M. V. Valeiko

Surface plasmon resonance interferometry for micro-array biosensing

Interferometry that detects the phase of a beam reflected under surface plasmon resonance (SPR) has been developed for bio and chemical sensing. The conditions have been found, under which the phase reveals abrupt jumps in response to a minute increase in the effective thickness of a receptor layer that binds analyte particles on the sensor surface. This forms the basis for biosensing with sensitivity much higher as compared to traditional SPR sensors. Besides, SPR interferometry (SPRI) provides spatial resolution at the micron scale. The enhanced sensitivity attributed to the phase jump and interferometric imaging of variations of the phase over the surface are demonstrated, which open up new avenues for micro-array biosensing.

AMORPHOUS MAGNETIC FILMS PRODUCED BY PULSED LASER DEPOSITION

Amorphous magnetic Fe–Co–Ni–Si–B films have been produced on silicon and glass substrates by means of XeCl excimer laser ablation of amorphous magnetic ribbons. Laser fluence, the number of pulses, and target–substrate distance were the variable parameters. The films were studied with x-ray specular reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, profilometry, and ellipsometry. Laser ablation has been found to provide a good transfer of composition and structure from the ribbon targets to the deposited films, with excellent mechanical and optical quality of the films. Magnetic properties of the films were examined by a technique based on the magneto-optical Kerr effect. The films revealed well-defined in-plane uniaxial anisotropy. They demonstrated coercivity and anisotropy field values comparable to those of the initial ribbons, and much higher steepness of substantially rectangular hysteresis loops. The films can have a number of prospective applications in magnetic sensors, switches,...

Polariton enhancement of the Faraday magnetooptic effect

Enhancement of the Faraday magnetooptic effect by the excitation of surface polariton on an interface between an iron garnet and silver is observed. The main contribution to this effect is due to the rotation of the polarization of a surface polariton as the polariton propagates along the interface.

Deposition of thin ferromagnetic films for application in magnetic sensor microsystems

A number of soft ferromagnetic compositions have been used to fabricate thin-film cores for magnetic sensor microsystems. Techniques based on magnetron sputtering and laser ablation deposition have been extensively explored. The properties of the films have been found to depend strongly on a particular deposition regime and the type of material and, weakly, on an a priori difference between the laser- and magnetron-assisted methods. As-deposited films demonstrate relatively low coercivity H c ∼ (0.1-1) Oe and composition-dependent low (H k < 5 Oe) or high (H k ∼ 20 Oe) in-plane anisotropy, which is governed by the magnetic conditions of the deposition. Both types of films are promising for application in different types of sensors.

Magnetic field sensors based on thin film multi-layer structures

Abstract Thin film multi-layer structures were deposited and optimised for various low noise magnetic field sensors. Original bridge schemes have been tested for the magnetoresitive sensors, which are sensitive not only to amplitude but also to the magnetic field direction. Double-layer anisotropic magnetoresistive sensors have showed decreased hysteresis and lower influence of previous measurements. Deposited spin-dependent structures with antiferromagnetic fixing layer of Fe 50 Mn 50 had 30% magnetoresistive effect.

Faraday effect in thin amorphous magnetic films

Abstract The Faraday effect in thin amorphous magnetic films has been investigated for the first time. The films of general composition FeCoNiSiB were deposited onto glass substrates by laser ablation of amorphous ribbon targets in high vacuum. Since the films have been found to have in-plane anisotropy the Faraday effect measurements were carried out under oblique incidence of 632.8 nm HeNe laser beam. It has been established that the Faraday rotation angle has a linear dependence on the film thickness in the range from 20 to 1300 A. The Verdet constant was estimated to be as high as 3 deg (Oe cm) −1 . This vaue is an order of magnitude higher than the known one for YIG at the same wavelength. The comparative studies of Faraday and Kerr rotation under the same fields have been performed in different geometries. The experimental data were in a good agreement with the results obtained by theoretical evaluations. It has been found that at a thickness exceeding 200 A, the Faraday effect in deposited films prevailed over the Kerr one. The Faraday effect in the produced films is attractive for designing thin-film miniaturized magnetic sensors on the basis of fiber optics and optoelectronics.

Sandwiched thin-film structures for the magnetoresistive spin-tunnelling sensors

Abstract Sandwiched thin-film Ti (80 nm)/Fe 19 Ni 81 (5 nm)/Al 2 O 3 (0.6–1.5 nm)/Co 68 Fe 5 Si 12 B 15 (5 nm)/Ti (6 nm) structures have been deposited by magnetron sputtering technique onto oxidised Si wafers. Magnetic, magneto-optic characteristics and magnetoresistance in perpendicular direction of the deposited layers have been investigated by inductive integrating loop tracer, transverse Kerr effect technique and four-point probe method, respectively. It has been found that magnetic layers are coupled with exchange interaction depending on insulator layer thickness that corresponds to magnetic field strength of 3–4 Oe. Besides, magnetic and magneto-optic measurements showed that the structures can reveal either single-film or double-film properties depending on insulator thickness, with the magnetisation reversal characteristics which were found to be magnetic field strength dependent. The synthesised structures demonstrated magnetoresistive spin-tunnelling (MRST) effect up to 5% under the application of planar magnetic fields in the range of 40 Oe.

Influence of triboelectric treatment on the coercivity of magnetic films

A study has been made to determine how the properties of magnetic films are influenced by the triboelectric fields accompanying the polishing of articles with fur and results are presented. For insulating films of bismuth-containing iron garnet an increase in the coercivity was observed, evidently caused by the electromagnetic effect, in spite of reduced defects in the crystal structure.