G.J. Jin

Magnetic anisotropy of sputtered Ni/Ag multilayers

Abstract We have studied the magnetic properties and structure of Ni/Ag multilayers, fabricated by the dc magnetron sputtering method. The in-plane uniaxial anisotropy, which is closely related to the sample preparation, has been detected by both vibrating magnetometer (VSM) and ferromagnetic resonance (FMR) measurements where the FMR spectra were obtained as a function of the applied magnetic field orientation in the film plane. The variation of the resonance field with the angle of the applied magnetic field can be well explained by a theoretical model including the in-plane uniaxial anisotropy up to the second-order term. Moreover, both in-plane and perpendicular anisotropy parameters have been deduced by a data-fitting analysis and a negative interface anisotropy constant has been determined.

Raman scattering by longitudinal acoustic phonons in a three-component TaAl Fibonacci superlattice

Abstract Raman scattering from longitudinal acoustic phonons in a three-component Ta Al Fibonacci superlattice is studied both experimentally and theoretically. Based on the Kronig-Penney model, the normal-mode frequencies and the relative intensities are calculated by using a transfer-matrix method. Good agreement between the measured and quantitative results is obtained. The phonon spectra exhibit a rich structure of gaps which correlate with the positions of the measured Raman-activated peaks. The Raman peaks are successfully labeled by the the quasiperiodicity index (p, q, r).

Phonon properties of WTi Thue-Morse superlattices☆

Abstract Based on the Kronig-Penney model and transfer matrix method, we have calculated the phonon spectra of W Ti Thue-Morse superlattices which are neither periodic, quasiperiodic, nor random. Both periodic boundary conditions and free-edge boundary conditions are taken into account during simulations. The calculated phonon spectra are a Cantor set and show more point-like features which may imply that there is a smaller degree of order in this sequence compared with the quasiperiodic system.

Raman scattering by longitudinal acoustic phonons in metallic W/Ti Fibonacci superlattice

Raman scattering from longitudinal acoustic phonons in W/Ti Fibonacci superlattice is studied. Doublet peaks which result from the folded longitudinal acoustic phonons appear in the Raman spectra as expected. Based on the Kronig–Penney model or the Rytov model, both the normal‐mode frequencies and scattering intensities are numerically calculated by using a transfer‐matrix method. Noticeable agreement is obtained between the results of quantitative calculations and experimental data.

Surface effect on the depletion potential between two spheres in a suspension of rods

We study the influence of a surface on the depletion potential between two spheres in a suspension of rods through Monte Carlo simulations under some simple approximate treatment on the statistical expression of free energy. If the length of the rods is larger than the radius of the spheres, the depletion potential between the two spheres when they are on a flat surface is remarkably weaker than that when they are in the bulk solution. If the surface is concave, as the curvature increases, the depletion potential will increase between a sphere and the surface but decrease between the two spheres. Contrarily, for a convex surface, as the curvature increases, the depletion potential will decrease between a sphere and the surface but increase between the two spheres. It is found that surface curvature brings about a much stronger effect to the depletion interaction between a sphere and the surface than that between the two spheres.

Electronic transport in k-component Fibonacci quantum waveguides

We present a study of electronic behaviours in the k-component Fibonacci (KCF) quantum waveguides, in which k different incommensurate intervals are arranged according to a substitution rule. On the basis of the transfer matrix method, the quantum transmission properties of the KCF stub structures are obtained. It is shown that the transmission coefficient depends on the wavevector of the electron and the number of different incommensurate intervals k. For the KCF waveguides with the same k, on increasing the number of stubs, the minima in transmission extend gradually into the band gap over which the transmission is blocked. Meanwhile more transmission peaks appear. For finite KCF stub structures, on increasing the number of different incommensurate intervals k, the total transmission over the spectral region of interest decreases gradually and the width of the electronic band gap is enlarged. Moreover, when the value of k is large enough, the transmission is basically shut off, except at a few energies where resonant tunnelling takes place. These properties make it possible to use this kind of KCF waveguide as a switching device for digital applications. On the other hand, the charge-density distributions in these structures are singularly continuous. We propose that they can be analysed using a multifractal concept. A dimensional spectrum of singularities associated with the charge density, f (α), demonstrates that the electronic transport in the KCF waveguide presents scaling properties; hence the charge-density distribution shows a genuine multifractality.

Growth-induced magnetic anisotropy behavior in Ni thin films

The magnetic anisotropy of Ni thin films fabricated under different growth conditions have been studied by the ferromagnetic resonance (FMR) method. The FMR data have been fitted theoretically. The results show that the anisotropy is an orthorhombic anisotropy, and there exists an optimal rotary speed of the sample for a fixed deposition rate. Near the optimal speed, the anisotropy field along the in-plane easy axis exhibits a maximum, while the anisotropy held perpendicular to the film plane exhibits a minimum. The origin of orthorhombic anisotropy has been discussed

Magnetic anisotropy of Ni/Al multilayers

Abstract The magnetic anisotropy of Ni/Al multilayers has been investigated by vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The FMR spectra are obtained as a function of the orientation of the applied magnetic field from in-plane to out-of-plane, and are fitted theoretically to determine the magnetic anisotropy. From VSM and FMR, a positive value for Ni/Al interface anisotropy, favoring a perpendicular easy axis, is obtained. Furthermore, for the ultrathin magnetic layer below a critical Ni thickness of 20 A, a perpendicular easy axis of magnetization can be extrapolated.

Field-modulated structural transformation of planar binary dipolar hard spheres

Monte Carlo simulations are used to study the structural transformation of binary dipolar hard spherical particles. The particles are confined in a homogeneous plane and each dipole can orient out of the plane. Any two dipoles are parallel with each other when they belong to the same kind of particle, but antiparallel for the different kinds of particles. When the orientations of the dipoles rotate from being perpendicular to the plane to being parallel with the plane, various morphologies, such as the isotropic clusters, anisotropic clusters, an expanded block, long chains, and columns, emerge sequentially. We study the transformations between these structures by analyzing the orientation of the linking lines between the nearest neighbors, radius distribution functions and the average energies. In addition, numerical calculation of the energies of four ideal structures is carried out for the comprehension of these transformations.

Quantum behavior in one-dimensional mesoscopic Thue-Morse rings

Abstract Using a tight-binding model, we have investigated the energy spectra and persistent currents in one-dimensional mesoscopic rings threaded with a magnetic flux φ. The mesoscopic ring is constructed by a Thue-Morse chain with N sites. By applying a transfer-matrix method, the flux-dependent energy spectra have been obtained. It is shown that the electron eigenenergies E(φ) gradually form “bands” as the disorder increases in the quantum system. Meanwhile, the persistent currents in the rings exhibit a rich structure, which depends on the number of electrons and the disorder of system. On the other hand, as increasing the disorder of system, the “bandwidths” are getting narrower in the energy spectra: thereafter the maximum persistent current decreases obviously in the rings. A metal-insulator transition can be easily found in the half-filled electron system.