Surface Magnetic Polaritons Research Articles

Magnetic polaritons in metamagnet thin films

We investigate the magnetic polariton modes which propagate in metamagnet thin films, consisting of ferromagnetically ordered layers, with the intralayer ferromagnetic exchange interactions being much stronger than the weak antiferromagnetic interaction between adjacent layers. We consider also the presence of an external magnetic field H 0 applied perpendicular to the layers. We confine our discussion to the metamagnet materials FeCl 2 and FeBr 2 in which the magnetic anisotropy is sufficiently large compared with the weak antiferromagnetic coupling, so that there is no spin-flop phase intermediate between the AFM and FM phases. The dynamic response of a metamagnetic material is derived within the classical torque equation of motion model. Our theoretical results indicate that there is a larger frequency separation in FeBr 2, compared with FeCl 2 in the surface magnetic polariton spectra, which favor the former material for experimental studies.

Spin canted magnetic polaritons in thin films

We study the bulk and surface magnetic polariton modes that propagate in thin antiferromagnetic films, whose thickness is much larger than the interatomic distances. We consider the presence of an external magnetic field applied perpendicular to the easy axis of the magnetic material. The presence of this field gives rise to an interesting geometry where the spins are rotated through a canting angle θ. The magnetic polariton spectra are presented numerically for a variety of layering patterns, with interesting profiles. We confine our discussion to uniaxial antiferromagnets fluorides which have a body-centered tetragonal (or rutile) structure (e.g. XF 2, with X=Mn or Fe).

Magnetic polaritons at the junctions of magnetic superlattice and magnetic material

Surface magnetic polaritons localized at the junction of the magnetic superlattice and the magnetic material are discussed using electromagnetic wave theory in the Voigt configuration. The dispersion equation for localized magnetic polaritons are derived in the long-wavelength limit. The dispersion curves are calculated numerically and given at some typical values.

New Mechanism of a Surface Magnetic Polaritons Formation in Magnet with the Linear Magnetoelectric Effect

It is shown that in the frame of the phenomenological approach the most complete calculation of the spatial dispersion effect allows to predict some new types of the surface magnetic TM and EH surface polariton in the magnetic crystal with the linear magnetoelectric interaction.

A new class of surface magnetic TM polaritons in crystals with linear magnetoelectric effect

The conditions necessary for the formation of a new type of a surface magnetic TM polariton at the magnetic dielectric-nonmagnetic metal or the magnetic dielectric-nomagnetic dielectric interfaces are determined. The formation of a surface electromagnetic wave of this type is caused by the effect of spatial dispersion of a magnetic dielectric medium.

Scattering of surface magnetic polaritons rom order-parameter fluctuations near second-order magnetic phase transitions

A study is reported of the scattering of surface magnetic polaritons in the vicinity of second-order spin-reorientational phase transitions, which is caused by spatial fluctuations of the order parameter. A four-sublattice antiferromagnet α-Fe2O3 is used as an example to derive expressions for the vacuum-scattered radiation near exchange magnetic-vibration frequencies. The scattering of surface magnetic polaritons is shown to be resonantly enhanced in characteristic regions of their spectrum. Estimates made for α-Fe2O3 indicate a possibility of experimental observation of surface magnetic-polariton scattering from fluctuations of the refractive index near second-order spin-reorientational phase transitions.

A high-resolution Fourier transform spectrometer for far infrared magneto-optic spectroscopy of magnetic materials

We describe a high-resolution (0.015 cm −1) Fourier transform spectrometer which has been developed to investigate bulk and surface magnetic polaritons in magnetic media by far infrared magneto-optic spectroscopy. The spectrometer uses a novel combination of laser-controlled sampling of the interferogram and phase modulation of the infrared beam to combine very accurate sampling and low signal-to-noise ratio. The spectrometer is coupled to a liquid helium cryostat with a 7 T superconducting magnet, and a liquid helium-cooled silicon bolometer is used as the detector. Samples can be mounted in the cryostat for polarised oblique incidence reflection measurements in the Voigt geometry with the applied magnetic field vertical. Measurements on surface polaritons are made by using attenuated total reflection (ATR) spectroscopy with silicon prisms to obtain the necessary wave vector enhancement. The resolution of the instrument is demonstrated with measurements on the rotational lines of water vapour, and a selection of measurements on a bulk single crystal of FeF 2, a uniaxial antiferromagnet, is presented to illustrate the performance of the instrument as a probe of magnetic excitations.

Self-localized nonlinear surface magnetic polaritons in a ferromagnetic medium

The properties of electromagnetic waves propagating in a semibounded, nonlinear, ferromagnetic medium are investigated. It is shown that under certain conditions the interaction between the spin and electromagnetic waves results in the localization of volume polaritons near the surface. Self-localization of surface polaritons due to the nonlinear properties of the medium occurs thereby. The nonlinear Schrodinger equation for nonlinear surface and volume polaritons is derived, and the conditions under which solitons of these waves exist are determined. The wave intensity required to observe the predicted effects is estimated.

Nonlinear surface magnetic polaritons in a nonuniform magnetic field

High-frequency surface magnetic polaritons of finite amplitude propagating along the interface between a ferrite and a nonlinear insulator in a weakly nonuniform, shaft-shaped external magnetic field are investigated theoretically. The analysis is based on employment of the variational method together with bilinear relations having the form of Lorentz’s lemma. It is shown that the wave dispersion and the transverse profile of a wave along the field nonuniformity depend significantly on the amplitude of the wave.

