Self-standing 3D magnetoplasmonic nanostructures with enhanced Faraday effect and outstanding sensing performance

Three-dimensional magnetoplasmonic nanostructures possess more novel and richer optical and magneto-optical (MO) behaviors compared with planar nanostructures, and exhibit attractive potential applications in micro-nano non-reciprocal photonic devices. However, fabrication of three-dimensional magnetoplasmonic nanostructures is difficult using the usual nanofabrication methods. This work constructs three-dimensional substrate-free Au/Co/Au structures prepared using focused ion beam (FIB) technology. In the three-dimensional split-ring structure, with y-polarized light normal incidence, a three-dimensional coupling current is formed between the vertical split-ring and the bottom square hole, which causes excitation of the Fano resonance. The Fano resonance causes a significant enhancement of the local magnetic field, resulting in a larger Faraday rotation (FR). The resonance also brings about a sign reversal of FR, which is related to the direction of the Lorentz force on electrons. Similar effects also exist in the three-dimensional nanopillar structure and the three-dimensional nanoring structure in the simulation results. Due to the high flexibility of FIB machining, the height and shape of the three-dimensional split-ring can be arbitrarily changed, which means the FR intensity and the position of the FR null point are tunable. The designed three-dimensional structures provide a new route to regulate the Faraday effect, and broaden the possibilities for the design and construction of MO devices.

Summary form only given. In recent years, Inoue and Fujii have studied theoretically and experimentally, the one-dimensional magnetophotonic crystal (1-D MPC) multilayer films composed of magneto-optical and dielectric materials. This 1-D MPC film exhibits an extremely large magneto-optical Faraday rotation due to the weak localization of light Such 1-D MPC film offers the possibility of realizing a rotation of 45/spl deg/ with a thickness of only several microns. The application from showing high transmittance (T) and large Faraday rotation (/sup /spl Theta///sub F/) to a variety of magneto-optical devices for optical communication (ex. film-based optical isolator) is expected. Therefore, we investigated on the possibility of the application to optical isolator (T>95%, /sup /spl Theta///sub F/=45/spl deg/) for the optical communication of 1-D MPC from the theory.

Magnetoplasmonic nanostructures with enhanced magneto-optical (MO) activity hold great promise for the active manipulation of plasmon propagation. In this Rapid Communication, we demonstrate that the shape of elliptical nanocylinder plays an essential role on the large enhanced MO activity: (1) saturated MO activity component depends on the angle of polarization plane of incident light with respect to the semimajor axis of elliptical nanocylinder and (2) a low magnetic field induces MO activity with nonferromagnetic origin exhibiting a giant linear component added to the saturated component in the MO loops. The intriguing optical and MO properties were well interpreted within one model by assigning a biaxial effective permittivity tensor to the elliptical nanocylinder array. It is suggested that the shape enhanced MO activity can be maximized by elaborately tuning the plasmon resonance as well as increasing the aspect ratio of elliptical nanocylinder.

Large Faraday Rotation in Pyrolysis Synthesized Carbon Dots

Large Faraday rotations are reported tor Rh4+-substituted magnetic garnets in the visible wavelength region, in comparison with those observed in Ir4+ substituted ones. Although rather strong absorptions are observed in the visible region, no absorption peaks corresponding to the Faraday rotation peaks are observed in the absorption spectra. In order to study the origin of the Faraday rotations, Rh4+-and Ir4+-substituted nonmagnetic garnet films are prepared by an LPE method and optical absorption spectra are measured. In addition, the electronic state calculation of (M4+O62-)8- (M=Rh,Ir) octahedral clusters are performed by using the SCF-Unrestricted -SW Xα method. From the observed absorption spectra in nonmagnetic garnets and the electronic state calculations, large Faraday rotations are assigned to the charge transfer transitions of an electron from O 2p to Rh 4d or Ir 5d orbitals, or t1un → t2g* and t2un → t2g* transitions.

We investigate the polar magneto-optical Kerr effect as a function of the angle of incidence in Co/Au thin films under attenuated total reflection conditions. An experimental method is proposed to measure the intrinsic polar magneto-optical Kerr rotation of the magnetoplasmonic films while considering the influence of the glass Faraday magneto-optical effect. The experimental results demonstrate that the Kerr rotations of these films are greatly affected by a number of factors including the angle of incidence, the linear polarization of the incident light, and the film thickness. The results suggest that the polar magneto-optical activity is affected by the evanescent fields decaying inside the films; these fields arise not only from attenuated total reflection at the glass/metal interface but also from the surface plasmon polaritons at the metal/air interface. A close relationship between the magneto-optical activity and the electromagnetic field distribution within the magnetoplasmonic films is clearly revealed.

There are several radio sources with Faraday rotation measures larger than 500 rad m−2 (ref. 1). Because most of these sources are located near the galactic plane, the large rotation measures can be attributed to the galactic medium2. However, a few sources at high galactic latitude also show large rotation, implying intrinsic Faraday rotation within the source. Until now, no sources have been discovered to have a rotation measure > 1,000 rad m−2. Using a multichannel polarimeter at 10 GHz attached to the 45-m radio telescope at Nobeyama, we have observed about 100 extragalactic radio sources which were suspected to have large rotation from our polarization catalogue1. Four of these 100 sources were found to have an intrinsic rotation measure > 1,000 rad m−2. Here we report rotation measures which are two orders of magnitude larger than those observed so far for most extragalactic radio sources. Two of these four sources are classified as compact steep-spectrum sources.

