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The magnetic properties of Ni nanoparticles (NPs) with diameter D are investigated using spin-lattice dynamics (SLD) simulations. Using exchange interactions fitted to ab-initio results we obtain a Curie temperature, T c , similar, but lower, than experiments. In order to reproduce quantitatively the bulk Curie temperature and the experimental results, the exchange energy has to be increased by 25% compared to the ab-initio value. During the simulated time, Ni NPs remain ferromagnetic down to the smallest sizes investigated here, containing around 500 atoms. The average magnetic moment of the NPs is slightly smaller than that determined experimentally. By considering a core-shell model for NPs, in which the shell atoms are assigned a larger magnetic moment, this discrepancy can be removed. T c is lower for a moving lattice than for a frozen lattice, as expected, but this difference decreases with NP size because smaller NPs include higher surface disorder which dominates the transition. For NPs, T c decreases with the NP diameter D by at most 10% at D = 2 nm, in agreement with several experiments, and unlike some modeling or theoretical scaling results which predict a considerably larger decrease. The decrease of T c is well described by finite-size scaling models, with a critical exponent that depends on the SLD settings for a frozen or moving lattice, and also depends on the procedure for determining T c . Extrapolating the inverse of the magnetization as function of temperature near T c gives a lower T c than the maximum of the susceptibility. [ABSTRACT FROM AUTHOR]

Low-dimensional perovskite (PVK) materials have attracted significant research interest, because of their quantum-confined effect, tunable band gap structures, and higher stability than that of three-dimensional (3D) PVKs. In semiconductor optoelectronic devices, high speed and small size are closely interlinked. The development of high-speed devices requires researchers to fully understand the properties of materials, especially the dynamic processes such as carrier recombination, separation, and transport, which often play a crucial role in the performance of devices. As an indispensable part of dynamic research, spin relaxation is also of great significance in studying the properties of materials and explore possible applications. Lead halide PVK materials have strong spin-orbit coupling (SOC), which provides a basis for information storage and processing by using spin degrees of freedom. Therefore, studying the carrier and spin dynamics of low-dimensional PVKs is an effective way to understand the internal properties of low-dimensional PVKs clearly. This paper summarizes the latest research progress on the ultrafast carrier and spin dynamics in low-dimensional PVKs, to comprehensively understand their carrier and spin behaviors and present an outlook for relevant studies in this area. [ABSTRACT FROM AUTHOR]

The spin dynamics in magnetically disordered GdCu2 nanoparticles, varying the nanoparticle size in the range 53 to 7 nm, has been scrutinized. Dynamic χAC susceptibility measurements have revealed the existence of dissipation at Tg = 18 K, which is associated to the spin freezing transition, for all the ensembles. Besides, the superantiferromagnetic ensembles (〈D〉≥ 24 nm) also showcase a dissipation contribution close to the vicinity of the Néel transition, TN = 40.2 K. This dissipation, which takes the form of two humps located at Td1 = 33.5(5) K and Td2 = 40.0(5) K, is associated to uncompensated antiferromagnetic moments. Time-dependent phenomena (ageing and memory effects) are only evidenced below the spin freezing transition, evidencing that solely this low-temperature disordered phase is driven by the frustration of RKKY exchange interactions. Consequently, GdCu2 nanoparticles display a dual disorder-driven magnetic dynamics, which are the one ascribed to the magnetically frustrated moments located at the nanoparticle surface; and that of uncompensated antiferromagnetic moments located within the nanoparticle core. [ABSTRACT FROM AUTHOR]

Ensembles of negatively charged nitrogen-vacancy centers (NV−) in diamond have been proposed for sensing of magnetic fields and paramagnetic agents, and as a source of spin-order for the hyperpolarization of nuclei in magnetic resonance applications. To this end, strongly fluorescent nanodiamonds (NDs) represent promising materials, with large surface areas and dense ensembles of NV−. However, surface effects tend to favor the less useful neutral form, the NV0 centers, and strategies to increase the density of shallow NV− centers have been proposed, including irradiation with strong laser power (Gorrini in ACS Appl Mater Interfaces. 13:43221–43232, 2021). Here, we study the fluorescence properties and optically detected magnetic resonance (ODMR) of NV− centers as a function of laser power in strongly fluorescent bulk diamond and in nanodiamonds obtained by nanomilling of the native material. In bulk diamond, we find that increasing laser power increases ODMR contrast, consistent with a power-dependent increase in spin-polarization. Conversely, in nanodiamonds we observe a non-monotonic behavior, with a decrease in ODMR contrast at higher laser power. We hypothesize that this phenomenon may be ascribed to more efficient NV−→NV0 photoconversion in nanodiamonds compared to bulk diamond, resulting in depletion of the NV− pool. A similar behavior is shown for NDs internalized in macrophage cells under the typical experimental conditions of imaging bioassays. Our results suggest strong laser irradiation is not an effective strategy in NDs, where the interplay between surface effects and local microenvironment determine the optimal experimental conditions. [ABSTRACT FROM AUTHOR]

