Magnetism of a cobalt-gold planar nanostructure on the silicon surface

The structural and magnetic properties of a cobalt nanolayer placed between a silicon substrate and a protective gold layer are studied. At a cobalt layer mass thickness of 1–2 nm, a nanoisland structure is shown to form. This thickness range is characterized by a local maximum of the magnetooptical Kerr effect and enhanced nonlinear optical and magnetic nonlinear optical responses at the second-harmonic frequency. This enhancement can be caused by the excitation of local surface plasmons and an increase in the local fields at the probing-radiation and second-harmonic frequencies in metallic nanoislands. The surface-sensitive nonlinear magnetooptical Kerr effect at the second-harmonic frequency is maximal at a cobalt layer thickness of about 2 nm, which corresponds to the characteristic scale of magnetization formation in the near-surface layer in cobalt.     

Generation of second optical harmonic and magnetooptical Kerr effect in ferromagnet-semiconductor heterostructures CaF2/MnAs/Si(111)

The second optical harmonic generation and magnetooptical Kerr effect are investigated for the light (λ=800 nm) reflected by ferromagnet-semiconductor heterostructures CaF₂/MnAs/Si(111). The observed change in the second-harmonic intensity is odd in magnetization. A phenomenological analysis of possible contributions to the second harmonic is carried out, and the sources of optically nonlinear signals are determined from the experimental azimuthal dependences of the light intensity at double frequency. The difference in the field dependences of the second harmonic and the magnetooptical Kerr effect is observed.     

Growth of nanosized MnAs/Si(111) magnetoelectronic heterostructures and their magnetooptical study

Thin (6–12 nm) epitaxial MnAs films were MBE-grown on Si(111) substrates under different technological conditions. The films feature essentially different surface morphology. This manifests itself in the formation, on the silicon surface, of hexagonal-shaped crystallites, whose dimensions vary depending on the growth conditions. The volume and surface magnetic properties of the films were studied using the magnetooptical Kerr effect and optical second harmonic generation. The Kerr effect was found to scale linearly with the effective thickness of the magnetic layer. The thickness of the magnetically disordered transition layer formed near the interface with the substrate was estimated. The surface and volume hysteresis properties of the films were found to be different. A contribution to the second-harmonic intensity was observed which is an odd function of magnetization. This effect originates from the interference of the magnetic and nonmagnetic contributions to the nonlinear polarization.     

Anisotropy of magnetooptical response of nanoperforated permalloy films

The azimuthal anisotropy of the linear and nonlinear magnetooptical Kerr effect has been studied for a structure that is an ordered array with 420-nm-diameter pores in a 30-nm-thick permalloy film on a silicon substrate. The azimuthal anisotropy of the magnetooptical Kerr effect and the coercive force, corresponding to 4 m symmetry of a planar nanopore array, has been established experimentally. The measurements are accompanied with the numerical calculation of the anisotropic magnetization distribution in the structure at different orientations of the applied magnetic field.     

Optical and magnetooptical properties of FePt-SiO<Subscript>2</Subscript> magnetic nanocomposites

The magnetic, optical, and magnetooptical properties of granular (FePt)_1?x(SiO₂)_x nanocomposites in the disordered state and after heat treatment were studied. The magnetooptical response of samples in which the concentration of the metallic component approached the percolation threshold was observed to become considerably enhanced. Modeling transverse Kerr effect (TKE) spectra in a straightforward effective medium approximation provided a qualitative fit to the experimental data over a broad concentration range. The dependences of the Kerr effect on the SiO₂ concentration in the nanocomposite are not monotonic and exhibit a sharp break near the percolation threshold. An analysis of the field dependences of the TKE and magnetization curves revealed that structural changes associated with ordering in annealed FePt films occur only in nanocomposites with fairly large grains.     

Magnetic and magnetooptical properties of multilayer ferromagnet-semiconductor nanostructures

The magnetic and magnetooptical properties of spin-tunneling multilayer permalloy-silicon carbide nanoheterostructures deposited by rf sputtering have been studied. Magnetometric and magnetooptical methods are used to show that the magnetic-semiconducting nanostructures have a complex magnetic structure and to track the evolution of the magnetic properties of these structures as functions of the magnetizing field and the thickness and sequence order of ferromagnetic and semiconducting layers in them. The induction response and the field and orientation dependences of the transversal Kerr effect are found to have anomalies. The experimental results are interpreted under the assumption that there is exchange interaction between the ferromagnetic and semiconducting layers through a thin magnetically ordered transition layer formed inside the interface.     

