Magneto-optical Coefficient Research Articles

Resonant amplification of the magnetoelectric effect in ferrite-piezoelectric composites

The magnetoelectric effect in ferrite-piezoelectric composites is considered. A theory of the magnetoelectric effect in the electromechanical-resonance region for disk-shaped samples is presented. The magnetooptical coefficient is calculated for longitudinal and transverse orientations of electric and magnetic fields. It is shown that the effect increases by a few orders of magnitude at the electromechanical-resonance frequency. The frequency dependence of the effect is experimentally studied for a ferrite-nickel spinel-PZT composite. A resonant increase in the effect is observed (in agreement with the theory); the highest value of the magnetoelectric coefficient was 15 V/(cm Oe).

Optimization of surface-plasmon-enhanced magneto-optical effects

Kretschmann prism couplers, including magneto-optical media such as Co, Fe, and Ni, allow enhancement of the magneto-optical response, such as conversion of light polarization, thanks to the resonant excitation of surface plasmons. Since these media have high losses, they support overdamped surface plasmons. A way to get high-quality surface-plasmon resonance is to use noble-metal/ferromagnetic-metal multilayer thin films. The question that arises is, which surface-plasmon resonance leads to the largest enhancement: is it the overdamped or the high-quality one? We show that the best optimization not only depends on the orientation of the magnetic field but also on the magneto-optical coefficients. The most effective enhancer of the magneto-optical effects is the high-quality surface plasmons for the transverse orientation and may be the overdamped surface plasmons for the polar and longitudinal ones. This applies when the noble metal is gold and the magneto-optical medium is cobalt.

OPTICAL AMPLITUDE AND PHASE EVOLUTION IN NONLINEAR MAGNETO-OPTICAL BRAGG GRATINGS

We present a theory on stratified nonlinear magneto-photonic crystals, with arbitrary spatial distribution of the refractive index and magneto-optical coefficients. The coupled mode theory is formulated for plane waves inside the crystal, and a perturbation series of integral solutions for the spectral response of the crystal is presented. Material issues and configurations are discussed, and the described theory is applied to the calculation of transmission spectra of binary magneto-photonic crystals.

Two-magnon Raman scattering in the antiferromagnet CoF 2: theory and experiment

Measurements are reported for the temperature and polarization dependences of two-magnon Raman light scattering in the rutile-structure antiferromagnet CoF 2 over the temperature range from 4 to 40 K . An effective spin model is employed to obtain a good description of the line shapes and peak frequencies for temperatures up to 0.4 T N. The results are also deduced for the relative values of the two-magnon magneto-optical coupling coefficients.

Alternative geometries for the determination of x-ray magneto-optical coefficients

Two alternative geometries are proposed for x-ray magneto-optical (MO)spectroscopy with linearly polarized light in photon-in/photon-out reflectionexperiments, without sophisticated polarization analysis of the reflected x-rayradiation. One of the geometries yields an MO effect that is odd in the magnetizationM,i.e., to first order linear in . The other geometry yields a magneto-x-ray effect that is even inM,i.e., to lowest order proportional to . This second MO effect is a promising tool for the x-ray reflection spectroscopy ofantiferromagnets. The applicability of these spectroscopies is demonstrated by experimentalresults.

Linear and quadratic magneto-optical Kerr effects in continuous and granular ultrathin monocrystalline Fe films

The effects of nanostructuration on the magneto-optic properties of ultrathin monocrystalline iron films grown on MgO (001) are investigated through the magneto-optic coefficients, which have a linear and quadratic dependence on the magnetization. The photon energy dependence of such magneto-optic coefficients is determined by measuring the relative variations of the reflectivity (ΔR p p /R p p ) for p-polarized incident and reflected light (p-p polarized) when the magnetization rotates in the plane of the sample. Thick Fe films present a magneto-optical anisotropy, which has a quadratic dependence on the magnetization. Such anisotropy is strongly reduced in nanostructured iron thin films formed by nanometric iron islands. The modifications induced by the nanostructuration are stronger for the magneto-optical coefficients, which have a quadratic dependence on the magnetization in contrast to the linear terms. A self-consistent effective-medium formalism is presented that explains the modifications induced in the magneto-optical coefficients by nanostructuration.

