This PDF file contains the front matter associated with SPIE Proceedings Volume 8813, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Skyrmions, which have originally been introduced to explain how baryons could topologically emerge from a continuous meson field, have found many exciting applications in condensed-matter physics, where they describe topological states of matter in a wide range of systems. In magnetic materials they emerge as excitations corresponding to a spin arrangement in which the spins point in all the directions wrapping a sphere. Skyrmions have indeed been observed in chiral magnets, where they form regular lattices and are stabilized under an external magnetic field thanks to the presence of the Dzyaloshinskii-Moriya interaction (DMI). More recently, a new mechanism of Skyrmion materialization has been proposed, in which the frustration introduced in a thin ferromagnetic film by the magnetic dipole-dipole interaction leads to the stabilization of Skyrmions larger than those stabilized by DMI, consisting of magnetic domains at the center of which the magnetization points out of the film plane in the opposite direction with respect to the magnetization of the surrounding material. We report about the real-space observation by means of near-field optical Faraday microscopy of such stable Skyrmions in a thin TbFeCo film. The Skyrmions are generated after local excitation of the magnetic system by means of an intense laser pulse and do not need an external magnetic field for stabilization. The unique combination of ultrashort laser-induced magnetic excitation with subdiffraction near-field optical microscopy allows us not only to produce and observe Skyrmions as individual entities, but to also create and characterize bound Skyrmion-antiSkyrmion pairs, forming a topologically neutral entity.

The thermoelectric analog of spin-polarized tunneling, namely Seebeck spin tunneling, is a recently discovered phenomenon that arises from the spin-dependent Seebeck coefficient of a magnetic tunnel contact. In a tunnel junction with one ferromagnetic electrode and one non-magnetic electrode, a temperature difference between the two electrodes creates a spin current across the contact. Here, the basic principle and the observation of Seebeck spin tunneling are described. It is shown how it can be used to create a spin accumulation in silicon driven by a heat flow across a magnetic tunnel contact, without a charge tunnel current. The sign of the spin current depends on the direction of the heat flow, whereas its magnitude is anisotropic, i.e., dependent on the absolute orientation of the magnetization of the ferromagnet. The connection between Seebeck spin tunneling and the tunnel magneto-Seebeck effect, observed in metal magnetic tunnel junctions, is also clarified. Seebeck spin tunneling may be used to convert waste heat into useful thermal spin currents that aid or replace electrical spin current, and thereby improve the energy efficiency of spintronic devices and technologies.

Thermokinetic considerations are appled to the case of a generic spintronic device in which a magneto-voltaic response is measured, in the absence of electric current, on an electrode placed perpendicular to a ferromagnetic layer (see Fig. 1). The magnetovoltaic signal is a response to a power excitation, that is related to the ferromagnetic degrees of freedom. This excitation can be performed by ferromagnetic resonance (electromagnetic excitations), by a temperature gradient, by magnetomechanical coupling or by magneto optic coupling (see these proceedings). The description of this generic device allows the so-called spin-Seebeck effects and spin-pumping effects^17-16 to be addressed.

Semiconductor quantum dots can be utilized to capture single electron or hole spins and they have therewith promise for various applications in fields like spintronics, spin based quantum information processing and chiral photonics. We integrate quantum dots into semiconductor microcavities to enhance light-matter interaction for ultrafast optical manipulation and read-out. Single electron and single hole spins can be statistically or deterministically loaded into the quantum dots and coherently controlled. Within the about μs-coherence times of the spins about 10⁵ complete single qubit rotations can be performed with ultrafast optical pulses. By utilizing a Λ-type energy level system of a single quantum-dot electron spin in a magnetic field and ultrafast non-linear frequency conversion, quantum-dot spin-photon entanglement is observed.

Magnetic ion-doped semiconductor nanocrystals (NCs) have recently drawn a great deal of interest because of the intriguing physical properties and the application potential in spintronics and magneto-electronics. In this work, we report on theoretical studies of magnetism in colloidal CdSe NCs doped with Mn²⁺ ions. Numerically, the exact diagonalization (ED) technique is employed to calculate the electronic structures and magnetizations of singly changed CdSe NCs doped with four Mn ions in various spatial distributions. The numerical results show that the magnetism in a few-Mn doped NC is not only determined by the total number of Mn ions, but also sensitively depends on the individual locations, which are however hardly considered by widely used mean field theory. Remarkably, the formation of Mn clusters in a NC leads to the significant deviation of the magnetization from the standard Brillouin function description for an ideal paramagnet. The quantum size effect is shown to enhance the magnetizations of magnetic NCs via the interactions between the quantum confined carriers and Mn-clusters. A solvable constant interaction model (CIM) with the consideration of individual Mn spins is presented for the explanation of the numerical data.

