G-factor Values Research Articles

Exchange Enhancement of g-Factor in Narrow-Gap InAs/AlSb Quantum Well Heterostructures

We report on the study of exchange enhancement of g-factor in 2D electron gas in n-type narrow-gap semiconductor heterostructures that feature a strong nonparabolicity of electric subbands. We demonstrate that exchange g-factor enhancement not only shows maxima at odd values of Landau level filling factors but, due to subband nonparabolicity, persists at even filling factor values as well. The magnitude of the exchange enhancement, the amplitude and shape of the g-factor oscillations are governed by both the screening of electron-electron interaction and the Landau level width. The enhanced g-factor values calculated for 2D electron gas in InAs/AlSb quantum well heterostructures are compared with previous experimental magnetotransport data.

Lifetime and magnetic moment measurements

The g-Plunger technique has been introduced, which allows for the simultaneous measurement of lifetimes and absolute values of g-factors using a plunger device in inverse kinematics. Experiments on the 104,106,108Pd isotopes using Coulomb excitation resulted in g-factors in agreement with literature data. Lifetimes of 2+1 states have in part significantly changed in this work.

Oscillations of the photon echo intensity in a pulsed magnetic field: Zeeman splitting in LiLuF4:Er3+

A method of high-resolution time-resolved optical spectroscopy using oscillations of the photon echo intensity in the presence of a perturbation, which splits the optical frequencies of the transitions of two or more ion subgroups, has been proposed and demonstrated. This method has been applied to systems in which the Zee-man effect is manifested. The transition frequencies of ions are switched by a pulsed magnetic field. Oscillations of the photon echo intensity were observed in LiLuF4:Er3+ and LiYF4:Er3+. The first minimum corresponding to the accumulated phase of the electric dipole moment π/2 is reached in the pulsed magnetic field with an amplitude of ∼2 G at a duration of 30 ns. The Zeeman splitting in this field is ∼10 MHz, which is much less than the laser spectral width (0.15 A ∼ 9 GHz). The g factor of the 4F9/2(I) excited state of the Er3+ ion in the LiLuF4 matrix has been determined in zero magnetic field. The comparison with the g-factor value found from the measurement of the absorption spectrum in a magnetic field of 8 kG has been performed.

Magnetization and magnetic susceptibility in a quantum-dot superlattice at low temperature

At low temperature, the magnetization and the magnetic susceptibility of the electronic system in quantum-dot superlattices (QDSL’s) of GaAs, InAs, and InSb, respectively, with an isotropic parabolic potential under a magnetic field are investigated on the basis of canonical ensemble statistics including the Zeeman effect. The dependences of the magnetization and the magnetic susceptibility on the confinement frequency of the isotropic parabolic potential and the electronic density in the QDSL’s of GaAs, InSb, and InAs, respectively, are studied numerically at low temperature. Furthermore, the dependences of the peak shifts of the magnetization and the magnetic susceptibility on the effective g-factor value in QDSL’s of GaAs, InSb, and InAs, respectively, at low temperature are obtained numerically.

Theory of g-factor enhancement in narrow-gap quantum well heterostructures

We report on the study of the exchange enhancement of the g-factor in the two-dimensional (2D) electron gas in n-type narrow-gap semiconductor heterostructures. Our approach is based on the eight-band k⋅p Hamiltonian and takes into account the band nonparabolicity, the lattice deformation, the spin–orbit coupling and the Landau level broadening in the δ-correlated random potential model. Using the ‘screened’ Hartree–Fock approximation we demonstrate that the exchange g-factor enhancement not only shows maxima at odd values of Landau level filling factors but, due to the conduction band nonparabolicity, persists at even filling factor values as well. The magnitude of the exchange enhancement, the amplitude and the shape of the g-factor oscillations are determined by both the screening of the electron–electron interaction and the Landau level width. The ‘enhanced’ g-factor values calculated for the 2D electron gas in InAs/AlSb quantum well heterostructures are compared with our earlier experimental data and with those obtained by Mendez et al (1993 Phys. Rev. B 47 13937) in magnetic fields up to 30 T.

