Maximum Faraday Rotation Research Articles

Praseodymium-dopant effect on bismuth-substituted yttrium iron garnet films on fused silica glass substrate at the 1310 and 1550-nm wavelengths

The optical and magneto-optic (MO) properties of the praseodymium (Pr)-dopant effect on bismuth-substituted yttrium iron garnet (Bi:YIG) films coated on fused silica glass substrates by using the metal-organic-decomposition (MOD) method with chemical solutions were investigated at the 1310 and 1550-nm wavelength regions. The maximum Faraday rotation angle of the Pr-codoped Bi:YIG (Pr,By:YIG) film was observed to be 0.09 and 0.046 deg/μm at the wavelengths of 1310 and 1550 nm, respectively, when the film was annealed at a temperature of 750 °C, while those of the plain Bi:YIG film were 0.059 and 0.039 deg/μm. More than 50% improvement in the Faraday rotation value of the Pr,Bi:YIG film was observed compared to that of the Bi:YIG film at the 1310 nm wavelength. The absorption coefficient of the Pr,Bi:YIG film was comparable to that of the Bi:YIG film. Therefore, the Pr,Bi:YIG film prepared with the MOD method is potentially useful for MO applications such as optical isolators and circulators.

Tunable Faraday effect in Graphene/SiO2/Ta2O5 layered structure using a pump He-Ne laser light

Faraday rotation spectrum of a Graphene/SiO2/Ta2O5 layered structure under an external magnetic field and a pump light of a He-Ne laser with the wavelength of 632.8 nm is investigated in the THz frequency region. The results showed that, when the pump light is turned off and the magnetic field strength is increased, the maximum Faraday rotation angle frequency shifts toward the higher frequencies, as well as, the value of the maximum Faraday rotation angle increases. Furthermore, for a constant external magnetic field, by increasing the pump light power, the value of Faraday rotation increases, and the maximum Faraday rotation frequency shifts toward the lower frequencies. However, the noticeable changes in the transmission spectrum were not observed by changing the magnetic field strength and the pump light power. These results would have potential applications in designing the magneto-optical devices with tuning property of the Faraday rotation using a pump He-Ne laser.

Optical and magneto-optical properties of bismuth-substituted neodymium iron gallium garnet films on glass substrates at the 1310-nm and 1550-nm wavelengths

We describe measured results of optical and magneto-optical (MO) properties of bismuth-substituted neodymium iron gallium garnet (Bi1Nd2Fe4Ga1O12, Bi1:NIGG) films prepared by spin coating on glass substrates and crystallized by metal–organic decomposition (MOD) method in the near-infrared (NIR) wavelengths of 1310 nm and 1550 nm. The optical constants of the Bi1:NIGG films were determined with a spectrophotometer measurement. The measured refractive index and absorption coefficient were about 1.835 and 55.8 cm−1, respectively, at the 1310 nm wavelength and about 1.837 and 29.8 cm−1 at the 1550 nm wavelength. The MO properties of the films were determined by measuring the Faraday rotation in the saturated magnetization region. The measured maximum Faraday rotation of the Bi1:NIGG film of about 1055-nm thickness was 0.032 °/μm and 0.016 °/μm at 1310-nm and 1550-nm wavelengths, respectively. The corresponding Figure-of-Merits (FoMs) were 5.64 deg/dB and 5.22 deg/dB at each wavelength. Our measured result indicates that the Bi1:NIGG films prepared by the MOD method are useful for integrated optical isolator and MO sensor applications because of relatively good optical transparency and MO characteristics.

Tunable Faraday rotation of ferromagnet thin film in whole visible region coupled with aluminum plasmonic arrays

Abstract To date, the plasmonic nanostructure utilized for magneto-optical (MO) enhancement has been limited to noble metals with resulted enhancement in the green-red part of visible spectrum. In this study, we fabricated a diffractive hexagonal array composed of Al nanoparticles (NPs) with a thin 7.5 nm ferromagnetic film and pushed the enhanced Faraday rotation (FR) into the blue to green range of the visible light. The freedom and ability to control the working spectral region in the whole visible range from 400 to 800 nm were also demonstrated by changing the lattice constant and the dielectric environment of plasmonic nanostructures. Particularly, in the blue range we obtained the maximum FR 0.57° at 410 nm with a broad boosting region around 0.5° from 400 to 500 nm. Moreover, the largest FR 1.66° was shown at 638 nm by tuning the dielectric environment into a higher refractive index medium. The results of our investigation demonstrate the potential of Al-based magnetoplasmonic effect and offer opportunities to push the MO spectral response out of visible range into the ultraviolet-blue range.

