Kerr Rotation Angle Research Articles

Terahertz radiation-induced conductivity, Kerr and Faraday angles, and spin textures in a two-dimensional electron gas with spin-orbit coupling subjected to a high magnetic field and periodic potential

The terahertz radiation-induced conductivity and dielectric polarization tensors as well as the Faraday and Kerr rotation angles and the non-equilibrium spin textures are studied for two-dimensional electron gas with strong spin-orbit coupling subjected to high magnetic field and to tunable periodic potential of a two-dimensional gated superlattice. It is found that both real and imaginary parts of the frequency-dependent induced conductivity approach maximum values with sharp and detectable peaks at frequencies corresponding to the inter-subband transitions between spin-split magnetic subbands. The observed properties of the conductivity tensor frequency dependence are applied for the description of the Kerr and Faraday rotation angles which can be used as another experimental tool for describing the electron gas in periodic structures with significant spin-orbit coupling. The formation of radiation-induced spin textures is predicted having both in-plane and out-of-plane components with space distribution scale comparable to the superlattice cell size which can be observed experimentally.

Magneto-Optical Observation of CPP-GMR Device With Perpendicular Magnetic Anisotropy Driven by Spin Transfer Switching Using Transparent Top Electrode

A new magneto-optical (MO) spatial light modulator (SLM) driven by spin transfer switching (STS) promises the realization of an ultra-high resolution SLM. However, its Kerr rotation angle was inadequate and required improvement using polar Kerr. Gd-Fe film, known as a material for MO disks, has a large MO effect. In this study, we applied a composite film with a Gd-Fe layer and multiple Co/Ni layers for a free layer of a CPP-GMR device. We fabricated a CPP-GMR device with perpendicular magnetic anisotropy and succeeded in magneto-optical observations driven by STS using a transparent top electrode.

Fabrication and characteristics of one-dimensional magnetophotonic crystals for magneto-optic spatial light phase modulators

We prepared the reflection type magnetophotonic crystals (R-MPC) to enhance the magneto-optic property of magneto-optic spatial light phase modulator (MOSLM). Magnetophotonic crystals have a localized wavelength by using a defect layer in which the magneto-optic property can be increased tremendously. By the calculation, it was revealed clearly that Kerr rotation can be enhanced with increasing the repetition number (k) which is the number of dielectric layer. In this study, Dy1.0Bi1.5Y1.0Fe3.8Al1.2O12 (DyBi:YIG) garnet material, of which Faraday rotation angle is about −3 deg/μm, was utilized as a defect layer. At the designed wavelength of 532 nm and k=5, SGGG/[SiO2/Ta2O5]2/DyBi:YIG/[SiO2/Ta2O5]k structure fabricated with garnet thickness of 347.6 nm showed Kerr rotation angle of 26° and reflectivity of 0.2% which is coincident considerably with the results (θk=30° and R=0.59%) calculated by the matrix approach method. The fabricated R-MPC-MOSLM structure exhibited the magneto-optic property of about 25 times higher than single garnet film in consideration of the thickness of magneto-optic material.

Local field effects in magneto-optics of two-dimensional arrays of ferromagnetic nanoparticles

A theory of the polar magneto-optical Kerr effect in a layer of small ferromagnetic particles has been developed in the framework of the Green’s function method of electrodynamics. The manifestation in magneto-optics of the local field effect, which is initiated by the contribution to the effective field of dipole moments induced in particles, has been studied in terms of the model of a square lattice of ferromagnetic ellipsoids. The magneto-optical Kerr effect stimulated under normal incidence of a linearly polarized electromagnetic wave on a layer of particles magnetized perpendicular to the layer plane has been analyzed. The dependence of the Kerr rotation angle in an array of ellipsoidal Co particles embedded in the transparent dielectric CaF2 on the light frequency, the parameters of the ellipsoidal particles, and the lattice period (concentration of the magnet in the layer) has been studied numerically. It has been shown that, within a broad (2.0–4.5 eV) spectral range, the local field effect studied as a function of increasing concentration of Co particles in the layer manifests itself in the reversal of the sign of the Kerr rotation compared to that observed in a single ellipsoid or a solid Co film.