High-throughput comprehensive analysis of d- and l-amino acids using ultra-high performance liquid chromatography with a circular dichroism (CD) detector and its application to food samples

A rapid and comprehensive analytical method for d- and l-enantiomers of proteinogenic amino acids was developed using ultra-high performance liquid chromatography (UHPLC) equipped with a circular dichroism (CD) detector. Pre-column derivatization reagents were examined for enhanced sensitivity and selectivity for UV and CD detection: 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was selected. The method, using a CD detector, does not require separation of optical isomers on a column to calculate the enantio ratio (% D) using the g-factor value and produces a simple chromatogram in comparison to other reported methods. Using this advantage, combined with UHPLC technology, analysis time for the derivatized proteinogenic amino acids was within 5.5 min. The UV detection limit was 4.9–23 pmol/injection and the CD detection limit was 11–64 pmol/injection. The method was applied to the analysis of d- and l-amino acids in food samples. d-Ala, d-Asp, d-Glu and d-Ser were detected at high concentrations in some Japanese black vinegars, fermented milks and yogurts. The results were identical to the results determined by the OPA method. We suggest the UHPLC–CD method would be useful in screening the d-amino acid content of foods and in helping to clarify the importance and reason for the presence of d-amino acids in foods.

Measuring signal‐to‐noise ratio in partially parallel imaging MRI

To assess five different methods of signal-to-noise ratio (SNR) measurement for partially parallel imaging (PPI) acquisitions. Measurements were performed on a spherical phantom and three volunteers using a multichannel head coil a clinical 3T MRI system to produce echo planar, fast spin echo, gradient echo, and balanced steady state free precession image acquisitions. Two different PPI acquisitions, generalized autocalibrating partially parallel acquisition algorithm and modified sensitivity encoding with acceleration factors (R) of 2-4, were evaluated and compared to nonaccelerated acquisitions. Five standard SNR measurement techniques were investigated and Bland-Altman analysis was used to determine agreement between the various SNR methods. The estimated g-factor values, associated with each method of SNR calculation and PPI reconstruction method, were also subjected to assessments that considered the effects on SNR due to reconstruction method, phase encoding direction, and R-value. Only two SNR measurement methods produced g-factors in agreement with theoretical expectations (g ≥ 1). Bland-Altman tests demonstrated that these two methods also gave the most similar results relative to the other three measurements. R-value was the only factor of the three we considered that showed significant influence on SNR changes. Non-signal methods used in SNR evaluation do not produce results consistent with expectations in the investigated PPI protocols. Two of the methods studied provided the most accurate and useful results. Of these two methods, it is recommended, when evaluating PPI protocols, the image subtraction method be used for SNR calculations due to its relative accuracy and ease of implementation.

Influence of the β coefficient in the superposition model on the spin-Hamiltonian parameters of the ground state of paramagnetic ions

The relationship between the β coefficient in the superposition model and the spin-Hamiltonian (SH) parameters of ground state of the paramagnetic ion is studied based on the crystal-field theory. The complete diagonalization method is used in calculations and is used in studies of the variation of the SH parameters of the ground state with the β coefficient for the CsMgCl3:Ni2+ (Pd2+) system. These studies show that β has almost no effect on the theoretical values of g-factors (g∥ and g⊥) of the ground state, but has a strong effect on the zero-field splitting parameter D.

Control of electron spin dynamics in a wide GaAs quantum well by a lateral confining potential

The spin dynamics of electrons laterally confined in a wide GaAs quantum well with the use of a special mosaic electrode deposited onto the sample plane has been investigated. Comparative measurements with a semitransparent electrode have been simultaneously carried out to distinguish changes in electron spin dynamics due to the band bending from those due to the lateral confinement controlled by applying an external bias. The electron spin lifetimes in the traps has been found to increase strongly with the applied bias. The measured values of the electron g-factor in the quantum well plane and the magnetic-field dependence of the electron spin lifetimes indicate the emergence of strong three-dimensional confinement in the center of an orifice in the mosaic electrode. The examined electron spin relaxation anisotropy is caused by the anisotropy of the confining potential.

FMR and TEM Studies of Co and Ni Nanoparticles Implanted in the SiO2 Matrix

Fused silica plates have been implanted with 40 keV Co+ or Ni+ ions to high doses in the range of (0.25–1.0) × 1017 ions/cm2, and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO2 matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and Ni nanoparticles implanted in the SiO2 matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature are presented.

Singlet–Triplet Mixing Due to g-Factor Mismatch in Double Quantum Dot

Two electron spins form the spin singlet or triplet state if these spins have the same g-factor value, or a mix state consisting of both the singlet and triplet states if these spins have different g-factor values. It is considered that two energy levels of electrons are formed in a double quantum dot device for use in quantum information processing; however, the g-factors of the electrons have not been treated as an important factor because they cannot be changed easily in experiments. We introduce a numerical calculation method for the singlet–triplet mix state due to the g-factor mismatch in double quantum dots. It is found that this mismatch changes the energy levels of the original singlet and triplet states; thus, it affects the intersecting points of the energy levels of the singlet and triplet states where a dynamic nuclear polarization appears via hyperfine interaction.