Magnetic droplets, a class of highly nonlinear magnetodynamic solitons, can be nucleated and stabilized in nanocontact spin-torque nano-oscillators. Here we experimentally demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet nucleation is accompanied by power enhancement compared with its ferromagnetic resonance modes. The nucleation and stabilization of droplets are ascribed to the double-CoFeB free-layer structure in the all-perpendicular MTJ, which provides a low Zhang-Li torque and a high pinning field. Our results enable better electrical sensitivity in fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications and materials science. [ABSTRACT FROM AUTHOR]

In the past decade, nuclear magnetic resonance (NMR) has been actively used to study the basic principles of quantum computers. It is assumed that quantum correlations play a significant role in their performance. They exist at both low and high temperatures. At the same time, the time correlation functions of nuclear spin systems of solids determine the observed signals in traditional NMR implementations. The separation of such signals into quantum and classical components has not previously been carried out and will be performed in this study for the most important of the correlational functions observed in magnetic resonance: the free induction decay (FID). [ABSTRACT FROM AUTHOR]

Materials having magnetoelectricity is one of the highest priority research topics for the development of novel multifunctional materials. Recently, Ho2Ti2O7 and Dy2Ti2O7 pyrochlores show the coexistence of ferroelectricity with complex magnetism. The present study shows that these spin ices show an anomalous nature of relaxation taking place at ~ 4 K. Arrhenius nature of frequency dispersion behavior and order of characteristic relaxation time τ0 suggest that observed relaxation is associated with non-interacting electric dipoles induced by lattice distortions. These lattice distortions are associated with prevailing 3in-1out spin structure via magnetostriction mechanism, thus enabling the control of ferroelectricity though magnetism. [ABSTRACT FROM AUTHOR]

We review our studies on spin-dependent phenomena in various colloidal nanocrystals (quantum dots, dot-in-rod, and nanoplatelets). Several magneto-optical techniques are used in high magnetic fields: magnetic-field-induced polarization of neutral and charged excitons, spin-flip Raman scattering, and pump-probe Faraday rotation. We focus on spin properties and spin dynamics of neutral and charged excitons in order to identify them and measure g-factors and spin relaxation times. Pump-probe time-resolved Faraday rotation experiments with additional prepump allow us to measure coherent spin dynamics of carriers in CdS NCs at room temperature, and to study interplay between the negative and positive photocharging processes. We discuss the role of the dangling bond spins for recombination of the dark excitons and for formation of the dangling bond magnetic polaron. [ABSTRACT FROM AUTHOR]

We apply innovative mathematical tools coming from optimal control theory to improve theoretical and experimental techniques in Magnetic Resonance Imaging (MRI). This approach allows us to explore and to experimentally reach the physical limits of the corresponding spin dynamics in the presence of typical experimental imperfections and limitations. We study in this paper two important goals, namely the optimization of image contrast and the maximization of the signal to noise per unit time. We anticipate that the proposed techniques will find practical applications in medical imaging in a near future to help the medical diagnosis. [ABSTRACT FROM AUTHOR]

We present the laser-induced ultrafast spin and rotational dynamics in a cobalt trimer cation cluster. With the help of an attached CO ligand which lowers the high symmetry of the cluster, a local spin switch within around 500 fs is achieved. Furthermore, by including an additional degree of freedom in our calculations, i.e., molecular rotation, we investigate the possibility of laser-induced ultrafast molecular rotational control in both a model system and our studied realistic cluster. The results indicate that both spin and molecular rotation can be manipulated with ultrashort laser pulses at subpicosecond timescales, a fact which provides significant theoretical guidance for the design of spin logic nanodevices and sheds some light on the application-oriented path for driving molecular directional motions. [ABSTRACT FROM AUTHOR]

The results of theoretical study of the spin crossover dynamics in the cobalt octaethylporphyrin molecule under the action of an external pulsed magnetic field with an induction of 36.8 T are presented. It is shown that, in the case of the high-spin state, under the action of a pulsed magnetic field, spin switching occurs in the system, and the system is characterized by a large relaxation time. In the case of the low-spin state, the system relaxes rapidly to the ground state. The temperature dependence of the product of the magnetic susceptibility and the temperature has a feature in the vicinity of 40 K related to the transition between spin states. [ABSTRACT FROM AUTHOR]