Optically probed symmetry breaking in the chiral magnetCu2OSeO3

We report on the linear optical properties of the chiral magnet Cu2OSeO3, specifically associated with the absence of inversion symmetry, the chiral crystallographic structure, and magnetic order. Through spectroscopic ellipsometry, we observe local crystal-field excitations below the charge-transfer gap. These crystal-field excitations are optically allowed due to the lack of inversion symmetry at the Cu sites. Optical polarization rotation measurements were used to study the structural chirality and magnetic order. The temperature dependence of the natural optical rotation, originating in the chiral crystal structure, provides evidence for a finite magneto-electric effect in the helimagnetic phase. We find a large magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the ferrimagnetic phase. The large value of V can be explained by considering spin cluster formation and the relative ease of domain reorientation in this metamagnetic material. The magneto-optical activity allows us to map the magnetic phase diagram, including the skyrmion lattice phase. In addition to this, we probe and discuss the nature of the various magnetic phase transitions in Cu2OSeO3.

(Invited) Magneto-Optical and Plasmonic Composite Particles Synthesized By Deposition of Au Nanoparticles on Bismuth-Substituted Yttrium-Iron Garnet Core

Although immunochromatograph using nanoparticles has some merits such as an ease of use and a quick response, it has some issues such as a poor sensitivity and a lack of quantitativity. To overcome the issues, we propose a new immunoassay method using a magneto-optical (MO) effect based on nanoparticle technologies. It is expected that the MO immunoassay leads to a higher sensitivity and a quantitative measurement. Nanoparticles with a high MO effect are required for this technique. Bismuth-substituted yttrium-iron garnet (Bi-YIG) is one of the candidates, which exhibits a large Faraday effect. To enhance the Faraday effect for highly sensitive MO immunoassay, surface plasmon resonance (SPR) effect is employed in the preset study. Au nanoparticles have an absorption peak based on the SPR effect in the wavelength range of 500-600 nm by optimizing their size and interparticle distance. Since Bi-YIG has a peak in its MO spectrum at around 550 nm, the SPR absorption will enhance the MO effect, obtaining a maximum Faraday rotation in the range.In the present study, we fabricated MO and plasmonic particles composed of a Bi-YIG particle as a core and Au nanoparticles deposited on the core. First, Bi-YIG particles of 300-600 nm in size as the core were synthesized by coprecipitation and heat-treatment for crystallization, followed by milling to optimize the size. Then, Au nanoparticles were deposited on the Bi-YIG particles by a polyol reduction method using formaldehyde as a reducing agent. Morphological properties such as size and interparticle distance of the Au nanoparticles manipulated by the concentrations of Au ion and formaldehyde for their deposition are important in the SPR effect, resulting in the enhancement of the magneto-optical effect. The specimens were characterized by transmission electron microscopy, X-ray diffraction (XRD), optical absorption spectroscopy, and magneto-optical evaluations in a transmission mode (Faraday rotation).The morphology of Au nanoparticles on Bi-YIG particles depended on the deposition conditions. The clear SPR absorption and the MO enhancement were obtained in the composites with a larger amount of Au nanoparticles deposited on Bi-YIG particles as shown in Fig. 1. The enhancement of the Faraday rotation was observed in the range of 500-700 nm (Fig. 1(a)), corresponding to the wavelength range where the clear SPR absorption was observed (Fig. 1(b)). The enhancement of the Faraday rotation reached 1.54 times in maximum at around 550 nm of wavelength. The dependence of optical and magneto-optical properties as a function of Au concentration was attributed to the morphology of the Au nanoparticles deposited on Bi-YIG particles. The coverage of Au nanoparticles on Bi-YIG strongly influenced the enhancement of the Faraday rotation based on the SPR effect. Although the quantity of the deposited Au nanoparticles confirmed by XRD was increased, the MO enhancement was not confirmed in the case that large Au nanoparticles were deposited and the coverage was low on the Bi-YIG surface. Figure 1

High sensitivity far infrared laser diagnostics for the C-2U advanced beam-driven field-reversed configuration plasmas.