Magnetic resonance study of phases in FeVO 4–Co 3V 2O 8 system

Multicomponent vanadates Co 3+ x Fe 4− x V 6O 24 have been synthesized using the solid state reaction method from Co 3V 2O 8 and FeVO 4.oxides. The electron paramagnetic resonance/ferromagnetic resonance (EPR/FMR) spectra of 20 samples containing solid state phases formed in the FeVO 4–Co 3V 2O 8 system have been recorded at room temperature. The howardevansite structure (H-type phase) is produced, which corresponds to the Co 2.616Fe 4.256V 6O 24 formula while a homogeneity range of lyonsite (L-type phase) type structure could be described by the Co 3+1.5 x Fe 4− x V 6O 24 formula (0.476< x<1.667). Considering the values of g-factor and linewidth of each registered spectrum the existence of three types of magnetic centers was inferred and correlated with phases detected by XRD method.

Magnetic Properties of New Diluted Magnetic Semiconductors Pb&lt;sub&gt;1-X-Y&lt;/sub&gt;Mg&lt;sub&gt;X&lt;/sub&gt;Yb&lt;sub&gt;Y&lt;/sub&gt;Te

We have studied the magnetic susceptibility, magnetization and electron paramagnetic resonance (EPR) in the diluted magnetic semiconductor Pb1-x-yMgxYbyTe. The magnetic susceptibility of this system is a superposition of the matrix diamagnetism, the paramagnetic contribution of electrons localized in the ytterbium band, and the Curie-Weiss paramagnetism provided by Yb3+ ions. The concentration of Yb3+ ions monotonically increases with the ytterbium content, while a significant fraction of ytterbium ions remains in a nonmagnetic Yb2+ state. A pronounced hyperfine structure was revealed in the EPR spectra. It was ascribed to the interaction between the electron magnetic moment of an unfilled electron shell of Yb3+ ions and nuclear magnetic moment of the 173Yb isotope. The estimated values of the effective g-factor (g1.997 0.002) and the hyperfine-interaction constant (173A=0,56 cm-1) were found to be almost independent of both alloy composition and temperature.

Anomalies in electron spin resonance spectra of Ge1−xMnxTe diluted magnetic semiconductors

We report on magnetic properties and X-band electron spin resonance (ESR) study (80–430 K) of diluted magnetic semiconductors Ge1−xMnxTe (x=0.07–0.44) revealing ferromagnetism with the Curie temperature achieving 90 K. Effective magnetic moment peff per Mn2+ ion estimated from the Curie constant in the range 0.15≤x≤0.26 increases from 2.27 to 2.95 μB. The temperature evolution of ESR spectra was found to have a complicated character. We observed the presence of two distinct absorption lines of Dysonian type, associated with two resonance centers in these diluted magnetic semiconductors. Possible origin of these two lines has been analyzed and clustering effect was proposed to be most likely responsible for anomalous behavior. Anomalies in temperature dependencies of the linewidths and g-factors were observed at temperatures lower than 160 K. We connect these anomalies with magnetic fluctuations in the vicinity of transition to ferromagnetic phases. The anomalous broadening of the linewidth in paramagnetic region occurs with decreasing of the temperature similarly to ESR behavior of related A M2nB6 diluted magnetic semiconductors. This broadening is satisfactorily described in the framework of modified Huber’s theory. At the same time, the g-factor is essentially independent on both temperature and alloy composition. Average values of effective g-factor for two resolved spectral components at room temperature were found to be g1=2.02–2.07 and g2≈1.99.

Energy spectra for quantum wires and two-dimensional electron gases in magnetic fields with Rashba and Dresselhaus spin-orbit interactions

We introduce an analytical approximation scheme to diagonalize parabolically confined two dimensional electron systems with both the Rashba and Dresselhaus spin-orbit interactions. The starting point of our perturbative expansion is a zeroth-order Hamiltonian for an electron confined in a quantum wire with an effective spin-orbit induced magnetic field along the wire, obtained by properly rotating the usual spin-orbit Hamiltonian. We find that the spin-orbit-related transverse coupling terms can be recast into two parts W and V, which couple crossing and non-crossing adjacent transverse modes, respectively. Interestingly, the zeroth-order Hamiltonian together with W can be solved exactly, as it maps onto the Jaynes-Cummings model of quantum optics. We treat the V coupling by performing a Schrieffer-Wolff transformation. This allows us to obtain an effective Hamiltonian to third order in the coupling strength k_Rl of V, which can be straightforwardly diagonalized via an additional unitary transformation. We also apply our approach to other types of effective parabolic confinement, e.g., 2D electrons in a perpendicular magnetic field. To demonstrate the usefulness of our approximate eigensolutions, we obtain analytical expressions for the n^th Landau-level g_n-factors in the presence of both Rashba and Dresselhaus couplings. For small values of the bulk g-factors, we find that spin-orbit effects cancel out entirely for particular values of the spin-orbit couplings. By solving simple transcendental equations we also obtain the band minima of a Rashba-coupled quantum wire as a function of an external magnetic field. These can be used to describe Shubnikov-de Haas oscillations. This procedure makes it easier to extract the strength of the spin-orbit interaction in these systems via proper fitting of the data.

