Y. Souche

TMOKE hysteresis loops in Bragg diffraction from 2D patterns

Abstract Two-dimensional arrays of micrometer-scale thin square slabs of amorphous Sm 0.2 Co 0.8 were prepared by means of e-beam lithography and dc sputtering. When a laser beam is Bragg-diffracted by this structure, under transverse magneto-optical-Kerr effect geometry, the intensities of the various diffracted beams have very different variations as a function of applied magnetic field. The diffraction hysteresis loops provided by the various Bragg-diffracted beams yield information about the average domain structure of the individual particles.

Irreversible evolution in the topology of magnetic domains (invited)

Hysteresis does not vanish in materials essentially free from defects and domain wall pinning. It arises from the existence of many geometrically different domain structures separated by intrinsic energy barriers. Although generally metastable, these states can nevertheless be explored by suitable excursion in the manifold of domain structures, along which irreducible irreversibility is present. This idea is illustrated by experiments performed on garnet layers with uniaxial anisotropy (bubble material). Cooling the layer from T>Tc in a field H normal to it results in various states: parallel stripes (H=0), bubbles of increasing diameters and mixtures of bubbles and stripes (H<52 Oe), and mazes of convoluted stripes with defects (forks, dead ends). Cycling the applied field at constant temperature also causes evolution of the structure. For example, starting from parallel stripes the structure evolves toward a maze with intermediate steps corresponding to stripe folding, and then there is the onset of def...

Laser ablation deposition and magnetic characterization of metallic thin films based on rare earth and transition metals

Abstract Laser ablation deposition (LAD) is a very promising technique for the preparation of thin films and multilayers. Technical difficulties inherent in the method have been solved. In particular a velocity selector has been developed leading to almost complete elimination of the droplets ejected from the target. The magnetic properties of a series of model systems prepared by LAD have been studied. The anisotropy of 30AFe(110)/W(110)/Al 2 O 3 (112¯0) is discussed. Epitaxial bilayers of 5AGd(0001)/25AFe(110)/W(110) have been obtained; the Gd moments are antiparallel to the Fe moments. Thin films of Y 2 Co 17 (0001) have been successfully grown on W(110)/Al 2 O 3 (112¯0) and their magnetic properties have been characterized.

Transverse magneto-optical Kerr effect: the phase change of reflected light

Abstract 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.

DOMAINS AND GIANT MAGNETO-IMPEDANCE IN AMORPHOUS RIBBONS BY MAGNETO-OPTICAL KERR EFFECT

By longitudinal magneto‐optical Kerr effect microscopy we analyzed the development of the domain structure in Co70.4Fe4.6Si15B10 amorphous ribbons for which giant magneto‐impedance had been observed. Using transverse and longitudinal magneto‐optical Kerr effect magnetometry we measured the magnetization direction around the hysteresis loop. These results allowed us to model the domain structure of the sample during the giant magneto‐impedance measurements.

Photoelectrodeposition of patterned cobalt films on silicon substrates

Cobalt films have been electrodeposited directly onto p-type (1 0 0) 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.

Magneto-optical diffraction and transverse Kerr effect

Abstract The transverse non-specular magneto-optical Kerr effect was measured in diffraction from an inhomogeneous grating made of ferromagnetic Fe 0.75 Si 0.25 wires on a silicon substrate. The relative change in intensity of the diffracted beams when magnetisation is reversed (Δ I/I ) n shows a large enhancement (from 1.8 × 10 −2 up to 3 × 10 −1 ) for angles of incidence corresponding to minima of I n . The relative magnetic response, Δ D n , where D n is the diffraction efficiency ( I n /I inc ), reaches maximum values for non-zero diffracted orders and is higher than that obtained in specular conditions.

Non-specular magneto-optical Kerr effect

Abstract A grating coated with a magnetic film is illuminated by a laser beam and produces Bragg-diffracted beams. The non-zero-order beams, leaving the specimen, feature the magneto-optical Kerr effect just as well as the zero-order specular one. We show the results of systematic measurements of the change in reflectivity between oppositely saturated states, for various diffracted beams from a simple grating, in the geometry corresponding to the transverse non-specular Kerr effect, on varying the angle of incidence.

Local hysteresis loop measurements by magneto-optical scanning near-field optical microscope

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 200nm. 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.

Magnetic properties of amorphous Y-Co/Gd-Co/Y-Co sandwiches

Abstract In amorphous YCo/GdCo/YCo sandwiches, antiferromagnetic coupling between layers leads to magnetic field induced transitions between a macroscopic ferrimagnetic state and a saturated state. This transition is associated with the existence of two large planar Bloch walls parallel to the surface. These phenomena are studied for samples of different thickness by magnetization measurements and magneto-optical Kerr effects.