Magnetic Anisotropy and Magneto-Optical Kerr Effect of BCC Ni(001) Films: Ab-initio

Using the full potential linearized augmented plane wave (FLAPW) method, we have investigated the thickness dependent magnetic anisotropy and the magneto-optical kerr eect (MOKE) of bodycentered-cubic (BCC) Ni films in the range from 15 monolayer (ML) to 21 ML. Through magnetic anisotropy calculations, we have realized that the clean BCC Ni(001) has an in-plane magnetization along the (100) direction until 19 ML, but it changes to the (110) direction at a 21 ML thickness. Interestingly, the Au capped BCC Ni(001) film always displays a perpendicular magnetic anisotropy (PMA). This implies that the influence of the interface contribution on the magnetic anisotropy is an essential factor. The kerr rotation angle has been shown to be insensitive to the film’s thickness or the Au capping layer. Also, thickness dependent X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) have been presented.

Determination of the Voigt constant of phthalocyanines by magneto-optical Kerr-effect spectroscopy

Thin films of organic molecular semiconductors from the class of phthalocyanines are investigated by means of magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. A numerical analysis of the energy dispersion of the real and imaginary part of the complex magneto-optical Kerr rotation angle in the visible to near ultraviolet spectral range allows the first determination of the magneto-optical material constant, the so-called Voigt constant, for a molecular material and the results are compared to density-functional theory calculations. The Voigt constant is only 1--2 orders of magnitude smaller compared with soft ferromagnetic materials such as Ni. The amplitude of the Voigt constant is exploited to determine the molecular orientation in thin films with high accuracy.

Time‐resolved photoinduced Kerr rotation in semiconductor microcavity

AbstractWe studied photoinduced Kerr effect in cavity polaritons in a semiconductor microcavity by carefully measuring the time‐resolved Kerr rotation and ellipticity spectra. The Kerr rotation angle of the microcavity polaritons is a hundred times larger than a conventional single quantum well. A spectral shape analysis of the observed spectra suggests that the photoindeced Kerr effect mainly results from a line broadening of the polarions due to spin‐polarized polariton‐polariton scattering. Enhancement in oscillator strength also contributes to the large rotation angle. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic and magneto-optical properties of FeRh thin films

The magnetic and magneto-optical properties of FeRh thin films epitaxially deposited onto MgO(1 0 0) substrates by RF sputter-deposition system have been investigated in conjunction with the structure. An intriguing virgin effect has been found in the M– T curves of the as-deposited FeRh thin films, which is presumably interpreted in term of a change in structural phase when heating. Also, a (negative) maximum peak of Kerr rotation at around 3.8 eV has been observed when FeRh thin films are in ferromagnetic state. The polar Kerr rotation angle is found to increase at temperatures above 100 °C, which corresponds to the antiferromagnet (AF)–ferromagnet (FM) transition of FeRh thin films.

Impurity-induced polar Kerr effect in a chiralp-wave superconductor

We discuss the polar Kerr effect in a chiral $p$-wave (${p}_{x}+i{p}_{y}$-wave) superconductor. It is found that the off-diagonal component of a current-current correlation function is induced by impurity scattering in the chiral $p$-wave condensate, and a nonzero Hall conductivity is obtained using the Kubo formula. We estimate the Kerr rotation angle by using this impurity-induced Hall conductivity and compare it with experimental results [J. Xia et al., Phys. Rev. Lett. 97, 167002 (2006)].

Electrically controlled Kerr effect in magnetophotonic crystals based on nematic liquid crystals

An electrically controllable Kerr effect in magnetophotonic crystals consisting of magnetic materials and nematic liquid crystals is presented by considering the properties of nematic liquid crystals. Numerical results show that the Kerr effect is changed remarkably by adjusting the permittivity of liquid crystal, and the maximum value of the Kerr rotation angle is enhanced with the increase in the permittivity of liquid crystal. Such properties demonstrate the possibility of tunable magneto-optical devices based on nematic liquid crystals.