A high sensitivity multi-channel far infrared laser diagnostics with switchable interferometry and polarimetry operation modes for the advanced neutral beam-driven C-2U field-reversed configuration (FRC) plasmas is described. The interferometer achieved superior resolution of 1 × 1016 m-2 at >1.5 MHz bandwidth, illustrated by measurement of small amplitude high frequency fluctuations. The polarimetry achieved 0.04° instrument resolution and 0.1° actual resolution in the challenging high density gradient environment with >0.5 MHz bandwidth, making it suitable for weak internal magnetic field measurements in the C-2U plasmas, where the maximum Faraday rotation angle is less than 1°. The polarimetry resolution data is analyzed, and high resolution Faraday rotation data in C-2U is presented together with direct evidences of field reversal in FRC magnetic structure obtained for the first time by a non-perturbative method.

Tunable Faraday effect in one-dimensional photonic crystals doped by plasma

In this paper, a four by four transfer matrix method has been used to investigate the optical and magneto-optical properties of a one-dimensional photonic crystal (1D-PC) doped by plasma. We show theoretically that there are a tunable resonance splitting form and a magnetically induced birefringence in a 1D-PC doped by plasma. The Faraday rotation can be seen clearly in this kind of structures. It is also figured out that the magnitude and the frequency of maximum Faraday rotation affected by the variation of the plasma density and the external magnetic field. This prospective advantage of the structure is useful for tunable filters in millimeter-wave region.

Minimum light transmission in graphene in the presence of a magnetic field

We show that, on general theoretical grounds, transmission of light in graphene always presents a non-vanishing minimum value independently of any material and physical condition, the transmission coefficient being higher in the presence of a substrate, and getting increasing when QED corrections higher than α come into play. Explicit numerical calculations for typical cases are carried out when an external magnetic field is applied to the sample, showing that, in epitaxial graphene, a threshold effect exists leading to a non-trivial minimum transmission, for a non-vanishing light frequency, only for field values larger than a critical one, both in the large and in the intermediate chemical potential regime. Such a threshold effect manifests even in the maximum Faraday rotation polarization of light, which is substantially controlled by the applied magnetic field. Instead, more transmission minima in suspended graphene enters in the considered light frequency region for increasing magnetic field, displaying an effective shift of frequency bands where the sample gets more or less absorptive with a suitable tuning of the external field. Two transition regions in different magnetic field ranges are found, where the shift effect towards higher frequency values occurs both in the transmission coefficient and in the Faraday rotation angle. Potential technological application of the results presented are envisaged.

Preparation of yttrium iron garnet thin films by mist chemical vapor deposition method and their magneto-optical properties

Polycrystalline and epitaxial thin films composed of a single phase of yttrium iron garnet (YIG) have been synthesized on silica glass and single-crystalline gadolinium gallium garnet substrates, respectively, by the mist chemical vapor deposition (CVD) method. The element Y can be found in the deposited thin films only when an aprotic polar solvent such as acetone is employed for the preparation of the precursor solutions. The crystal structure, magnetic properties, and magneto-optical properties of the thin films are explored. The maximum Faraday rotation angle observed in the present epitaxial YIG thin film is 3.66°/µm at 441 nm, as far as we know, which is higher than those reported for YIG films prepared by other methods, suggesting that the mist CVD method is effective for obtaining epitaxial thin films of multiple oxides.

A Magnetic and Magneto-Optical Investigation of Co-Pt Alloy Nanowire Arrays

We have investigated the magneto-optical properties of highly ordered Co-Pt alloy nanowire arrays embedded in anodic aluminum oxide templates. The magnetic field-dependent Stokes parameters, Faraday rotation angle and ellipticity were investigated by an in-house magneto-optical measurement system. The extracted hysteresis loops are broadly consistent with magnetic hysteresis loops obtained from the vibrating sample magnetometer. The maximum Faraday rotation angle and ellipticity of these samples were examined as a function of nanowire composition. With an increase of platinum content from 9 at.% to 86 at.% in the as-deposited nanowire arrays, the maximum Faraday rotation angle per length decreases linearly from 1.39 x 10(3) degrees/cm to 1.58 x 10(2) degrees/cm. The maximum ellipticity shows a similar behavior with the composition. These linear relationships suggest a dilution model for the magnetic moment in the alloy nanowires. Our results indicate that magneto-optical measurements comprise an effective and sensitive method for monitoring the behavior of AAO-based magnetic nanowire arrays.

Preparation of nanocrystalline bismuth-substituted yttrium iron garnet films with enhanced Faraday magneto-optical figure of merit by pyrolysis of coprecipitated hydroxide slurry

Nanocrystalline Bi-substituted yttrium iron garnet films have been prepared by coprecipitation titration, once-through coating of hydroxide slurry, and pyrolysis. The resulting films with grain sizes of 10–20 nm are fabricated at a pH value of 12 and heat treated of 700 °C for 1 h. At the incident light wavelength of 633 nm, the maximum special Faraday rotation of 3.6×10 4°/cm and Faraday magneto-optical figure of merit of 6.7°/dB were obtained. The influence of pH value and heat treatment on film grain size, crystallinity, and magneto-optical properties is demonstrated.

