A simple differential set up for measuring changes in reflectivity of a flat surface of a ferromagnetic material, the so-called transverse magneto-optic Kerr effect, is described. The differential procedure is used with the aim of minimizing mechanical and optical noise. Hysteresis cycles have been plotted for several ferromagnetic films of sputtered amorphous R-M alloys (R - Y, La; M - Co, Ni) and reveal good proportionality between ΔR/R, the relative change of reflectivity, and the magnetization $${\rm{\vec M}}$$ measured with a SQUID magnetometer.

We study both experimentally and theoretically the driven motion of domain walls in extended amorphous magnetic films patterned with a periodic array of asymmetric holes. We find two crossed-ratchet effects of opposite sign that change the preferred sense for domain wall propagation, depending on whether a flat or a kinked wall is moving. By solving numerically a simple phi(4) model we show that the essential physical ingredients for this effect are quite generic and could be realized in other experimental systems involving elastic interfaces moving in multidimensional ratchet potentials.

Antiferromagnetic coupling in magnetic multilayers with few nanometer thick metallic spacers has been intensively studied in the last years so that, nowadays, the fundamental aspects of the physics of the process are well established [1]. In addition, the application of the peculiar electronic transport properties of some of these systems to the design of spin-valve type read heads of hard disks has lead to a big increase in their sensitivity and, consequently, to a marked increase of the areal density of information recorded in commercial hard disk drives [1]. However, the case of the magnetic coupling in multilayers with semiconducting spacers has been much less studied. As a consequence, in spite of the strong technological interest of semiconductor materials like Si, the role of this type of spacers in the magnetic coupling is not fully understood.

1. Depto. Física, Universidad de Oviedo CINN, Oviedo, Asturias, Spain. 2. Depto. Física Atómica, Molecular y Nuclear, and GISC, Universidad Complutense de Madrid, Madrid, Comunidad de Madrid, Spain. 3. Depto. Dispositivos, Sensores y Biosensores, Instituto de Microlectrónica de Madrid (CNM-CSIC), Madrid, Comunidad de Madrid, Spain. 4.NANO, Institut Néel, CNRS and Universite Joseph Fourier, Grenoble, Grenoble, France.

Soft x-ray resonant magnetic scattering (SXRMS) has been used to probe the interlayer coupling in amorphous ferromagnetic/semiconductor multilayers. It is shown that the [Co(73)Si(27) (50 angstrom)/Si (30 angstrom)] system exhibits an antiferromagnetic (AF) coupling at low fields. Moreover, another aspect of SXRMS effect is reported. Using circularly polarized photons, a shift in the AF order Bragg peaks' position is observed and related to two opposite AF states with the spin direction longitudinally aligned. As a consequence, the sensitivity of SXRMS to AF domains having the same spin axis but opposite senses is shown. A physical explanation for the origin of this effect is provided in terms of magnetic-resonant-refraction corrections to Bragg's angle, taking into account the phase shifts between layers with opposite magnetization directions at different in-depth positions. Numerical simulations are performed that reproduced the experimental observations.

The transverse magneto-optical Kerr effect (TMOKE) was investigated on multilayers of Au/Co/Au at the attenuated total reflection configuration (ATR), where light was incident upon the film from a glass prism (n = 1.45). For a Co layer of thickness t(Co) = 5 nm, experimental and theoretical results of the TMOKE response for lambda = 670 nm showed that the highest amplitude of the effect is achieved when the Au layer, which is adjacent to Co and air is absent. Since the surface plasmon resonance (SPR) is highly damped in Co, this result suggests that the excitation of SPR is not a necessary condition to produce an important TMOKE response. Numerical simulations of the TMOKE spectra as a function of the angle of incidence and the thickness of the layers have also shown that, when the sum of the thickness of the two Au layers is held constant at 30 nm, the structures which yield the highest TMOKE amplitudes have the thickness of the Co layer in the range 10<d(Co)(nm)<15 and the thickness of the Au layer, which is adjacent to Co and air in the range 7.5<x( nm)<17.5, observed at the angles of incidences around 45 degrees. (C) 2006 Elsevier B. V. All rights reserved.