Fabrication of Bi-doped YIG optical thin film for electric current sensor by pulsed laser deposition

Bi-doped yttrium iron garnet (Bi x Y 3− x Fe 5O 12, Bi:YIG) thin films, which can be used as electric current sensors, are grown on Gd 3Ga 5O 12 (GGG) substrates by pulsed laser deposition (PLD) using an ArF excimer laser. The growth condition for high quality epitaxial Bi:YIG thin films is investigated by varying the PLD process parameters, such as the substrate temperature and ambient oxygen gas pressure. The epitaxial film growth is attained at the substrate temperature of around 500 °C and at ambient oxygen pressure between 125 and 175 mTorr. The optical properties of epitaxial films are measured and the maximum magneto-optic sensitivity coefficient is observed to be 44.1°/T with a film thickness of about 0.7 μm at a wavelength of 500 nm. The results indicate that the PLD technique can be useful for realizing a miniature current sensing device with the Bi:YIG thin film.

Non-linear optics and magneto-optics on nano-structured interfaces

The behaviour of the reflectivity and Kerr magneto-optic effects in the non-linear second-harmonic (SH) field diffracted from nano-scale structured ferromagnetic interfaces is reported. Measurements are made in both the linear and non-linear fields at two different fundamental wavelengths (1064 nm and 800 nm) and their associated harmonics. Resonant behaviour observed as a function of angle of incidence is identified with surface-plasmon production that is known to intensify the local field within the interface. Radiation incident at angles of incidence that optimise coupling to the electron plasma produces an increase in the SH field radiated in the vicinity of those angles. Similarly, at those angles of incidence where radiation at the SH wavelengths (532 nm and 400 nm) couples optimally to the electron plasma, troughs are seen in the angular spectrum of the generated SH radiation. Kerr magneto-optic measurements taken in both the linear field and the SH field both show very significant enhancement at angles meeting the plasma-resonance condition. The totality of experimental data presented allows the conclusion that intensification of the interface electric field due to plasmon creation enhances not only the SH reflection coefficient, as was already known, but also the magneto-optic reflection coefficients in both linear and SH fields.

Characteristics of Bi:YIG Magneto-Optic Thin Films Fabricated by Pulsed Laser Deposition Method for an Optical Current Transformer

Pulsed laser deposition (PLD) technique is applied for fabricating Bi doped yttrium iron garnet (BixY3-xFe5O12) (Bi:YIG) thin films which can be used for optical current transformer. Growth conditions of high quality Bi:YIG thin films on Gd3Ga5O12 (GGG) substrates are investigated by varying PLD process parameters. The magneto-optic sensitivity coefficient of the fabricated Bi-YIG thin film is measured as 44 deg/T at a wavelength of 500 nm.

Quantum theory of the magneto-optical effect and magnetization of Nd-substituted yttrium iron garnet

The magneto-optical and magnetic properties of Nd 3+ ions in Y 3Fe 5O 12 garnet are analyzed by using quantum theory. In the spontaneous state, the magneto-optical effects originate mainly from the intra-ionic electric dipole transitions between the 4 f 3 and 4 f 25d states split by the spin-orbit, crystal field, and superexchange interactions. For the excited configuration, the coupling scheme of Yanase is extended to the Nd 3+ ion. The magneto-optical resonance frequencies are mainly determined by the splitting of the 5d states induced by the crystal field. The theoretical results of both Nd magnetization and Faraday rotation are in good agreement with experiments. The observed Faraday rotation is proved to be of the paramagnetic type. Although the value of the magneto-optical resonance frequency derived from a macroscopic analysis is approximately confirmed by our theoretical study, a new assignment about the transitions associated with this resonance is unambiguously determined. The spin-orbit coupling of the ground configuration has a great influence on both the Faraday rotation and magnetization, but, unlike the theoretical results obtained in some metals and alloys, the relation between the Faraday rotation and the spin-orbit coupling strength is more complex than a linear one. The magnitude of the magneto-optical coefficient increases as the spin-orbit interaction strength of the ground configuration decreases when the strength is not very weak. Finally, the temperature dependence of the magneto-optical coefficient and the effect of the mixing of different ground-term multiplets induced by the crystal field are analyzed.

Analytic propagation matrix method for anisotropic magneto-optic layered media

Simplified analytic expressions are derived for the optical propagation matrix of magnetic anisotropic Kerr media using the Lagrange-Sylvester interpolation polynomial. This expression is used to investigate magnetic Kerr films in Fabry-Perot configurations, magneto-optic recording quadrilayers and alternating periodic stacks. It is found that the magneto-optic reflection coefficients are enhanced by a few orders of magnitude due to multiple reflections. Bragg-type reflection peaks from periodic structure appear solely due to the gyrotropy and it is shown that omnidirectional reflection is possible under certain conditions. This analytic approach is faster than using direct numerical calculation.

