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We report on magneto-optical studies of the quasi-two-dimensional van der Waals antiferromagnet FePS

Magnetic layered materials have emerged recently as promising systems to introduce magnetism in structures based on two-dimensional (2D) materials and to investigate exotic magnetic ground states in the 2D limit. In this work, we apply high hydrostatic pressures up to

We report the observation of gyromagnetic and bi-gyrotropic properties in magneto-optical nanostructures. Anomalous s-polarized transverse magneto-optical Kerr effect is observed in magneto-optical Mie resonators and split ring resonators, featuring giant gyrotropic permeability tensors at the near infrared.

The concept of Berry phase and Berry curvature has become ubiquitous in solid state physics as it relates to variety of phenomena, such as topological insulators, polarization, and various Hall effects. It is well known that large Berry curvatures arise from close proximity of hybridiz-ing bands, however, the vectorial nature of the Berry curvature is not utilized in current research. On bulk bcc Fe, we demonstrate the flow of the Berry curvature vector field which features not only monopoles but also higher dimensional structures with its own topological features. They can provide a novel unique view on the electronic structure in all three dimensions. This knowledge is also used to quantify particular contributions to the intrinsic anomalous Hall effect in a simple analytical form.

Hexagonal rare-earth manganese oxide YMnO3 thin films were prepared on yttria-stabilized zirconia (111) substrates by metal organic decomposition method. The crystallinity and morphology of YMnO3 thin films crystallized at various temperatures were examined by X-ray diffraction and atomic force microscopy measurements, respectively. Single phase YMnO3 was obtained for the sample prepared by annealing temperatures of 950 °C. AFM analysis revealed that a smooth surface with a roughness of 0.15 nm was achieved for YMnO3 thin film annealed at 950 °C and 1000 °C, while three-dimensional growth for other samples prepared at 750–900 °C, 1050 °C, and 1100 °C. A narrow band at 1.6 eV and a broad band at 5 eV due to electronic transitions in the manganese and oxygen bands were observed in an absorption spectrum.

Magneto-optical effects are among the basic tools for characterization of magnetic materials. Although these effects are routinely calculated by the ab initio codes, there is very little knowledge about their origin in the electronic structure. Here, we analyze the magneto-optical effect in bcc Fe and show that it originates in avoided band-crossings due to the spin-orbit interaction. Therefore, only limited number of bands and k-points in the Brillouin zone contribute to the effect. Furthermore, these contributions always come in pairs with opposite sign but they do not cancel out due to different band curvatures providing different number of contributing reciprocal points. The magneto-optical transitions are classified by the dimensionality of the manifold that is formed by the hybridization of the generating bands as one- or two-dimensional, and by the position relative to the magnetization direction as parallel and perpendicular. The strongest magneto-optical signal is provided by two-dimensional parallel transitions.

To obtain a material exhibiting magnetically induced reorientation (MIR), one of the magnetic shape memory effects, a well-developed method for single crystal growth is crucial. A [ 100 ] oriented Ni2MnGa single crystal exhibiting MIR was successfully prepared using the floating-zone technique with a high speed of 80 mm/h. The comparison with a sample grown by Bridgman method and a reference sample grown in AdaptaMat Ltd. by directional solidification is provided based on elemental homogeneity, crystallographic quality by x-ray diffraction, transformation behaviour and magnetic properties. All these methods indicated that the single crystal grown by floating zone with high speed is comparable or superior to the samples prepared by other methods. Importantly, the magnetization measurement revealed that the single crystal prepared this way exhibits MIR down to 10 K.

The Heusler compound ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ is an interesting material for spintronic applications due to its predicted half-metal ferromagnetic character with a large band gap in the minority states. In this work, we present the optical and magneto-optical properties of a ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ bulk sample at room temperature. The spectral permittivity is found to be dominated by an absorption peak at 1.4 eV, originating mostly from absorptions by minority electrons. The best agreement between the experimentally obtained spectral permittivity tensor and the ab initio calculated one is for the local density approximation potential, closely followed by the generalized gradient approximation potential. However, the half-metallic ferromagnet character with $100%$ spin polarization is preserved only in calculations employing the Coulomb interaction correction (+U). This suggests that ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ is probably not a half metal as a single minority $d$-band dips below the Fermi level.

