Influence Of In-plane Magnetic Field Research Articles

Helimagnet-based nonvolatile multi-bit memory units

In this Letter, we present a design of a helimagnet-based emerging memory device that is capable of storing multiple bits of information per device. The device consists of a helimagnet layer placed between two ferromagnetic layers, which allows us to lock-in specific spin configurations. The bottom pinned layer has high anisotropy energy or stays exchange biased, which keeps its spin configuration fixed on a specific direction, while the top layer is free to rotate under the influence of in-plane magnetic fields. We begin by finding the relaxed spin structure, which is the result of the competition between the Dzyaloshinskii–Moriya interaction (DMI) and exchange energy and is referred to as the equilibrium state (“0”). The writing of a memory state is simulated by applying an in-plane field that rotates and transforms the spin configurations of the memory device. Our results indicate that stable configurations can be achieved at rotations of an integer multiple of 180° (corresponding to states “−2,” “−1,” “1,” “2,” etc.), where the anisotropy stabilizes the free layer and, thus, the exchange coupled helimagnet. These states are separated by magnetic energy barriers and intermediate, unstable spin configurations tend to revert to their adjacent states. By simply changing the direction of the field, we can achieve multi-bit data storage per unit memory cell. The maximum number of bits is reached when the anisotropy energy barriers cannot withstand the strong DMI energy. Reading can be done by evaluating the different resistance states due to the twisted spin texture.

Nonlinear Vibrations of Embedded Nanoplates Under In-Plane Magnetic Field Based on Nonlocal Elasticity Theory

AbstractNonlinear vibrations of the orthotropic nanoplates subjected to an influence of in-plane magnetic field are considered. The model is based on the nonlocal elasticity theory. The governing equations for geometrically nonlinear vibrations use the von Kármán plate theory. Both the stress formulation and the Airy stress function are employed. The influence of the magnetic field is taken into account due to the Lorentz force yielded by Maxwell's equations. The developed approach is based on applying the Bubnov–Galerkin method and reducing partial differential equations to an ordinary differential equation. The effect of the magnetic field, elastic foundation, nonlocal parameter, and plate aspect ratio on the linear frequencies and the nonlinear ratio is illustrated and discussed.

Hygrothermal wave propagation in viscoelastic graphene under in-plane magnetic field based on nonlocal strain gradient theory

A size-dependent model is developed for the hygrothermal wave propagation analysis of an embedded viscoelastic single layer graphene sheet (SLGS) under the influence of in-plane magnetic field. The bi-Helmholtz nonlocal strain gradient theory involving three small scale parameters is introduced to account for the size-dependent effects. The size-dependent model is deduced based on Hamilton's principle. The closed-form solution of eigenfrequency relation between wave number and phase velocity is achieved. By studying the size-dependent effects on the flexural wave of SLGS, the dispersion relation predicted by the developed size-dependent model can show a good match with experimental data. The influence of in-plane magnetic field, temperature and moisture of environs, structural damping, damped substrate, lower and higher order nonlocal parameters and the material characteristic parameter on the phase velocity of SLGS is explored.

Vibrating nonlocal multi-nanoplate system under inplane magnetic field

The recent development in nanotechnology resulted in growing of various nanoplate like structures. High attention was devoted to graphene sheet nanostructure, which enforced the scientist to start developing various theoretical models to investigate its physical properties. Magnetic field effects on nanoplates, especially graphene sheets, have also attracted a considerable attention of the scientific community. Here, by using the nonlocal theory, we examine the influence of in-plane magnetic field on the viscoelastic orthotropic multi-nanoplate system (VOMNPS) embedded in a viscoelastic medium. We derive the system of m partial differential equations describing the free transverse vibration of VOMNPS under the uniaxial in-plane magnetic field using the Eringen's nonlocal elasticity and Kirchhoff's plate theory considering the viscoelastic and orthotropic material properties of nanoplates. Closed form solutions for complex natural frequencies are derived by applying the Navier's and trigonometric method for the case of simply supported nanoplates. The results obtained with analytical method are validated with the results obtained by using the numerical method. In addition, numerical examples are given to show the effects of nonlocal parameter, internal damping, damping and stiffness of viscoelastic medium, rotary inertia and uniaxial in-plane magnetic force on the real and the imaginary parts of complex natural frequencies of VOMNPS. This study can be useful as a starting point for the research and design of nanoelectromechanical devices based on graphene sheets.