We report on a Terahertz magnetospectroscopy study of a set of five HgTe quantum wells of different thickness, from below to above the critical thickness d_c. In quantizing magnetic fields up to 11 T, both intraband and interband transitions have been observed. In samples with inverted band structures, we confirm the observation of the crossing avoiding of the zero-mode Landau levels at a critical value of the magnetic field. In samples with non-inverted band structures, close to the critical thickness, we report on the square root dependence of the intraband transition energy on the magnetic field, as expected in the single-particle model of massless Dirac fermions. The obtained results are compared with the allowed transition energies calculated using the 8 × 8 Kane model.

Random, spatially uncorrelated nuclear-hyperfine fields in organic materials dramatically affect electronic transport properties such as electrical conductivity, photoconductivity, and electroluminescence. Competition between spin-dynamics due to these spatially uncorrelated fields and an applied magnetic field leads to large magnetoresistance, even at room temperature where the thermodynamic influences of the resulting nuclear and electronic Zeeman splittings are negligible. Here, we discuss a new method of controlling the electrical conductivity of an organic film at room temperature, using the spatially varying magnetic fringe fields of a magnetically unsaturated ferromagnet. Fringe-field magnetoresistance has a magnitude of several percent, and is hysteretic and anisotropic. This new method of control is sensitive to even remanent magnetic states, leading to different conductivity values in the absence of an applied field. The fringe field effects are insensitive to the ferromagnetic film’s thickness (and therefore the fringe field magnitude) but sensitive to the magnetic domain’s correlation length. This points at fringe-field gradients as an important ingredient of this mechanism. We develop a model based on fringe-field induced polaron-pair spin-dynamics that successfully describes several key features of the experimental fringe-field magnetoresistance.

We demonstrate electrical injection, extraction and detection of spin polarization in a lateral transport structure consisting of ferromagnetic Co₂FeSi stripes on a nonmagnetic n-GaAs transport channel. For the lateral transport based on electrical spin injection, the characteristic spin-valve signatures are observed both in the nonlocal and local configurations. The comparatively large magnitude of the local spin valve signal and the high signal-to-noise ratio are attributed to the large spin polarization at the Fermi energy of Co₂FeSi in the well-ordered L2₁ phase. Furthermore, we elucidate a device concept in which the basic building block consists of a local spin valve utilizing spin extraction instead of injection at the ferromagnetic stripes for its fundamental operation principle. An extended device comprises an array of such extraction-spin valves in which the spin polarization in the transport channel results from a cascade of spin extraction events. Such a multiple-extraction spin valve acts as a nonvolatile reconfigurable current divider in which a single electrical output corresponds to a particular magnetization configuration of the entire stripe array (2^m-1 electrical output levels for m ferromagnetic contacts). We discuss potential implementations of this concept for spintronic memory circuits and for sources of highly spin-polarized drift currents.

Spin provides for a well-known extension to the information capacity of nanometer-scale electronic devices. Spin transfer can be effected with high fidelity between quantum dots, this type of emission being primarily associated with emission dipoles. However, in seeking to extend the more common spectroscopic connection of dipole transitions with orbital angular momentum, it has been shown impossible to securely transmit information on any other multipolar basis – partly because point detectors are confined to polarization measurement. Standard polarization methods in optics provide for only two independent degrees of freedom, such as the circular states of opposing handedness associated with photon spin. Complex light beams with structured wave-fronts or vector polarization do, however, offer a basis for additional degrees of freedom, enabling individual photons to convey far more information content. A familiar example is afforded by Laguerre-Gaussian modes, whose helically twisted wave-front and vortex fields are associated with orbital angular momentum. Each individual photon in such a beam has been shown to carry the entire spatial helical-mode information, supporting an experimental basis for sorting beams of different angular momentum content. One very recent development is a scheme for such optical vortices to be directly generated through electronic relaxation processes in structured molecular chromophore arrays.

