Background and Objectives: One of the main tasks for developing magnonic devices is to form and control spin wave beams. For this purpose, the decoration of ferrite films with magnetic or non-magnetic metal areas can be used. The aim of this work is to study the peculiarities of magnetostatic surface wave (MSSW) propagation in the channels formed in yttrium-iron garnet (YIG) films by deposition of 1.5 μm thick metal decorations from chromium (Cr) and permalloy (Py). Materials and Methods: Studied samples were fabricated on the base of 6.5 μm-thick epitaxial YIG film by the DC magnetron sputtering, photolithography, and ion etching techniques. Frequency dependencies of magnitude and phase of the transmitted MSSW signal at different applied magnetic field were measured with the help of a vector network analyzer and a microwave probe station. Calculation of the dispersions and insertion losses for MSSW propagating in the metallized YIG film was performed on the basis of Maxwell’s equations in the magnetostatic approximation, the Landau-Lifshitz equation, and standard electrodynamic boundary conditions. Results and Conclusion: The optimal channel width w relative to the antenna aperture providing channeling of the MSSW signal with the possibility of “antireflective effect” for the transmitted signal has been found to be w = 200 μm. It has been shown that for the formation of channeling effect, one needs to use a non-magnetic metal with the thickness leading to a transition to the “metallic” branch of the MSSW dispersion or a magnetic metal with the thickness resulting in bending of a short-wavelength part of MSSW dispersion. For the studied samples, it is d(Cr) = 1.5 μm and d(Py) = 30 nm, respectively. The obtained results demonstrate the possibility of using the channels in metallic decorations for the formation of directed spin wave beams.

Experimental results on the magnetostatic surface wave (MSSW) propagation in an yttrium-iron garnet film with a periodical array of metal stripes on the surface are presented. An effect of the pass bands formation in the MSSW transmission characteristics contrasting to the known Bragg stop bands inherent in a periodical structure is reported and discussed. Our findings provide one more way to affect the spin wave propagation and realize a control in magnonic devices.

Background and Objectives: Layered structures based on ferrite and metal films are actively studied in magnonics. Usually, the effects associated with the finite conductivity of the metal are not taken into account. The aim of this work was to investigate the influence of the thickness of a metal with finite conductivity on the dispersion and damping of a magnetostatic backward volume wave (MSBVW) in the ferrite-metal and ferrite-insulator-metal structures. Materials and Methods: The dispersion equation for MSBVW was derived using Maxwell’s equations in the magnetostatic approximation, the Landau-Lifshitz equation, and standard electrodynamic boundary conditions. Calculations were performed for the structures based on yttrium iron garnet (YIG) films with metal resistivity characteristic of silver, indium, and copper. Results of the calculation we compared with results of an experiment on MSBVW propagation in a YIG film metallized by copper performed using a vector network analyzer and microstrip antennas for excitation and detection of the MSBVW. Results and Conclusions: It was found that, the metallization always suppresses MSBVW propagation, and at metal thicknesses t ≥ 10 nm, the ohmic losses due to the metal significantly exceed the intrinsic magnetic losses in the ferrite. It was also shown that the gap between the ferrite and metal can be used to suppress the long-wavelength part of the MSBVW spectrum.

With the help of micromagnetic modeling, we considered particularities of dispersions and amplitude-frequency response of spin waves in a magnonic crystal (MC) formed by etching an array of grooves in the surface of yttrium iron garnet film having linear distribution of magnetization across the thickness from 1.7 kG at the upper surface till 2.02 kG at the bottom. For the geometry of surface magnetostatic spin waves (MSSW), it is shown that nonuniformity of magnetization distribution across the thickness leads to the appearance of frequency regions in the MC spectrum where MSSW propagation is unidirectional and, as the consequence, does not have Bragg resonances. It was also demonstrated that the MC spectrum is determined by the choice of surface used for the formation of the array of grooves. Keywords: spin wave, micromagnetic modelling, film of yttrium iron garnet, magnonic crystal.

The results of study of bias voltage Ub and substrate temperature Ts influence on the texture of FeCo films with the thickness of 180 nm deposited on Si/SiO2 substrates by DC magnetron sputtering are presented. It is shown that the change of Ub from -250 V to 80 V leads to the growth of films with (110) texture. Further change of Ub from 80 V to 250 V causes the growth of films having (200) texture. Films deposited at Ub=0 and Ts=60-300oC have (200) texture. Further increase of Ts results in the change of film texture to (110). Keywords: FeCo films, magnetron sputtering, texture, coercitivity.

With the help of micromagnetic modeling, we considered particularities of dispersions and amplitude-frequency response of spin waves in a magnonic crystal (MC) formed by etching an array of grooves in the surface of yttrium iron garnet film having linear distribution of magnetization across the thickness from 1.7 kG at the upper surface till 2.02 kG at the bottom. For the geometry of surface magnetostatic spin waves (MSSW), it is shown that nonuniformity of magnetization distribution across the thickness leads to the appearance of frequency regions in the MC spectrum where MSSW propagation is unidirectional and, as the consequence, does not have Bragg resonances. It was also demonstrated that the MC spectrum is determined by the choice of surface used for the formation of the array of grooves.

The results of study of bias voltage Ub and substrate temperature Ts influence on the texture of FeCo films with the thickness of 180 nm deposited on Si/SiO2 substrates by DC magnetron sputtering are presented. It is shown that the change of Ub from -250 V to ~ 80 V leads to the growth of films with (110) texture. Further change of Ub from 80 V to 250 V causes the growth of films having (200) texture. Films deposited at Ub = 0 and Ts = 60º – 300º C have (200) texture. Further increase of Ts results in the change of film texture to (110).