Active bandwidth and global quality factor are the two main metrics used to quantitatively compare the performance of TOCSY mixing sequences. Active bandwidth refers to the spectral region over which at least 50 % of the magnetization is transferred via a coupling. Global quality factor scores mixing sequences according to the worst-case transfer over a range of possible mixing times and chemical shifts. Both metrics reward high transfer efficiency away from the main diagonal of a two-dimensional spectrum. They can therefore be used to design mixing sequences that will function favorably in experiments. Here, we develop optimization methods tailored to these two metrics, including precise control of off-diagonal cross peak buildup rates. These methods produce square shaped transfer efficiency profiles, directly matching the desirable properties that the metrics are intended to measure. The optimization methods are analytical, rather than numerical. The two resultant shaped pulses have significantly higher active bandwidth and quality factor, respectively, than all other known sequences. They are therefore highly suitable for use in NMR spectroscopy. We include experimental verification of these improved waveforms on small molecule and protein samples. [ABSTRACT FROM AUTHOR]

The shape of NMR absorption line for typical ionic crystals, molecular crystals, and glasses is studied. The proposed theory and available experimental results suggest that the shape of NMR spectra of conventional dielectric crystals (and even molecular) is the convolution of a frequency-truncated nearly-rectangle-shaped function (characteristic oscillations in free precession signals) and a Gaussian-like function. A Gaussian-like shape of the spectra of glasses with a rigid structure (no oscillations in the free precession signal) is probably associated with a random scatter of interatomic distances. The results are interpreted within the framework of the proposed theory. It is demonstrated that, at least for solids the lattice of which contains no isolated groups of nuclei and are not quasi-one-dimensional, the structure only weakly affects the shape of the spectrum, which in turn is associated with the onset of dynamic chaos in the spin system. [ABSTRACT FROM AUTHOR]

We review history, materials and underlying physics that form a background common to magnetic refrigeration and spin-lattice relaxation. To illustrate how these subjects are profoundly interrelated with each other, we describe studies performed on the molecular nanomagnets with formula [Gd(W5O18)2]9- and [Gd(P5W30O110)12-. Each molecular unit carries a single ion of gadolinium, which is coordinated to different polyoxometalate moieties, respectively. Each Gd3+ spin is magnetically isolated and maintains thermal equilibrium with the lattice down to temperatures close to absolute zero. For T ≲ 200 mK, the spinlattice relaxation becomes dominated by pure quantum tunneling events. We discuss these properties with a keen eye for promising applications of molecular nanomagnets, namely, as magnetic refrigerants for attaining such low temperatures and spin qubits in quantum information processing. [ABSTRACT FROM AUTHOR]

In this paper, a formalism for studying the dynamics of quantum systems coupled to classical spin environments is reviewed. The theory is based on generalized antisymmetric brackets and naturally predicts open-path off-diagonal geometric phases in the evolution of the density matrix. It is shown that such geometric phases must also be considered in the quantum-classical Liouville equation for a classical bath with canonical phase space coordinates; this occurs whenever the adiabatics basis is complex (as in the case of a magnetic field coupled to the quantum subsystem). When the quantum subsystem is weakly coupled to the spin environment, non-adiabatic transitions can be neglected and one can construct an effective non-Markovian computer simulation scheme for open quantum system dynamics in classical spin environments. In order to tackle this case, integration algorithms based on the symmetric Trotter factorization of the classical-like spin propagator are derived. Such algorithms are applied to a model comprising a quantum two-level system coupled to a single classical spin in an external magnetic field. Starting from an excited state, the population difference and the coherences of this two-state model are simulated in time while the dynamics of the classical spin is monitored in detail. It is the author's opinion that the numerical evidence provided in this paper is a first step toward developing the simulation of quantum dynamics in classical spin environments into an effective tool. In turn, the ability to simulate such a dynamics can have a positive impact on various fields, among which, for example, nanoscience. [ABSTRACT FROM AUTHOR]

We develop a theory that allows considering and describing the development of multiparticle correlations in paramagnetic spin systems. We show that in crystals with many equivalent nearest neighbors around a spin in a lattice, an infinite system (of size ∼ 10) of coupled differential equations for time correlation functions describing multiparticle correlations is reducible to the diffusion equation with an imaginary diffusion coefficient. The equation can be solved analytically in the lowest-order approximation of the theory. The equation obtained in the next approximation must be solved numerically because a discontinuity of the diffusion coefficient appears. The obtained results agree well with experimental data. The observed mutual similarity of the calculated time correlation functions and several other characteristic features appearing in the spin system dynamics are consequences of the development of dynamical chaos. [ABSTRACT FROM AUTHOR]

