) depends largely on the conditions of photoexcitation (mainly the power density). This is explained by the dynamic model of the spin-dependent capture of electrons from a quantum well into a δ-〈Mn〉 layer and manifests as nonstationary polarization in the pulsed mode. The stationary mechanism of carrier polarization also plays an important role in structures with a narrow spacer (ds ≤ 3 nm), due to their exchange coupling with the δ-〈Mn〉 layer.

The luminescence kinetics of Er ions in Y2O3:Er nanospheres with diameters of 75–270 nm has been studied. A pronounced decrease in the luminescence decay times for Er3+ ion transitions in the green-red visible range is observed with increasing diameter up to 270 nm, unlike near-infrared emission at ∼1.5 μm. This finding is attributed to the appearance of photonic modes accelerating spontaneous luminescence, which is confirmed by a model calculation of bound optical states in the studied nanospheres.