Sergej O. Demokritov

We show experimentally and by numerical simulations that spin waves propagating in a magnetic film can pass through a region of a magnetic field inhomogeneity or they can be reflected by the region depending on the sign of the inhomogeneity. If the reflecting region is narrow enough, spin-wave tunneling takes place. We investigate the tunneling mechanism and demonstrate that it has a magnetic dipole origin.

The experimental observation of self-generation of two-dimensional, self-focusing nonlinear spin wave packets—spin wave bullets—in an active ring is reported. The ring is composed of a ferrite film with two antennae for excitation and detection of the wave packets, and a microwave amplifier connecting the antennae and closing the ring. Experimental observation has been made by using the time and space resolved Brillouin light scattering technique. The parameters of spin wave bullets self-generated from noise in an active ring are similar to those of bullets coherently excited by external microwave pulses. The observed self-generation process provides unambiguous evidence that wave bullets are intrinsic excitations of a two-dimensional nonlinear medium with dissipation that is focusing in both directions.

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We show experimentally and by model calculations that in finite, nonellipsoidal, micrometer size magnetic thin film elements the dynamic magnetic eigenexcitations (spin waves) may exhibit strong spatial localization. This localization is due to the formation of a potential well for spin waves in the highly inhomogeneous internal magnetic field within the element.

An advanced space- and time-resolved Brillouin light-scattering technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigation of two-dimensional spin-wave propagation with high spatial and temporal resolution. Linear effects, such as the unidirectional excitation of magnetostatic surface waves and the propagation of backward volume magnetostatic waves (BVMSW) in two preferential directions due to the noncollinearity of their phase and group velocities, are investigated in detail. In the nonlinear regime, stationary and nonstationary self-focusing effects are studied. It is shown that nonlinear evolution of a stationary BVMSW beam, having a finite transverse aperture, leads to self-focusing of the beam at one spatial point. Evolution of a finite-duration (nonstationary) BVMSW pulse leads to space-time self-focusing and formation of a strongly localized two-dimensional wave packet (spin-wave bullet). Theoretical modeling of the self-focusing and diffraction processes by using a variational approach and direct numerical integration of the two-dimensional nonlinear Schrödinger equation provides a good qualitative description of the observed phenomena.