First-Principles Study of Structural, Electronic, Magnetic, Optical, and Magneto-Optical Properties of NpN

We study the structural, electronic, magnetic, optical, and magneto-optical properties of NpN in detail using the fully relativistic full-potential calculations based on the density functional theory within the local spin density approximation. We successfully reproduce the positive sign of the electric field gradient (EFG) at Np nuclei. The positive EFG is in striking contrast to the negative EFG in a Np 3+ free ion, indicating the importance of the interplay between spin–orbit coupling and covalent bonding in NpN. Also, the calculated band structure shows large splittings induced by spin polarization and spin–orbit coupling, suggesting that both effects are indispensable for understanding the electronic properties of this material. This results in a large Kerr rotation angle of about 2°, which is comparable to those of uranium calcogenides.

ROTMOKE: An assessment of macroscopic models for bcc Ni/Ni(100)

Ab-initio Kerr angles for a multilayer system were calculated by means of Luttinger's formalism within the spin-polarized relativistic screened Korringa-Kohn-Rostoker method by including all multiple reflections and optical interferences via the 2 × 2 matrix technique. Two further macroscopic models are suggested for a multilayer system; i.e., the two-media approach and the three-media approach. The Kerr angles obtained using the two-media approach show that 75 % of the Kerr rotation angles arise from surface contributions when compared to the 2 × 2 matrix approach. Furthermore, by comparing the three-media approach to the 2 × 2 matrix technique it is found that almost 25 % of the Kerr rotation angles are due to interfaces between the atomic layers.

Preparation and magnetic properties of TbFeCo on the porous alumina templates

A self-ordered hexagonal array of nanopores has been fabricated by anodizing a thin film of Al on glass and subsequently the magnetic properties of TbFeCo on this templates were studied. We carried out anodic oxidation of a sputtered Al film at the anodic voltage in the range of 10–30 V and temperature in the range of 5–40 °C, and found that the density of the nanohole arrays increased with the decrease in anodization voltage and temperature. On the other hand, hole diameter decreased with the decrease in anodic voltage and temperature. Then TbFeCo was deposited onto this porous array by sputtering with a thickness of around 90 nm and subsequently was overcoated with 10 nm SiN for the protection from surface oxidation. The TbFeCo deposited on this porous layer shows complete perpendicular anisotropy and the AAO template can promote the growth of the microcolumnar structure in TbFeCo films. The coercivity increased with the decrease of hole diameter. The coercivity of the TbFeCo deposited on the porous array with a mean hole diameter of around 15 nm is 5.6 kOe and larger than that on bare glass, but the squareness ratio gets poorer than that on bare glass. It seems that there were no significant changes in Ms and Kerr rotation angle.

Effects of Nd substitution on magnetic and magneto-optical properties of TbCo/Cr films

NdTbCo/Cr amorphous films with high perpendicular magnetic anisotropy were prepared onto glass substrates by rf magnetron sputtering. The effects of Nd substitution on the magnetic and magneto-optical properties of TbCo/Cr films were investigated. It was found that partial Tb substitution by Nd would increase the saturation magnetization and the Kerr rotation angle, change the temperature dependence of magneto-optical characteristics. These results can be explained by the ferrimagnetic structure of the rare earth-transition metal alloy. When the magnetic layer composition was (Nd0.265Tb0.735)31Co69, a saturation magnetization of 247 emu/cm3 and a coercivity of 3.8 kOe at room temperature could be obtained.

Ab initiomagneto-optical properties of bccNi∕Ni(100)

The inter- and intralayer contributions to the layer-resolved complex optical conductivity tensor for semi-infinite layered systems are calculated in terms of the Luttinger formula within the spin-polarized relativistic screened Korringa-Kohn-Rostoker method. Ab initio Kerr angles are then obtained for arbitrary geometry and incidence via a $2\ifmmode\times\else\texttimes\fi{}2$ matrix technique including all multiple reflections and all optical interferences. Applied to in-plane single-domain magnetized bcc $\mathrm{Ni}∕\mathrm{Ni}(100)$, it is proven that the assumed appropriate formula of Kerr angles widely used to explain magneto-optical Kerr effect with rotating magnetic field measurements fully agrees with our ab initio Kerr data. From the experimental Kerr data of Tian et al. [Phys. Rev. Lett. 94, 137210 (2005)], however, it cannot be concluded that the deduced magnetic properties apply for bulk Ni, since about 75% of the contributions to the Kerr rotation angle arise from the surface.