We study the dynamical correlations between two coupled spins depending on time and the value of the spin quantum numbers. In the high-temperature approximation, we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations. We consider both orthogonal and nonorthogonal measurements in the basis of spin coherent states. We show that at small times, the quantum part of correlations becomes much less than the classical part as the spin quantum numbers increase, while the situation is quite different at times equal to half the quantum period. [ABSTRACT FROM AUTHOR]

Studies of spin dynamics of highly polarized dilute mixtures of He in superfluid He have been performed by various researchers over the past three decades. One series of experiments performed at Cornell University in the early 1990's revealed a novel long timescale excitation. We present the numerical solution of the non-linear Leggett spin dynamics equation in one spatial dimension subject to boundary conditions consistent with the Cornell experiments. Experimentally observed phenomena are composed of trains of bursts in the transverse magnetization lasting several seconds. The simulations capture the time evolution of the individual bursts localized in time. Preliminary results of two dimensional simulations are also presented. [ABSTRACT FROM AUTHOR]

Using a full ab initio method, based on quantum chemical wave function methods with the inclusion of spin-orbit coupling and a static external magnetic field, we investigate the laser-induced, ultrafast spin transfer in the three-magnetic-center cluster NiNa under various static distortions. In this manuscript we study and identify three important factors, i.e. the interatomic distances, the number of bridging atoms, and the spin direction, in order to obtain a series of rules of thumb. It is found that the spin transfer between Ni atoms mainly depends on the number of Na atoms and the spin direction on the Ni atoms, and only the scenarios between Ni2 and Ni3 atoms with the spin direction at Ni3 atom along the x and z axes can be achieved. [ABSTRACT FROM AUTHOR]

We study the appearance of the entangled states in a one-dimensional finite chain of dipolar-coupling nuclear spins of 1/2 in the conditions of thermodynamic equilibrium. It is shown that entanglement is achieved by the application of a low external magnetic field in which the Zeeman interaction energy is the order of or even less than the dipolar interaction one. When these energies are equal, the critical temperature, i. e. the temperature of the entanglement appearance, coincides with the temperature at which the heat capacity of the spin chain achieves its maximum. The obtained relationship between the critical temperature and the magnetic field can be considered as an entanglement witness. The dependences of the heat capacity on temperature and magnetic field have different character for entangled and separable states and can be served for experimental detection of entangled states. [ABSTRACT FROM AUTHOR]

A direct method showing the Thomas precession for an evolution of any vector quantity (a spatial part of a four-vector) is proposed. A useful application of this method is a possibility to trace correctly the presence of the Thomas precession in the Bargmann-Michel-Telegdi equation. It is pointed out that the Thomas precession is not incorporated in the kinematical term of the Bargmann-Michel-Telegdi equation, as it is commonly believed. When the Bargmann-Michel-Telegdi equation is interpreted in curved spacetimes, this term is shown to be equivalent to the affine connection term in the covariant derivative of the spin four-vector evolving in a gravitational field. It then contributes to the geodetic precession. The described problem is an interesting and unexpected example showing that approximate methods used in special relativity, in this case to identify the Thomas precession, can distort the true meaning of physical laws. [ABSTRACT FROM AUTHOR]

Spin dynamics in mechanochemically obtained nanoparticle manganite LaCaMnO was investigated in this study by means of a series of AC and DC magnetic measurements. AC susceptibility indicates the presence of sizeable interparticle interactions, yielding collective magnetic behavior. The related properties were probed by experiments in weak DC field: memory effects were analyzed in both field-cooled (FC) and zero field-cooled (ZFC) regimes, while, after ZFC aging, magnetic relaxation was recorded. The system appears to be sensitive to magnetothermal history, in analogy with spin-glass-like compounds. The analysis of the data indicates the occurrence of slow dynamics in an ensemble of strongly interacting super spins. [ABSTRACT FROM AUTHOR]

We demonstrate that the femtosecond time-resolved magneto-optical Kerr rotation oscillates with the direction of polarization of the probe beam when a sample of AlGaAs/GaAs multi-quantum wells is excited by a circularly polarized pump and detected by a linearly polarized probe at wavelengths from 800 to 830 nm. Analytical expressions are derived to explain the mechanism, which is in good agreement with the numerical computation and the experimental data. The results suggest that the Kerr signal can be enhanced by choosing an optimal direction of polarization, which is of benefit to the measurement of the weak Kerr rotation. [ABSTRACT FROM AUTHOR]

