Narrow Results

When monolayer (ML) MoS₂ is placed on a substrate, the proximity-induced interactions such as the Rashba spin-orbit coupling (RSOC) and exchange interaction (EI) can be introduced. Thus, the electronic system can behave like a spintronic device. In this study, we present a theoretical study on how the presence of the RSCO and EI can lead to the band splitting, the lifting of the valley degeneracy and to the spin polarization in $n$- and $p$-type ML MoS₂. We find that the maxima of the in-plane spin orientation in the conduction and valence bands in ML MoS₂ depend on the Rashba parameter and the effective Zeeman field factor. At a fixed Rashba parameter, the minima of the split conduction band and the maxima of the split valence band along with the spin polarization in ML MoS₂ can be tuned effectively by varying the effective Zeeman field factor. On the basis that the EI can be induced by placing the ML MoS₂ on a ferromagnetic substrate or by magnetic doping in ML MoS₂, we predict that the interesting spintronic effects can be observed in $n$- and $p$-type ML MoS₂. This work can be helpful to gain an in-depth understanding of the basic physical properties of ML MoS₂ for application in advanced electronic and optoelectronic devices.

A diamond anvil cell (DAC) made of reinforced plastic has been developed for magneto-photoluminescence experiments in pulsed high magnetic fields. Our DAC has a standard and simple structure equipped with a stainless steel gasket. We have made magneto-photoluminescence experiments of CdTe/Cd_0.8Mn_0.2Te multiple quantum wells up to 41 T at 4.2 K in the pressure range 0 to 2.3 GPa. We found that the effect of the eddy current heating of the gasket can be negligible small when we use the pulsed field whose duration is a few tens of milliseconds or longer. We have also found that the exciton Zeeman shift strongly depends on the pressure, which can be a manifestation of the enhancement of the sp-d and d-d exchange interactions in the Gd_0.8Mn_0.2Te layer by applying high pressures.

Granular Co₃₀Pt₇₀/C and Co₄₅Pt₅₅/C films, consisting of nanoparticle CoPt phases embedded in a carbon matrix, have been made by co-sputtering from CoPt and C targets using a tandem deposition mode. X-ray diffraction shows the existence of hard CoPt phase embedded in an amorphous C matrix after annealing. The coercivities for CoPt/C are strongly dependent on C and Pt composition. Films with coercivity of up to 5.4 kOe and grain size of 7 nm can be obtained. The development of shoulder in hysteresis loop may be contributed to the co-existence of magnetic soft CoPt₃ and hard CoPt phases and the magnetic interactions between them. High remanence M_r/M_s (>0.8) found in our samples indicates the presence of the intergranular interactions in the samples. Observed positive contributions of δm also give evidence of the existence of exchange interaction. High coercivity and large M_r/M_s make granular CoPt/C film with magnetic nanoparticles very attractive for next-generation high-density recording.

Magnetic properties of Bi³⁺-doped La_0.67-xBi_xCa_0.33MnO₃(x = 0, 0.05, 0.1, 0.2) are investigated. Using the mean-field and ferromagnetic spin-wave theory at low temperatures, total exchange integrals and Curie temperatures are calculated in the range 0≤x≤0.2. Calculated values of T_c are in good agreement with those obtained by magnetic measurements. In addition, the total exchange integral decrease with Bi³⁺ shows the existence of canted ferromagnetic order in the samples, as observed in experimental results.

The magnetic response of the near-band-edge optical properties is studied in EuTe layers. In several magneto-optical experiments, the absorption and emission are described as well as the related Stokes shift. Specifically, we present the first experimental report of the photoluminescence excitation (PLE) spectrum in Faraday configuration. The PLE spectra shows to be related with the absorption spectra through the observation of resonance between the excitation light and the zero-field band-gap. A new emission line appears at 1.6 eV at a moderate magnetic field in the photoluminescence (PL) spectra. Furthermore, we examine the absorption and PL red-shift induced by the magnetic field in the light of the d-f exchange interaction energy involved in these processes. Whereas the absorption red-shift shows a quadratic dependence on the field, the PL red-shift shows a linear dependence which is explained by spin relaxation of the excited state.