The hybridization of magnons (spin waves) with phonons, if sufficiently strong and comprising long wavelength excitations, may offer a new playground when manipulating the magnetically ordered systems with light. Applying a magnetic field to a quasi-2D antiferromagnet, FePS3, we tune the magnon-gap excitation towards coincidence with the initially lower-in-energy phonon modes. Hybrid magnon-phonon modes, the magnon polarons are unveiled with demonstration of a pronounced avoided crossing between the otherwise bare magnon and phonon excitations. The magnon polarons in FePS3 are primary traced with Raman scattering experiments, but, as we show, they also couple directly to terahertz photons, what evokes their further explorations in the domain of antiferromagnetic optospintronics., Comment: 10 pages, 4 figures and Supplementary Materials, to be published in Phys. Rev. B

Dielectric Mie nanoresonators showing strong light-matter interaction at the nanoscale may enable new functionality in photonic devices. Recently, strong magneto-optical effects have been observed in magneto-optical nanophotonic devices due to the electromagnetic field localization. However, most reports so far have been focused on the enhancement of conventional magneto-optical effects. Here, we report the observation of circular displacement current induced anomalous magneto-optical effects in high-index-contrast Si/Ce:YIG/YIG/SiO2 Mie resonators. In particular, giant modulation of light intensity in transverse magnetic configuration up to 6.4 % under s-polarized incidence appears, which is non-existent in planar magneto-optical thin films. Apart from that, we observe a large rotation of transmitted light polarization in the longitudinal magnetic configuration under near normal incidence conditions, which is two orders of magnitude higher than for a planar magneto-optical thin film. These phenomena are essentially originated from the unique circular displacement current when exciting the magnetic resonance modes in the Mie resonators, which changes the incident electric field direction locally. Our work indicates an uncharted territory of light polarization control based on the complex modal profiles in all-dielectric magneto-optical Mie resonators and metasurfaces, which opens the door for versatile control of light propagation by magnetization for a variety of applications in vectoral magnetic field and biosensing, free space non-reciprocal photonic devices, magneto-optical imaging and optomagnetic memories.

Ferrimagnetic garnets are promising materials for applications in integrated non-reciprocal devices due to their low optical absorption and relatively large magneto-optical response at telecommunication wavelengths. However, their implementation into phonotic chips is rather difficult due to large lattice parameters and thermal expansion mismatch with common photonic substrates. In this talk, we present our latest progress in the growth, fabrication and characterization of various ferrimagnetic iron garnets on silicon substrates with excellent optical and magnetooptical properties expressed in terms of high Figure of Merit.

Giant magnetic-field-induced strain up to 12% in Ni–Mn–Ga single crystal is due to magnetically-induced reorientation of the twinned martensitic low symmetry crystal structure. An important interplay is arising from the interaction between ferroelastic domains (twin domains) and magnetic domains. Here, we studied the magnetic domains in an Ni50Mn28Ga22 single crystal exhibiting 6% strain by using a magneto-optical indicator film and for the first time also directly by the Kerr magneto-optical microscopy. To compare the magnetization behavior of bulk and surface, we measured the magnetization loops by the Kerr effect (MOKE) and by the vibrating sample magnetometry. We demonstrate that using a particular arrangement of the Kerr microscopy enables visualizing the magnetic domains structure and its evolution in the magnetic field.

Polycrystalline Ce:YIG thin films deposited on silicon are promising material candidates for integrated nonreciprocal photonic devices. So far, the reported Faraday rotation of polycrystalline Ce:YIG thin films on silicon is much lower than that of their single crystal or epitaxial thin film counterparts, limiting the magneto-optical figure of merit, device bandwidth and fabrication tolerance. In this paper, we report the growth of Ce:YIG thin films on silicon from targets with high Ce concentration up to nominally Y 1.5 Ce 1.5 Fe 5 O 12 by pulsed laser deposition. The polycrystalline Y 1.5 Ce 1.5 Fe 5 O 12 thin film showed pure garnet phase, smooth surface roughness of 0.7 nm, a dominant Ce 3+ valence state and a bulk-like saturation magnetization of 125 emu/cm 3 at room temperature. This material shows high Faraday rotation of −6410 deg/cm at 1550 nm wavelength, exceeding that of an Y 2 Ce 1 Fe 5 O 12 epitaxial thin film on a GGG (100) substrate. However higher loss and lower figure of merit is also observed at 1550 nm wavelength compared to Y 2 Ce 1 Fe 5 O 12 thin films, possibly due to the low oxygen partial pressure during fabrication. Low deposition oxygen partial pressure is essential to enhance the Ce solubility and Ce 3+ concentration, which results in large Faraday rotation.