The magnetic, electron transport, and optical properties of ordered nano- and heterostructures of Group III-V and Group IV diluted magnetic semiconductors are studied. A comparative analysis of the magnetic and electron transport properties of nanowires, thin films, and bulk semiconductors doped with transition metals is carried out. The size effect on the spin dynamics, magnetic properties, and magnetoresistance is discussed. Prospects for application of nano- and heterostructures with combined magnetic, electrical, and optical properties are considered. [ABSTRACT FROM AUTHOR]

The heavy-fermion system CeCuAu which exhibits antiferromagnetic order for Au concentrations x>0.1, can be easily tuned to a quantum phase transition, either by chemical composition, i.e., Au concentration, or by an external magnetic field. We present extensive inelastic neutron scattering measurements in order to study the momentum and energy dependence of the critical spin fluctuations for concentration- and magnetic field-tuned CeCuAu. The quasi-2D fluctuations, observed for x=0.1 at the magnetic instability, are already present in pure CeCu and persist to x=0.2, i.e., well into the magnetically ordered regime. This is a strong hint that disorder does not play a major role in this system. The magnetic response for quantum critical CeCuAu exhibits critical slowing down and obeys scaling relations that depend on the tuning parameter. While the E/ T scaling of the dynamic susceptibility in concentration-tuned CeCuAu is an indication for local quantum criticality, the E/ T scaling in field-tuned CeCuAu points to a conventional spin-density-wave instability. [ABSTRACT FROM AUTHOR]

With the purpose to reveal consistency between multiple quantum (MQ) coherences and entanglement, we investigate numerically the dynamics of these phenomena in one-dimensional linear chains and ring of nuclear spins 1/2 coupled by dipole–dipole interactions. As opposed to the calculation of the MQ coherence intensity based on the density matrix describing the spin system as a whole, we consider the “differentiated” intensity related only to the chosen spin pair based on the reduced density matrix. It is shown that the entanglement and the MQ coherence have similar dynamics only for nearest neighbors while we did not obtained any consistency for remote spins. [ABSTRACT FROM AUTHOR]

We investigated relationships between entanglement measures and the order parameter (nuclear polarization) in nuclear spin systems controlled by the nuclear magnetic resonance (NMR) technique. Since spin polarization can be easily manipulated by the NMR technique, experimentalists are presented with an opportunity to study the dynamic properties of entanglement, i.e., the creation and evolution of entangled states. Our approach may constitute the basis for researching the relations between the entanglement measures and measurable parameters of order in other quantum systems. [ABSTRACT FROM AUTHOR]

Electron-spin dynamics in semiconductor-based heterostructures has been investigated in oblique magnetic fields. Spins are generated optically by a circularly polarized light, and the dynamics of spins in dependence of the orientation ( θ) of the magnetic field are studied. The electron-spin precession frequency, polarization amplitude, and decay rate as a function of θ are obtained and the reasons for their dependences are discussed. From the measured data, the values of the longitudinal and transverse components of the electron g-factor are estimated and are found to be in good agreement with those obtained in earlier investigations. The possible mechanisms responsible for the observed effects are also discussed. [ABSTRACT FROM AUTHOR]

The recent neutron scattering data for spin-wave dispersion in HoMnO3 are well-described by an anisotropic Hubbard model on a triangular lattice with a planar (XY) spin anisotropy. Best fit indicates that magnetic excitations in HoMnO3 correspond to the strong-coupling limit U/t >∼ 15, with planar exchange energy J = 4t2/U ⋍ 2.5 meV and planar anisotropy ΔU ⋍ 0.35 meV. [ABSTRACT FROM AUTHOR]

The recent neutron scattering data for spin-wave dispersion in HoMnO3 are well-described by an anisotropic Hubbard model on a triangular lattice with a planar (XY) spin anisotropy. Best fit indicates that magnetic excitations in HoMnO3 correspond to the strong-coupling limit U/t >∼ 15, with planar exchange energy J = 4t2/U ⋍ 2.5 meV and planar anisotropy ΔU ⋍ 0.35 meV. [ABSTRACT FROM AUTHOR]

Stimulated wave of polarization, triggered by a flip of a single spin, presents a simple model of quantum amplification. Recently, it has been demonstrated that, in an idealized one-dimensional Ising spin 1/2 chain with nearest-neighbor interactions and realistic spin 1/2 chain including the natural dipole-dipole interactions, irradiated by a weak resonant transverse field, a wave of flipped spins can be triggered by a single spin flip. Here we focuse on control of polarization wave in chain of spin 3/2, where the nuclear quadrupole interaction is dominant. Results of simulations for 1D spin chains and rings with up to five spins are presented. [ABSTRACT FROM AUTHOR]