Quadratic power dependence of the magneto-optic coupling coefficient in the magnetostatic wave–optical interaction (abstract)

The transverse magnetostatic wave (MSW)–optical interaction was first observed at relatively low microwave power levels.1 Recent investigations show that a change in the demagnetizing field due to an increase in the dynamic magnetization causes a shift in the microwave passband2 and consequently a shift in the MSW–optical interaction spectrum.3 We now focus our efforts on determining the effects of high microwave power on the magneto-optic coupling coefficient (κ). A microstrip T transducer excited forward volume MSWs in a bismuth–lutetium–iron–garnet film. An optical beam is edge coupled into the film and the transverse MSW–optical interaction is observed at high microwave power levels. Using the coupled mode equations, we show that the amplitude of the diffracted beam is a product of κ and the phase mismatch between the optical guided modes and the MSWs. Taylor series expansions for κ and the MSW wave number (β) are used to obtain an analytic expression for the MSW–optical interaction. The dependence on β causes a shift in the interaction passband with increasing microwave power. After correcting for this nonlinear shift, the residual dependence of the output optical intensity on input microwave power is attributed to a quadratic power dependence in κ. The coefficient of the quadratic term was observed to be ∼1% of the coefficient of the linear term and its effect at high power is comparable to that of the nonlinear frequency shift.

Quadratic power corrections to the dynamic magnetization using the transverse magnetostatic wave-optical interaction

A microstrip T-transducer excites forward volume magnetostatic waves (MSWs) in a [BiLu]3Fe5O12 film. An optical beam is edge coupled into the film and the transverse MSW–optical interaction is observed at high microwave power levels. Using the coupled mode equations, we demonstrate that a T-transducer causes the intensity of the diffracted beam to be a product of terms involving the magneto-optic coupling coefficient (κ) and the phase mismatch between the optical guided modes and the MSWs. Taylor series expansions for κ and the MSW wave number (β) are used to obtain an analytic expression for the MSW–optical interaction. The dependence on β causes a shift in the interaction spectrum with increasing power. After correcting for this shift, the residual dependence on power is attributed to a quadratic correction to the dynamic magnetization which in turn affects κ. We demonstrate how the quadratic dependence plays an important role in accurately determining an expansion for the MSW dispersion relation.

A study of the Faraday effect in yttrium aluminium garnets doped with cerium

Calculations of the Faraday rotation (FR) and magnetic circular dichroism spectra in the wavelength region between 300 nm and 650 nm caused by the Ce3+ ions in the Ce substituted aluminium garnets (YAG) based on the quantum theory are presented. The Faraday effect contributed by the Ce3+ ions is caused mainly by the intraionic electrical dipole transitions between the 4f and 5d configurations. The effect of the crystal field (CF) and spin orbit coupling on the Faraday effect has been discussed. The CF upon the Ce3+ ions doped in garnets depends strongly on the nature of the next-nearest neighbors. The CF upon the Ce3+ ions in YAG is weaker than that in yttrium iron garnets (YIG). Therefore, compared with Ce: YIG, the anomalous rotatory dispersions occur at higher frequencies. The shape of the FR spectrum caused by the Ce3+ ions in YAG is different from that caused by the Ce3+ ions in YIG. An explanation of this difference is given. The influence of the mixing of different multiplets of the ground configuration on the Faraday effect is discussed. Such mixing is one of the causes which make the magneto-optical coefficient vary with temperature.

Variations in the magneto-optic coupling coefficient in a bismuth-lutetium-iron-garnet film

Magnetostatic wave-optical interactions are studied in the transverse geometry using a [BiLu]/sub 3/Fe/sub 5/O/sub 12/ film. Non-monotonic variations in the magneto-optic coupling coefficient are observed as we increase the input microwave power at a fixed frequency. Similar variations are also seen in the transmitted microwave signal, though the features appear at higher power levels. The non-monotonic behavior is due to a shift in the microwave passband with increasing power. Density plots are used to correlate the two sets of data over a 350 MHz region. The discrepancy in power levels associated with a feature in the line plots is a consequence of the different curvatures of the two density plots.

Magnetooptical properties of YIG:Sc single crystals

Faraday rotation measurements at 1152 nm were performed on single-crystal oriented platelets of ferrimagnetic garnets of formula Y 3Fe 5 − x Sc x O 12 (0 < x < 0.55) as a function of temperature and magnetic field. Sc 3+ ions substituting for octahedral Fe 3+ have a much greater influence on the spontaneous Faraday rotation than found for the corresponding tetrahedral diamagnetic substitution. The Faraday rotation susceptibility is constant and independent of Sc concentration. The results are interpreted as the sum of magneto-optical contributions from the [a] and (d) sublattices proportional to their magnetizations and induced by magnetic and electric dipole transitions. The electric magneto-optical coefficients deduced from a least squares fit of the experimental values are linear functions of the Sc concentration.