Permalloy is a widespread material used in numerous fundamental experiments and novel spintronic, optoelectronic devices. In order to model their response or tailor the optimal experimental parameters it is necessary to know the optical and magneto-optical properties of this material over a wide spectral range. We report on the systematic study of optical and magneto-optical properties of 10 nm and 150 nm thick permalloy films by means of spectroscopic ellipsometry and magneto-optical spectroscopy. To study the influence of the surface oxidization, the samples were prepared with and without Au capping layer. Spectral dependence of the complete permittivity tensor was derived from experimental data in a broad spectral range covering IR, visible and UV regions. All samples exhibited metallic-like optical and magneto-optical properties with clear differences in 10 nm thick bare sample. These differences to overall optical and magneto-optical properties of nanometer-thick permalloy layers were ascribed to a strong influence of the surface oxide. Keywords: Permalloy, Thin films, Spectroscopic ellipsometry, Magnetooptical Kerr effect spectroscopy, Complex permittivity tensor, Oxidation

Performance of CdZnTe-based detectors is highly related to surface preparation. Mechanical polishing, chemical etching and passivation are routinely employed for this purpose. However, the relation between these processes and the detector performance in terms of underlying physical phenomena has not been fully explained. The dynamics and properties of CdZnTe surface oxide layers, created by passivation with KOH and NH4F/H2O2 solutions, were studied by optical ellipsometry and X-ray photoelectron spectroscopy (XPS). Thicknesses and growth rates of the surface oxide layers differed for each of the passivation methods. Leakage currents which influence the final spectral resolution of the detector were measured simultaneously with ellipsometry. Results of both optical and electrical investigation showed the same trends in the time evolution and correlated to each other. NH4F/H2O2 passivation showed to be a method which produces the most desirable properties of the surface oxide layer.

Influence of epitaxial strain and oxygen octahedra rotations on electronic structure of ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$ ultrathin films was systematically studied. The investigated films were grown by pulsed laser deposition on four different substrates: cubic (001)-oriented ${\mathrm{LaAlO}}_{3}$, (001) ${({\mathrm{LaAlO}}_{3})}_{1/3}{({\mathrm{Sr}}_{2}{\mathrm{AlTaO}}_{6})}_{2/3}$, (001) ${\mathrm{SrTiO}}_{3}$, and orthorhombic (110) ${\mathrm{DyScO}}_{3}$, providing a broad range of induced epitaxial strains. Magnetic properties were found to deteriorate with increasing value of the epitaxial strain, as expected due to unit cell distortion increasingly deviating from the bulk and effect of the magnetically inert layer. A combination of spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy was used to determine spectra of the diagonal and off-diagonal elements of permittivity tensor. The off-diagonal elements at room temperature confirmed the presence of two previously reported electronic transitions in the spectra of all films. Moreover they revealed another electronic transition around 4.3 eV only in the spectra of films grown under compressive strain. We proposed classification of this transition as a crystal field paramagnetic Mn ${t}_{2g}\ensuremath{\rightarrow}{e}_{g}$ transition. Ab initio calculations were employed to distinguish between the potential influence of oxygen octahedra rotations and distortions. The ab initio calculations indicated a negligible influence of oxygen octahedra rotations on magneto-optical properties of ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$. They further supported the proposed classification of the additional electronic transition, showing a key role of strain in controlling the electronic structure of ultrathin perovskite films.

Unlike ferromagnetic materials, ferrimagnetic metals have recently received considerable attention due to their bulk perpendicular magnetic anisotropy, low net magnetization and tunable magnetic properties. This makes them perfect candidates for the research of recently discovered spin-torque related phenomena. Among other ferrimagnetic metals, GdFe has an advantage in relatively large magnetic moments in both sublattices and tunability of compensation point above the room temperature by small changes in its composition. We present a systematic study of optical and magneto-optical properties of amorphous GdxFe(100-x) thin films of various compositions (x = 18.3, 20.0, 24.7, 26.7) prepared by DC sputtering on thermally oxidized SiO2 substrates. A combination of spectroscopic ellipsometry and magneto-optical spectroscopy in the photon energy range from 1.5 to 5.5 eV with advanced theoretical models allowed us to deduce the spectral dependence of complete permittivity tensors across the compensation point. Such information is important for further optical detection of spin related phenomena driven by vicinity of compensation point in nanostructures containing GdFe.