Spin–orbit interaction effects on the optical properties of quantum wires under the influence of in-plane magnetic fields

In this work, we studied the effects of in-plane magnetic field and Rashba spin–orbit interaction on the intersubband optical absorption coefficients and changes in refractive index for transitions between the first two lower-lying electronic levels of quantum wire represented by a parabolic confining potential. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of quantum wire radius, strength and orientation of magnetic field, strength of Rashba spin–orbit interaction and photon energies. Numerical results reveal that the optical absorption coefficients and refractive index changes are strongly affected and thus can be controlled by these parameters.

Spin polarization in non-magnetic nanostructures

Quantum transport that takes into account spin polarization has a high potential for research on optimal heterostructures for fabrication of nano-spintronic devices and quantum computing. This work theoretically analyzed different materials on the basis of type-II strained heterostructures like InAs/GaSb, InSb/GaSb, InSb/GaAs, and GaSb/GaAs by means of the spin polarization that considers the interacting spin coupling type: k3- Dresselhaus and Rashba in the electric barriers and the influence of in-plane magnetic field on spin polarization. The results obtained for the polarization of spin are in function of the energy applied to the electron, well width, height of barrier, and magnetic field intensity. This suggests that these features could be engineered in the fabricating of tunable spin- dependent electronic devices, such as spin switches based on double-barrier non-magnetic semiconductors.

Stress induced anisotropy and applied field dependence of second order perturbed energy of thick ferromagnetic films

The energy of thick ferromagnetic films up to 10000 layers has been explained in this report using classical Heisenberg Hamiltonian with second order perturbation. Especially the effect of applied magnetic field and stress on energy of sc(001) ferromagnetic thick films has been investigated. Under the influence of perpendicular magnetic field given by = 6, the sc(001) ferromagnetic film with 10000 layers can be easily oriented in 0.5 radians direction. The easy direction of sc(001) ferromagnetic film with 10000 layers was found to be 0.6 radians when the in-plane magnetic field of = 4.2 is applied. Because the easy axis oriented magnetic films are useful in magnetic memory devices and monolithic microwave integrated circuits (MMIC), the determination of easy direction is important. If the stress given by = 2.6 is applied in perpendicular direction to the film plane, the film can be easily oriented in direction of 3 radians. Energy under influence of perpendicular magnetic field is larger than the energy under the influence of in-plane magnetic field. After introducing the second order perturbation to the Heisenberg Hamiltonian, even some small variations of energy could be investigated as indicated in the graphs in this manuscript.Keywords: Ferromagnetic materials, thick films, Heisenberg Hamiltonian, stress induced anisotropyDOI: http://dx.doi.org/10.4038/josuk.v6i0.4223J Sci.Univ.Kelaniya 6 (2011) : 77-84

Effective Hamiltonian, energy spectrum, and phase transition induced by in-plane magnetic field in symmetric HgTe quantum wells

The effective $6\ifmmode\times\else\texttimes\fi{}6$ matrix Hamiltonian for two-dimensional states in HgTe/CdTe quantum wells is derived. The use of the extended basis (in contrast to the previously studied $4\ifmmode\times\else\texttimes\fi{}4$ matrix Hamiltonian) allows us to describe quantum wells with arbitrary orientation of interfaces and investigate the influence of in-plane magnetic field. The Hamiltonian is applied to calculation of energy spectra of both two-dimensional subbands and edge states in the range of well widths corresponding to the topological insulator phase. It is found that the in-plane magnetic field opens a gap in the edge-state spectrum, and the increase in the field causes disappearance of one of the edge-state branches. A strong (about 10 T) magnetic field induces a phase transition from the gapped state to a gapless two-dimensional state, with energy spectrum similar to that of bulk HgTe. An analytical expression for the transition field through the parameters of the effective Hamiltonian is obtained.

Influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k3-Dresselhaus spin–orbit coupling

The influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k 3 -Dresselhaus spin–orbit coupling was investigated. The k 3 -Dresselhaus term can produce a limited spin polarization. The in-plane magnetic field plays a great role in the tunneling process. It can generate the perfect spin polarization of the electrons and the ideal transmission coefficient for spin up and down simultaneously. In energy scale, complete separation between spin up and down resonance was obtained by a relatively higher in-plane magnetic field while a comparatively lower in-plane magnetic field vanishes the spin separation. On the other hand, the spin relaxation can be suppressed by compensating the oft-neglected k 3 -Dresselhaus spin orbit coupling using a relatively lower in-plane magnetic field.

Exchange-correlation effects on quantum wires with spin-orbit interactions under the influence of in-plane magnetic fields

Within the noncollinear local spin-density approximation, we have studied the ground state structure of a parabolically confined quantum wire submitted to an in-plane magnetic field, including both Rashba and Dresselhaus spin-orbit interactions. We have explored a wide range of linear electronic densities in the weak strong coupling regimes that appear when the ratio of spin-orbit to confining energy is small large. These results are used to obtain the conductance of the wire. In the strong coupling limit, the interplay between the applied magnetic field—irrespective of the in-plane direction, the exchange-correlation energy, and the spinorbit energy—produces anomalous plateaus in the conductance vs linear density plots that are otherwise absent, or washes out plateaus that appear when the exchange-correlation energy is not taken into account.

Orbital magnetic susceptibility of disordered mesoscopic systems

In this paper we study the orbital weak-field susceptibility of two-dimensional diffusive mesoscopic systems. For the previously unstudied regime of temperatures lower than the mean level spacing we find unexpected strong temperature as well as statistical ensemble dependence of the average and typical susceptibilities. An explanation for these features is given in terms of the long tail of the zero-temperature susceptibility distribution, including the parametric form of the temperature dependence. For temperatures higher than the mean level spacing we calculate the difference between the true canonical ensemble and the effective grand-canonical ensemble. We also perform numerical simulations, which seem to generally confirm previous theoretical predictions for this regime of temperatures, although some difficulties arise. The important role of gauge-invariance, especially how it renders Random Matrix Theory inapplicable to the study of orbital susceptibility, is discussed. We conclude by considering interaction effects, giving a new interpretation to previous results as well as demonstrating the influence of in-plane magnetic field on the interaction-induced orbital response.

Strong influence of in-plane magnetic fields on the cyclotron effective electron mass at the GaAs/Al0.3Ga0.7As heterojunction

An in-plane magnetic field B∥, added to a perpendicular one B⊥, and applied to the quasi-two-dimensional electron gas at the GaAs/AlGaAs heterojunction, may increase the cyclotron effective mass mc∗ due to the distortion of the Fermi contour by B∥. We study the increase of mc∗(B∥) by the Shubnikov-de Haas effect, for the first time for five different ratios B∥/B⊥, ranging from 1.5 to 13 (compared to the one ratio of 6.0 in an earlier investigation). The observed field dependence extends from mc∗=0.067m0 for B∥=0T to mc∗=0.1m0 for B∥=13T. This drastic increase of mc∗(B∥) of 50% is caused not only by the higher applied in-plane field, but rather by the stronger field dependence of the carriers with a density of n=1.7×1011cm−2. We discuss our results, also in view of spin splitting and magnetophonon resonance measurements in tilted magnetic fields.

Domain structure in YIG films subjected to magnetic fields and stresses

Magnetic domain structure in epitaxial YIG films was investigated using Faraday effect and Bitter method. These experiments have shown complex structures of closure domains. The influence of in-plane magnetic fields and stresses on the magnetization position was measured. The observed variation was interpreted in the light of a simple theory involving anisotropy, magnetostriction and magnetostatic energies. A new determination of the induced stress was inferred from this study, X-ray experiments were also performed. Interfacial dislocations have been observed which are consistent with the rather small value found for the stress.