M. P. Tikhomirova

‘‘Exchange’’ spin waves in nonuniform yttrium iron garnet films

Spin wave resonance spectra have been observed in yttrium iron garnet films. The spectra exhibit as many as 120 strongly excited modes with large deviation from quadratic spacing, which are interpreted in terms of a thickness variation of the effective magnetization 4πM(x) depending both on the magnetization and the anisotropy field. Profiles of 4πM(x) are calculated from the spectra measured both in parallel and in perpendicular bias magnetic fields. It has been shown that the films tested have monotonic variations of the effective magnetization. The difference 4πΔM between upper and lower 4πM(x) values is as large as 330 G. It is shown that exchange‐dominated spin waves (ESW) with the maximum wave number of 2.5×105 cm−1 have been excited under experiment conditions. Microwave pulse delay due to ESW propagation across the film thickness has been observed. Delay versus frequency characteristics strongly depend on the profile M(x) and the direction of the applied magnetic field. Profiles M(x) have been calculated to provide both constant and linear delay‐versus‐frequency characteristics.

Principal Mode of the Nonlinear Spin-Wave Resonance in Perpendicular Magnetized Ferrite Films

The paper reports a theoretical and experimental study of the nonlinear spin-wave resonance (SWR) modes in normally magnetized ferrite films. Particular attention is focused on the principal, lowest frequency, SWR mode. It is shown theoretically that, as the precession amplitude increases, the profile of the principal mode changes to make the excitation distribution across the film thickness more uniform. The nonlinear shift of the resonance field depends on the surface-spin pinning parameters. An experimental study has been made of YIG films with a strong uniaxial anisotropy field gradient over the film thickness, as well as of YIG films of submicron thickness. As the microwave power was increased, the principal-mode resonance field was observed undergoing a sublinear shift accompanied by a superlinear growth of absorbed power. This behavior is attributed to a change in the profile of the spatial distribution of ac magnetization.

Magnetoelastic interaction in yttrium iron garnet films with magnetic inhomogeneities through the film thickness

Experimental study of the spin‐wave resonance (SWR) spectrum of a nonuniform yttrium iron garnet (YIG) film has revealed an existence of sharp disturbances inside the spectrum. The experiments were carried out at frequency range 4–12 GHz. The observation has been attributed to excitation of acoustic waves. The interpretation follows from the facts that (1) nonuniformity of magnetic parameters across the thickness of the tested film results in effective excitation of spin waves; and (2) coincidence of phase velocities of the spin waves and the transverse acoustic waves leads to partial power, transforming from the magnetic into the elastic system.

Nonlinear spin wave resonance modes

Nonlinear spin wave resonance modes of magnetic films are studied both theoretically and experimentally. In the theoretical analysis the normal modes with arbitrary amplitudes are studied for a film magnetized perpendicular to its plane. The film is assumed to be uniform apart from a layer close to the surfaces, where the spins may be pinned. The spin wave resonance mode of the lowest frequency (principal mode) is considered in detail for the film with arbitrary surface spin pinning. The mode profile changes with increasing amplitude trying to redistribute itself in a more uniform manner across the film thickness. The nonlinear shift of the resonance field depends critically on the pinning. In experiments, we use yttrium–iron–garnet films with a strong gradient in the anisotropy field across the film thickness. With increasing pump power, the principal mode shows a sublinear shift of the resonance field and superlinear growth in the absorption amplitude. These features are explained in terms of the spatia...

Interaction of Exchange Spin Waves with Transversal and Longitudinal Hypersound in Ferrite Films with Magnetic Inhomogeneity

In [1,2] we reported the possibility of effective excitation of hypersound with the use of yttrium iron garnet (YIG) films having smooth variation in the anisotropy field across the film thickness. Effective excitation of the transverse acoustic wave has been demonstrated at frequencies from 2.5 to 16 GHz. An idea of such an acoustic transducer is based on the fact that inhomogeneity of the magnetic medium allows to excite an exchange spin wave (ESW) with a short wavelength. Magnetoelastic interaction between the ESW and an acoustic wave (AW), is most strong when spin and acoustic waves are synchronous, that is, the wave number q of ESW equals to the wave number of AW. At microwave frequencies (ω/2π = 1–20 GHz), the typical value of q at the point of synchronism is of the order of 105 cm-1. A direct linear excitation of short-wavelength spin waves in a homogeneous medium is difficult because of big difference in wave numbers between the ESW (q ∼ 105 cm-1) and the electromagnetic wave (qEMW ∼ 10 cm-1). If the magnetic medium is inhomogeneous, then q depends on coordinate, thus, one can efficiently excite a spin wave in a region of quasi-uniform ferromagnetic resonance, where q ∼ 0 and, at the same time, provide the condition of synchronism in a region where q is equal to the wave number of acoustic wave. The forward and reverse conversion of spin and acoustic waves at the point of synchronism was observed previously in experiments with YIG rods and studied theoretically in [3]. The origin of nonuniformity was the demagnetisation field existing at the end of a magnetised YIG rod.