Structural and magneto-optical properties of FeRh thin films

A systematic investigation of the magneto-optical properties in conjunction with structure and magnetic properties of FeRh thin films epitaxially deposited onto MgO(100) substrates by rf sputter-deposition system was performed. The result, for the first time, shows a (negative) maximum peak of Kerr rotation at around 3.8eV when FeRh thin films are in ferromagnetic state. The polar Kerr rotation angle is found to increase at temperatures above 100°C, which corresponds to the antiferromagnetic-ferromagnetic transition of FeRh thin films.

Study on Magnetic Garnet Films for Voltage Driven Magneto-Optic Spatial Light Phase Modulators with One Dimensional Magneto Photonic Crystal

The dysprosium substituted yttrium iron garnet (Dy:YIG) film was investigated because of high magnetstriction for operating voltage driven type magneto-optic spatial light modulators (V-MOSLMs). The fabricated Dy:YIG film had magnetostriction of 3.5 ppm, soft magnetic property, transmittance of 47 % and faraday rotation of -2.7 deg./μm at 532 nm wavelength. Furthermore, a reflection type one dimensional magneto photonic crystal (1D-MPC) by using the Dy:YIG film as a defect layer was fabricated for enhancement of Kerr rotation. In the case of the defect layer of 147 nm thick, a Kerr rotation angle was 15 times higher than the single layer at localized wavelength.

Carrier spin relaxation in (Ga,Mn)As at room temperature

In this paper, the excitation energy density dependence of carrier spin relaxation is studied at room temperature for the as-grown and annealed (Ga,Mn)As samples using femtosecond time-resolved pump-probe Kerr spectroscopy. It is found that spin relaxation lifetime of electrons lengthens with increasing excitation energy density for both samples, and the annealed (Ga,Mn)As has shorter carrier recombination and electron spin relaxation lifetimes as well as larger Kerr rotation angle than the as-grown (Ga,Mn)As under the same excitation condition, which shows that DP mechanism is dominant in the spin relaxation process for (Ga,Mn)As at room temperature. The enhanced ultrafast Kerr effect in the annealed (Ga,Mn)As shows the potential application of the annealed (Ga,Mn)As in ultrafast all-optical spin switches, and also provides a further evidence for the p-d exchange mechanism of the ferromagnetic origin of (Ga,Mn)As.

Characteristics of Magneto-Photonic Crystals based Magneto-Optic SLMs for Spatial Light Phase Modulators

We demonstrate a newly developed magneto-photonic crystal (MPC) based magneto-optic spatial light modulator (MOSLM) which was designed to enhance the performance of a conventional MOSLM, and describe the preparation and fundamental properties of it. By introduction of MPC, the magneto-optical property of MOSLM was improved, and as driving properties, the saturation of brightness was shown around ±1 kOe and the change occurred from about ±300 Oe by external magnetic field. Also, we conformed that Kerr rotation angle of this device was varied by applying voltage to PZT film. The change of each pixel by applying voltage, however, could not be detected because of the small variation of brightness.

Fully Relativistic Calculations of Magneto-Optical Kerr Effect

We study the magneto-optical Kerr effect using fully relativistic calculations. Spin–orbit coupling is dealt with exactly solving the Dirac equation directly and the matrix elements of the Dirac matrices α are used in a fully relativistic expression of the Kubo formula for the optical conductivity derived with a relativistic sum rule. We also perform approximate calculations of the optical conductivity to examine the accuracy of a partly relativistic expression in which the matrix elements of the momentum operator p are used instead. As an example, we carry out calculations for bcc Fe and fcc Ni using the fully relativistic full-potential linear-combination-of-atomic-orbitals method. It is found that the partly relativistic treatment is good for the diagonal optical conductivity while it is not very good for the off-diagonal optical conductivity, the Kerr rotation angle, and the Kerr ellipticity. The results of the present study are compared to those of experimental and other theoretical studies.