[en] Published in summary form only

[en] Short communication

[en] There is a time delay between the switch on of the pumping and the time when parametric excitation of spin waves becomes stationary. This time delay is critically dependent on the pumping field, h, and exhibits a critical slowing down behavior near the threshold field h_c. It is very short for pumping fields far beyond the threshold and it approaches infinity as h->h _c from above. We name this time delay as the buildup time. Buildup times and stationary values of spin wave excitations near the instability threshold are calculated numerically. The study is done in the framework of the two-mode model. It is shown that if a finite medium correction term is introduced to the equations of motion the threshold of the pumping field amplitude is below γ/ν where ryγ is the spin wave relaxation rate and v ν is the coupling of the spin wave to the pumping field. The time evolution of the excitation may approach the steady state via oscillations that may last for a very long time. The stationary excitation No, and the buildup time τ_b depend on the pumping power p, and the pumping field h via power laws: No B(p/pc - 1)^δ and τ_b = A(h/h_c - 1)^-Δ =0.5 for the case of an infinite medium and no de-tuning of the mode frequencies from ω_p/2. For modes that are de-tuned from ω_p/2, it is 0.37 for an infinite medium and 0.42 for a finite medium. AΔ = 0.98 for the case of an infinite medium and no de-tuning of the mode. For modes that are de-tuned from ω_p/2, it is 1.06 for an infinite medium and 0.98 for a finite medium. The power law dependence is consistent with experiments but the numerical results for δ and Δ do not agree with experiments

[en] Forbidden magnon scattering from Gd was investigated using polarized neutrons. In contrast to earlier results for itinerant electron ferromagnets, forbidden magnons were not observed for this Heisenberg ferromagnet. This suggests that magnetic short range order is more important in the thermally-induced spin-disordering of the itinerant electron systems

[en] The MF-RPA model for H0₉₀Tb₁₀, developed previously, is utilized for calculating the c-axis spin-wave energies of Ho. The low-temperature spin waves in the conical and helical phases agree well with the experiments of Stringfellow et al. At higher temperatures the calculations indicate that the hexagonal anisotropy still has appreciable effects on the spin waves, studied experimentally by Nicklow

[en] The spectrum of exchange spin waves in a magnonic crystal (periodic magnetic multilayer) with diffuse interfaces is derived for a model with a cosine-like profile of the uniaxial anisotropy value at the interfaces. The dependence of the band gap size upon the interface thickness and the depth of modulation of the anisotropy value is analyzed. In particular, it is shown that diffuse interfaces may lead to a magnonic spectrum in which band gaps have size equal to or even larger than those in the model with sharp (infinitely thin) interfaces (Kronnig-Penney model)

[en] A detailed and quantitative study of the low-temperature spin-wave dynamics was made for the classical Heisenberg-coupled chain using computer simulation. Results for the spin-wave damping rates and the renormalization of the spin-wave frequencies are presented and compared with existing predictions

[en] We study the effects of quantum fluctuations on the dynamical generation of a gap and on the evolution of the spin-wave spectra of a frustrated magnet on a triangular lattice with bond-dependent Ising couplings, analog of the Kitaev honeycomb model. The quantum fluctuations lift the subextensive degeneracy of the classical ground-state manifold by a quantum order-by-disorder mechanism. Nearest-neighbor chains remain decoupled and the surviving discrete degeneracy of the ground state is protected by a hidden model symmetry. We show how the four-spin interaction, emergent from the fluctuations, generates a spin gap shifting the nodal lines of the linear spin-wave spectrum to finite energies.

[en] It is shown that the long-wavelength spin-wave spectrum of antiferromagnetic superconductors differs substantially from the usual spectrum. In the case of an easy-axis anisotropy, the spectrum should have a dip at a finite value of the wave vector

[en] We show, by experiments and micromagnetic simulations in vortex structures, that an active “dual frequency” excitation of both the sub-GHz vortex gyromode and multi-GHz spin waves considerably changes the frequency response of spin wave mediated vortex core reversal. Besides additional minima in the switching threshold, a significant broadband reduction of the switching amplitudes is observed, which can be explained by non-linear interaction between the vortex gyromode and the spin waves. We conclude that the well known frequency spectra of azimuthal spin waves in vortex structures are altered substantially, when the vortex gyromode is actively excited simultaneously