Magneto-optical properties of yttrium iron garnet (YIG) thin films elaborated by radio frequency sputtering

Thin films of yttrium iron garnet (YIG) are grown by radio frequency magnetron non reactive sputtering system. Thin films are crystallised by heat-treatment to obtain magneto-optical properties. On quartz substrate, the network of cracks observed on the annealed samples can be explained by the difference between the thermal expansion coefficient of substrate and YIG. Physico-chemical analysis shown that the obtained material has a correct stoichiometry and is crystallised as FCC. The Faraday rotation of thin films is measured with a classical ellipsometric system based on transmission which allows us to obtained an accuracy of 0.01°. The variation of Faraday rotation is studied on the one hand versus radio frequency power applied to the cathode during the deposition and on the other hand versus the applied magnetic field. The results are compared with those obtained by vibrating sample magnetometer analysis in perpendicular configuration. A maximum Faraday rotation is observed to be 1900°/cm at the wavelength of 594nm for a YIG thin film formed on quartz substrate and annealed at 740°C. The values of the Faraday rotation coefficients obtained in the study versus the wavelength are comparable to those of the literature for the bulk material. In order to eliminate the stress due to the heat-treatment, we made some films on single crystals of gadolinium gallium garnet (111) substrates for which thermal expansion coefficient is near than the YIG one. The material crystallises with no crackles and the Faraday effect is equivalent.

Evolution of properties of epitaxial bismuth iron garnet films with increasing thickness

Bismuth iron garnet (BIG) films of thicknesses from 470 to 2560 nm were prepared by pulsed laser deposition under identical deposition conditions. All films are epitaxial, bismuth deficient, and show rms surface roughnesses between 15 and 40 nm . X-ray coherence lengths decrease with increasing film thickness. Films below approximately 1 μm are free of cracks, thicker films possess a network of cracks. From fits of optical transmission spectra, real and imaginary parts of the refractive indices were found for wavelengths from 500 to 850 nm . The effects of thin film interference and surface roughness were included. With these data as input information, each of our experimental Faraday rotation spectra was described by a single diamagnetic line in visible light. The measured spectra could be reproduced and parameters of the magneto-optical transition were obtained. We observed a broadening of the transition with increasing film thickness and a red shift of the center frequency. This corresponds to our experimental observation that the wavelength of maximum Faraday rotation for BIG films in visible light shifts to longer wavelengths by almost 40 nm for a 2560-nm-thick film as compared to a 470-nm-thick film. As BIG is not thermodynamically stable, aging is a crucial question. We found that careful annealing in oxygen below the deposition temperature increases the angle of Faraday rotation, while film properties deteriorate during long annealing times at the deposition temperature.

Pulsed laser deposition of Y3Fe5O12 and Bi3Fe5O12 films on garnet substrates

We prepared Y3Fe5O12 (YIG) and Bi3Fe5O12 (BIG) films by pulsed laser deposition and present some practical aspects here. Low laser repetition rates result in a loss of oxygen and reduce the saturation magnetization of YIG by a factor of 5. Small changes of deposition conditions and lattice match for BIG films have little influence on the spectra of Faraday rotation but change magnetic coercivities by a factor of 10. Thin BIG films show higher coercivities than thick films. Coercivities increase with lattice mismatch between film and substrate. The wavelength of maximum Faraday rotation for BIG films in visible light depends on film thickness: We observed a redshift of almost 40 nm for a 2.6 μm thick film as compared to a 470 nm thick film.

Magnetic fields in the Centaurus cluster

We present multi-frequency VLA observations of the radio galaxy PKS 1246-410 at the center of the Centaurus Cluster, and compare these results to recent Chandra observations. The unusual radio morphology of PKS 1246-410 probably results from interactions with the hot, X-ray emitting gas. This gas, along with cluster magnetic fields, also produces substantial Faraday Rotation Measures towards PKS 1246-410. We discuss these observations in the context of a sample of 14 luminous X-ray clusters with embedded radio galaxies and possible cooling flows. A correlation is found between the cooling flow rate and the maximum Faraday Rotation Measures. Magnetic fields of strength 10-40 uG are found to be common to the centers of clusters with strong cooling flows, and somewhat lower field strengths of 2-10 uG are found in the non cooling-flow clusters.

