Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
Abstract
The wave solutions of the Landau–Lifshitz equation (spin waves) are characterized by some of the most
complex and peculiar dispersion relations among all waves. For example, the spin-wave (“magnonic”) dispersion
can range from the parabolic law (typical for a quantum-mechanical electron) at short wavelengths to the
nonanalytical linear type (typical for light and acoustic phonons) at long wavelengths. Moreover, the longwavelength
magnonic dispersion has a gap and is inherently anisotropic, being naturally negative for a range of
relative orientations between the effective field and the spin-wave wave vector. Nonuniformities in the effective
field and magnetization configurations enable the guiding and steering of spin waves in a deliberate manner and
therefore represent landscapes of graded refractive index (graded magnonic index). By analogy to the fields of
graded-index photonics and transformation optics, the studies of spin waves in graded magnonic landscapes can
be united under the umbrella of the graded-index magnonics theme and are reviewed here with focus on the challenges
and opportunities ahead of this exciting research direction
