Magneto-optical Faraday Rotation Research Articles

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

We investigated the adjustability and enhancement of magneto-optical Faraday rotation in one-dimensional magneto photonic crystal. The Faraday rotation can be adjusted through optical contrast ratio engineering in the resonator structure via equivalent layers theory. Also, simultaneous enhancement of the transmission magnitude and Faraday rotation of the structure can be obtained by optimizing the optical contrast ratio-magnetic defect layer thickness product. In a special design of magneto photonic crystal which consists of SiO 2 and Ta 2O 5 as the basic element of the resonator and Bi substituted yttrium iron garnet as the defect magnetic layer, by changing the optical contrast ratio from 1.43 to 1.09, the Faraday rotation can be adjusted from −3.35 to −0.74 deg in 65 nm wide range of wavelength. Finally, in the case which the optical contrast ratio optimized at 1.22 and the thickness of magnetic defect layer changed to one quarter of design wavelength, dramatic simultaneous enhancement of Faraday rotation and transmission magnitude can be obtained succesfully (the Faraday rotation and transmittance have their maximum value, −11.77 deg, and 99.67%).

Oxide glasses with magnetic nanoparticles: transparent magnets (Faraday rotation and electron magnetic resonance studies)

AbstractIn the first part of this paper we outline the state of the art in the field of magnetic nanoparticles in oxide glasses. We describe the theoretical background of two complementary techniques used for the studies of the state of paramagnetic ions, clusters and magnetic particles in a diamagnetic matrix, viz., magnetooptical Faraday rotation (FR) and electron magnetic resonance (EMR) and we overview previous results obtained with these techniques for several glass systems. In the second part, we highlight the case of potassium‐alumina‐borate glasses – a glassy system where doping with paramagnetic oxides results in formation of magnetic particles at very low contents of paramagnetic additions: Fe2O3 and MnO. In the special case when the ratio of the iron and manganese oxides in the charge is 3/2, magnetic nanoparticles with characteristics close to those of manganese ferrite are formed already at the first stage of the glass preparation. After thermal treatment all glasses show FR and EMR spectra attesting to the presence of superparamagnetic nanoparticles, characterized by relatively broad size and shape distributions. The formation of magnetic nanoparticles confers to these glasses magnetic and magneto‐optical properties typical of magnetically ordered substances. At the same time, the glasses remain transparent in a part of the visible and near infrared spectral range and display a high FR value. Such properties make them particularly interesting for use as new media for various magneto‐optical devices.

Magnetization process of geometrically frustrated spinel oxide up to an ultra-high magnetic field

We conducted precise magneto-optical Faraday rotation measurements in CdCr2O4and ZnCr2O4up to ultra-high magnetic fields using methods of the single turn coil(up to 190 T) and also the electro-magnetic flux compression(up to 360 T). In CdCr2O4, we have succeeded in observation of the full magnetization process. In ZnCr2O4, we observed magnetization process up to 2.7 μB(the full moment is 3.0 μB). The magnetization processes of both materials were well described by a 4 sub-lattice Heisenberg-spin model including spin-lattice interactions.

Enhancement of Faraday rotation in 3D/Bi:YIG/1D photonic heterostructures

We suggest a new design of magnetophotonic crystals. Microcavity-type magnetic photonic heterostructures exhibiting enhanced magneto-optical Faraday rotation have been fabricated. Such a heterostructure comprises an opal film (3D photonic crystals), a bismuth substituted iron garnet (Bi:YIG) spacer film acting as the defect layer, and a dielectric multilayer (1D photonic crystal). Localized mode was shown to exist in the photonic band gap as a result of resonant interference in heterostructures. The observed enhancement of Faraday rotation was more than three times as compared with that of the Bi:YIG constituent. We have also found that the heterostructures exhibit an unusual polarization-dependent response.

Soft X-ray magmeto-optical Faraday rotation measurements with the multilayer polarizer

We measured magneto-optical (MO) Faraday rotation around the M2,3 edges (60—70 eV) of Ni film on 3W1B beam line of Beijing Synchrotron Radiation Facility (BSRF) in the soft X-ray region through a versatile polarimeter with mutilayer polarizers, which is mainly composed of polarizer, analyzer, sample frame, round NdFeB permanent-magnet and MCP detector. We used the reflective aperiodic molybdenum/silicon broadband multilayer polarizers as the polarizer and the analyzer in the versatile polarimeter, and obtained a series of Faraday rotation results in the 60—70 eV region. The results demonstrate that the Faraday rotation angles are obviously large around Ni M2,3 edges, the rotation angles are 179±019°(average rotation angle in parallel and antiparallel magnet fields) and -076±009°(average rotation angle in parallel and antiparallel magnet fields) at the energy 655 eV and 68 eV, respectively.