Bi 3+ -substituted composite rare-earth iron net (TbYbBiIG) bulk single crystals were successfully grown by the flux method. The Faraday rotation F = 100 to 200 degree/mm and the optical transmission spectrum were measured in the near-infrared wavelength range of 1.0 to 1.7 μm. The temperature coefficient of Faraday rotation d F /dT = 2.0 × 10 2 degree mm -1 K 1 at wavelength λ = 1.55 μm in the temperature range of 273 to 360 K. It shows that the new type TbYbBiIG bulk single crystals have not only larger Faraday rotation F but also smaller d F /dT value than those of other rare-earth iron garnets.

The Faraday effect of magnetic opal films is studied at the visible wavelength slightly detuned from the Bragg diffraction wavelength. At this wavelength, we can expect the reduced group velocity of light and the enhancement of the Faraday rotation. The magnetic opal was self-assembled from a suspension of magnetic-core/silica-shell spherical particles onto glass substrates using vertical deposition. Despite of the structural disorder in the thick opal film, the optical rotation was enhanced 70 times over that of the structure less bulk at 10 T. The thin film with the highest structural quality shows an enhancement factor of 175. Thus, structure-induced enhancement was explicitly demonstrated.

Magnetooptic (MO) effects in magnetic multilayers with periodically stratified regions are analyzed for the case of normal light wave incidence and polar magnetization (Faraday and polar Kerr effects). From the universal 4 x 4-matrix formalism simplified analytical representations restricted to terms linear in the off-diagonal permittivity tensor elements are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions useful for the evaluation of trends in MO effects are given for periodic multilayers consisting of blocks with ultrathin magnetic films. The procedure is illustrated on periodic systems built of symmetric units. Limits on the ultrathin approximation are discussed.

We theoretically investigate and optimize a multilayer planar structure with enhanced magneto-optical (MO) activity. The extraordinary optical transmission observed in a periodically perforated metal plate with subwavelength holes is used to produce a higher MO activity. We consider a three-layer structure that consists of a dielectric layer placed between the perforated metal and the MO layers. In this structure, we obtained the enhancement of Faraday rotation by three times and the Kerr effect by an order as compared to the published results.

We present a two-step homogenization method for studying the Faraday magneto-optical effect in graded metal-dielectric composite films of width W, in which the volume fraction of metal particles in a slice varies along the direction perpendicular to the film surface. First, we adopt the effective-medium theory to formulate the equivalent (local) dielectric permittivity tensor for a z slice. Second, the graded composite films are homogenized with an effective (overall) dielectric permittivity tensor including the diagonal and off-diagonal elements. Faraday rotation is studied as a function of the graded profile p(z) with the same total volume fraction. For a power-law form p(z)=a(z/W)m with different m, it is found that with increasing m, the magnitude of Faraday rotation becomes weak near the surface plasmon resonant band, accompanied with the redshift of the resonant center. Interestingly, it is possible to achieve strongly enhanced Faraday rotation in the high-frequency region, and to change the direction of rotation in the low-frequency one. Moreover, the magnitude can be further enhanced for needle-like particles. In the dilute limit, we show that Faraday rotation is indeed independent of m within Maxwell-Garnett theory.

Adjustable Faraday rotation by using engineered one-dimensional magneto photonic crystals

To control light by magnetic field magneto-optical nanostructures can be used. Response of well-known periodical structures is narrowband and depending on light's incident angle. In present work we investigated magneto- optical properties of 2D periodic and quasicrystalline structures. These structures consist of gold grating-patterned layer on top of magnetic dielectric film. We showed that in 2D quasicrystalline structures magnetoplasmonic effects, such as the transverse magneto-optical Kerr effect (TMOKE) and Faraday effect, are broadband. Moreover, their independence of light's polarization and incident angle was demonstrated.

One of the best magneto‐optical claddings for optical isolators in photonic integrated circuits is sputter deposited cerium‐doped terbium iron garnet (Ce:TbIG) which has a large Faraday rotation (≈−3500° cm−1 at 1550 nm). Near‐ideal stoichiometry of Ce0.5Tb2.5Fe4.75O12 is found to have a 44 nm magnetic dead layer that can impede the interaction of propagating modes with garnet claddings. The effective anisotropy of Ce:TbIG on Si is also important, but calculations using bulk thermal mismatch overestimate the effective anisotropy. Here, X‐ray diffraction measurements yield highly accurate measurements of strain that show anisotropy favors an in‐plane magnetization in agreement with the positive magnetostriction of Ce:TbIG. Upon doping TbIG with Ce, a slight decrease in compensation temperature occurs which points to preferential rare‐earth occupation in dodecahedral sites and an absence of cation redistribution between different lattice sites. The high Faraday rotation, large remanent ratio, large coercivity, and preferential in‐plane magnetization enable Ce:TbIG to be an in‐plane latched garnet, immune to stray fields with magnetization collinear to direction of light propagation.