On scattering, the high strength singularity of a vortex beam breaks into a configuration of single charge vortices. The precise geometry of such a vortex constellation depends on the angle of incidence and the material properties of the scatterer, but also on the optical spin-orbit coupling as choosing different input and output polarization results in a family of vortex constellation. Measuring the position of the individual vortices allows us to reconstruct elements in an systematic expansion of the scattering matrix, in an analogy to optical aberration theory. We discuss in detail the dependence of the constellation geometry on external parameters, which is the basis for an optical metrology based on vortices.

Optical vortices are employed for quantum information encoding, where the wave front structure combined to the polarization vector of an optical beam can be regarded as a spin-orbit realization of a two-qubit system. We will discuss quantum information protocols that can be implemented in these degrees of freedom.

Spinoptics provides a route to control light, whereby the photon helicity (spin angular momentum) degeneracy is removed due to a geometric gradient onto a metasurface. The alliance of spinoptics and metamaterials offers the dispersion engineering of a structured matter in a polarization helicity dependent manner. We show that polarization-controlled optical modes of metamaterials arise where the spatial inversion symmetry is violated. The emerged spin-split dispersion of spontaneous emission originates from the spin-orbit interaction of light, generating a selection rule based on symmetry restrictions in a spinoptical metamaterial. The inversion asymmetric metasurface is obtained via anisotropic optical antenna patterns. This type of metamaterial provides a route for spin-controlled nanophotonic applications based on the design of the metasurface symmetry properties.

Efficient electrical spin injection into semiconductor based devices at room temperature is one of the most important requirements for the development of applicable spintronic devices in the near future and is thus an important and very active research field. Here we report experimental results for the electrical spin injection in spin light-emitting diodes (spin-LEDs) without external magnetic fields at room temperature. Our devices consist of a Fe/Tb multilayer spin injector with remanent out-of-plane magnetization, an MgO tunnel barrier for efficient spin injection and an InAs quantum dot light-emitting diode. Using a series of samples with different injection path lengths allows us to experimentally determine the spin relaxation during vertical transport from the spin injector to the active region at room temperature. In combination with our concept for remanent spin injection, we are additionally able to investigate the influence of an external magnetic field on the spin relaxation process during transport. While the spin relaxation length at room temperature without external magnetic field is determined to be 27 nm, this value almost doubles if an external magnetic field of 2 Tesla is applied in Faraday geometry. This demonstrates that the results for spin injection and spin relaxation obtained with or without magnetic field can hardly be compared. The efficiency of spin-induced effects is overestimated as long as magnetic fields are involved. Since strong magnetic fields are not acceptable in application settings, this may lead to wrong conclusions and potentially impairs proper device development.

We performed photoinduced inverse spin Hall effect (ISHE) measurements on Pt/GaAs(001) and Pt/Ge(001) junctions at room temperature. The spin-oriented electrons, photogenerated at the direct gap of the semiconductor using circularly polarized light, provide a net spin current which yields an electromotive field E_ISHE in the Pt layer. Such a signal is clearly detected in GaAs, where electrons diffuse around the Γ point of the Brillouin zone, and also in Ge, despite the strong Γ to L scattering which electrons undergo in the Ge conduction band. The ISHE signal dependence on the exciting photon energy is investigated in both junctions.

We exploit nanoscale metallic contacts for detection of ferromagnetic resonance. In our experiments we use mechanical point contacts between a copper wire tip and a ferromagnetic sample of interest to inject both dc and microwave currents into the sample. A small dc voltage develops across the contact subject to microwaves that can be attributed to rectification processes in the contact. The rectification signal was found to increase linearly with the applied dc current as expected for a point contact in the thermal regime. Here the point contact acts as a nanoscale bolometer which monitors the microwave current absorbed by the sample. When the microwave absorption increases at ferromagnetic resonance the rectification signal reveals the resonance. Our point-contact technique enables the electrical detection of ferromagnetic resonance in sample volumes as small as a few cubic nanometers.

