Yu. V. Khivintsev

Standing spin waves in magnonic crystals

The features of standing spin waves (SWs) excited during ferromagnetic resonance in three different one-dimensional magnonic crystals (MC) are intensively studied. The investigated magnonic crystals were: an array of air-spaced cobalt stripes, an array of air-spaced permalloy (Py) stripes, and a bi-component MC composed of alternating Co and Py stripes. All MC structures were made by etching technique from Co and Py thin films deposited onto Si substrates. Two configurations are considered with the in-plane external magnetic field applied parallel or perpendicular to the stripes. The supporting calculations are performed by the finite element method in the frequency domain. A number of intensive SW modes occurred in periodic structures under ferromagnetic resonance conditions as a consequence of standing spin waves excitation. These modes were analyzed theoretically in order to explain the origins of SW excitations. With the support of numerical calculations, we analyze also the possible scenarios for the occurrence of standing SWs in the investigated structures. It is demonstrated that the SW propagation length is an important factor conditioning the standing SW formation in MCs.

Ferromagnetic resonance in submicron permalloy stripes

Abstract We present systematic experimental investigation and micromagnetic simulation of ferromagnetic resonance (FMR) in planar rectangular permalloy microstripes. The experimental microwave absorption was studied for different sample orientations in an external magnetic field. To analyze the FMR modes we developed the algorithm for the simulation of spectrum and spatial distribution of magnetization oscillations in dependence on swept external magnetic field based on numerical solution of Landau-Lifshitz-Gilbert equation. It was shown good agreement between experimental and model FMR spectra that enables the reliable visualization for spatial distributions of oscillating magnetization in modes of spin-wave resonances for different excitation conditions.

Hybridization of spin-wave modes in a ferromagnetic microstrip

The dependence of the spectrum of spin-wave modes (SWMs) in a permalloy microstrip on the angle θ between the microstrip axis and the direction of the in-plane bias magnetic field has been studied with the use of ferromagnetic resonance at a frequency of 9.85 GHz. Hybridization between the quasi-homogeneous SWM and weakly localized SWM, which manifests itself as the repulsion of absorption lines of the microstrip spectrum, has been discovered at the angle θ ≈ 70°. The experimental results are in fair agreement with the numerically calculated SWM spectrum.

Surface spin waves in one-dimensional magnonic crystals with two spatial periods

We have experimentally studied the propagation of spin surface waves (SSWs) in a one-dimensional magnonic crystal comprising two planar periodic structures—a lattice of grooves etched on the surface of an yttrium iron garnet (YIG) film and a lattice of metal stripes, separated by a dielectric spacer. It is established that the frequency dependence of the SSW transmission coefficient depends on the overlap of bandgaps determined by the Bragg resonances of SSWs on both lattices and can be modified by changing the mutual orientation of wave vectors of the two lattices and/or the dielectric spacer thickness.

Magnetoelastic waves in an in-plane magnetized ferromagnetic plate

The spectrum of magnetoelastic waves propagating along the magnetic field in an in-plane magnetized ferromagnetic plate is numerically investigated in the exchangeless approximation. No restrictions are imposed either on the field pattern of backward volume magnetostatic waves (BVMSWs) or elastic waves supported by a plate of a given geometry across the plate or on the relationship between the sound velocity vS and the phase velocity of the magnetoelastic waves v=ω/q (ω is the frequency, q is the wave number). The resonance interaction of the BVMSWs and elastic waves is accompanied, as a rule, by the formation of “stop” bands δω that are proportional to the magnetoelastic coupling constant b. When the BVMSWs are in resonance with Lamb and shear elastic modes the values of the magnetoelastic gaps δω at v≈vS turn out to be of the same order. For v≫vS, the efficiency of the interaction between the BVMSWs and transverse Lamb modes is almost one order of magnitude higher. If the frequency spacing Δω between the elastic modes is smaller than the mag-netoelastic gap in the spectrum (Δω≤δω), which takes place, particularly, in the region of crowding the elastic mode spectrum (v≈vS), the resonant interaction results in mixing the dispersion laws for the elastic modes. Namely, a surface mode may transform into a volume one and a shear mode, into the Lamb mode or into a shear mode with another number. The resonance interaction of the shear and Lamb elastic modes not only forms the magnetoelastic gaps δω∼b2 but also changes the efficiency of elastic wave coupling with the magnetic subsystem. This may show up as the coexistence of the effects of “repulsing” both the dispersion laws and the damping decrements of the elastic waves at the resonance frequency. It is shown that magnetostriction splits the cutoff frequencies of both transverse Lamb modes and shear modes, as well as the long-wave (q → 0) frequency limits f0 of the BVMSW modes. This may cause the resonance interaction between BVMSW modes of equal evenness in a narrow frequency band Δ∼b near f0.