The magnetooptic Kerr effect (MOKE) is a well known and handy tool to characterize ferro-, ferri- and antiferromagnetic materials. Many of the MOKE techniques employ effects solely linear in magnetization $\bm{M}$. Nevertheless, a higher-order term being proportional to $\bm{M}^2$ and called quadratic MOKE (QMOKE) can additionally contribute to the experimental data. Here, we present detailed QMOKE spectroscopy measurements in the range of 0.8 -- 5.5\,eV based on a modified 8-directional method applied on ferromagnetic bcc Fe thin films grown on MgO substrates. From the measured QMOKE spectra, two further complex spectra of the QMOKE parameters $G_s$ and $2G_{44}$ are yielded. The difference between those two parameters, known as $\Delta G$, denotes the strength of the QMOKE anisotropy. Those QMOKE parameters give rise to the QMOKE tensor $\bm{G}$, fully describing the perturbation of the permittivity tensor in the second order in $\bm{M}$ for cubic crystal structures. We further present experimental measurements of ellipsometry and linear MOKE spectra, wherefrom permittivity in the zeroth and the first order in $\bm{M}$ are obtained, respectively. Finally, all those spectra are described by ab-initio calculations., Comment: 15 pages + references, , 15 Figures

An extensive experimental investigation of Fe-based Heusler alloys has been performed in order to potentially prepare new materials which are tetragonally distorted and have large perpendicular magnetic anisotropy crucial not only for the STT-MRAM applications but also for magnetic shape memory devices. Based on criteria demanded for the MSM applications 25 Fe2YZ various compounds were selected for the synthesis using arc melting from more than 60 systems suggested theoretically. Only four compounds Fe2MnSn, Fe2NiSi, Fe2NiGe, and Fe3Ga were homogeneous single phase. None of the studied Fe-based materials exhibited the predicted tetragonal structure. Magnetic measurements confirmed that all investigated compounds are soft ferromagnets with no sign of a structural transition. Our results contradict the ab-initio calculations showing the limits of theoretical predictions by incomplete high throughput calculations as well as the limitations of the standard synthesis techniques.

The X/Co 3 nm/Y (where X, Y = Au, Pt) trilayers with as deposited in-plane magnetization alignment were irradiated with 30 keV Ga+ ions in the wide range of ion fluence. The samples were investigated by means of complementary techniques: magneto-optical magnetometry and spectroscopy (in the photon energy range from 1.2 eV to 4.5 eV), magnetic force microscopy, positron annihilation spectroscopy, x-ray diffraction and reflectivity. Difference in miscibility of interface atoms is clearly manifested in various intermixing extent at Co/Pt and Co/Au interfaces and consequently in magnetic properties of the irradiated trilayers. Low irradiation fluence (∼1014 ions cm−2) leads to ∼1 nm interfaces broadening without visible surface etching for all samples, which is related with a distinct drop of magnetic anisotropy. However, the high irradiation fluence (∼5 × 1015 ions cm−2) results in enhanced interface broadening and significant surface etching (∼5 nm) partially removing also Co atoms. Tensile strains (up to 0.5%) were developed in the cover layers. The tensile strain, layers intermixing and the creation of Co–Pt(Au) alloys with different composition formed by irradiation are correlated with the increase of magnetic anisotropy. Moreover it was observed that substitution of Au instead of Pt (as a cap or buffer layer) results in substantial increase of perpendicular magnetic anisotropy. Maximal increase of magnetooptical parameters was observed for Pt/Co/Pt layer. Irradiation induced changes of concentration profiles are revealed using magnetooptical spectra, x-ray reflectivity spectra and simulations with use of binary collision approximation.

Fe2MnSn compound was prepared in the form of polycrystalline ingot by arc-melting. In contrast to the theoretical predictions of stable tetragonal Heusler compound, the material crystallizes in a hexagonal DO19 crystal structure and orders ferromagnetically below TC = 586(10) K that is only about half of the calculated value of 1012 K. Magnetic moment 5.87 μB at 10 K is less or about in line with various theoretical predictions. However, electrical resistivity and optical studies reveal no signs of half-metallic behavior predicted theoretically. The change in the slope of the MOKE spectra below 1.5 eV suggests the main influence of a low energy inter-band transition which points to the loss of half-metallicity in agreement with resistivity and optical measurements.