Nonlinear magneto-optical rotation and Zeeman and hyperfine relaxation of potassium atoms in a paraffin-coated cell

Nonlinear magneto-optical Faraday rotation (NMOR) on the potassium D1 and D2 lines was used to study Zeeman relaxation rates in an antirelaxation paraffin-coated $3\text{\ensuremath{-}}\mathrm{cm}$-diameter potassium vapor cell. Intrinsic Zeeman relaxation rates of ${\ensuremath{\gamma}}^{NMOR}∕2\ensuremath{\pi}=2.0(6)\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$ were observed. The relatively small hyperfine intervals in potassium lead to significant differences in NMOR in potassium compared to rubidium and cesium. Using laser optical pumping, widths and frequency shifts were also determined for transitions between ground-state hyperfine sublevels of $^{39}\mathrm{K}$ atoms contained in the same paraffin-coated cell. The intrinsic hyperfine relaxation rate of ${\ensuremath{\gamma}}_{\mathit{expt}}^{\mathit{hf}}∕2\ensuremath{\pi}=10.6(7)\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$ and a shift of $\ensuremath{-}9.1(2)\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$ were observed. These results show that adiabatic relaxation gives only a small contribution to the overall hyperfine relaxation in the case of potassium, and the relaxation is dominated by other mechanisms similar to those observed in previous studies with rubidium.

Magnetooptical properties of perforated metallic films

It is shown that optical transmittance and the magnetooptical (MO) Faraday rotation in the heterostructure of a periodically perforated metallic layer attached to a smooth magnetic dielectric thin film demonstrate resonance dependences on the wavelength and magnetic-film thickness. It is possible to adjust geometrical and MO parameters of the system in order to get these resonance peaks close in wavelength and get enhanced Faraday rotation (by a factor of 5–10) along with sufficient transmittance (30–40%). The phenomenon is explained in terms of the excitation of the surface plasmon polaritons waves coupled with waveguided modes of the magnetic film.

Comparison of Bi 3Fe 5O 12 film giant Faraday rotators grown on (111) and (001) Gd 3Ga 5O 12 single crystals

Bismuth iron garnet (Bi 3Fe 5O 12, BIG) epitaxial thin films were grown on single crystal (Gd 3Ga 5O 12, GGG) (111) and (001) substrates by rf-magnetron sputtering technique. Processing parameters have been optimized to obtain high deposition rate (2.74 μm/h) and the surface rms roughness less than 10 nm. X-ray diffraction reveals films epitaxial quality: exclusive (111) or (001) orientation with narrow rocking curves and strong in-plane texture. Films possess low optical loss and magneto-optical Faraday rotation (FR) as high as 5 deg/μm at 677 nm wavelength. Comparative analysis of films grown on (111) and (001) substrates clearly shows significant superiority of BIG/GGG(001) film. For this film, the coercive field ∼100 Oe appears to be 2.5 times lower while the optical transmission to be 10% higher than that for BIG/GGG(111) film. Enhanced magneto-optical performance of BIG/GGG(001) films relies upon better accommodation of the film-to-substrate mismatch strain through the tetragonal BIG lattice distortions compared to the rhombohedral one in BIG/GGG(111) films.

Growth and characterization of ZnMnO thin films

Zn 1− x Mn x O ( 0 ≤ x ≤ 0.1 ) thin films were grown on sapphire substrates by pulsed laser deposition and rf magnetron sputtering methods. As a target source ceramic pellets prepared by mixing ZnO and Mn 3O 4 powders were used. The shift of the absorption edge due to increase the energy band gap with increasing Mn content was observed in optical absorption spectra of the Zn 1− x Mn x O thin films. Magnetic susceptibility and magneto-optical Faraday rotation experiments show paramagnetic behavior and absence of ferromagnetic ordering in the studied films.

Enhanced Magnetooptical Response in Dumbbell-like Ag−CoFe2O4 Nanoparticle Pairs

We study magnetooptical Faraday rotation in a colloidal solution of "dumbbell-like", physically conjoined nanoparticle pairs composed of a ferromagnetic (CoFe2O4) and a noble metal (Ag). We show that outside the CoFe2O4 interband dominated spectral regime, the coupled dumbbells show significantly enhanced magnetooptic response relative to single CoFe2O4 nanoparticles, derived from plasmonic contribution by the Ag nanoparticles.

