Faraday Rotation Spectra Research Articles

Growth and magneto-optical properties of NaTb(MoO 4) 2 crystals

A sodium terbium molybdate (NaTb(MoO 4) 2) single crystal with dimensions of ∅ 20 mm×25 mm was grown by the Czochralski method. The lattice parameters of the crystal were determined by XRD analysis. The absorption spectrum and Faraday rotation spectrum ( B=1.07 T) were investigated at wavelengths of 400–1500 nm at room temperature. The Verdet constants of NaTb(MoO 4) 2 crystal were measured at 532, 633 and 1064 nm wavelengths by the extinction method. The results show that NaTb(MoO 4) 2 has a larger magneto-optical figure of merit than that of TGG at wavelengths of 660–1500 nm.

Improvements on Faraday Rotation Wavelength and Temperature Characteristics of TbYbBiIG Bulk Crystals in 1550 nm Band

This paper is concerned with the preparation and magneto-optical characterization of the Bi, Tb, and Yb partially substituted rare earth ferrite garnet bulk single crystals of Tb3-x-yYbyBixFe5O12. Here we focus our studies on improvements on the wavelength and temperature dependences of Faraday rotation (FR) by combining two types of bismuth substituted ferrite garnets with opposite FR wavelength coefficient (FWC) and FR temperature coefficient (FTC) signs. The FR and optical absorption spectra were measured and discussed in 1550 nm band. The specific FR of Tb0.91Yb1.38Bi0.71Fe5O12 crystal under magnetic field at saturation was found to be about -1617°/cm at λ=1550 nm, FWC = 0.009%/nm in the wavelength range of 1500–1620 nm and FTC = 3.92×10-5/K at λ= 1550 nm have been obtained due to the compensation effect, which are much smaller than that of YIG.

Preparation and magneto-optical properties of BiY 2Fe 5O 12 organic nanocomposite films

Bi-substituted yttrium iron garnet with a composition of BiY 2Fe 5O 12 (Bi-YIG) nanoparticles was prepared via mechanochemical processing and subsequent heat treatment. The maximum milling time was 8 h and the annealing was carried out at different temperatures up to 1000 °C for 4 h. Phase formation of the as-milled and annealed powders was investigated by X-ray diffraction (XRD). This investigation shows that there was no trace of garnet phase in the as-milled powder or the powders annealed below 800 °C. In the XRD patterns of the powders annealed above 800 °C, the peaks belonging to the garnet phase appeared and a single-phase garnet was finally obtained at 950 °C. Magnetic parameters of the powders were measured, using a SQUID unit, and a saturation magnetization of 22 Am 2/kg was obtained. Mean crystallite size of the single-phase powder, which was evaluated by Scherrer's formula was about 45 nm. Morphology of the powders was investigated by TEM, which shows that the particles were agglomerated. The single-phase powders were then dispersed in an organic binder for various Bi-YIG/binder weight ratios and for various dispersing times up to 80 h to obtain magnetic inks. Particulate films were made by the spin-coating method, using the magnetic inks. Magneto-optical properties (Faraday rotation) of the spin-coated films were investigated in the visible wavelength range of 470–625 nm. The results show that as Bi-YIG/binder weight ratios increases, the values of the Faraday rotation spectra increase too and their maximum values shift to shorter wavelengths.

Faraday rotation spectra analysis of Bi-substituted mixed rare-earth iron garnet crystals in optical communication band

Through combining two types of Bi-substituted rare-earth iron garnet crystals with opposite Faraday rotation wavelength coefficient (FWC) signs, the Bi-substituted mixed rare-earth iron garnet (Tb3−x−yYbyBixFe5O12) crystals with low FWC are used in optical isolators for broadband optical communication. However, the Faraday rotation (FR) spectra of bismuth-substituted mixed rare-earth iron garnet crystals have not yet been theoretically studied in the optical communication band [wavelength (λ)=1.5–1.62μm]. In order to interpret their FR spectra, a theory based on molecular-orbital levels of Fe3+ in tetrahedral (d) and octahedral (a) sites is used. It is shown that in the case of higher Bi3+ substitution, FR depends mainly on the contributions of Fe3+ in the octahedral sites. Furthermore, two types of rare-earth ions (Tb3+ and Yb3+) moderate the contributions to FR from Fe3+ in octahedral and decahedral sites and eventually have caused that Tb3−x−yYbyBixFe5O12 crystals has a near-zero FWC.

