The Propagation of Spin Excitations in Hexagonal Ferromagnetic Semiconductor Superlattice Nanowires at Low Temperatures

Phase transition in ising magnetic superlattice nanowires: Molecular field theory approach

The propagation of surface and bulk spin excitations in ferromagnetic semiconductor superlattices consisting of alternating monoatomic layers of two types of cubic Heisenberg ferromagnets is considered. The Green’s function method is used to obtain the dispersion relations describing the propagation of surface and bulk spin waves in the superlattices and also the temperature dependence of the magnetization of the localized spins. The results are integrated numerically and presented graphically.

We investigate the nonlinear spin excitation in a Heisenberg ferromagnetic nanowire with the higher order octupole-dipole interaction. In this study, the nonlinear dynamical equation of motion is obtained by a semi-classical limit employing Glauber’s coherent state analysis along with Holstein-Primakoff bosonic representation for the spin operators. In the framework of linear stability analysis, we employ the Modulational Instability for the ferromagnetic nanowire with octupole-dipole interaction. It is found that the occurance of octupole-dipole exchange interaction systematically helps to localize the excitation which improve the growth of high amplitude localized robust solitons in the ferromagnetic nanowire lattice.KeywordsNonlinear excitationOctupole-dipole interactionModulational instability analysisHeisenberg ferromagnetic nanowire

We study the electronic states of hexagonal core multishell semiconductor nanowires, including the effect of magnetic fields. We find that the two dimensional electron states formed at the interface between different layers are mostly localized at the six edges of the hexagonal prism, and behave as a set of quasi-1D quantum channels. They can be manipulated by magnetic fields either parallel or perpendicular to the wire axis. These results can be rationalized in terms of Aharonov-Bohm oscillations or Landau level formation. We also show that inter-channel coupling and magnetic behavior is influenced by the geometric details of the nanowires.

Synthesis and magnetic properties of FeSex/FeTey/FeSezTe1-z nanowires

Spin-wave dispersion in ferromagnetic semiconductor superlattices and thin films in the narrow-band limit

Domain structure of EuS/PbS and EuS/YbSe superlattices studied by polarized neutron reflectometry

The ballistic spin-filter effect from a ferromagnetic metal into a semiconductor has theoretically been studied with an intention of detecting the spin polarizability of density of states in FM layer at a higher energy level. The physical model for the ballistic spin filtering across the interface between ferromagnetic metals and semiconductor superlattice is developed by exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer at a much higher energy level and then ballistically tunneling through the barrier into the ferromagnetic film. Since both the helicity-modulated and static photocurrent responses are experimentally measurable quantities, the physical quantity of interest, the relative asymmetry of spin-polarized tunneling conductance, could be extracted experimentally in a more straightforward way, as compared with previous models. The present physical model serves guidance for studying spin detection with advanced performance in the future.

Ferromagnetic semiconductor superlattices studied by polarized neutron reflectometry

We present experimental studies of the in-plane magnetic anisotropy of ferromagnetic semiconductor superlattices. The samples have half-monolayer MnAs planes that alternate with GaAs spacers of thickness $t=28,$ 42, and 56 \AA{}. For the lowest-t samples, planar Hall effect and magnetization data indicate domain-wall-mediated magnetic switching between predominantly cubic easy axes, while samples with larger t exhibit uniaxial anisotropy. The data demonstrate that the structure of ferromagnetic semiconductor superlattices controls their magnetic anisotropy.

The organization of nano-objects on macroscopic surfaces is a key challenge for the technological improvement and implementation of nanotechnologies. For achieving operational functions, it is required to assemble nano-objects as controllable building blocks in highly ordered superstructures. Herein, we demonstrate the growth and self-organization of metallic nanowires on surfaces into hexagonal superlattices with tunable characteristic lengths depending of the stabilizing surfactants employed. Starting from a reacting mixture containing a Pt(111) substrate, a Co organometallic precursor, an amine, and an acid dissolved in a solvent, we quantify the structural evolution of superlattices of vertical single-crystalline Co nanowires on Pt, using a combined analysis of small angle neutron scattering, transmission, and scanning electron microscopies. We show the concerted steps of a spontaneous growth and self-organization of the nanowires into two-dimensional (2D) hexagonal lattice on Pt, at intervals starting from a few hours of reaction to a highly ordered superlattice at longer times. Furthermore, it is shown that apart from long-chain acid and long-chain aliphatic amine pairs used as stabilizers, the combination of a long-chain aliphatic and a short-chain aromatic ligand in the synthesis can also be employed for the nanowire superlattices development. Interestingly, the possibility to employ different pairs allows quantitative modulation of the nanowire arrays, such as the interwire distance and the packing fraction.

Two ferromagnetic semiconductor GaMnAs-based superlattices (SLs) were investigated by measuring the planar Hall effect (PHE) with the external magnetic field applied in the plane of the sample. The two GaMnAs/GaAs SLs differed only by the Be doping of the nonmagnetic GaAs spacer layers. Both SLs showed a typical two-step transition behavior in PHE field scans at 4.0 K, essentially the same as that normally observed on single GaMnAs ferromagnetic layers with two in-plane magnetic easy axes. As the temperature increased to 30 K, the behaviors of the PHE changed differently in the two SL samples. The PHE in the undoped SL can be described simply by the temperature dependence of the magnetic anisotropy within the film plane of a GaMnAs film. However, the Be-doped SL revealed a completely different behavior, showing a transition of magnetization with a negative coercive field. The observation of this feature in a ferromagnetic multilayer indicates the presence of spontaneous anti-parallel interlayer exchange coupling between the GaMnAs magnetic layers.

Low-energy spin and charge excitations of one-dimensional interacting fermions are completely decoupled and propagate with different velocities. These modes, however, can decay due to several possible mechanisms. In this Letter we expose a new facet of spin-charge separation: not only the speeds but also the damping rates of spin and charge excitations are different. While the propagation of long-wavelength charge excitations is essentially ballistic, spin propagation is intrinsically damped and diffusive. We suggest that cold Fermi gases trapped inside a tight atomic waveguide offer the opportunity to measure the spin-drag relaxation rate that controls the broadening of a spin packet.

Magnetic skyrmions, topological solitons characterized by a two-dimensional swirling spin texture, have recently attracted attention as stable particle-like objects. In a three-dimensional system, a skyrmion can extend in the third dimension forming a robust and flexible string structure, whose unique topology and symmetry are anticipated to host nontrivial functional responses. Here we experimentally demonstrate the coherent propagation of spin excitations along skyrmion strings for the chiral-lattice magnet Cu2OSeO3. We find that this propagation is directionally non-reciprocal and the degree of non-reciprocity, as well as group velocity and decay length, are strongly dependent on the character of the excitation modes. These spin excitations can propagate over a distance exceeding 50 μm, demonstrating the excellent long-range ordered nature of the skyrmion-string structure. Our combined experimental and theoretical analyses offer a comprehensive account of the propagation dynamics of skyrmion-string excitations and suggest the possibility of unidirectional information transfer along such topologically protected strings.

We investigate the propagation of spin excitations in a one-dimensional ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this system is soundlike, the dispersion of transverse spin excitations is quadratic, making a direct application of the Luttinger liquid theory impossible. By using a combination of different analytic methods we derive the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion. The result has an unusual structure associated with a crossover from the regime of trapped spin wave to an open regime and does not have analogues in known low-energy universality classes of quantum 1D systems.