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. Thulium iron garnet (TmIG) has been successfully grown and TmIG/Pt heterostructures have been characterized. However, TmIG is not the only rare-earth iron garnet that can be grown with PMA. We report the growth, magnetic, and spintronic properties of epitaxial terbium iron garnet (TbIG) and europium iron garnet (EuIG) thin films with PMA. Reciprocal space mapping shows the films are lattice matched to the substrate without strain relaxation, even for films up to 56 nm thick. The lattice strain and magnetostriction coefficient produce PMA in certain cases. TbIG grows on (111) gadolinium gallium garnet (GGG) with PMA due to the in-plane compressive strain, whereas TbIG on (111) substituted GGG (SGGG) is in tension and has an in-plane easy axis. EuIG grows with PMA on (100) and (111) GGG substrates, which facilitates the investigation of spintronic properties as a function of orientation. Both garnets have excess rare earth, which is believed to occupy Fe octahedral sites and in the case of TbIG is associated with an increase in the compensation temperature to 330 K, higher than the bulk value. Anomalous Hall effect (AHE) measurements of Pt/EuIG Hall crosses show that the spin mixing conductance of Pt/ (111) and (100) EuIG is similar. AHE measurements of Pt/TbIG Hall crosses reveal a sign change in the AHE amplitude at the compensation point analogous to all-metallic systems.

Erbium (Er 3+ ) doped ytterbium garnet (Er:Yb 3 Al 5− y Ga y O 12 ; y = 0, 0.55 and 1.1) single crystalline thick films have been grown by the low-temperature liquid phase epitaxy method (LPE). The composition of the films was determined using the high resolution XRD, the particle-induced X-ray emission spectroscopy (PIXE) and the particle-induced gamma-ray emission spectroscopy (PIGE). The lattice mismatch between films and substrates was investigated by the high-resolution X-ray diffraction. The surface analysis was carried out by the atomic force microscopy (AFM). Pure infrared emission of Er 3+ ions was observed in all films containing gallium. The characteristics such as refractive index, thickness and light propagation were studied by the m-line spectroscopy (MLS) using several wavelengths (633, 964, 1311 and 1552 nm). All samples, where y = 1.1, were multimode waveguides. For these reasons, the Er:Yb 3 Al 3.9 Ga 1.1 O 12 seems to be a promising material for light amplifiers in the IR region.

The validity of the Fourier factorization (FF) rules used in the constitutive relations in the Fourier modal method is analyzed for one-dimensional diffraction gratings made as a thin film with uniform thickness and several examples of continuous lateral profiles of permittivity. The comparison of the method using the correct FF rules with other FF choices demonstrates the validity of the FF rules for any inhomogeneous, not only discontinuous profile.

The rigorous coupled wave analysis is demonstrated by employing a recursive propagation algorithm based on an Airy-like internal reflection series, modified for a general cross-sectional distribution of permittivity. The method is capable of determining the electromagnetic field value at any point of the structure of any depth. Examples of simulation are presented on a nearly sinusoidal relief grating fabricated on the top of a Ni substrate.

Surface oxide formation was examined on low resistivity p-type CdTe single crystals immersed into distilled water held at 50 °C. The oxide thickness and roughness were investigated by spectroscopic ellipsometry, and its composition was studied by X-ray photoelectron spectroscopy. It was observed that after the fast growth of thin oxide layer with the thickness 1.7 nm the growth of oxide layer is proportional to a square root of the immersion time. The oxidation was described by a model in which the oxidation rate is limited by the drift of positive Cd ions from the CdTe-oxide interface into water. The penetration of Na and erosion of CdTe immersed in saturated NaCl solution was investigated by secondary ion mass spectrometry measurements on samples treated in NaCl solution for different time intervals. Very low determined diffusion coefficient of Na was explained by trapping of Na on acceptor-type defects in Cd sublattice.

We review recent advances in optical and magnetooptical (MO) scatterometry applied to periodically ordered nanostructures such as periodically patterned lines, wires, dots, or holes. The techniques are based on spectroscopic ellipsometry (SE), either in the basic or generalized modes, Mueller matrix polarimetry, and MO spectroscopy mainly based on MO Kerr effect measurements. We briefly present experimental setups, commonly used theoretical approaches, and experimental results obtained by SE and MO spectroscopic analyses of various samples. The reviewed analyses are mainly related to monitoring optical critical dimensions such as the widths, depths, and periods of the patterned elements, their real shapes, and their line edge or linewidth roughness. We also discuss the advantages and disadvantages of the optical spectroscopic techniques compared to direct monitoring techniques.