Magnetic and magnetooptical properties of Fe/Pt and Fe/Pt/Fe thin-film magnetic structures

Results of a study of magnetic and magnetooptical properties of Fe/Pt double-layer and Fe/Pt/Fe three-layer thin-film magnetic structures are presented. A strong effect of the Pt layer on magnetic properties of the studied samples was revealed. It was established that the saturation field of three-layer magnetic structures has an oscillating magnitude with varying Pt layer thickness, and the oscillation period is a function of the Fe layer thickness. The data obtained are explained by the presence of exchange interaction between the Fe layers via the Pt layer. A strong effect of Pt on spectral dependences of the equatorial Kerr effect in the thin-film structures under study is revealed.     

Magnetic and magnetooptical properties of ferromagnetic semiconductor GaN : Cr

Magnetic and magnetooptical properties of the Cr-doped GaN layers have been investigated in the temperature range 50–400 K. A high saturation magnetization of 25 G has been observed in the obtained material. Spectra of the magnetooptical transversal Kerr effect have revealed strong magnetic response in the energy range less than 3.0 eV due to the appearance of new spin-polarization states in the band gap of GaN upon Cr doping.     

一维磁光子晶体的法拉第效应

由于一维磁光子晶体能同时展示出很好的光透射率和法拉第旋转,故可用于实现小尺度的磁光隔离器。采用传输矩阵法研究了由磁光膜(Bi∶YIG)和电介质膜(Ta2O5,SiO2)构成的一维磁光子晶体,分别讨论了在垂直入射和斜入射条件下的法拉第效应,并给出了几种可行性结构,对磁光隔离器件的进一步改进设计具有一定的参考价值。     

Second order nonlinear spectroscopy of nickel nanorods

The results of optical second harmonic generation (SHG) spectroscopy in an ensemble of nickel nanorods are presented. Enhancement of the magnetic nonlinear optical Kerr effect at the fundamental wavelength (750–780 nm) is observed. The effect is attributed to resonance excitation of localized surface plasmons in nickel nanorods.     

Magnetooptical images of inhomogeneous magnetic fields in metallic films with in-plane anisotropy

The magnetooptical (MO) images of the inhomogeneous field created by permanent magnets in magnetic metallic films with in-plane anisotropy are experimentally studied. The MO images recorded using the longitudinal Kerr effect are the superposition of two pictures, namely, a polar-sensitivity MO image and a longitudinal-sensitivity MO image. An analysis of these images after separation shows that the polar-sensitivity MO image reflects the distribution of the inhomogeneous field component that is normal to the surface of an indicator film in an analog manner. The longitudinal-sensitivity MO image reflects the angular distribution of the in-plane component of a stray field in an analog manner. The coincidence of the experimental and corresponding simulated MO images makes it possible to interpret the experimental images. In particular, it is shown that the specific features detected in the topological characteristics of the inhomogeneous field correspond to experimental singular points. Hidden magnetic images (magnetic bar codes) are shown to be visualized with metallic CoFe films. As an example, the stray field of a magnetic system made of cylindrical magnets is mapped.     

Magnetic and magnetooptical properties of nanothick polycrystalline Co-P films

Features of the formation of chemically deposited polycrystalline Co-P films with nanometer thicknesses are established by magnetic measurements and analysis of film surface morphology. It is found that the specific value of the magnetooptical Faraday effect in Co-P films exceeds that in Co films by a factor of more than two. This is attributed to the magnetic polarization of a Pd underlayer. It is shown the Kerr effect in Co films is negligibly influenced by the embedding of phosphorus.     

Formation of clusters and the magnetooptical Kerr effect in gallium arsenide implanted with manganese ions

The surface morphology and magnetic properties of GaAs irradiated by manganese ions are studied at room temperature using atomic-force microscopy and the magnetooptical Kerr effect. It is shown that ferromagnetism takes place in the surface layer of the irradiated semiconductor subjected to annealing at 715–750°C. The magnetic properties of this layer are related to the evolution of submicron clusters in GaAs doped with Mn.     

