Ferrimagnets possess collinear and noncollinear magnetic phases. Here we identify a crucial influence of the magnetic phase on the excited spin modes. The spin dynamics is launched in a rare-earth iron garnet film by femtosecond laser pulses. The noncollinearity cardinally changes the behavior of spin mode frequencies: the high-frequency one becomes highly sensitive to the external magnetic field while the low-frequency one gets almost field insensitive and even drops with the field growth near the transition to the collinear phase. Near the magnetization compensation point the frequencies of these modes get close to equality.

The ferromagnetic resonance (FMR) spectra of epitaxial yttrium iron garnet films are experimentally studied. The field dependences of the FR frequency are used to determine the effective fields induced by the first and second anisotropy constants and the effective uniaxial anisotropy field. The FMR frequency and linewidth are found to increase in the fields lower than 8 Oe applied in the bismuth-containing film plane. This increase is related to the formation of a nonuniform magnetization distribution, which is supported by a direct magnetooptical observation. The FMR spectra are found to be modulated by a set of narrow lines, the amplitude of which is proportional to the FMR signal intensity. The frequency position of the lines is independent of the magnitude and direction of a dc magnetic field. This modulation is shown to be associated with the resonance excitation of transverse elastic vibration modes. The effective magnetoelastic coupling parameter and the linewidth of the elastic vibrations excited by resonance pumping are estimated.

Ferromagnetic resonance is widely acknowledged as a robust tool for characterizing magnetic materials and studying physical phenomena. Low-temperature magnonics has recently garnered substantial attention; however, it lacks convenient methods for acquiring key magnetic material characteristics. In this study, we introduce a rapid and universal method to determine the temperature dependence of magnetic anisotropy constants of (111)-oriented garnet films using ferromagnetic resonance measurements, demonstrated specifically on the bismuth-substituted iron garnet film grown on a diamagnetic substrate. Our observations reveal a competitive interplay of different anisotropy types as temperature decreases. Notably, the uniaxial magnetic anisotropy constant Ku undergoes a sign change from negative to positive around 120 K, while the anisotropy type remains consistent.

The experimental discovery of the suppression effect of the non-collinear phase in strong magnetic fields near the compensation point in ferrimagnetic structures was made. The observations were carried out using the magneto-optical method by creating a lateral temperature gradient in the plane of the epitaxial films of iron garnets. The non-collinear phase is absent in weak magnetic fields. If an external magnetic field exceeds the first critical value, the non-collinear phase arises near the compensation point. The temperature range of the non-collinear phase expands due to the field increase up to the second critical value. Further field increases conversely reduce the temperature range of the non-collinear phase so that the field above the second critical value causes the disappearance of the non-collinear phase. The effect of the occurrence and suppression of the non-collinear phase is demonstrated on samples of two types of iron garnet films with two and three magnetic sublattices. Phase diagrams of the magnetic states in the vicinity of the critical point are constructed, and it is shown that the region of existence of the non-collinear phase in a two-sublattice magnet is smaller than in a three-sublattice one.

Low-field ferromagnetic resonance in garnet ferrite epitaxial films of different composition with easy-plane anisotropy has been investigated. In ferromagnetic resonance spectra obtained by frequency sweeping, the modulation of the spectral line intensity by a set of narrow (about 100 kHz wide) lines equidistant in frequency has been observed. The lines are spaced in accordance with the resonance of the standing modes of transverse elastic vibrations along the thickness of the film–substrate structure. The modulation depth decreases with rising frequency, since the magnetoelastic coupling depends on the frequency of the elastic vibration mode. In some samples, the modulation depth drops monotonically, whereas in others it oscillates. Such behavior is explained by strong and weak spin pinning on the surface, respectively. The influence of the film–substrate interface and the hybridization of spin-wave and elastic vibration modes under magnetoacoustic resonance conditions have been discussed.