We report on investigation of the spin dynamics in InAs and InSb films grown on GaAs at a temperature range from 77 K to 290 K. For both materials, the large lattice mismatch with the GaAs substrate results in the formation of an interface accumulation layer with a large defect concentration, which strongly affects the spin relaxation in these areas. Moreover, the native surface defect in the InAs films resulted in an additional charge accumulation layer with high conductivity, but very short spin lifetime. In contrast, in InSb layers, the surface states introduce a depletion region. We have correlated the spin relaxation with a multi-layer analysis of the transport properties, and find that in a 1 μm thick InAs film, approximately 70% of the total current flows through the interface and surface accumulation layers, which have sub-picosecond lifetimes, whereas in InSb films of the same thickness, the semiconducting layer carries more than 90% of the total current, and the spin lifetime in the accumulation layer is only slightly less than that of the central semiconducting layer. We suggest that InSb could be a more attractive candidate for spintronic applications than InAs. [ABSTRACT FROM AUTHOR]

We present mathematical transformations which allow us to calculate the spin dynamics of an ultra-small nanoscale molecular magnet consisting of a dimer system of classical (high) Heisenberg spins. We derive exact analytic expressions (in integral form) for the time-dependent spin autocorrelation function and several other quantities. The properties of the time-dependent spin autocorrelation function in terms of various coupling parameters and temperature are discussed in detail. [ABSTRACT FROM AUTHOR]

We develop a new general model for rigorous theoretical description of circularly polarised ultrashort optical pulse interactions with the resonant non-linearities in semiconductor QDs embedded in optical waveguides and semiconductor microcavities. The method is based on the self-consistent FDTD-solution of the vector Maxwell equations coupled via macroscopic polarisation to the originally derived time-evolution equations of a discrete four-level quantum system in terms of the real pseudospin (coherence) vector exploiting the SU(4) group formalism. Selective excitation of specific spin-states with predefined helicity of the optical pulse and formation of polarised Self-Induced Transparency (SIT)-solitons in a specially prepared degenerate four-level system is numerically demonstrated. The model is applied to the stimulated optical dipole transitions of the trion state in a singly charged QD taking into account the spin relaxation dynamics. Our theoretical and numerical approach yields the time evolution of the spin population of the trion state which is in good agreement with the time-resolved polarised photoluminescence experimental data. [ABSTRACT FROM AUTHOR]

We present a Mössbauer study of a S = 0 ground state magnetic Fe(III)-dimer in the presence of an applied 5 T longitudinal magnetic field, between 7.6 and 33 K. The values obtained for the isomer shift and the quadrupolar splitting are comparable with the ones of Fe(III) ions coordinated to eight oxygen ions. Regarding the spin dynamics, both intramultiplet and intermultiplet transitions are considered. In the chosen temperature range the rate of the former transitions is constant, within the errors, while the rate of the latter ones quickly increases with the temperature. [ABSTRACT FROM AUTHOR]

Giant Zeeman effects and spin dynamics of excitons are studied in dense self-organized quantum dots (QDs) of CdSe and Cd1− xMn xSe. Microphotoluminescence (PL) measurements for each individual dot reveal the typical dot diameter of 3.5 ± 0.2 nm and the density of 5000 μm−2 in the CdSe QDs. The exciton lifetime is shorter in smaller dots with higher energies, indicating energy transfer and tunneling processes among the dots. Circular polarization of excitonic PL is observed at 0 T with an opposite sign to that of the excited light and with the rise time of 50 ps. The CdSe QDs coupled with a Zn1− xMn xSe layer show the giant Zeeman shift of exciton, arising from overlapping of exciton wavefunctions in the dots with Mn ions. Spin polarization dynamics in the coupled QDs is also studied. [ABSTRACT FROM AUTHOR]

Spin-orbit (SO) interaction critically influences electron spin dynamics and spin transport in bulk semiconductors and semiconductor microstructures. This interaction couples electron spin to dc and ac electric fields. Spin coupling to ac electric fields allows efficient spin manipulating by the electric component of electromagnetic field through the electric dipole spin resonance (EDSR) mechanism. Usually, it is much more efficient than the magnetic manipulation due to a larger coupling constant and the easier access to spins at a nanometer scale. The dependence of the EDSR intensity on the magnetic field direction allows measuring the relative strengths of the competing SO coupling mechanisms in quantum wells. Spin coupling to an in-plane electric field is much stronger than to a perpendicular field. Because electron bands in microstructures are spin split by SO interaction, electron spin is not conserved and spin transport in them is controlled by a number of competing parameters, hence, it is rather nontrivial. The relation between spin transport, spin currents, and spin populations is critically discussed. Importance of transients and sharp gradients for generating spin magnetization by electric fields and for ballistic spin transport is clarified. [ABSTRACT FROM AUTHOR]