Magnetic cluster systems can be considered as nanomagnets consisting of a small number of interacting spins that are magnetically isolated from the neighboring clusters of the compound by nonmagnetic ligands. Inelastic neutron scattering is a powerful experimental tool for the study of magnetic clusters, since it provides direct access to energy splittings. The present work provides an overview on this subject. The underlying concepts are presented and illustrated for some representative examples such as single-molecule magnets, diluted magnets, magnetic polarons, and dimer based compounds associated with quantum phase transitions and Bose–Einstein condensation as well as spin-Peierls dimerization. It is shown that — besides the dominant Heisenberg interaction — anisotropic and higher-order exchange terms are often needed to rationalize the experimental data.

In this paper, we investigate nonlocal correlation (beyond entanglement) captured by measurement induced nonlocality and geometric quantum discord for a pair of interacting spin-1/2 particles at thermal equilibrium. It is shown that both the measures are identical in measuring the correlation. We show that nonlocal correlation between the spins exist even without entanglement and the correlation vanishes only for maximal mixture of product bases. We also observe that while interaction between the spins is responsible for enhancement of correlation, this non-classicality decreases with the intervention of external magnetic field.

We report here a microscopic theory of the temperature dependence of specific heat in high-T_c cuprate superconductors. The system is described by a model Hamiltonian consisting the antiferromagnetic spin fluctuations due to the impurity f-electrons as well as the conduction electrons, besides the superconducting interaction due to the itinerant electrons. The Hamiltonian is treated within a mean-field approach. The transverse spin fluctuation parameters and the superconducting gap are calculated by Zubarev's Green's function technique and solved self-consistently. The temperature dependent specific heat is calculated from the free energy in order to study the anomalies appearing at the spin fluctuation and superconducting transition temperatures. The evolutions of these anomalies are studied by varying the model parameters of the systems and results are discussed in reference to experimental observations.

The electronic structure and magnetic properties of the Gd₅Si₄ compound have been investigated by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT) using the WIEN2k code. The Coulomb corrected local-spin density approximation (LSDA + U) in the self-interaction correction (SIC) has been used for the exchange-correlation potential. Based on the calculated results, the ground state of Gd₅Si₄ is found to be ferromagnetic (FM). The optimized structural parameters and magnetic properties including the lattice constants and magnetic moments are in good agreement with experimental data. The magnetic moments of the Gd atoms in Gd₅Si₄ are smaller than that of the elemental gadolinium. The magnetic moment of Gd₅Si₄ is found to be 37.8 μ_B/f.u. DOS results show that the magnetic properties of the compound depend on the hybridization between Si-3p and Gd-5d states which have an effective role in the RKKY interaction. The existence of the very flat bands at -7 eV for spin up and at +3 eV for spin down that is mainly Gd-4f characters shows that the LSDA + U method provides the better description of our systems. The obvious overlap of electron densities between the Gd1 and Si atoms indicates a covalent-like bonding between them.

We study a mixed-state Schrödinger–Poisson–Slater system (SPSS). This system combines the nonlinear and nonlocal Coulomb interaction with a local potential nonlinearity known as the "Slater exchange term" which models a fermionic effect. The origin of the model is explained and related models are also proposed. Existence, uniqueness and regularity of local-in-time and global solutions are analyzed in ℝ³ with L² or H¹ initial data. Stationary solutions and conservation laws are also analyzed by using a variational approach due to E. Lieb.

The magnetic properties and giant magnetostriction effect (GMS) of the amorphous alternant [Tb/Fe/Dy]_n (named S1) and [Fe/Tb/Fe/Dy]_m (named S2) nano-multilayer films have been studied. The magnetic hysteresis loops show that easy magnetic direction changes from perpendicular to the film plane (S1) to parallel to the film plane (S2). S2 has better soft magnetic properties and low-field giant magnetostriction effect than that of S1, due to the exchanging interaction between the hard GMS layer and the soft layer Fe. The different magnetic behavior is explained by considering the nature of the magnetization process, i.e. domain-wall motion and spin rotation.