Determination of neutron temperature in irradiation channels of reactor.

The neutron temperature is a characteristic parameter in irradiation channels of reactor. For nuclides which have resonances in the thermal neutron energy range, their Westcott g-factors are different from unity. The values of g-factors and cross-sections of (n, γ) reaction of these nuclides are temperature dependence. The standard energy for tabulation of thermal neutron cross-section (σ0) is that of room temperature (293.59 K or 20.43 °C), corresponding to a neutron energy 0.0253 eV or to a neutron velocity of 2200 m/s. However, in the irradiation channels of reactor, the temperature is not exact at 20.43 °C. Thus, the temperature at the irradiation position must be known to convert σ0 to σ(T). A method for determination of the neutron temperature in irradiation channels of Dalat reactor is presented by fitting the thermal neutron spectrum obtained from the calculation using MCNP code.

Определение зарядового состояния ионов переходных металлов, входящих в Li1 + xNi1 / 3Co1 / 3Mn1 / 3O2, магнитными методами

The complex oxides Li1 + xNi1 / 3Co1 / 3Mn1 / 3O2 were obtained by solid state method. The conclusion about influence of lithium concentration on Ni2+ and Ni3+ ions ratio in Li1 + xNi1 / 3Co1 / 3Mn1 / 3O2 is made. Monotonous decrease of g-factor value identified by EPR method testifies the intensification of local exchange interactions with temperature descent. That is in agreement with magnetic susceptibility data indicating the antiferromagnetic ordering at T=4 K.

Containing Manganese DMSs Nanostructures via a Nonaqueous Route

The structure and the magnetic properties of 3.0 and 0.3 at.% Mn-containing ZnO-based DMSs, synthesized by a straightforward and experimentally simple nonaqueous route, have been investigated by various characterization techniques, including XRD, HRTEM, and EPR. The as-synthesized doped ZnO nanocrystals retain the wurtzite structure with a morphology in the form of flower-like shape. EPR spectra with g-factor values of 2.0023(3% at.%) and 2.0019(0.3 at.%), respectively, at room temperature were obtained, confirming that the Mn2+ is substitutionally incorporated into the ZnO nanocrystals.

Influence of Copper(II) Ions on Radicals in DOPA–Melanin

DOPA–melanin (DOPA = 3,4-dihydroxyphenyl-alanine) complexes with Cu(II) cations were studied by electron paramagnetic resonance (EPR) spectroscopy. After the addition of metal cations to the melanin polymer, the EPR spectra parameters were measured. The axial g-factor values are g || = 2.20 and $$ g_{ \bot } = 2.0 5 $$ . Since $$ g_{||} > g_{ \bot } > 2 $$ , the ground state orbital of the unpaired electron of the Cu(II) complex is $$ \left| {{{x}}^{ 2} } \right. \, - \, \left. {{{y}}^{ 2} } \right\rangle $$ . Square coordination of these cations in melanin is proposed. The influence of the Cu(II) concentration in solution used during synthesis on the concentration of melanin radicals was investigated. Cu(II) cations causes the decrease in the paramagnetic center concentration in melanin. The Cu(II) EPR spectra are not saturated within the microwave power range of 0.7–70 mW used in our experiment.

ESR and fluorescence studies of Mn-doped Na 2ZnP 2O 7 single crystal and glasses

X-band electron spin resonance (ESR) spectra and fluorescence measurements were performed on Mn-doped Na 2ZnP 2O 7 (NZPO) single crystal synthesized by the Czochralski pulling method and glasses synthesized by the quenching process. For the single crystal, ESR angular dependences were measured in both the zx and xy plans of the NZPO lattice. The fine and hyperfine structure parameters and g-factor values were determined by modelling the experimental spectra. Using the Newman superposition model, the resonating centres in the single crystal and powder (crushed from crystals) samples are assigned to Mn 2+ ions substituting for both zinc and sodium. For the glass sample the analysis of the ESR data shows that Mn 2+ ions substitute for the Na + ions. These interpretations are confirmed by the fluorescence measurements with a unique broad red band for the glassy compound and the presence of two emission bands (green and red) in the case of the crystal sample.