This article presents a theoretical formalism for a magneto‐optical scanning near‐field microscope (MO‐SNOM) in the transverse magneto‐optical Kerr effect configuration. Polarized light emitted by a nanosource is scattered by the magnetic object towards the detector. The nanosource is modelled as a circular aperture in an infinitely thin, perfectly conducting screen following the Bethe–Bouwkamp model. The theorem of reciprocity is used for calculating the detected signal in a constant‐height scanning mode for a Co thin film pattern. Two magnetic distributions are investigated: the single domain and the Bloch wall. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A set-up able to achieve a magnetic characterization at a sub-micron scale will be presented. Together with topographic and optical images, it is possible to plot local hysteresis loops (LHL) and magneto-optical differential susceptibility (MODS) using a. transverse MOKE-like configuration. We will show how MODS allows to follow the evolution of the wall and domains on a micron sized object. A comparison between the images of domains and the micromagnetic simulations on several micron sized objects will be finally presented. C 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report magneto-optical scanning near-field optical microscopy images for 4x4x0.08 mu m(3) and 16x16x0.08 mu m(3) low magnetic anisotropy Co70.4Fe4.6Si15B10 particles. Measuring magneto-optical differential susceptibility we acquired images of the domain wall movement driven by an applied magnetic field with a spatial resolution better than lambda/4. For the 4x4x0.08 mu m(3) sized particle, a sequence of 27 magneto-optical differential susceptibility images reveals the evolution of the magnetic domain structure between positive and negative saturation fields passing through the four-domain flux-closure magnetization structure. On the 16x16x0.08 mu m(3) particle, we studied the role of the oscillating driving field on the susceptibility distribution. Comparing the different magneto-optical differential susceptibility sequences, the role of the shape anisotropy on the field induced domain wall movement is evidenced. Micromagnetic simulations were used to provide a better understanding of the domain wall movement. (c) 2006 American Institute of Physics.

We performed magnetic-field-induced experiments on micron-sized patterned Co70.4Fe4.6Si15B10 square thin-film elements with in-plane magnetic anisotropy by magneto-optical scanning near-field optical microscopy (MO-SNOM) with a spatial resolution better than 200 nm. Markedly different local hysteresis loops (LHLs) were measured on selected positions in one element. Some LHLs presented an unusual shape intrinsic of local magnetic-field-induced process. Comparison of the MO-SNOM imaging results with high-resolution far-field Kerr microscopy has confirmed the local character of the MO-SNOM measurements. This has also helped us to understand the unusual LHLs shapes as related to the field-induced rearrangement of the domain structure within the square element during the magnetization process. The magnetic structure in small field is well described by two overlapping four-domain flux-closure configurations that are well modeled by micromagnetic calculations.

The present paper concerns the interaction between a surface plasmon and a magnetic material with a transverse Kerr effect configuration type. The surface plasmon is optically generated at the surface of a gold layer. The associated evanescent wave interacts with a cobalt diffraction grating patterned on gold. The magneto-optical interaction is observed in reflection and transmission modes by measuring the intensity of diffraction orders and the enhancement of the magneto-optical effect due to the surface plasmon is discussed.

Summary This paper reports on the development of a magneto‐optical scanning near‐field optical microscope and the experimental near‐field study of the domain structure for a model magnetic particle of 16 × 16 µm 2 of a Co 70.4 Fe 4.6 Si 15 B 10 amorphous thin film, deposited on a silicon substrate. We present the topographic, optical and magneto‐optical differential susceptibility (MODS) images of the particle. Imaging by using the local MODS reveals the domain structure. These images are also used for positioning the tip in order to acquire local hysteresis loops, with submicrometre spatial resolution.

Summary form only given. Magnetic material technical applications are progressively being miniaturized. As a consequence, the research community needs to develop new instrumentation to study the magnetic properties in a sub-micron or nanoscopic scale. In this paper we present the development of a scanning near-field optical microscope (SNOM) devoted to the study of magnetic thin films. We have incorporated the capability of analyzing the light polarization to get magnetic information by means of the transverse magneto-optical Kerr effect (MO).

Cobalt films have been electrodeposited directly onto p-type (100) silicon substrates. Since electrons were required for reduction of the cobalt in solution, deposition only occurred in the presence of illumination. Projection of an optical grating onto the substrate during deposition demonstrated direct patterning of the Co which could lead to novel methods of defining magnetic structures on semiconductor substrates.

The transverse Kerr effect corresponds to a change of p-light reflectivity of a ferromagnetic surface without the change of polarisation when magnetisation is reversed. A phase change occurs that can also be measured. The phenomenological analysis is followed by the description of the set-up and by the first experimental results before discussion and conclusion.

An expression for the Fresnel coefficient r pp is established in the general case of an interface between two semi-infinite media and is extended to multilayers. By analogy with the well-known Θ K R for polar Kerr effect, a figure of merit is proposed for the transverse geometry. It is an alternative characterizing quantity to the relative change of reflectivity for p polarization, Δ R p / R p .

We developed a LED based Transverse Magneto-Optical Kerr Effect (TMOKE) magnetometer that operates at room temperature, in an up to 12 kA/m magnetic field. This equipment works with three wavelengths: blue (lambda = 450 nm), green (lambda = 563 nm) and red (lambda = 660 nm). As a test for the equipment, we obtained the dependence of the saturation TMOKE signal as a function of the wavelength. We measured Co and Fe thin films, and REI.,Co, amorphous films (where RE = Dy, Ho, Gd and Y; and x = 0.6, 0.67). Our results showed that the saturation TMOKE signal raises when decreasing the wavelength for RE-Co amorphous films, while it is almost constant for Co. It means that the rare earth contribution for the TMOKE signal increases for blue light. For x approximate to 0.6, this contribution decreases from Dy-Co to Gd-Co and to Y-Co.