We report on a theoretical study of the fine structure of excited excitonic levels in semiconductor quantum disks. A particular attention is paid to the effect of electron–hole long-range exchange interaction. We demonstrate that even in the axisymmetric quantum disks, the exciton P-shell is split into three sublevels. The analytical results are obtained in the limiting cases of strong and weak confinement. A possibility of exciton spin relaxation due to the resonant LO-phonon-assisted coupling between the P and S shells is discussed.

The indirect exchange interaction between two magnetic impurities in a two-dimensional electron system under a strong magnetic field is studied. The nuclear spin coupling is mediated by Landau electrons bound to these impurities. We consider the contact hyperfine coupling of the bound Landau electrons, which is an s-type wave function and is therefore significant. The d electrons are indirectly involved in the contact interaction through their resonance scattering potential, which is found to be spin selective and therefore binds Landau electrons with proper spin polarization. Thus, the resulting superexchange interaction between two different sites involves the bound Landau states of one site and the impurity d states of the second site, resulting in an antiferromagnetic interaction between the nuclear spins of the impurities. The coupling constant between these nuclear spins, J, is found to depend strongly on the ratio of the impurity separation over the magnetic length. Possible applications of these results may include a long-range mechanism for coupling between two nuclear spins to be used as a qubit interaction with a spacing distance of the order of magnitude of the magnetic length.

Magnetization measurements were performed on a series of Zn_0.9-xFe_0.1Cu_xO samples (0 ≤ x ≤ 0.10). Small hysteresis losses are seen at low temperatures. The ferromagnetic exchange interaction has been evaluated from the inverse DC magnetic susceptibility versus T and the molecular field theory. We found that Cu-doping greatly enhances the FM exchange interaction, increases the saturation magnetization, hysteresis losses and the magnetic susceptibility. Arrott-Kouvel plot has been used to study the spontaneous magnetic moment at low temperatures. We show that hysteresis losses cannot be taken as the only evidence for the appearance of the ferromagnetic order in these semiconducting semi-magnetic materials.

We analyze the magnetization versus magnetic field curves of Fe-based nanoparticles embedded inside CNT. Measurements were performed at different temperatures and orientations of the magnetic field. We demonstrate that, for the parallel field the magnetic anisotropy dominates and the coherent anisotropy is of great importance at low temperatures. At high temperatures, the exchange coupling becomes stronger, but the coherent anisotropy still occurs. For the perpendicular field, the coherence anisotropy is absent, and the dimensionality of the system reduces to 2D. The results are discussed in the framework of the correlation functions of the magnetic anisotropy axes.

We analyze analytically and numerically quantum logic gates in a one-dimensional spin chain with Heisenberg interaction. Analytic solutions for basic one-qubit gates and swap gate are obtained for a quantum computer based on logical qubits. We calculated the errors caused by imperfect pulses which implement the quantum logic gates. It is numerically demonstrated that the probability error is proportional to ε⁴, while the phase error is proportional to ε, where ε is the characteristic deviation from the perfect pulse duration.

Inhomogeneous magneto-electric effect (IMEE) driven by exchange forces is studied. A phenomenological theory of the effect is proposed. The theory predicts the existence of the radial electric polarization in the systems with the magnetic structures of vortex type. Polarization does not depend on the sign of the winding number and appears even in a magnetic “hedgehog”. A microscopic theory of the exchange IMEE in a medium with the vortex magnetization distribution is developed. Electric polarization is caused by the exchange interaction of free charge carriers with the localized ones. On the basis of the microscopic theory, the electrical polarization is estimated for vortices in magnetic semiconductors and metals.

A diamond anvil cell (DAC) made of reinforced plastic has been developed for magneto-photoluminescence experiments in pulsed high magnetic fields. Our DAC has a standard and simple structure equipped with a stainless steel gasket. We have made magneto-photoluminescence experiments of CdTe/Cd_0.8Mn_0.2Te multiple quantum wells up to 41 T at 4.2 K in the pressure range 0 to 2.3 GPa. We found that the effect of the eddy current heating of the gasket can be negligible small when we use the pulsed field whose duration is a few tens of milliseconds or longer. We have also found that the exciton Zeeman shift strongly depends on the pressure, which can be a manifestation of the enhancement of the sp − d and d − d exchange interactions in the Cd_0.8Mn_0.2Te layer by applying high pressures.