The Kerr rotation of a bilayer graphene deposited at the center of a specially designed multilayer structure of dielectric media is investigated theoretically within the generalized 4 4 matrix approach. The reflection and transmission coefficients are analytically derived for a mirrored structure with any number of the double layers. The maximum Kerr rotation is obtained for two sequence of the double-layer with figure of merit of degree.

The transport through a domain wall pinned at a nanoconstriction in (Ga,Mn)As wires is investigated theoretically using the Landauer-Buttiker approach by considering the Rashba and Dresselhaus spin-orbit interactions. The local nonequilibrium spin densities produced by electrical spin injection at the nanoconstriction are calculated numerically along the nanowire. The adiabatic and nonadiabatic components of the spin-transfer torque, expressed in terms of the gradient of the spin current density, are also computed. An oscillatory behavior in the spin-transfer torque is observed for the systems containing atomically sharp domain walls, due to the strong reflections at the domain wall caused by the large magnetization gradient. It is demonstrated that the strength of the oscillations for nonadiabatic spin torque increases by the negative Rashba parameter alpha(x), while it decreases with increasing positive values of alpha(x). However, the nonadiabatic spin torque increases with |alpha(y)|, regardless of its sign. Furthermore, it is shown that the Dresselhaus coupling beta does not considerably alter the z component of the spin torque, while the other two components are effectively changed by the Dresselhaus spin-orbit interaction.

In this paper, a new type of flat-band slow light structure with high group index (n g) and large normalized delay-bandwidth product (NDBP) in a silicon on insulator (SOI) based photonic crystal (PC) slab waveguide with a triangular lattice of circular holes is demonstrated. The dispersion engineering is performed by infiltrating optical fluids with different refractive indices n f in the first row and shifting the second row of air holes adjacent to the PC waveguide (PCW) in the longitudinal direction. In the optimized case, a high NDBP of 0.32 with a group index of 54.55 and a bandwidth of 9.13 nm could be obtained. Furthermore, an ultra-low group velocity dispersion (GVD) in the range of 10–20 s2/m is achieved in all of the structures. These results are obtained by numerical simulations based on three-dimensional (3D) plane wave expansion (PWE) method.

Controlling the conductance and current flow through nanostructured magnetic point contacts is a key challenge for future spintronic devices. This could be achieved by exploiting the Rashba spin-orbit coupling effect induced by an external gate in the middle of two pinned domain walls at the point contacts. Here, I investigate the electrical conductance of a half-metallic diluted magnetic semiconductor nanowire with a double point contact exploitable in switching devices controlled by lateral gate voltage. The coherent quantum interference between forward and backward-scattered waves in the spin quantum well formed by the double point contact leads to quasibound states with finite lifetimes. The energetic position of these quasibound states could be adjusted by the lateral gate voltage so that the incident energy coincides with one of the quasibound energy levels in the spin quantum well. Conductance calculations in the presence of an applied electric field perpendicular to the nanowire surface exhibit typical resonant tunneling behavior, where the nanostructure switches to the low-resistance ON state by tuning the Rashba coupling strength in the range of a few tens of meV nm. This study paves the way for utilizing the gate-controlled Rashba spin-orbit coupling effect to design and develop practical spintronic devices.

The ballistic magnetoresistance (MR) of a domain wall constricted in a nanocontact between two p-type semiconducting magnetic nanowires is studied theoretically using the Landauer-Buttiker approach. Our analysis is based on coherent scattering of the carriers by the spin-dependent potential associated with the wall structure. The transmission properties of coherent states are obtained by introducing an algorithm to solve the coupled spin channels Schrodinger equation with mixed Dirichlet-Neumann boundary conditions applied far from the domain wall. Then, the local accumulated spin densities along the nanowire produced by electrical spin injection at the nanocontact are numerically calculated. It is demonstrated that the induced voltage drop due to the longitudinal spin accumulation considerably increases in the case of the narrow domain walls. Furthermore, it is shown that two spin accumulation and mistracking effects give approximately equal contributions to the wall MR ratio in the limit of the sharp domain walls. However, the MR ratio is dominantly determined by the spin accumulation effect as the domain wall width increases.

In this study, the optical conductivity of substitutionary doped graphene is investigated in the presence of the Rashba spin orbit coupling (RSOC). Calculations have been performed within the coherent potential approximation (CPA) beyond the Dirac cone approximation. Results of the current study demonstrate that the optical conductivity is increased by increasing the RSOC strength. Meanwhile it was observed that the anisotropy of the band energy results in a considerable anisotropic optical conductivity (AOC) in monolayer graphene. The sign and magnitude of this anisotropic conductivity was shown to be controlled by the external field frequency. It was also shown that the Rashba interaction results in electron–hole asymmetry in monolayer graphene.

In this study, one band Schrödinger equation for InAs/GaAs quantum dots coupled to their wetting layer was solved numerically by using a finite element method (FEM). We have carried out the conduction of the Woods–Saxon (WS) potential in the quantum dots (QDs) as well as a constant finite barrier between InAs quantum dot/wetting layer and GaAs matrix is considered for comparison. It is found by WS potential that the envelope functions never become completely localized inside the dot; therefore this delocalization leads to strong alternations in absorption and dispersion profiles which is not negligible. Also, it is found that group velocity is affected by the WS potential and reveals remarkable blue-shift in comparison to the constant finite potential.

In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.