Tunable giant Faraday rotation of exciton in semiconductor quantum wells embedded in a microcavity

The Faraday rotation of an exciton in a GaAs quantum well (QW) embedded in a microcavity is investigated theoretically. The authors find that the Faraday rotation is enhanced remarkably by the microcavity, with a magnitude about two orders of magnitude larger than that of a single QW without microcavity. The Faraday rotation can be tuned by changing the incident angle of the pump and probe lights, or by varying the temperature or an external electric field. With an appropriate detuning between the cavity mode of the pump and probe lights, the Faraday rotation spectrum displays a strongly asymmetric line shape, which can easily be detected experimentally.

Theoretical investigation of the optical and magneto-optical properties of EuX (X=S, Se, and Te)

The optical and magneto-optical (MO) properties of europium sulphide (EuS) have been studied by employing the full potential linearized augmented plane wave method as implemented in the WIEN2K code, with the Coulomb corrected local spin density approximation (LSDA+U) in the self-interaction correction (SIC). Our calculations give an energy gap of 1.58 eV for ferromagnetic semiconductor EuS in fair agreement with experiment. The calculated Faraday rotation spectrum of EuS is in better agreement with available experimental data, compared to a previous calculation. We have also performed calculations for EuSe and EuTe in the fictitious ferromagnetic phase with a view of exploring the effect of replacing S by Se and Te on the optical and magneto-optical properties.

Magnetic behavior of Fe 3O 4 nanostructure fabricated by template method

One dimensional nanostructured magnetic materials are interesting because of their enhanced magnetic properties and potential applications such as information storage and biosensor. To prepare uniform nanostructure with controlled diameter, we have utilized porous anodic alumina template (AAT). The nanowire arrays are prepared by incorporation of monosized 10 nm magnetite nanoparticles into AAT, accompanied by thermal annealing. Transmission electron microscope and field emission scanning electron microscope showed that the nanoparticles were changed to the polycrystalline nanowire phase in AAT. The annealing procedure, which improved crystallinity of the nanoparticles and caused clustering of nanoparticles into nanowires, had a dramatic effect on their magnetic properties. For example, coercivity measured at cryogenic temperature increased from 350 to 8000 Oe after annealing. Clustering of the nanoparticles had also significant effect on the Faraday rotation spectra of the material. For example, inter-valence charge transfer transition of isolated magnetite nanoparticles vanished in wire assembles. It might be due to significant improvement of crystallinity of the wires, which might consists of enlarged Fe 3O 4 nanoparticles lined up in quasi-1D wires.

Optical and magneto-optical spectra of europium-doped strontium tetraborate single crystals

Abstract Optical absorption, luminescence, magnetic circular dichroism and Faraday rotation spectra of Sr 0.95 Eu 0.05 B 4 O 7 single crystals are studied. The crystal field parameter for europium ions is found to be equal to 790 cm −1 . Excitation spectrum of luminescence strongly differs from that of low-doped polycrystalline strontium tetraborate. The Verdet constant in the ultraviolet is comparable to that of terbium gallium garnet in the visible.