We report on the temperature dependence of the magnetic and magneto-optical properties in cerium-substituted yttrium iron garnet (Ce: YIG) thin films. Measurements of the Faraday rotation as a function of temperature show that the magnetic easy axis of thin Ce: YIG films reorients from in-plane to out-of-plane on cooling below -100 degrees C. We argue that the temperature-dependence of the magnetostriction and magnetocrystalline anisotropy of Ce: YIG is the dominant factor contributing to the change in easy axis direction, and we describe the changes in the magneto-optical spectra with temperature., National Science Foundation (U.S.) (Award ECCS-1607865), United States. Defense Advanced Research Projects Agency (Award FA8650-16-1-7641)

We provide unified phenomenological description of magnetooptic effects being linear and quadratic in magnetization. The description is based on few principal spectra, describing elements of permittivity tensor up to the second order in magnetization. Each permittivity tensor element for any magnetization direction and any sample surface orientation is simply determined by weighted summation of the principal spectra, where weights are given by crystallographic and magnetization orientations. The number of principal spectra depends on the symmetry of the crystal. In cubic crystals owning point symmetry we need only four principal spectra. Here, the principal spectra are expressed by ab initio calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard and soft x-ray energy range, i.e. at the 2 p - and 3 p -edges. We also express principal spectra analytically using modified Kubo formula.

Ferrimagnetic bismuth substituted yttrium iron garnet Bi(x)Y(3-x)Fe(5)O(12) (BiYIG) films with x=1 and 2 pulsed laser deposited onto (111) Gd(3)Ga(5)O(12) (GGG) substrates were studied using magneto-optical (MO) Kerr spectroscopy in the photon energy range of 1.8-5 eV at both polar and longitudinal magnetizations. The interference at lower photon energies provided the refined film thicknesses ranging between 70 and 200 nm. The films were grown under compressive strain and displayed saturation magnetizations (mu(0)M(s)) lower than that of their bulk counterparts due to the presence of nanograins forming BiYIG layers and/or magnetically dead interface layers. The trends in the MO spectra agree with those deduced from the published permittivity tensor data for BiYIG using a transfer matrix model applied to a film (BiYIG)-substrate (GGG) system. Due to the reduced mu(0)M(s) the predicted amplitudes are typically higher. The agreement was improved using effective medium approach or by incorporating into the model MO passive interface layers. The information on MO activity at longitudinal magnetization in the garnet layers below 100 nm presents interest for MO imaging and magnetophotonic devices. The results suggest that the MO Kerr spectroscopy combined with MO Kerr magnetometry may represent a valuable, cheap and nondestructive tool for the characterization of magnetic garnet films less than 200 nm thick. (C) 2011 Elsevier B.V. All rights reserved.

Optical and magneto-optical properties of amorphous Gd22Fe78 (GdFe) thin films prepared by direct current (DC) sputtering on thermally oxidized substrates were characterized by the combination of spectroscopic ellipsometry and magneto-optical spectroscopy in the photon energy range from 1.5 to 5.5 eV. Thin SiNx and Ru coatings were used to prevent the GdFe surface oxidation and contamination. Using advanced theoretical models spectral dependence of the complete permittivity tensor and spectral dependence of the absorption coefficient were deduced from experimental data. No significant changes in the optical properties upon different coatings were observed, indicating reliability of used analysis.

Methodology and selected applications of magneto-optical (MO) spectroscopic scatterometry (MOSS) are presented on various types of magnetic gratings made by lithographic patterning. Three types of theoretical models with different levels of accuracy are described in detail: a rigorous one, an analytical approximation, and a model mostly appropriate for real structures affected by line-edge roughness (LER). The MOSS approach, based on explaining diffracted MO Kerr effect measurements by simulations employing the mentioned models, is demonstrated as a technique highly sensitive to nanoscale features such as native oxide overlayers, as well as capable of determining the LER characteristic quantitatively. Further possibilities to study unsaturated magnetic structures and compositions of magnetic materials including imperfect deposition or aging processes are suggested.