The ability to control magnetism using electric fields in non-conducting materials is of great fundamental and practical interest, potentially leading to novel magnetic memories and spin-based devices that dissipate much less energy. The conventional mechanism for electrical control of magnetism has to do with the sensitivity of magnetic anisotropy on the filling of d-bands in ferromagnetic metals and semiconductors. Such a mechanism can not be operative in insulators, implying that E-field control of magnetic order is a great challenge in these materials. An exception to this rule is the room temperature magnetoelectric material bismuth ferrite (BiFeO₃ or BFO): In the past few years there were several demonstrations of the control of its magnetic properties by electrically switching its ferroelectric polarization P. Here I review the microscopic origin of these effects, that are mainly due to the electrical manipulation of the spin-current interaction. Nevertheless, the spin-current interaction is not the only magnetoelectric coupling present in BFO. I wil describe recent experimental and theoretical developments that showed that BFO has a strong magnetic anisotropy that scales linearly with an external E-field. This leads to a giant E-field effect on magnon spectra, that is 10⁵ times larger than what is observed in other materials. The E field converts the antiferromagnetic spiral (cycloidal) ground state into a homogeneous antiferromagnet, with a weak ferromagnetic moment whose orientation can be controlled by the E field direction. Remarkably, this kind of E-field control of magnetism occurs without switching P, hence it is expected to be a low energy dissipation process. Thus it might have applications in spin-based devices made of insulators.

Materials possessing perpendicular anisotropy have applications in high density magnetic data storage technology. In this paper, we present initial attempts to measure the fast magnetization switching from out-of-plane to in-plane in perpendicular anisotropy Co/Pt multilayers. Interaction with surface acoustic waves (SAW) results in strain induced anisotropy changes in Co/Pt multilayers arising from the magnetostrictive properties of ferromagnetic Co, and changing the easy axis of magnetization. The strain amplitude required to overcome perpendicular magnetic anisotropy is close to 1%. Such large strains are achievable using annular interdigital transducers (AIDT), in which the electrodes follow the velocity curve of the piezoelectric substrate. When excited at the fundamental resonance frequency, SAW propagating towards the center undergo constructive interference and create an intense strain at the focal center. We successfully fabricated AIDT using photolithography with a fundamental resonance of 87.56 MHz. An elliptic structure of Co/Pt multilayers was deposited at the focal center using electron beam lithography (EBL) and magnetron sputtering. The magnetization of the elliptic patterned Co/Pt was measured using focused MOKE and magnetic force microscopy (MFM), confirming that the ellipse is in a single domain state with out of plane anisotropy. Preliminary attempts to measure the magnetization rotation arising from the strain waves did not show the expected magnetization rotation signature. Possible reasons for this are discussed.

A quantum treatment of magnetization dynamics of a nanomagnet between a thousand and a million spins may be needed as the magnet interacts with quantum control. The advantage of the all-quantum approach over the classical treatment of magnetization is the accounting for the correlation between the magnet and the control agent and the first-principles source of noise. This supplement to the conference talk will concentrate on an overview of the theory with a presentation of the basic ideas which could have wide applications and illustrations with some results. Details of applications to specific models are or will be published elsewhere. A clear concept of the structure of the ground and excited macrospin states as magnetization rotation states and magnons in the Bloch/Dyson sense gives rise to a consistent theory of the magnetization dynamics of a ferromagnet modeled by the Heisenberg Hamiltonian. An example of quantum control is the spin torque transfer, treated here as a sequence of scatterings of each current electron with the localized electrons of the ferromagnet, yields in each encounter a probability distribution of the magnetization recoil state correlated with each outgoing state of the electron. This picture provides a natural Monte Carlo process for simulation of the dynamics in which the probability is determined by quantum mechanics. The computed results of mean motion, noise and damping of the magnetization will be discussed.

Graphene's two dimensional nature and high surface sensitivity have led to fascinating predictions regarding induced spin-based phenomena through careful control of adsorbates on the graphene surface, including the extrinsic spin Hall effect, band gap opening, and induced magnetism. By taking advantage of atomic scale control provided by MBE, we have investigated submonolayer deposition of adsorbates and their interactions with graphene. Spin transport measurements performed in-situ during systematic introduction of atomic hydrogen demonstrated that hydrogen adsorbed on graphene forms magnetic moments that couple via exchange to the injected spin current. The effects of induced magnetic moments are evident in the non-local magnetoresistance and Hanle spin precession. Exchange coupling between the injected spin current and the induced moments impact the Hanle curves through an effective exchange field leading to new interpretations of Hanle spin precession data and analysis. Here we present a simple procedure in which Hanle curves can be reliably interpreted.