Magnetoelastic Waves in Submicron Yttrium–Iron Garnet Films Manufactured by Means of Ion-Beam Sputtering onto Gadolinium–Gallium Garnet Substrates

A series of equidistant oscillations have been revealed in the transmission spectrum and dispersion law of Damon–Eshbach surface magnetostatic waves (SMSWs) propagating in submicron (200-nm) yttrium–iron garnet (YIG) films manufactured by means of ion-beam sputtering onto gadolinium–gallium garnet (GGG) substrates. These oscillations correspond to the excitation of magnetoelastic waves in the YIG–GGG structure at frequencies of resonant interaction between the surface magnetostatic waves and the elastic shear modes of the wave-guiding YIG–GGG structure. The obtained results show that the studied YIG films are characterized by an efficient magnetoelastic coupling between their spin and elastic subsystems and the matching of acoustic impedances at the YIG–GGG interface, thus providing the possibility to consider the ion-beam sputtering of YIG films onto GGG substrates as a promising technology for the creation of magnonic and straintronic devices.

Investigation of influence of different parameters on results of probe oxidation

Fabrication of nanosized lines on magnetic films is of special interest because such lines can be used as nanosized elements for fabrication of planar tunnel junctions [1] or periodic planar structures that can serve as surface phononic crystal (SPC) for hypersonic frequency range that could be controlled by magnetic field [2]. Probe oxidation is one of the perspective tools to create such nanostructures. It is based on the electrochemical reaction of oxidation in the water meniscus under the sharp tip of the atomic force microscope (AFM). The reaction is stimulated by applied voltage between the tip and the sample [3]. There are only few works on probe oxidation of Ni [1, 4-5] and FeCo films [5]. But there is no investigation on influence of wide range of parameters on oxidation results. In this work investigation of dependences of probe oxidation of ferromagnetic metal films Ni and FeCo on different probe oxidation parameters is presented. Definition of optimal process parameters for fabrication structures with certain sizes was done.

Fabrication of tunnel barrier by scanning probe lithography

Atomic force microscope was used to fabricate nano oxide line crossing nickel microstructure. After oxidation current-voltage characteristics of the structure showed tunnel barrier behavior.

Fabrication of magnetic nanostructures using atomic force microscopy

Local anodic oxidation (LAO) of nickel, iron and cobalt films is experimentally studied. Most easy and efficient oxidation was found for iron where as the best repeatability was achieved for nickel films in the experiment. Threshold and optimal parameters for LAO on nickel and iron were determined.

Permalloy films on patterned silicon substrates

In this paper we study effect of patterning for ferromagnetic films in the case of deposition of continuous films on pre-patterned substrates. Striped structures with the different profile depth were fabricated using photolithography, ion etching and magnetron sputtering. Magnetic force microscopy (MFM), vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) were applied to characterize the structures. Obtained results show that such patterned ferromagnetic structures can be interesting in a sense of application in planar microwave devices based on ferromagnetic films (such as notch filters, for example) for busting operational frequency in the case when magnetic filling factor (amount of the magnetic material interacting with microwaves) is important.