Faraday rotation in a two-dimensional photonic crystal with a magneto-optic defect

We study the magneto-optic (MO) Faraday rotation in a two-dimensional square-lattice photonic crystal with a central MO defect layer in the optical wavelength range. We show that when a TM plane wave is incident upon a photonic crystal, an enhancement of Faraday rotation takes place in a region where a resonance peak appears in the photonic bandgap. In this region the mode conversion is high.

Enhanced Faraday rotation in all-garnet magneto-optical photonic crystal

Research on magneto-optical photonic crystals has so far been focused on theoretical investigations, because suitable multilayers of iron garnet, the most promising material, have not been readily available. We report the preparation and characterization of a one-dimensional magneto-optical photonic crystal composed of 17 heteroepitaxial layers of bismuth iron garnet and yttrium iron garnet. The magneto-optical Faraday rotation was increased by 140% while transmission decreased by just 16% at the design wavelength of 750 nm as compared with a single-layer bismuth iron garnet film of equivalent thickness. The sample is free of cracks, and good agreement of simulated and experimental spectra of optical transmission and Faraday rotation indicate high quality of the sample and robustness of the preparation technique.

Enhanced Faraday rotation in garnet films and multilayers

AbstractFilms were prepared by pulsed laser deposition. We investigated or measured crystallinity, morphology, film-substrate interface, cracks, roughness, composition, magnetic coercivity, refractive index and extinction coefficient, and magneto-optical Faraday rotation (FR) and ellipticity. The investigations were partly performed on selected samples, and partly on two series of films on different substrates and of different thicknesses. BIG films were successfully tested for the application of magneto-optical visualization. The effect of annealing in oxygen atmosphere was also investigated - very careful annealing can increase FR by up to 20%.Periodical BIG-YIG multilayers with up to 25 single layers were designed and prepared with the purpose to enhance FR at a selected wavelength. A central BIG layer was introduced as defect layer into this one-dimensional magneto-optical photonic crystal (MOPC) and generated resonances in optical transmittance and FR at a chosen design wavelength. In a 17-layer structure, at the wavelength of 748 nm, FR was increased from–2.6 deg/μm to –6.3 deg/μm at a small reduction in transmittance from 69% to 58% as compared to a single-layer BIG film of equivalent thickness. In contrast to thick BIG films, the MOPCs did not crack. We were first to report preparation of all-garnet MOPCs and second to experimentally demonstrate the MOPC principle in magneto-optical garnets.

Optical transmission and Faraday rotation spectra of a bismuth iron garnet film

We prepared an epitaxial 530-nm-thick bismuth iron garnet (BIG) film on a Gd3Ga5O12(GGG) (111) substrate by pulsed laser deposition and measured spectra of optical transmission and magneto-optical Faraday rotation θF(λ) in visible light. Both spectra are shaped by the dispersion relations of the dielectric tensor and the effects of multiple-beam interference in the thin film. From fitting of the transmission spectrum, dispersion relations of the real and imaginary parts of the refractive index were found for the wavelength range from 515 to 1000 nm, n(λ)=2.36+(413 nm/λ)2 and k(λ)=(λ/4π nm)×exp[(1660 nm/λ)2−15.2]. With these data as input information, a single diamagnetic line centered at λ=486 nm was fitted to the experimentally recorded magneto-optical spectrum. The effects of thin film interference and surface roughness were included in order to closely reproduce the measured spectrum. The roughness determined from spectral analysis was compared to the rms roughness measured by atomic force microscopy. The values agree within a deviation of less than 20% and are approximately 3% of film thickness. The magneto-optical figure of merit 2|θF|/α (α is the absorption coefficient) of our film increases strongly with wavelength and exceeds 100° at 740 nm. The optical efficiency for magneto-optical visualization |exp(−2αd)sin(4θFd)| (d is film thickness) possesses a maximum value of 29% at 600 nm. Both quantities were calculated using the obtained dispersion relations for absorption and Faraday rotation.

RE containing glasses as effective magneto-optical materials for 200–400 nm range

Magneto-optical Faraday rotation (FR), optical absorption and magnetization of oxide glasses with high concentration of rare earth (RE) ions (up to 25 mol.% of R 2O 3, R: Pr 3+, Dy 3+, Eu 2+) are investigated. These glasses had a good transparence and high value of Verdet constant simultaneously. They can be considered as materials of high magneto-optical quality in the wavelength range 200–400 nm.