Spin-polarized lasers are highly attractive spintronic devices providing characteristics superior to their conventional purely charge-based counterparts. Spin-polarized vertical-cavity surface emitting lasers (spin-VCSELs) promise to offer lower thresholds, enhanced emission intensity, spin amplification, full polarization control, chirp control and ultrafast dynamics. In particular, the ability to control and modulate the polarization state of the laser emission with extraordinarily high frequencies is very attractive for many applications like broadband optical communication and ultrafast optical switches. After briefly reviewing the state of research in this emerging field of spintronics, we present a novel concept for ultrafast spin-VCSELs which has the potential to overcome the conventional speed limitation for directly modulated lasers and to reach modulation frequencies significantly above 100 GHz. The concept is based on the coupled spin-photon dynamics in birefringent micro-cavity lasers. By injecting spin-polarized carriers in the VCSEL, oscillations of the coupled spin-photon system can by induced which lead to oscillations of the polarization state of the laser emission. These oscillations are decoupled from conventional relaxation oscillations of the carrier-photon system and can be much faster than those. Utilizing these polarization oscillations is thus a very promising approach to develop ultrafast spin-VCSELs for high speed optical data communication in the near future.

Semiconductor optical isolators for integrated optics are presented. The requirements and demands for semiconductor optical isolators which can be monolithically integrated with semiconductor lasers and waveguide are discussed. Fundamental theories of magneto-optic effect in optical waveguides including magnetic materials are shown and transverse magneto-optic Kerr effect is reported on ferromagnetic metal Fe, Co, and Fe₅₀Co₅₀ thin films. Based on the fundamental properties, design, fabrication, and characterization of semiconductor optical isolators based on nonreciprocal loss are shown. Transverse electric (TE-) and transverse magnetic (TM-) mode semiconductor optical isolators are reported in telecommunication wavelengths of 1.3 – 1.55 μm with (1) an optical isolation of 14.7 dB/mm in a TE mode semiconductor optical isolator, (2) amplifying characteristics in a TM mode semiconductor optical isolator, and (3) an optical isolation of 18.3 dB by using of nonreciprocal polarization rotation. Furthermore, monolithic integration of a semiconductor optical isolator with distributed feedback laser diode (DFB-LD) is reported. Optical isolator performances are compared with those of previously reported waveguide optical isolators. Finally, future prospect and applications of semiconductor optical isolators are discussed.

Two recently proposed spintronic logic families, spin-diode logic and emitter-coupled spin-transistor logic, provide an opportunity for high-performance cascaded logic circuits. These logic families make use of magnetoresistive semiconductor heterojunctions, in which the presence of a magnetic field causes a large increase in resistance. Spin-diode logic and emitter-coupled spin-transistor logic produce highly compact circuits with superior speed and power characteristics. In particular, circuits realized in these logic families use three to ten times fewer devices than conventional CMOS. Additionally, there is minimal dynamic power dissipation, presenting a pathway for low power high performance computing beyond 10 GHz.

The monolayers of group VI transition metal dichalcogenides feature a valence band spin splitting with opposite sign in the two valleys located at corners of 1st Brillouin zone. This spin-valley coupling, particularly pronounced in tungsten dichalcogenides, can benefit potential spintronics and valleytronics with the important consequences of spin-valley interplay and the suppression of spin and valley relaxations. Here we report the optical studies of MoS2,WS2 and WSe2 monolayers and multilayers. The efficiency of second harmonic generation (SHG) shows a dramatic even-odd oscillation consistent with the presence (absence) of inversion symmetry in even (odd) layer. Photoluminescence (PL) measurements show the crossover from an indirect band gap semiconductor at mutilayers to a direct-gap one at monolayers. The PL spectra and first-principle calculations consistently reveal a spin-valley coupling of 0.4 eV which suppresses interlayer hopping and manifests as a thickness independent splitting pattern at valence band edge near K points. This giant spin-valley coupling, together with the valley dependent physical properties, may lead to rich possibilities for manipulating spin and valley degrees of freedom in these atomically thin 2D materials.

