37 research outputs found
Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films
A magnetostatic spin wave analog of integer quantum Hall (IQH) state is
proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape
anisotropy, magnetic moments in a thin film lie within the plane, while all
spin-wave excitations are fully gapped. Under an out-of-plane magnetic field,
the film acquires a finite magnetization, where some of the gapped magnons
become significantly softened near a saturation field. It is shown that, owing
to a spin-orbit locking nature of the magnetic dipolar interaction, these soft
spin-wave volume-mode bands become chiral volume-mode bands with finite
topological Chern integers. A bulk-edge correspondence in IQH physics suggests
that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave
edge mode. The existence of the edge mode is justified both by micromagnetic
simulations and by band calculations based on a linearized Landau-Lifshitz
equation. Employing intuitive physical arguments, we introduce proper
tight-binding models for these soft volume-mode bands. Based on the
tight-binding models, we further discuss possible applications to other systems
such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).Comment: 20 pages, 12 figure
Chiral spin-wave edge modes in dipolar magnetic thin films
Based on a linearized Landau-Lifshitz equation, we show that two-dimensional
periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole
interactions supports chiral spin-wave edge modes, when subjected under the
magnetic field applied perpendicular to the plane. The mode propagates along a
one-dimensional boundary of the system in a unidirectional way and it always
has a chiral dispersion within a band gap for spin-wave volume modes. Contrary
to the well-known Damon-Eshbach surface mode, the sense of the rotation depends
not only on the direction of the field but also on the strength of the field;
its chiral direction is generally determined by the sum of the so-called Chern
integers defined for spin-wave volume modes below the band gap. Using simple
tight-binding descriptions, we explain how the magnetic dipolar interaction
endows spin-wave volume modes with non-zero Chern integers and how their values
will be changed by the field.Comment: 18 pages, 16 figures, some trivial typo in equations are fixe