We find the spin oscillation branch with the frequency ω = (μH/ħ)(k/kc)2 in the paramagnetic phase for systems with exchange interaction in the presence of an external magnetic field $\backslash vec\; H$. We show that the spin constituent of the current in the linear regime of excitation of the transverse spin modes has the resonance character. [ABSTRACT FROM AUTHOR]

We investigate generating functions for equipped trees composed of double bonds of two sorts on a hypercubic lattice of dimension d with built-in fragments. Rules for constructing these clusters are chosen to ensure the estimate for coefficients of power series in time for the longitudinal and transverse autocorrelation functions of the spin system with axially symmetric interaction. We derive a system of two equations for the tree-generating functions and an equation for the generating functions of chains leading from the root to a fragment in a tree using the Bethe approximation and under the condition that mainly bonds of one sort are taken into account. For the face-centered hypercubic lattice, we find the first terms of the 1/d expansion for the coordinate of the singular point of the generating function in both the anisotropic and the isotropic cases taking fragments in the forms of a triangle from four bonds and a four-fold bound pair into account. The obtained result is written in terms of ratios of lattice sums and is generalized to nuclear spin systems with dipole–dipole interaction. The theoretical value of the singular-point coordinate agrees well with the experimental value calculated from the tail of the absorption spectrum of the nuclear magnetic resonance in a barium fluoride monocrystal. [ABSTRACT FROM AUTHOR]

The long-time behavior of certain fast-decaying infinite temperature correlation functions on one-, two-, and three-dimensional lattices of classical spins with various kinds of nearest-neighbor interactions is studied numerically, and evidence is presented that the functional form of this behavior is either simple exponential or exponential multiplied by cosine. Due to the fast characteristic timescale of the long-time decay, such a universality cannot be explained on the basis of conventional Markovian assumptions. It is suggested that this behavior is related to the chaotic properties of the spin dynamics. [ABSTRACT FROM AUTHOR]

We have studied effects of the digital-doping profile of MnSe layers on the giant magneto-optical properties in Zn1− xMn xSe-based quantum wells. The giant Zeeman shift energy increases monotonically with increasing spatial overlap of the exciton wavefunction with the 0.5 monatomic-thick effective Mn layers at the interfaces between the digitally doped MnSe layers and nonmagnetic ZnSe layers. Also, a field-induced enhancement factor of the excitonic photoluminescence intensity, because of the suppression of the exciton energy transfer into the d- d transition of Mn-ions, increases linearly with increasing such overlap of the exciton wavefunction with the effective Mn layer. In addition, the formation energy as large as 18.6 meV and the formation time of the magnetic polaron are determined, which are also affected by the digital-doping profile. [ABSTRACT FROM AUTHOR]

Magnetic-field-induced level crossing and the spin dynamics of excitons in a Zn1− xMn xTe/ZnTe single quantum well are studied. The circularly-polarized photoluminescence (PL) shows that the down spin branch of the Zn1− xMn xTe exciton overlaps with both the up and down spin branches of the ZnTe exciton at a crossing field ( Hc) of 4 T, due to the giant Zeeman shift of Zn1− xMn xTe. The PL intensities and lifetimes in each layer become gradually equal toward Hc, which shows the mixing of wavefunctions of the excitons generated in each layer. Above Hc, each branch of the spin-polarized exciton separates again. The lifetimes of the spin-polarized exciton PL reflect the spin-flip relaxation in ZnTe and the spin mixing between Zn1− xMn xTe and ZnTe layers. [ABSTRACT FROM AUTHOR]

We study the spin fluctuations of pure and Zn-substituted La2 − xSr xCuO4 using the muon spin relaxation technique. Superconductivity is found to coexist with low-frequency spin fluctuations over a large region of the superconducting phase diagram. The characteristic temperature of spin fluctuations detected by μSR decreases with increasing x and vanishes above a critical doping xc ≈ 0.19. This value of xc coincides with the doping at which the normal state pseudogap extrapolates to zero. These results are discussed in terms of a quantum transition that separates the superconducting phase diagram of high-temperature superconductors into two distinct ground states. [ABSTRACT FROM AUTHOR]