A compounded rare-earth iron garnet single crystal exhibiting stable Faraday rotation against wavelength and temperature variation in the 1.55 μm band

The Bi, Tb and Yb partially substituted iron garnet bulk single crystals of Tb 3− x − y Yb y Bi x Fe 5O 12 were grown by using Bi 2O 3/B 2O 3 as flux and accelerated crucible rotation technique for single-crystal growth. Faraday rotation (FR) spectra showed that the specific FR of the (Tb 0.91Yb 1.38Bi 0.71)Fe 5O 12 crystal under magnetic field at saturation was measured to be about −1617°/cm at λ=1.55 μm, Faraday rotation wavelength coefficient (FWC, 0.009%/nm) in the wavelength range of 1.50–1.62 μm and Faraday rotation temperature coefficient (FTC, 3.92×10 −5/K) at λ=1.55 μm were even smaller than that of YIG. It is proven that through combining two types of Bi-substituted rare-earth iron garnets with opposite FWC and FTC signs, the compound rare-earth iron garnets with low FWC and FTC may be obtained due to the compensation effect. The saturation magnetization of (Tb 0.91Yb 1.38Bi 0.71) Fe 5O 12 crystal is 0.48×10 6 A/M and is also much smaller than that of YIG. We have found empirically that there is a simple relationship between the FR θ f( x) and Bi content x for Tb 3− x − y Yb y Bi x Fe 5O 12, which is given by θ f( x)=(−2759 x+400)°/cm.

The investigation of mechanisms of the magneto-optical activity of rare-earth iron garnet single crystals

The magnetic and magneto-optical properties (MO) of the typical representatives of three rare-earth iron garnets (RIG) groups: (1) with heavy rare-earth elements Yb, Er, Dy, Tb; (2) with elements from the middle of lanthanide series Gd, Sm; (3) with light rare-earth element Nd are presented. In contradistinction to other work on the Faraday rotation (FR), which were done only at 1152 nm (8696 cm −1); here, we present FR spectra obtained in the energy region 5500–20,000 cm −1 with high optical resolution. The investigations have been done at temperatures of 5, 82, 130 and 295 K using magnetic field up to 25 kOe applied parallel to the [1 1 1] crystallographic axis of the crystals. It has been shown that the contribution proportional to the magnetic field and independent of temperature to the mixing of the ground state multiplets exceeds the paramagnetic contribution in YbIG, ErIG, GdIG and SmIG. In Tb and Dy iron garnets contributions from the two mechanisms have opposite signs, and the paramagnetic mechanism gives the greatest contribution to FR. Nevertheless, the contribution of the diamagnetic mechanism, caused by the influence of the exchange field in the iron-sublattices on R ions, is significant, and it is necessary to take it into account. Anomalously large MO activity is observed in NdYIG. This is the result of contributions of in the same sign and approximately equal magnitude from the paramagnetic and diamagnetic mechanisms.

Optical Properties of a Semimagnetic Quantum Well in a Proximity of a Superconducting Film

We consider, via numerical calculations, a hybrid structure made of a semimagnetic Cd1ixMnxTe quantum well deposited in a close proximity to superconducting niobium fllm. We simulate photoluminescence and the Faraday rotation spectra, modifled by the presence of vortices in this type II superconductor. The magnitude of the evaluated efiects is small | the vortex induced spectral line shape variation is of the order of 1% at 1 K and 0.1% at 3 K and is expected to occur mainly in the fleld range between 0.03 T and 0.05 T.

Faraday-rotation spectrum of electron spins in microcavity-embedded GaAs quantum wells

Using the time-resolved magneto-optical Faraday effect, the dynamics of electron spins is measured in a GaAs quantum well embedded in a vertical one-dimensional optical cavity. The cavity leads to an enhancement of the Faraday-rotation amplitude that varies with the detuning between the QW absorption peak and the cavity resonance. We find a transition in the Faraday rotation spectrum that is triggered by the cavity detuning. This is attributed to a modification of the phase of the cavity reflectivity at the impedance-matching condition of the cavity. If the QW absorption is too small to compensate the asymmetry of the cavity mirrors, the Faraday-rotation signal is dominated by spin-induced circular birefringence, whereas contributions from circular dichroism predominate for higher quantum-well absorption. A numerical calculation of the Faraday-rotation spectrum is in good agreement with the experimental results.