Compact 1-D magnetophotonic crystals with simultaneous large magnetooptical Kerr rotation and high reflectance

We have investigated the case of reflection-type one-dimensional magnetophotonic crystals (MPCs) in order to achieve high reflectance and high magnetooptical Kerr effect, simultaneously, utilizing a low number of magnetic layers. In a MPC structure including only one Bi:YIG magnetic layer, we have achieved a Kerr rotation as huge as θ_k ≈ 90° with a reflectance of R > 97%. In addition, we have introduced a thinner structure having three Bi:YIG layers and with approximately the same Kerr rotation and reflectance. Both the structures are very compact with lengths of less than 9 μm.     

Optical and magnetooptical properties of CoFeB/SiO<Subscript>2</Subscript> and CoFeZr/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> granular magnetic nanostructures

The optical and magnetooptical properties of the new granular nanocomposites (CoFeB)/(SiO₂) and (CoFeZr)/(Al₂O₃), which are grains of amorphous ferromagnetic alloys embedded in dielectric matrices, have been studied. The dependence of the optical, magnetooptical, and magnetic properties of the nanocomposites on their qualitative and quantitative composition, as well as on the conditions of their preparation, was investigated. Spectra of the dielectric functions ε = ε₁ ? iε₂ were obtained by the ellipsometric method in the range 0.6–5.4 eV. Above 4.2 eV, the absorption coefficient of the (CoFeB)/(SiO₂) composites was found to be close to zero for all magnetic-grain concentrations. The polar Kerr effect measured at a photon energy of 1.96 eV in dc magnetic fields of up to 15 kOe reaches values as high as 0.25°–0.3° for these nanocomposites and depends only weakly on the conditions of preparation. On the other hand, the (CoFeZr)/(Al₂O₃) nanostructures reveal a considerable difference in the concentration dependences of the Kerr effect between samples prepared in a dc magnetic field and in zero field.     

Magnetooptical Kerr effect of Fe-gratings

The magnetooptical Kerr effect in longitudinal configuration is used to measure hysteresis loops of ferromagnetic Fe-gratings grown on Al₂O₃ at different orders of diffraction. At even order of diffraction the hysteresis loops exhibit anomalies which can be attributed to the interference of the magnetic and non-magnetic parts of the grating. The Kerr angle in saturation increases linearly with the order of diffraction.     

Magnetic and magnetooptical properties of Au/Cu-wedge/15-Å-NiFe sandwiches

The results of an investigation of the magnetic and magnetooptical properties of Au/Cu-wedge/15-Å-NiFe sandwiches are reported. Oscillations of the equatorial Kerr effect as a function of the copper wedge thickness are observed. The period of these oscillations is found to be of the order of 5–6 Å. The experimentally observed oscillations of the equatorial Kerr effect are attributed to a quantum size effect. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 33–36 (10 January 1998)     

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.     

Stabilization of the kerr effect by self-induced ionization: formation of optical light spatially localized structures

The nonlinear propagation of ultrashort laser pulses launched into the air is investigated. The formation of optical light "bullets," or spatially localized structures, has been experimentally observed recently. Their stability is shown as due to the occurrence of a dynamical balance between two opposite nonlinear effects: an optical focusing Kerr effect balanced by a defocusing self-induced multiphoton partial ionization of the neutral gas. Characteristics of the "bullets" are predicted analytically and confirmed numerically. They are found to be in agreement with observations.     

Magnetooptical Kerr effect in the near field of a nanowire supporting surface plasmons

In terms of Green’s functions, a theory is developed describing the resonant magnetooptical Kerr effect in light scattering by a linear probe that is parallel to the surface of a magnet and placed at a subwavelength distance from it. The probe is supposed to be a metal nanowire supporting long-lived surface plasmons and forming the near field of the “probe + image” complex. The resonant interaction between the probe and the sample is taken into account within a self-consistent approximation of multiple-scattering theory, and the magnetooptical interaction is included in the linear approximation in magnetization. The problem of scanning near-field magnetooptical microscopy with a linear probe is solved analytically in the case where the magnetization is parallel to both the magnet surface and the plane of incidence of light (longitudinal magnetooptical Kerr effect). The polarization, spectral, and angular characteristics of scattered light modulated by magnetization are discussed. It is shown that the magnetooptical modulation of the scattered light intensity is significantly enhanced when surface plasmons are resonantly excited in the nanowire.