Magnetic properties and magneto-optical effect of Co0.5Fe2.5O4 nanostructured films

Co 0.5 Fe 2.5 O 4 ferrite films with nanostructure have been prepared by rf sputtering on a quartz substrate and annealed at temperatures from 400 to 600 °C in air. The magnetic properties and magneto-optical effect have been studied. It has been found that nanocrystalline Co0.5Fe2.5O4 films exhibit good magnetic properties and a large magneto-optical effect. The magnetization, coercivity, remanence ratio, and maximum energy product are 455 emu/cm3, 2.8 kOe, 0.72 MGOe, and 2.4 MGOe, respectively. The magneto-optical Faraday rotation is <−3.4°/μm at short wavelength and 4°/μm at the wavelength of 740 nm. These characteristics make them very promising to be used for magneto-optical recording and for permanent magnets. The influence of the distribution of Co2+ ions on magnetic properties and magneto-optical effect has been discussed.

A mixed rare-earth iron garnet single crystal of ReYbBiIG for high-performance magneto-optical devices

A new type of magneto-optical (MO) Faraday rotation (FR) iron garnet bulk single-crystal with composition of ReYbBiIG (Re: Tb 3+ , Ho 3+ , etc.) was designed and grown by using Bi 2 O 3 /B 2 O 3 as the main flux and the accelerated crucible rotation technique. Through the combining of two types of Bi 3+ -substituted rare-earth iron garnets with opposite signs of FR, temperature and wavelength coefficients, the MO properties can be much improved. A series of nearinfrared (NIR) optical materials of ReYbBiIG with large MO figure of merit (>18°/dB), low saturation magnetic field (∼ 1.2 x 10 6 A/m), low NIR optical absorption (<6.58 cm -1 ), and very small FR temperature and wavelength coefficients at λ = 1.55 μm were obtained, including Ho 0.85 Yb 1.12 Bi 1.03 Fe 5 O1 2 and Tb 2.06 Yb 0.46 Bi 0.48 Fe 5 O 12 , etc. Indications are that these newly designed and grown MO FR crystals are good candidates for temperature stabilized and wideband optical isolators employed in wavelength division multiplexing optical fiber communication systems.

Magnetic and magneto-optical properties of oxide glasses containing Pr 3+, Dy 3+ and Nd 3+ ions

Magnetization of a number of oxide glasses containing Pr 3+, Dy 3+ and Nd 3+ ions has been measured as a function of the magnetic field (0–50 kOe) and temperature (5–300 K). Magneto-optical Faraday rotation (FR) in the same glasses has been measured as a function of the light wavelength (240–1000 nm) and temperature (80–350 K). Dispersion of FR has permitted us to find the positions of the effective transitions responsible for FR and their magneto-optical activities. Temperature dependencies of both FR and the magnetization at high temperatures obey the Curie–Weiss law with negative Weiss constants. High temperature magnetic moments of the rare-earth ions in the glasses are rather close to those of the free ions. At low temperatures, all studied glasses reveal downward curvature of the reciprocal magnetization variation with decreasing temperature. The origin of this behavior is discussed. Formation of antiferromagnetically ordered clusters in Dy glasses is supposed.

Prediction of huge x-ray Faraday rotation at the GdN4,5threshold

X-ray absorption spectra in a wide energy range around the 4d-4f excitation threshold of Gd were recorded by total electron yield from in-plane magnetized Gd metal films. Matching the experimental spectra to tabulated absorption data reveals unprecedented short light absorption lengths down to 3 nm. The associated real parts of the refractive index for circularly polarized light propagating parallel or antiparallel to the Gd magnetization, determined through the Kramers-Kronig transformation, correspond to a magneto-optical Faraday rotation of 0.7 degrees per atomic layer. This finding shall allow the study of magnetic structure and magnetization dynamics of lanthanide elements in nanosize systems and dilute alloys.

Structure, microstructure, and magneto-optical properties of laser deposited Bi3Fe5O12/Gd3Ga5O12(111) films

Bi 3 Fe 5 O 12 films were deposited onto single crystal Gd3Ga5O12(111) substrates by pulsed laser deposition. X-ray diffraction patterns and cross sectional transmission electron micrographs show epitaxial film growth and a flat interface between the film and substrate. However, there are small inclusions at the interface and a network of cracks is observed by optical microscope. The refractive index is 3.4 at 800 nm wavelength. The optical transmission is low below 540 nm but increases to 90% for a 1.8 μm thick film at 850 nm. The magneto-optical Faraday rotation is high, with a peak value of −24 deg/μm at 560 nm. The angle of Faraday ellipticity reaches a maximum value of 15 deg/μm at 545 nm.