Giant Faraday rotation of blue light in epitaxial CexY3−xFe5O12 films grown by pulsed laser deposition

We report crystalline, magnetic, and magneto-optic (MO) properties of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films epitaxially grown onto single crystal Gd3Ga5O12 (111) substrates using Nd:YAG pulsed laser deposition technique. Oxygen ambient pressure used for the growth is found to be the critical parameter to prepare CexY3−xFe5O12 films with good crystalline and magnetic properties as well as large MO effect. The film fabricated at 50 m Torr oxygen pressure exhibits a maximum Faraday rotation (FR) θF=1.78 and 4°/μm at λ=633 and 430 nm, respectively, a minimum in-plane coercivity Hc=35 Oe, and the narrowest full width at half maximum = 0.06° for the (444) x-ray Bragg reflection rocking curve. The analog of the Verdet constant V=θF/4πMs also found to be dependent on the oxygen ambient pressure reaches a value as high as 1.41°/μm kG at 633 nm, suggesting that this material is useful for MO applications. The energy dispersion FR spectra, measured over visible region 400 to 840 nm, clearly demonstrate that Ce substitution prominently enhances Faraday effect at 690 and at 430 nm blue-wavelength region.

Magnetic and Magneto-Optic Properties of Pulsed Laser Deposited CexY3−xFe5O12 Films

AbstractWe present experimental studies of crystalline, magnetic, and magneto-optic (MO) properties and their correlation with the processing parameters of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films grown epitaxially onto single crystal Gd3Ga5O12 (111) substrates by Nd:YAG pulsed laser deposition technique. Rutherford backscattering (RBS) analysis and microprobe energy dispersive spectrometry (EDS) prove the background oxygen pressure, used for films growth, control films stoichiometry. Oxygen ambient pressure appears to be an important parameter to grow CexY3−x, Fe5O12 films with good crystallinity, magnetic properties, as well as enhanced MO effect. It is found that the film fabricated at 50 mTorr oxygen pressure exhibits a maximum Faraday rotation (FR) øF = 1.78 deg/νtm at λ = 633 nm, a maximum saturation magnetization 4πMs = 1255 Gauss with a minimum in-plane coercivity Hc = 35 Oe, and the narrowest full width at half maximum FWHM = 0.06° of the (444) Bragg reflection rocking curve. The analog of the Verdet constant V = øF / 4πMs, also found to be dependent on the oxygen ambient pressure, reaches the value as high as 1.4 deg/νm-kG at 633 nm, suggesting that this material is useful for MO applications.

Enhancement of the Magneto-Optical Effect in Fe/SiO2 and Co/SiO2 Granular Films

We measured the Faraday rotation (FR) spectra (λ = 500-800 nm) in granular films of Ni/PVC (prepared by spin-coating polyvinyl chloride containing Ni fine powders of ∼20 nm diameter) and (Fe or Co)/SiO2 (prepared by RF-diode co-sputtering and annealed at 400-900°C). The FR spectrum in the Ni/PVC films was best-fitted by assuming that the volume fraction f of Ni is 0.27, though analysis resulted in f = 0.11, suggesting that the FR is enhanced; a possible explanation is “weak localization of light“ in the granular structure. The FR in the Fe/SiO2 and Co/SiO2 granular films increased as the annealing temperature (Ta) was raised, reaching a maximum followed by a decrease. The maximum FR was, however, much smaller than that calculated for the films, probably because the size of the metal particles became comparable with the wavelength of light.

Growth and Characterization of Liquid-Phase Epitaxial Bi-Substituted Iron Garnet Films for Magneto-Optic Application

The effects of the chemical species of host rate-earth ions, melt compositions and growth orientations on the Bi-substitution level and magneto-optic properties of Bi-substituted garnet films grown by liquid-phase epitaxy were examined. For Gd3+ ions, a higher level of Bi substitution was attained than for Y3+ or Lu3+ ions, when garnet films were grown under the same growth conditions. A maximum Faraday rotation coefficient of -2880°/cm at 1.30 µm was observed in the (GdBi)3(FeAlGa)5O12 film with a Bi-substitution level of 1.56 moles per garnet formula unit. The optical absorption coefficient was as small as 1.6 cm-1 in the (GdBi)3(FeAlGa)5O12 film with a Faraday rotation coefficient of -1800°/cm; consequently, a figure of merit of 267°/dB was attained at 1.30 µm.