Electronic valleys are energy extrema of Bloch bands in momentum space. In analogy to electrons with spin degrees of freedom, valley indices can be considered as pseudo-spins for new modes of electronic and photonic device operation. In this paper, we will review our experimental progress on the investigation of these pseudo-spins using atomically thin semiconductors (MoS₂, MoSe₂ etc.), which are either monolayer or bilayer group VI transition metal dichalcogenides. We will show that these new 2D semiconductors not only behave as remarkable excitonic systems, but also provide an ideal platform for realizing the optical manipulation and electrical control of valley degrees of freedom.

We describe the development of a magnetic logic device that is uniquely different from spintronic approaches based on magnetoresistive effects that derive from spin dependent transport of carriers. The core of our device is a thin film avalanche diode channel fabricated as a p-n bilayer. Because of the structural asymmetry, the carriers are sensitive to an in-plane magnetic field and the diode has a large magnetoresistance. We characterize our device as a current switch. The high- and low-current states are well defined and are determined by the magnetic field. Positive or negative field orientation with constant field strength is an appropriate selector. We then describe an integrated avalanche diode logic device in which the magnetic field is provided by the local fringe field from a patterned ferromagnetic film with nanometer dimensions. The magnetization orientation of the nanomagnet, and the sign of the magnetic field, is set by spin torque transfer (STT) using small amplitude current pulses. We describe how simple arrangements of these integrated devices can be used as dynamically reconfigurable logic gates. Reconfigurable Boolean AND/OR gates using early prototype structures with micron dimensions are shown. Scaling arguments that justify the plausibility of fabricating an integrated device with dimensions of 100 nm are presented. These arguments suggest that such a device could produce an output current driving STT write processes and provide fanout capability in an integrated network.

For more than a decade magnetism research focused on a fundamental understanding and controlling of spins on a nanoscale. The next step beyond the nanoscale will be governed by mesoscale phenomena. Those are expected to add complexity and functionality, which are essential design parameters e.g. for the realization of future spintronic devices. Advanced characterization techniques will play key roles in achieving mesoscience goals and multidimensional spectromicroscopies utilizing polarized soft x-rays offering a unique combination of spatiotemporal resolution, elemental and magnetic sensitivity, and tomographic capabilities are very promising. As an example for complex behavior we show experimental results of the stochastic character of the nucleation of magnetic vortex structures in arrays of permalloy nanodisk. We have used magnetic soft x-ray microscopy to image at 25nm spatial resolution and a field of view of about 8 μm diameter both the circularity and the polarity of the disk, which allowed us to categorize the nucleated vortex state without ambiguity. We have found a symmetry breaking effect in the final vortex state, represented by a preferred handedness. We were able to identify as the origin of the asymmetry an internal Dzyaloshinskii-Moriya interaction arising from a broken inversion symmetry at the top and bottom surface/interface of the disk. Full 3-dimensional micromagnetic simulations confirmed our experimental observation. Here we present our observations with regard to disk diameter and disk thickness. Various soft x-ray microscopy approaches are currently pursued to obtain full 3dimensional images of magnetic structures, including computed reconstruction of 2dim projection images.

In this article, we present recent advances in the development of spin wave logic devices utilizing spin waves for information transmission and processing. In particular, we describe the major components and the principle of operation of spin wave devices, possible logic gates for general and special task data processing, and provide an overview of the most notable experimental works demonstrating the operation of spin wave devices. One of the distinctive features of this approach is the ability to code logic 0 and 1 into the phase (0 or π) of the propagating spin wave and exploit wave interference for logic gate construction. This provides a fundamental advantage over the conventional transistor-based logic circuitry allowing us to build more functional logic gates with a fewer number of elements. We present the estimates on the potential functional throughput enhancement and compare it with the scaled CMOS. The shortcoming and potentials issues are also discussed.

Ferromagnetic resonance (FMR) measurements on Permalloy/graphene (Py/Gr) films show an enhancement of the Gilbert damping in the ferromagnetic layer as a consequence of spin pumping at the Py/Gr interface, which is driven by the Py magnetization dynamics. The remarkable increase in the FMR line-width compares with observations in other bilayer systems in which thick layers (thicker than the spin diffusion length) of heavy metals with strong spin-orbit interaction are employed as the non-magnetic layer. By reversing the stacking order of the graphene/ferromagnet, we rule out any interface effects and calculate the damping of the ferromagnet due to the graphene. Our results indicate that spin relaxation in CVD graphene must be greatly enhanced in order to account for the losses of angular momentum in the ferromagnet.

