Helical-mode magnetostatic resonances in small ferrite particles and singular metamaterials

Abstract

Small ferrite-disk particles with magnetostatic (magneto-dipole) oscillations are characterized by the topological-phase states-the vortex states. In a recently published paper (Kamenetskii et al 2010 Phys. Rev. A 81 053823), it was shown that such magnetic vortices act as traps, providing purely subwavelength confinement of electromagnetic fields. The symmetry properties of magnetostatic-vortex ferrite disks allow one to propose new-type subwavelength microwave structures. In this paper it is demonstrated that the unique topological properties of the fields in a ferrite disk are intimately related to the symmetry breaking effects of magnetostatic oscillations. This analysis is based on postulates about a physical meaning of the magnetostatic-potential function ψ(r, t) as a complex scalar wavefunction, which presumes a long-range phase coherence in magnetic dipole-dipole interactions. The proper solutions are found based on an analysis of magnetostatic-wave propagation in a helical coordinate system. It is shown that while a composition of two helical waves may acquire a geometrical phase over-running of 2π during a period, every separate helical wave has a dynamical phase over-running of π and so behaves as a double-valued function. This results in the appearance of helical-mode magnetostatic resonances in quasi-2D ferrite disks. The solutions give magnetostatic-wave power-flow-density vortices with cores at the disk center and azimuthally running waves of magnetization. The near fields of magnetostatic-vortex ferrite-disk particles are characterized by space-time symmetry violation. For incident electromagnetic waves, such particles, with sizes much less than the free-space electromagnetic wavelength, appear as local singular regions. From the properties of a composition of magnetostatic-vortex ferrite-disk particles, one may propose novel metamaterials-singular metamaterials.

Novel microwave near-field sensors for material characterization, biology, and nanotechnology

“…Following these results one observes restoration of an entire transmission spectrum when handedness of a sample is changed together with change of direction of a bias magnetic field. As it was shown in Refs [7,20,21], helicity of the near field is originated from double-helix resonances of MDM oscillations in a quasi-2D ferrite disk. For two helical modes, giving a double-helix resonance in a ferrite disk, there is no parity (  ) and time-reversal (  ) invariance -the  -invariance.…”

Magnetic-Dipolar-Mode Oscillations for Near- And Far-Field Manipulation of Microwave Radiation

“…In microwave experiments with quasi-2D ferrite disks, regular multiresonance MDM spectra have been observed [39][40][41][42][43]. A formulation of quasi-Hermitian eigenvalue problem and analytical spectral solutions for MDMs in these thin-film ferrite disks were shown recently [14][15][16][17]. Solutions are propagatingwave scalar functions ψ( r, t).…”

“…Scattering of the EM fields from the MDM-vortex particles is purely topological. For incident EM waves, the vortex topological singularities act as traps, providing strong subwavelength confinement of the microwave fields [17,18]. It appears that a vortex may turn out to generate a "radius of no return", beyond which the incident EM fields falls inevitably towards the vortex singularity.…”

“…Analytically, there are two spectral models for the MDM oscillations in a ferrite disk. These models are based on so-called the Gand L-mode spectral solutions [14][15][16][17][18][19][20][21][22]. The G-modes, are associated with a considered above differential operator G. There are modes with Hermitian Hamiltonian for MS-potential wave functions ψ( r, t).…”

“…There are small ferrite particles with magnetic-dipolar-mode (MDM) [or magnetostatic (MS)] oscillations [13]. In a series of recent publications, it was shown that small ferrite-disk particles may have unique spectral properties of MDM oscillations and the near fields originated from such particles are microwave superchiral fields with strong subwavelength localization of electromagnetic energy [14][15][16][17][18][19][20][21]. Specific long-distance topological properties of these fields are exhibited in the effects of path-dependent interference [22].…”