Quantum theory of the strong magneto-optical effect of Ce-substituted yttrium iron garnet.

Calculations of the Faraday rotation (FR) and ellipticity spectra in the wavelength region between 360 and 1260 nm caused by the ${\mathrm{Ce}}^{3+}$ ions in the Ce-substituted yttrium iron garnets based on the quantum theory are presented. The calculation of the temperature dependence of FR at 633 and 1150 nm wavelengths is presented as well. The Faraday effect contributed by the ${\mathrm{Ce}}^{3+}$ ions is caused mainly by the intraionic electrical dipole transitions between the 4f and 5d configurations. The effect of the crystal field (CF), superexchange interaction, and spin-orbit coupling on the magneto-optical (MO) effect has been discussed. The energy differences between the lowest and second CF-split 5d levels and the lowest CF-split 4f level are 1.36 and 3.10 eV, respectively. Therefore there are anomalous rotatory dispersions at about 1.36 and 3.10 eV. The difference of the transition intensity for the right- and left-handed circularly polarized light between the lowest CF-split 5d level and the ground state is negative, while the corresponding value for the transition between the second CF-split 5d level and the ground state is positive. So the FR is positive over the whole photon energy region between 1.36 and 3.10 eV and is negative outside this region. Since the energy differences between the CF splitting levels of the excited configuration are comparable with the energy difference between the mean energies of the excited and ground configurations, the MO coefficient varies with temperature. The admixing of different multiplets of the ground configuration is another cause which makes the MO coefficient vary with temperature.

The influence of the admixing of different multiplets on the spin magnetic moment and Faraday effect of rare earth ions in Garnets

The influence of the admixing of the excited multiplets of the ground configuration with the ground multiplet on the spin magnetic moment of the crystal- field- and exchange-interaction-split ground state, the Faraday rotation and the magneto-optic coefficient induced by the rare earth ions in rare-earth-substituted garnets Y3-xRxFe5O12 (R=Ce and Pr) has been calculated in this paper. It is found that, in the case of Ce3+ ions, the admixing of the 4f1 2F7/2 multiplet with the 2F5/2 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 140% and the Faraday rotation increase by 180% at 633 nm wavelength, and 150% at 1150 nm at 294 K. In the case of Pr3+ ions, the admixing of the 4f2 3H5 multiplet with the 3H4 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 34% and the Faraday rotation increase by 59% at 294 K. The admixing of different multiplets of the Ce3+ ions makes the ratio between the magneto-optic coefficients at 50 and 294 K increase by 7% at 633 nm wavelength and 15% at 1150 nm.

Faraday rotation of bismuth substituted dysprosium iron garnets

The Faraday rotation on single crystal garnets of composition Dy/sub 3-x/Bi/sub x/Fe/sub 5/O/sub 12/ with x=0.43 has been investigated in the temperature range 10 K<T<300 K at lambda =1150 nm. The data are described in terms of the corresponding sublattice magnetizations assuming that the contribution of the Fe/sup 3+/ ions to Faraday rotation (FR) is the same as for bismuth substituted yttrium garnet (for identical x value). The first order magnetooptical (MO) coefficient (C/sub e/) of the Dy3+ ion is deduced; in the spontaneous state, C/sub e/ is linear temperature dependent as previously found in pure DyIG with a decrease of C/sub e/ of about 30-50% induced by the presence of bismuth.<<ETX>>

Magnetic thin films for data storage

Applications of magnetic thin films in data storage technology and areas for future research on thin films are discussed. Recent work at various laboratories indicates that magnetic recording densities of at least two orders of magnitude greater than those of today will be achieved. Among the advances in thin film technology which are needed to make this possible are the following: improved wear resistant overcoats for magnetic media; higher coercivity thin film media with isolated grain structure and multilayers to achieve low noise; high magnetization, high permeability multilayer thin film materials for advanced recording heads; giant magnetoresistive materials for advanced read heads. Although magnetic recording is expected to continue to dominate the data storage industry for the next two decades, magnetic-optic recording is likely to play an increasingly large role as a removable storage medium for large files of data involving images and multimedia. For increased storage density in magneto-optic recording, new magneto-optic thin film materials which are sensitive in the blue (or shorter) wavelength spectrum are needed. These films must not only provide large magneto-optic coefficients, but must also have the proper microstructure so that noise is low during readback. In order for these advances to be possible, new materials, new processing techniques, improved models and improved resolution imaging systems for studying both the magnetic and physical microstructure of thin films are needed.