We investigate the switching statistics dependence on cell geometry by means of systematic micromagnetic simulations. We find that MTJs with a free layer composed of two ellipses with the axes a/2 and b inscribed into a rectangle a × b are characterized by the same switching speed and thermal stability as MTJs with a composite free layer (C-MTJs). As has been shown, the C-MTJs demonstrate a substantial decrease of the switching time and the switching current as compared to conventional MTJs with a monolithic free layer. Thus, while preserving all the advantages of the C-MTJs, the newly proposed structure does not require a narrow gap between the two parts of the composite layer and therefore can be easily fabricated.

The ability to control both spin and charge degrees of freedom in semiconductor nanostructrures is at heart of spintronic and quantum information technologies. Magnetically-doped semiconductor nanowires have emerged as a promising platform for spintronics, which warrants the exploration of their synthesis, electronic structure, and magnetic properties. Here we demonstrate the preparation of manganese-doped GaN and SnO₂ nanowires by chemical vapor deposition and solvothermal methods, respectively. The investigation of both systems by electron microscopy and x-ray absorption spectroscopy at ensemble and single nanowire levels indicates that manganese dopants exist in a dual oxidation state, Mn²⁺ and Mn³⁺, with Mn²⁺ being the majority species. X-ray magnetic circular dichroism studies of individual nanowires suggest ferromagnetic interactions of manganese dopants, and the nanowire orientation-dependent magnetization owing to the magnetocrystalline anisotropy. The results of these studies demonstrate quantitative determination of the dopant electronic structure at the molecular level, and allow for a prediction of the magnetic properties of diluted magnetic semiconductor nanowires based on their orientation and geometry.

Four-wave mixing techniques are applied to Ga_1-xMn_xAs, providing new insight into the fundamental properties of the III-Mn-V semiconductors. Clear signatures of (s,p)-d hybridization associated with the Mn_Ga substitutional impurity are observed in the spectrum of the four-wave mixing signal. Experiments on a ferromagnetic sample show no evidence of hole occupation in the valence band for x = 5%. A photon echo is observed on the interband transition, despite the strong exchange coupling and large defect density in this system. Rapid dephasing associated with Mn-hole spin-flip scattering is observed, with a measured upper bound on the spin-flip scattering time of 40 fs. An excitonic signature tied to many-body effects is observed in LT-GaAs.

The normal Zeeman effect gives rise to a three-fold splitting of atomic spectral lines in the presence of strong external magnetic fields. In n-doped semiconductor quantum wells, a similar three-fold splitting occurs in the intersubband spin plasmon resonance, as was recently demonstrated experimentally using inelastic light scattering. The plasmon splitting is caused by the interplay of intrinsic spin-orbit crystal magnetic fields and dynamical many-body effects. We show that it can be regarded as an intrinsic normal Zeeman effect in quantum wells. We present a formal framework for calculating the quantum well electronic states and their collective linear response in the presence of Rashba and Dresselhaus spin-orbit coupling, and we show how the intrinsic normal Zeeman effect of the spin plasmons can be controlled by external magnetic fields.

The spin degree of freedom of both mobile and localized electrons in silicon have extraordinary long spin relaxation times, making silicon an attractive candidate for spintronics applications and quantum information processing. In this talk, we will discuss recent results in measuring the conduction electron spin relaxation and coherence times in silicon MOS systems using electrically detected magnetic resonance. We will also discuss an all-electrical donor nuclear spin polarization method in silicon by exploiting the tunable interaction of donor bound electrons with conduction electrons, demonstrating that donor nuclear spins can be initialized through local gate control of electrical currents without the need for optical excitation.

Based on a proper definition of the current operators for non-quadratic Hamiltonians, we derive the expression for the transport current which involves the derivative of the imaginary part of the free-electron current, highlighting peculiarities of the extra terms. The expression of the probability current, when Spin-Orbit Interaction (SOI) is taken into account, requires a reformulation of the boudary conditions. This is especially important for tunnel heterojunctions made of non-centrosymmetric semiconductors. Therefore, we consider a model case: tunneling of conduction electrons through a [110]-oriented GaAs barrier. The new boundary conditions are reduced to two set of equations: the first one expresses the discontinuity of the envelope function at the interface while the other one expresses the discontinuity of the derivative of the envelope function.