The magneto-optical activity of rare-earth ion in Y-substituted erbium and neodymium iron garnets

The magnetic and magneto-optical (MO) properties of Er x Y 3− x Fe 5O 12 ( x = 0.4, 1.0, 1.5, 2.5 and 3.0) (ErYIG) and Nd x Y 3− x Fe 5O 12 ( x = 0.5, 0.96, 1.39 and 1.72) (NdYIG) single crystals have been presented. Faraday rotation (FR) spectra obtained in energy region 5500–13,000 cm −1 for the erbium garnets and in energy region 6000–17,000 cm −1 for the neodymium garnets with a high optical resolution have been presented here, in contrast to other researches of the FR performed only at 1152 nm (8696 cm −1). The investigations at 5, 130 and 295 K temperatures under magnetic field up to 20 kOe applied parallel to the [1 1 1] crystallographic axes of the crystals have been provided. Anomalous great MO activity is the result of joint action of similar in sign and approximately equal in quantity of paramagnetic and diamagnetic mechanisms in NdYIG. It has been shown that proportional to magnetic field and independent of temperature contribution of the mixing of the ground state multiplets mechanism exceeds paramagnetic contribution. Concentration dependence of MO coefficients confirms one-ion nature of MO activity of ErYIG.

Wavelength and temperature characteristics of BiYbIG film/YIG crystal composite structure for magneto-optical applications

We report the wavelength and temperature characteristics of novel Bi-substituted rare-earth iron garnet films grown on a YIG substrate by a modified liquid phase epitaxy (LPE) technique. The Faraday-rotation spectrum was measured by the magneto-optically modulated dual-frequency technique with the wavelength varied from 800 nm to 1700 nm. The resultant Bi0.37Yb2.63Fe5O12 (BiYbIG) LPE film/YIG crystal structure showed an increased Faraday-rotation coefficient due to Bi3+-ion doping on the dodecahedral sites of the iron garnet without increasing absorption loss; therefore, a good magneto-optical figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved (21.5 deg/dB and 30.2 deg/dB at 1300-nm and 1550-nm wavelengths, respectively, at room temperature). In addition, since the Yb3+ and Y3+ ions provide opposite contributions to the wavelength and temperature characteristics of the Faraday rotation, the resultant BiYbIG LPE film/YIG crystal structure showed a flat Faraday-rotation curve versus wavelength and temperature. The Faraday-rotation wavelength coefficient was reduced to 0.06 %/nm at 1550-nm wavelength. The Faraday-rotation temperature derivative was reduced to 0.006 deg/°C at 1300-nm wavelength and 0.007 deg/°C at 1550-nm wavelength, respectively.

Magneto-optical rotation of a one-dimensional all-garnet photonic crystal in transmission and reflection

We present spectra of transmittance, reflectance, and Faraday rotation of transmitted and reflected light for a periodic garnet multilayer structure with a central defect layer. The multilayer consists of alternating layers of bismuth and yttrium iron garnet, is $1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ thick, and was prepared by pulsed laser deposition. For the reflection measurements, a silver mirror was evaporated on top of the multilayer. Faraday rotation is strongly enhanced at resonances in transmission and reflection. The peak value obtained at 748 nm in transmission is 5.3\ifmmode^\circ\else\textdegree\fi{} and at 733 nm in reflection is 18\ifmmode^\circ\else\textdegree\fi{}. A single layer BIG film of equivalent thickness shows 2.2\ifmmode^\circ\else\textdegree\fi{} Faraday rotation at 748 nm. We find rather good agreement between measured and calculated spectra. Using calculations of the distributions of light intensities at different wavelengths inside the multilayer, we are able to give consistent qualitative explanations for the enhancement of Faraday rotation. We also find numerically that---at moderate strengths of the optical resonances---a linear relation exists between Faraday rotation and the intensity integrated over all magneto-optically active layers, if absorption is neglected.

