A. N. Kuchko

Spin wave interferometer employing a local nonuniformity of the effective magnetic field

We have investigated scattering of exchange spin waves by a model nonuniformity of the effective magnetic field. In particular, certain profiles of the nonuniformity are characterized by a total transmission of the spin wave intensity while inducing large shifts to the phase of transmitted spin waves. These properties are discussed in the context of potential application within a spin wave logic device—a spin wave interferometer containing such a nonuniformity in one of its branches. We demonstrate limitations imposed upon the size and the speed of operation of such a device by a requirement that it be controlled by an external uniform magnetic field.

Spin waves in a periodically layered magnetic nanowire

We report a simple theoretical derivation of the spectrum and damping of spin waves in a cylindrical periodically structured magnetic nanowire (cylindrical magnonic crystal) in the “effective-medium” approximation. The dependence of the “effective” magnetic parameters upon the individual layer parameters is shown to be different from the arithmetic average over the volume of the superlattice. The formulas that are obtained can be applied firstly in the description of spin-wave dispersion in the first allowed band of the structure and secondly in the design of a magnonic crystal with band gaps in an arbitrary part of the spin-wave spectrum.

Spin-wave spectrum of a magnonic crystal with an isolated defect

Real magnonic crystals—periodic magnetic media for spin-wave (magnon) propagation—may contain some defects. We report theoretical spin-wave spectra of a one-dimensional magnonic crystal with an isolated defect. The latter is modeled by insertion of an additional layer with thickness and magnetic anisotropy values different from those of the magnonic crystal constituent layers. The defect layer leads to appearance of several localized defect modes within the magnonic band gaps. The frequency and the number of the defect modes may be controlled by varying parameters of the constituent layers of the magnonic crystal.

Propagation and scattering of spin waves in curved magnonic waveguides

We report a continuous medium theory of dispersion and scattering of spin waves propagating in thin nanowire magnonic waveguides with curved regions. Assuming that the static magnetization is aligned along the waveguide, the curvature leads to a “geometrical” effective magnetic field term that is proportional to the square of the ratio of the exchange length to the radius of curvature of the waveguide. The term is small enough to favor the use of bended nanowire waveguides in planar magnonic data architectures. However, a stronger (multiple) winding (e.g., within helical structures) could enable design of magnonic waveguides with desired properties.

Spin-wave spectrum of an ideal multilayer magnet upon modulation of all parameters of the Landau-Lifshitz equation

The spectrum of exchange spin waves in a multilayer magnet is theoretically investigated without regard for dissipation upon periodic modulation of all magnetic material parameters (uniaxial anisotropy constant, exchange interaction constant, saturation magnetization, gyromagnetic ratio) entering into the Landau-Lifshitz equation. A graphical method is proposed for analyzing the dependence of the propagation of spin waves on the depth of modulation of the material parameters. Practical application of the results obtained and the effect of dissipation on the propagation of spin waves in the system are discussed.

Micromagnetic method of s-parameter characterization of magnonic devices

Designers of nano-scale magnonic devices would benefit from methods of their evaluation that do not require one to access the microscopic level of description or to construct device prototypes. Here, we propose a numerical micromagnetics version of such a method, in which magnonic devices are considered as two-port linear networks and can therefore be described in terms of their s-parameters (i.e., reflection and transmission characteristics). In the micromagnetic model, the sample is composed from a magnonic device-under-test situated between input and output magnonic waveguides. First, dispersion relations and amplitudes of spin waves in the input and output waveguides are calculated from the simulations. The results are then compared to derive the s-parameters of the device-under-test. We use a simple rectangular magnetic nonuniformity, for which analytical results are readily obtained, to evaluate the efficiency and limitations of the technique in the sub-terahertz band.

An effect of the curvature induced anisotropy on the spectrum of spin waves in a curved magnetic nanowire

Within the framework of the solid state theory, an expression for the spectrum of spin waves propagating in a thin magnetic nanowire curled into a helix (spiral) is obtained. Its modification under the effect of a periodic modulation of the helical pitch is analyzed. In particular, it is shown that the periodic modulation of the helix pitch leads to the appearance of band gaps in the spectrum of spin waves. The influence of the modulation depth of the helical pitch on a size of the first gap is considered.

Spectrum of spin waves in a magnonic crystal with a structure defect

Problem of the propagation of spin waves in a one-dimensional magnonic crystal with a structure defect has been analyzed theoretically. As a magnonic crystal, we consider a multilayer magnet representing an infinite system of plane-parallel alternate adjacent exchange-coupled slabs of magnets of two types. As a single structure defect that breaks the translational symmetry of the crystal, we consider a layer that is different from the layers composing the magnonic crystal. A dispersion law for spin-wave modes localized at the defect has been obtained. The appearance of several defect modes in the band gap has been analyzed depending on the parameters of the defect layer.

Investigation of after-action effects in magnetic film by means of STM

Abstract This article presents the result of an STM investigation of after-action effects in magnetic film by a method of normalized scope (the Hurst method). A characteristic relaxation time for the researched materials was calculated.

Modification of surface structure in the magnetic film-magnetic tip system of a scanning tunneling microscope

Abstract This paper reports the results of an experimental investigation of the creation of surface magnetic micro-inhomogeneities in a ferromagnetic material under the influence of an STM magnetic tip. A possible mechanism is proposed which could lead to the formation of these inhomogeneities in the surface structure of the material.