Molecular beam epitaxy grown Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au and Ag/Fe (t)/Ag sandwiches on MgO (001) substrates were investigated by means of classical and magneto-optic (MO) Kerr ellipsometry and relative reflectance spectroscopy at photon energies between 1.5 and 6 eV. The layer thickness t varied between 1.0 and 2.5nm for Au spacer and between 0.8 and 1.8nm for Fe. The MO polar and longitudinal Kerr effect spectra in Ag/Fe (t)/Ag can be explained using a single off-diagonal permittivity tensor element. This is not the case in Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au. Deviations of the longitudinal spectra from the model indicate the anisotropy in the permittivity tensor and are assigned to an Fe-Au interface layer of reduced symmetry. The interface effect, observed between 3 and 4.2 eV, is best resolved in Au/Fe/Au (t)/Fe/Au, but can also be seen on Au/Fe (t)/Au. The relative reflectance spectra in Au/Fe/Au (t)/Fe/Au with an Au reference reflector show a narrowing of the Au peak centered at the photon energy of 3.5 eV. It is proposed that the narrowing is induced by adjacent Fe layer with in-plane magnetization.

Bismuth selenide – the prominent topological insulator – has been recently reported as a material exhibiting an extraordinary strong Faraday rotation. This effect has been identified as due to interband excitations in bulk promoting electrons from the valence to the conduction band, in which the electron gas is partially spin-polarized due to the Zeeman effect. In this work, we test the Faraday rotation in Bi2 Se3 in high magnetic fields, when the conduction band electrons reach their full spin polarization. We find that the Faraday angle becomes in this regime almost independent of the applied magnetic field. This contrasts with the Faraday effect observed in this system at low magnetic fields, where the Faraday angle scales linearly with B and may thus be described by a conventional Verdet law.

A photonic crystal waveguide (PhC-WG) was reported to be usable as an optical sensor highly sensitive to various material parameters, which can be detected via changes in transmission through the PhC-WG caused by small changes of the refractive index of the medium filling its holes. To monitor these changes accurately, a precise optical model is required, for which the plane wave expansion (PWE) method is convenient. We here demonstrate the revision of the PWE method by employing the complex Fourier factorization approach, which enables the calculation of dispersion diagrams with fast convergence, i.e., with high precision in relatively short time. The PhC-WG is proposed as a line defect in a hexagonal array of cylindrical holes periodically arranged in bulk silicon, filled with a variable medium. The method of monitoring the refractive index changes is based on observing cutoff wavelengths in the PhC-WG dispersion diagrams. The PWE results are also compared with finite-difference time-domain calculations of transmittance carried out on a PhC-WG with finite dimensions.

We report on an improvement of structural and morphological quality of AlN/GaN superlattices when the multiple superlattice (MSL) structure is used. Such a structure contains strained AlN/GaN simple superlattices with a small number of periods separated by thick GaN layer. Hot wall epitaxy technique (HWE) was used to grow these structures and atomic force microscopy (AFM) as well as X-ray diffraction measurements were used to obtain the information about their structural and morphological properties. According to AFM measurements, the threading dislocation density and the surface roughness were decreased compare to the simple superlattice. Xray rocking curve (XRC) measurements exhibit narrower peaks, so the full width at half maximum (FWHM) of the 0th superlattice peak was decreased by 37%. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

EuTe/PbTe double-well superlattices with two kinds of PbTe quantum wells separated by monolayer EuTe were prepared on KCl(100) substrates by hot wall epitaxy. Strong intersubband absorptions as high as 2000 cm-1 in absorption coefficient were observed for n-type samples with a carrier concentration as high as 3×1018 cm-3 at normal incidence. The absorption was caused through the modulation of quantum-well potential along superlattice direction at L-point of the Brillouin zone. Temperature dependence of the optical transmission properties was also measured and the absorption peak showed a large tunability of 0.9 cm-1 K-1 caused by large temperature dependence of effective masses in PbTe.