Magneto-optical spectra of closely spaced magnetite nanoparticles

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe3O4 (magnetite) nanoparticles (8-nm diameter) and poly(methylmethacrylate). Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for (dilute composites) to 540 nm (concentrated). We present a theory based on the discrete-dipole approximation which accounts for optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental data suggest that the shifts in spectral peak position depend on both interparticle distance and geometrical configuration.

Magnetic rotation spectra of Co/Pt and Co/Cu multilayers in 50–90 eV region

Faraday rotation spectra of Co/Pt multilayers were obtained in the region including Co M 2,3 and Pt N 6,7 absorption edges by using multilayer polarizers, and were transformed to magnetic circular dichroism (MCD) spectra by Kramers–Krönig analysis (KKA). From the dependence of the rotation angle on the layer thickness, it was suggested that the magnetization of Co tends to be uniform in Co layers and that of Pt is localized at Co/Pt interfaces. The orbital magnetic moment of Co was estimated to be about 0.17 μ B /Co. The similarity of electronic states around magnetized Pt site between Co/Pt multilayers and CoPt 3 alloy is suggested by the resemblance of the MCD spectra of both materials around Pt N 6,7 edges. In addition, magnetic Kerr rotation of Co/Cu multilayer was measured and was observed around Co M 2,3 and Cu M 2,3 absorption edges.

Magneto-optical polarization spectroscopy with soft X-rays

X-ray magneto-optical polarization spectroscopy is a relatively new ellipsometric technique with which the complete polarization state of X-ray radiation after its interaction with magnetic matter can be measured. This comprises rotation and ellipticity, which fully quantify the light’s polarization. Employing this technique, the complete magneto-optical constants in the X-ray regime can directly be obtained, in contrast to the more commonly used intensity-only measurements. The Faraday and magneto-optical Kerr effects, being odd with respect to magnetization reversal, can be used for the examination of ferromagnetic (FM) materials. This we demonstrate here with Faraday and Kerr rotation and ellipticity spectra, measured at the 2p edges of Fe, Co, and Ni. The Voigt effect and magnetic linear dichroism (XMLD), which are even with respect to magnetization reversal, are applied to probe both FM and antiferromagnetic (AFM) materials. Using a new XMLD-reflection spectroscopy we present results obtained on technologically important buried AFM NiO layers.

Investigation on the diamagnetic Faraday rotation spectra in Pr-substituted yttrium iron garnet

By using the single particle model, the diamagnetic Faraday rotation (FR)spectra of Pr3+ ion in Pr:YIG crystal is presented based on the quantum theory. The linear dependence of λF-1/2θ on λ2 is calculated at 300 and 77K in the 105—13 micron wavelength range. It is found that the diamagn etic FR is 64% of paramagnetic FR at 77K and the two types of FR can be of more or less equal importance. The diamagnetic FR depends on the temperature and the exchange field for the ions with orbit single ground states derived from the cr ystal field.

Faraday rotation spectra of Co 2+ at distorted octahedral sites in magnetic oxides

Faraday rotation (FR) spectra of Co 2+(3d) 7 ions with high spin state at distorted octahedral sites in magnetic oxides are calculated on the basis of the crystal field theory. Since the spin-allowed transition from the ground 4T 1[(t 2) 5{ 2T 2}e 2{ 2A 2}] to the excited 4T 2[(t 2) 4{ 3T 1}e 3{ 2E}] states only contributes to the FR in the visible wavelength region, the FR spectra for this transition are calculated by taking account of the spin–orbit interaction V(SO), the low symmetry field V(D 2d), and the molecular field V(MF). Using the transition strengths calculated by the Racah–Wigner calculus, the FR spectra are calculated as a function of Δ / ζ , where Δ and ζ are parameters for V(D 2d) and V(SO), respectively. As a result, the FR at low temperature was found to change from a dispersive shape to an absorptive one as Δ / ζ becomes positive to negative.