The finite difference time domain method (FDTD) has been used to model the extinction cross section of silver (Ag) ellipsoidal nanoparticles. The localized surface Plasmon resonance frequencies strongly depend on the size and orientation of the nanoparticles. It has been calculated the longitudinal, transverse and hybrid modes for nanoparticles with prolate spheroid geometry. The longitudinal resonance mode occurs when the electric field of incident light is along the caxis of the prolate spheroid. Similarly, the transverse resonance mode occurs when the electric field of incident light is perpendicular to the c-axis. In our calculations, the dielectric function has been obtained according to the Drude-Sommerfeld

Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)](5) multilayer with perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of variable thickness t(CFB), are investigated using Brillouin light scattering. On reducing t(CFB) in the range 0.8-2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly 4-48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization with respect to the film normal. These findings are interpreted using a one-dimensional model in which each atomic layer is assumed to be uniformly magnetized, subjected to an effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack, and exchange coupled to its two nearest neighbour atomic layers. With respect to previously investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a narrower range of the soft layer thickness, is observed.

In this paper, we have performed a theoretical study on nonlinear optical rectification (OR) and second harmonic generation (SHG) for three-level dome-shaped InAs/GaAs quantum dots (QDs) in the presence of wetting layer (WL). We used the compact density matrix framework and effective mass approximation to investigate the second order nonlinear phenomena on InAs/GaAs QD. It is demonstrated that second harmonic generation (SHG), optical rectification (OR), and their mutual absorption and refractive index changes are quite sensitive to the size of QDs. The size variations have profound irregular behavior owing to distribution of envelope function on WL and QD simultaneously. Moreover it is found that R=13 nm is a critical radius where the regular variation takes place. It is shown that size variation causes blue shift until Critical radius ( R=13 nm) and after that, increasing the QD size lead to redshift in second order phenomena.

In this paper, the interaction between an oscillating dipole moment and a Silver nanoparticle has been studied. Our calculations are based on Mie scattering theory and discrete dipole approximation(DDA) method.At first, the resonance frequency due to excitingthe localized surface plasmons has been obtained using Mie scattering theory and then by exciting a dipole moment in theclose proximity of the nanoparticle, the induced charge distribution on the nanoparticle surface has been calculated. In our calculations, we have exploited the experimental data obtained by Johnson and Christy for dielectric function.

We have investigated the influence of spin accumulation on the domain wall resistance in the presence of the Rashba and the Dresselhaus spin–orbit interactions. In this order, we have employed a quantum kinetic model based on the Wigner distribution function formalism. Using the single-electron Hamiltonian and following the approach of Šimánek and Rebei (Phys. Rev. B 71:172405, 2005), we derive the coupled differential equations for transverse spin accumulation components and then calculate its contribution to the resistance of a domain wall. The results show that both the Rashba and the Dresselhaus spin–orbit interactions enhance the transverse spin accumulation and consequently increase the domain wall resistance.

We have investigated the spin accumulation effect in a Bloch-type magnetic domain wall in the presence of the Rashba spin-orbit interaction. The investigation has been done to study the excess voltage drop due to spin accumulation across the domain wall using the kinetic equation in Wigner space. It has been demonstrated that the Rashba interaction extremely increases the spin accumulation effect in the domain wall which in turn results in up to two orders of magnitude enhancement in the excess voltage drop.

We investigate a tunable spin configuration in [Co/Ni](4)/Co-NiFe exchange spring magnets. The strong perpendicular magnetic anisotropy of the Co/Ni multilayer, which competes with the in-plane shape anisotropy of the Ni81Fe19 (Py) layer, allows for unique magnetic configurations. By varying the NiFe thickness (t(NiFe)) from 2.6 to 3.0 nm, we show that the magnetization tilt angle can be easily tuned from completely out-of-plane (0 degrees) to in-plane (90 degrees). This transition, which occurs for a small range of t(NiFe), can be estimated from the major loop remanence and one-dimensional micromagnetic calculations. These tunable magnetization tilt spring magnets are highly promising for future applications in spin-transfer torque-based devices.

The magnetoresistance of a one-dimensional electron gas in a metallic ferromagnetic nanowire containing two atomic-size domain walls has been investigated in the presence of spin-orbit interaction. The magnetoresistance is calculated in the ballistic regime, within the Landauer-Buttiker formalism. It has been demonstrated that the conductance of a magnetic nanowire with double domain walls can be controlled through the domain walls separation. Also, we have represented another alternative way that enables us to handle easily the magnetoresistance of such a system as well as its conductance by utilizing the Rashba-type spin-orbit interaction induced by the external gates. 2012 JNS All rights reserved

By varying the Pd thickness (tPd) from 0 to 8nm in [Co/Pd]4/Co/Pd(tPd)/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd]4/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20○ to 80○, and (iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd]4/Co/Pd(tPd)/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom.

We study the magnetoresistance (MR) of a one‐dimensional electron gas in a ferromagnetic semiconducting nanocontact containing an atomic‐size domain wall, and in the presence of the Rashba and the Dresselhaus spin–orbit interactions. The MR is calculated in the ballistic regime, within the Landauer–Büttiker formalism. It is shown that, the Dresselhaus spin–orbit interaction which is the result of bulk‐induced inversion asymmetry makes a reduction in the domain wall MR. In contrast, the Rashba coupling may lead to a negative or positive change in the domain wall MR, depending on the Fermi energy and the lateral confinement potentials which can be induced by both parabolic lateral confinement and lateral gate potentials.

We demonstrate spin transfer torque (STT) switching in multi-nanocontact STT devices fabricated using hole mask colloidal lithography. We also study the STT device resistance and switching properties as a function of applied magnetic field and nanocontact current. At low nanocontact current, magnetoresistance measurements show sharp, single-step switching at low switching fields. When the current is increased, the switching becomes multistep, and the switching field increases dramatically. We explain these results as arising from a transition from a predominantly single domain like switching to switching involving a vortex state. Micromagnetic simulations corroborate this picture, indicating that a single magnetic vortex nucleates in between the nanocontacts through the influence from the total Oersted field generated by the nanocontact ensemble.