There is a renewed interest to study spin-polarized transport and spin dynamics in various electronic materials. Motivation to examine the spin degrees of freedom (mostly in electrons, but also in holes and nuclei) comes from various sources: ranging from novel applications which are either not feasible or ineffective with conventional electronics, to using the spin-dependent phenomena for exploring fundamental properties of solid-state systems. Taken in a broader context, term spintronics is addressing various aspects of these efforts and stimulating new interactions between different subfields of condensed matter physics. Recent advances in material fabrication made it possible to introduce the nonequilibrium spin in novel class of systems, including ferromagnetic semiconductors, high temperature superconductors, and carbon nanotubes—which leads to a question of how could such a spin be utilized. For this purpose it is important to extend the understanding of spin-polarized transport and spin dynamics to consider inhomogeneous systems, various heterostructures, and the role of interfaces. This article presents some views on novel aspects of spin-polarized transport and spin dynamics (referring also to the topics which were addressed at the conference Spintronics 2001) and suggests possible future research directions. [ABSTRACT FROM AUTHOR]

We investigate the spin precession and dephasing of electrons in semiconductors, using the kinetic Bloch equations for a four-spin-band model. Various scatterings, such as carrier–carrier, carrier–phonon, and carrier–impurity scatterings are taken into account. Their contributions to the evolution of carrier distribution, optical coherence, and more importantly, spin coherence in undoped semiconductor quantum wells and in n-type bulk semiconductors are considered. We highlight the importance of the kinetic theory approach by comparing our results with those from Fermi's golden rule. Furthermore, a new spin dephasing mechanism is proposed, that is, spin dephasing due to spin conserving scatterings in the presence of inhomogeneous broadening. [ABSTRACT FROM AUTHOR]

We study the role of spin correlations in nonlinear absorption due to optical transitions from a deep impurity level to states above a Fermi sea. We demonstrate that the Hubbard repulsion between two electrons occupying the impurity state leads to a logarithmic divergence of the third-order nonlinear optical susceptibility χ(3) at the absorption threshold. This divergence is a manifestation of the Kondo physics in the nonlinear optical response of Fermi sea systems. Remarkably, the light-induced Kondo temperature, which governs the shape of the Kondo-absorption spectrum, can be tuned by varying the intensity and frequency of the pump optical field. We also show that, for off-resonant pump excitation, the pump–probe spectrum exhibits a narrow peak below the linear absorption onset. [ABSTRACT FROM AUTHOR]

The study of the transport and relaxation of spin-polarized carriers in the solid state began about 30 years ago. Tunneling spectroscopy was applied to ferromagnet–insulator–superconductor junctions to demonstrate the polarization of interfacial currents. The use of a ferromagnetic material as an injector and/or detector of polarized carriers has since become a valuable tool, and spin injection has been applied to nonmagnetic metals, superconductors, and semiconductors. The spin injection phenomenology is reviewed in the context of two topics of continuing importance for basic and applied research: (i) the transmission of polarized carriers across ferromagnet/nonmagnetic material interfaces and (ii) carrier spin relaxation inside the nonmagnetic material. [ABSTRACT FROM AUTHOR]

Low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) can be utilized to investigate the magnetic properties of solids, and are especially useful when high sensitivity is required, for example in the study of small or dilute systems. Spins of stable isotopes can also be studied using NMR thermally detected by NO (NMR-TDNO) of the radioactive nuclei. An effect of nuclear spin coupling in ordered magnets is “frequency pulling” of the abundant spins, and this has been investigated in the quasi-2-dimensional ferromagnet 54Mn–Mn(COOCH3)2⋅4H2O by comparing the NMRON of the dilute radioactive nuclei with the NMR-TDNO of the abundant host nuclei. A structure in the spectra is observed that is yet to be explained. Recent LTNO experiments on magnetic multilayers are described. Experiments implanting radioactive ions into insulating magnets show that the implanted nuclei experience sizeable hyperfine fields, and this may be useful for probing magnetic materials that are difficult to dope by conventional means. [ABSTRACT FROM AUTHOR]

A critical examination of the spin dynamics in high- Tc cuprates is made in the light of recent inelastic neutron scattering results obtained by different groups. The neutron data show that incommensurate magnetic peaks in YBCO belong to the same excitation as the resonance peak observed at (π/ a, π/ a). Being observed only in the superconducting state, the incommensurability is rather difficult to reconcile with a stripe picture. We also discuss the link between the resonance peak spectral weight and the superconducting condensation energy. [ABSTRACT FROM AUTHOR]