Influence of the bias voltage Ub and the deposition rate  on the structure, grain size D, and coercivity Hc of NiFe films with the thickness d from 30 to 980 nm, grown onto Si / SiO2 substrates by DC magnetron sputtering, was studied. In the case Ub = 0, the decrease of  from ≈ nm/min to ≈ 7 nm/min is accompanied by the increase of the critical film thickness dcr from dcr ≈ 220 nm to dcr ≈ 270 nm. In this case, Hc in the films with d < dcr is characterized by the dependence Hc ~ D6 and varies from ~ 1 to ~ 20 Oe. In the case of Ub = -100 V, the effect of the deposition rate on the coercivity is much more noticeable. At ν = 7 and 14 nm / min, the films demonstrate soft magnetic properties (Нс ≈ 0.15 - 1.4 Oe) and the absence of dcr for the entire range of studied thicknesses. The films obtained at ν = 21 and 27 nm / min turn into the “supercritical” state at d ≥ dcr ≈ 520 nm, and, in the region d < dcr, they are characterized by the dependence Hc ~ D3 and by the increase of coercivity from ~ 0.35 to ~ 10 Oe.

The effect of elastic deformations on the ferromagnetic resonance spectrum of submicron polycrystalline films of yttrium iron garnet obtained by ion-beam sputtering on silicon and gallium arsenide substrates was studied. Magnetoelastic constants of the films on both substrates were calculated using the magnitude of the frequency shift of the absorption maximum in the ferromagnetic resonance spectrum. The value of constants did not exceed 16% of the known values for bulk polycrystalline garnet. The approach to increase the efficiency of electrical frequency tuning in composite multiferroic structures based on combination of static and dynamic (caused by the piezoelectric effect) deformations was proposed.

© А.С. Джумалиев, Ю.В. Никулин, Ю.А. Филимонов 1,2,3 1 Саратовский филиал Института радиотехники и электроники им. В.А. Котельникова РАН, 410019 Саратов, Россия 2 Саратовский национальный исследовательский государственный университет им. Н.Г. Чернышевского, 410012 Саратов, Россия 3 Саратовский государственный технический университет им. Ю.А. Гагарина, 410054 Саратов, Россия е-mail: yvnikulin@gmail.com

AbstractWe have studied the filtration of surface spin waves in yttrium iron garnet (YIG) films of variable width excited by focusing transducers integrated with the film.

The ferromagnetic resonance spectrum at a frequency of ~9.85 GHz for an in-plane magnetized 2D square lattice with the unit cell parameter а ≈ 15 μm consisting of orthogonal microwaveguides with a width of w ≈ 5 μm on the basis of a permalloy film with thickness of d ≈ 90 nm has been experimentally and numerically investigated. It is shown that upon variation in the angle θ between the magnetic field direction and the unit cell axis, the total spectrum of spin-wave excitations of the lattice can be presented as a superposition of the spectra of separate permalloy microstrips magnetized at angles θ and π/2–θ and regions corresponding to the lattice nodes. It has been found that, in the case of magnetization along the lattice diagonal (θ ≈ 45о), excitations localized at the lattice nodes dominate in the spectrum, whereas, at θ ≈ 0 and 90°, the main contribution is made by excitations localized mainly on the microwaveguide segments between the lattice nodes; at θ ≈ 10°–13° and 18–20°, “repulsion” of absorption lines in the spectrum is observed.

We have studied the filtration of surface spin waves in yttrium iron garnet (YIG) films of variable width excited by focusing transducers integrated with the film.

The influence of argon pressure P (0.13 ≤ P ≤ 1 Pa) and vacuum annealing on the microstructure and texture of d ≈ 300 nm thick cobalt films magnetron-sputtered on a SiO2/Si substrate has been investigated. It has been shown that the films deposited at 0.26 ≤ P < 1 Pa have a columnar microstructure with a mixed hcp-Co(002)/fcc-Co(111) phase. Annealing results in a more uniform microstructure owing to the grain size growth and improves the hcp-Co(002)/fcc-Co(111) texture. The films deposited at 0.13 ≤ P < 0.18 Pa have a mixed crystalline phase: the hcp-Co(002)/fcc-Co(111) and hcp-Co(101) phases coexist with an fcc crystalline phase and fcc-Co(200) texture. Finally, films grown at P ≈ 0.13 Pa are characterized by the fcc-Co(200) texture, and their microstructure is nonuniform over the thickness: at the film–substrate interface, there exists a dc ≈ 100–130 nm thick layer with a quasi-uniform microstructure, which becomes granulated at d > dc. Annealing results in a more uniform microstructure of these films due to grain growth, improves the fcc-Co(200) texture, and causes the appearance of the fcc-Co(111)/hcp-Co(002) phase.

Effect of argon pressure 0.09 ≤ P ≤ 1 Pa on the microcrystalline structure and magnetic properties of the cobalt films with a thickness of d ≈ 300 nm that are fabricated with the aid of magnetic sputtering on the SiO2/Si substrates is studied. It is demonstrated that the films obtained at a pressure of Р ≥ 0.2 Pa exhibit mixed crystal phase with close-packed hexagonal (CPH) and face-centered cubic (FCC) lattice with the CPH–Co(002)/FCC–Co(111) texture and column microstructure over thickness. The films deposited at a pressure of Р ≈ 0.09 Pa are characterized by the dominant FCC crystal phase with the FCC–Со(200) texture and inhomogeneous microstructure over thickness: at the interface with the substrate in a layer with a thickness of d1 ≈ 150 nm, the films exhibit quasi-homogeneous microstructure that is transformed into the granulated microstructure at d > d1. The films deposited at a pressure of Р ≈ 0.09 Pa have the saturation magnetization that is higher by 30% and the coercive force and linewidth of ferromagnetic resonance that are several times less than those of the film obtained at a pressure of Р ≈ 1 Pa.