In this work, we present a systematic study of optical and magneto-optical properties of Y3-xBixFe5O12 thin films with various Bi concentrations (x = 1.5, 2, 2.5, 3) prepared by Metal Organic Decomposition on Gd3Ga5O12 (100) substrates. We used magneto-optical spectroscopy and spectroscopic ellipsometry. Spectral dependence of complex refraction indexes obtained from ellipsometric measurements revealed increasing optical absorption with increasing Bi concentrations. Faraday and Kerr magneto-optical spectra measured in the photon energy range from 1.5 to 5.5 eV clearly demonstrated that the increasing Bi concentration enhances the spin-orbit coupling and influences the magneto-optical effect. Using the magneto-optical and ellipsometric experimental data we deduced a spectral dependence of complete permittivity tensor in a wide spectral range. Comparison of obtained results with the results reported on Liquid Phase Epitaxy bulk-like garnets with small Bi concentrations showed agreement and confirmed a high optical and magneto-optical quality of investigated films.

Photonic crystals are modern artificially designed periodical systems capable to affect the motion of photons in a similar way that the periodicity of the atomic potential in a semiconductor crystal affects the motion of electrons. The physical properties of light in a photonic crystal resemble those of electrons in atomic crystals, leading to forbidden propagation of electromagnetic modes at certain frequencies, as demonstrated by Yablonovitch (1987), Ho et al. (1990), Joannopoulos et al. (1995; 1997), etc. The existence of the optical band gap (which is the part of the spectrum for which the wave propagation is not possible) makes photonic crystals broadly interesting from many viewpoints of fundamental research and applications. Recent studies are motivated by promising applications such as purely optical integrated circuits [e.g., by Lin et al. (1998), Noda (2006), or Hugonin et al. (2007)], artificial metamaterials with high tunability [Datta et al. (1993); Genereux et al. (2001); Krokhin et al. (2002); Reyes et al. (2005)], high-sensitivity photonic biosensors [Block et al. (2008); Skivesen et al. (2007)], or devices based on phenomena not accessible in conventional media [Benisty (2009); Kosaka et al. (1998); Krokhin & Reyes (2004)]. It is also necessary for accounting for structural colors of wings of butterflies or beetles, feathers of birds, or iridescent plants [Kinoshita & Yoshioka (2005); Vukusic & Sambles (2003)].

Atomic force microscopy (AFM) is a state of the art imaging system that uses a sharp probe to scan backwards and forwards over the surface of an object. The probe tip can have atomic dimensions, meaning that AFM can image the surface of an object at near atomic resolution. Two big advantages of AFM compared to other methods (for example scanning tunneling microscopy) are: the samples in AFM measurements do not need to be conducting because the AFM tip responds to interatomic forces, a cumulative effect of all electrons instead of tunneling current, and AFM can operate at much higher distance from the surface (5-15 nm), preventing damage to sensitive surfaces.

We demonstrate an improvement of the plane wave expansion method treating two-dimensional photonic crystals by applying Fourier factorization with generally elliptic polarization bases. By studying one example of periodically arranged cylindrical elements, we compare our approach to the classical Ho method in which the permittivity function is simply expanded without changing coordinates, and to the normal vector method using a normal-tangential polarization transform. The compared calculations clearly show that our approach yields the best convergence properties owing to the complete continuity of our distribution of polarization bases.

We demonstrate an enhancement of the plane wave expansion method treating two-dimensional photonic crystals by applying Fourier factorization with generally elliptic polarization bases. By studying three examples of periodically arranged cylindrical elements, we compare our approach to the classical Ho method in which the permittivity function is simply expanded without changing coordinates, and to the normal vector method using a normal-tangential polarization transform. The compared calculations clearly show that our approach yields the best convergence properties owing to the complete continuity of our distribution of polarization bases. The presented methodology enables us to study more general systems such as periodic elements with an arbitrary cross-section or devices such as photonic crystal waveguides.

We report on ZnO nanopowder induced light scattering for improved visualization of emission sites in carbon nanotube films and arrays. We observed a significant reduction of the internal multiple light scattering phenomena, which are characteristic for ZnO micropowders. The microsized grains of the commercially available ZnO:Zn (P 15) were reduced to the nanometre scale by pulsed laser ablation at an oxygen ambient pressure of 10 kPa. Our investigations show no crystalline change and no shift of the broad green emission peak at 500 nm for the ZnO nanopowder. For the application in field emission displays, we demonstrate the possibility of achieving cathodoluminescence with a fine pitch size of 100 microm of the patterned pixels without requiring additional electron beam focusing and without a black matrix. Moreover, the presented results show the feasibility of employing ZnO nanopowder as a detection material for the phosphorus screen method, which is able to localize emission sites of carbon nanotube films and arrays with an accuracy comparable to scanning anode field emission microscopy.