Theory of far-infrared attenuated total reflection from surface magnetic polaritons in rare-earth superlattices

We present a theory for the attenuated total reflection (ATR) spectra to probe surface magnetic polaritons that propagate in semi-infinite superlattices made up of a rare-earth material intercalated by a nonmagnetic layer. We consider both the spiral and the cone states of the rare-earth constituent, apart from its simple ferromagnetic (antiferromagnetic) alignment due to the nearest (next-nearest) exchange coupling. We use the framework of the effective medium theory to determine the magnetic polariton’s dispersion relation, since it is very suitable to explain experimental observations of excitations in the far-infrared. Numerical results are presented to illustrate the ATR spectra, with emphasis in the surface polariton’s nonreciprocal aspect shown in the cone state of the rare-earth material.

Experimental determination of magnetic polariton dispersion curves inFeF2

A series of high-resolution attenuated total reflection and reflectivity measurements in the far infrared are used to obtain experimental dispersion curves for bulk and surface magnetic polaritons in uniaxial antiferromagnets. In addition to bulk and surface modes, the individual spectra also allow identification of, to the best of our knowledge, previously unseen surface resonances. The spectra also show huge nonreciprocity in infrared reflectivity at low fields, a feature unique to magnetic systems.

Experimental observation of magnetic surface polaritons in FeF2 by attenuated total reflection.

We present the first direct experimental evidence for the existence of magnetic surface polaritons in a uniaxial antiferromagnet. The modes are excited in Fe${\mathrm{F}}_{2}$ by attenuated total reflection with the uniaxis along an applied magnetic field ${H}_{0}$. The resonance is observed as an attenuation of the reflected intensity as the frequency of the far-infrared beam is scanned. We find nonreciprocity between the $+{H}_{0}$ and $\ensuremath{-}{H}_{0}$ spectra as a consequence of the nonreciprocity of the surface polariton modes when ${H}_{0}$ is introduced. We also observe broad dips due to the excitation of bulk modes.

Theory of far-infrared reflectivity and surface magnetic polaritons of rare-earth magnets

We derive expressions for oblique-incidence reflectivity of bulk and thin-film rare-earth magnets with helical magnetic orderings (spiral and cone states) in the far-infrared frequency region. The main question that is addressed is whether the high metallic reflectivity precludes detection of magnetic features. Significant dips are found at the magnetic resonance frequencies and nonreciprocal reflection can be seen in the spectra. The magnitudes of the dips depend on the magnon damping, which is unknown, but for likely values the dips are about at the limit of experimental detectability. Dispersion curves of surface magnetic polaritons on a semi-infinite rare earth in the Voigt geometry are presented for both spiral and cone states. In the spiral state, the surface polaritons are reciprocal and exhibit backbending near the magnetostatic frequency limit. In the cone state, we find new surface modes with no magnetostatic analogs and the propagation of the surface polaritons is nonreciprocal. The curves in this state also bend back toward the light line near the magnetostatic frequency limit. In addition, the surface wave in both states is strongly localized to the surface and highly attenuated during its propagation. We conclude with numerical calculations for the attenuated-total-reflection (ATR) spectra of these materials. The ATR dips are much stronger than those predicted for ordinary reflectivity and should be observable with existing experimental techniques. We speculate that this result is general, so that ATR essentially overcomes the problem of metallic reflectivity.

Calculations of Bulk and Surface Magnetic Polaritons in Modulated Antiferromagnetic / Non-Magnetic Superlattices

ABSTRACTRecent advances in molecular beam epitaxy have renewed research on the physics of artificially structured magnetic superlattices. In particular, there has been much theoretical research on the propagation of magnetic spin waves or magnetic polaritons in magnetic superlattices.1 In this work, we have studied the effect of modulating both the period of an antiferromagnetic/non-Magnetic semi-infinite superlattice and the relative thickness of its individual layers to see how the dispersion relationships co (k) for bulk and surface magnetic polaritons are effected. We have also calculated the effect of an external magnetic field on (u (k) and our calculation goes beyond the magnetostatic approximation by taking retardation effects into account.

Surface polaritons in antiferromagnetic superlattices with ordering perpendicular to the surface

An effective medium theory is used to study the surface magnetic polaritons in semi-infinite antiferromagnetic superlattices for the case where the direction of magnetic ordering is perpendicular to the surface. We consider a superlattice structure made up of alternating layers of two different uniaxial antiferromagnets. Results are obtained for the dispersion relations of the surface polaritons, and the applications to attenuated total reflection and reflectivity are discussed.

Spin waves in superlattices. III. Magnetic polaritons in the Voigt configuration

For pt.II see J. Phys. C, vol.21, p.4097 (1988). Dispersion relations for bulk and surface magnetic polaritons in semi-infinite layered structures composed of two different magnetic materials are analysed theoretically. The considerations are restricted to the case of in-plane magnetisation and to wave propagation in the Voigt geometry. Some exemplary wave spectra are presented for structures composed of magnetic and non-magnetic materials as well as for structures where both constituents are magnetic.

Surface excitations in anisotropic magnetic superlattices — Surface polaritons and spin waves

Surface magnetic polaritons and spin waves are examined in a unified framework for a promising kind of anisotropic FM/NM superlattices. Two types of the surface modes are classified, the coupled lower- surface modes and coupled standing waves. The modulation property of both the spectra and the envelop functions are discussed.

Influence of a magnetization profile on the surface magnetic polaritons of a ferromagnet

We have studied surface magnetic polaritons on a ferromagnetic semi-infinite material, including retardation effects, in the Voigt geometry. We focus our attention on the influence of a step-like magnetization profile in the ferromagnet. Numerical results are given for a YIG sample, considering the presence of a layer of variable thickness and smaller magnetization on top of it. We have found TE, elliptically polarized, non-reciprocal modes. Both surface and guided modes are presented.