A. B. Granovsky

Optical Tamm States in One-Dimensional Magnetophotonic Structures

We demonstrate the existence of a spectrally narrow localized surface state, the so-called optical Tamm state, at the interface between one-dimensional magnetophotonic and nonmagnetic photonic crystals. The state is spectrally located inside the photonic band gaps of each of the photonic crystals comprising this magnetophotonic structure. This state is associated with a sharp transmission peak through the sample and is responsible for the substantial enhancement of the Faraday rotation for the corresponding wavelength. The experimental results are in excellent agreement with the theoretical predictions.

Anomalous Faraday effect of a system with extraordinary optical transmittance.

It is shown theoretically that the Faraday rotation becomes anomalously large and exhibits extraordinary behavior near the frequencies of the extraordinary optical transmittance through optically thick perforated metal film with holes filled with a magneto-optically active material. This phenomenon is explained as result of strong confinement of the evanescent electromagnetic field within magnetic material, which occurs due to excitation of the coupled plasmon-polaritons on the opposite surfaces of the film.

Theory of giant magneto-impedance effect in composite amorphous wire

Abstract It is shown that for a composite wire consisting of a nonferromagnetic inner core and amorphous ferromagnetic shell layer the amplitude of the GMI effect has raised considerably when the conductivity of the inner core is much larger than that of the shell region.

Magnetorefractive effect in magnetic nanocomposites

The magnetorefractive effect in ferromagnetic metal-insulator granular nanostructures (CoFeZr)-SiOn, Co-Al-O, FeSiOn, and (CoFe)-(Mg-F) is investigated in the infrared spectral region in a wavelength range from 5 to 20 μm. The magnitude of the effect varies from 0.1 to 1.5% for different nanocomposites and strongly depends on the frequency of light and magnetoresistance. It is shown that the reflection coefficient changes in a magnetic field not only due to the magnetorefractive effect, but also due to the even magnetooptical effect. Simple relations describing this effect are given for the case when the reflection from the substrate is insignificant and in the case of a three-layer (insulator-film-substrate) system. The expression for the frequency dependence of the magnetorefractive effect in nanocomposites is derived and its features in the case of high-frequency spin-dependent tunneling are analyzed.

Optical and magneto-optical spectra of magnetic granular alloys

We present the results of the experimental and theoretical investigation of the optical and magneto-optical (MO) spectra of magnetic granular films (Co70Fe30)xAg1−x, CoxAg1−x, in the energy range 0.5-4.0 eV of incident light. The MO properties were investigated in the geometry of transverse Kerr effect. The MO spectra of granular alloys are quite different from the spectra of homogeneous films. The amplitude of Kerr signal and the MO spectra profile depend on the granular and matrix material, the concentration and the shape of the grains and the annealing temperature. We interpret the obtained spectra in the framework of the effective medium approximation that allows to make some conclusions about ferromagnetic particle concentration and their shape.

Direct measurements of field-induced adiabatic temperature changes near compound phase transitions in Ni–Mn–In based Heusler alloys

The adiabatic temperature changes (ΔTad) in the vicinity of the Curie and martensitic transition temperatures of Ni50Mn35In15 and Ni50Mn35In14Z (Z=Al and Ge) Heusler alloys have been studied using an adiabatic magnetocalorimeter of 250–350 K temperature interval for applied magnetic field changes up to ΔH=1.8 T. The largest measured changes were ΔTad=−2 and 2 K near the martensitic (first-order) and ferromagnetic (second-order) transitions for ΔH=1.8 T, respectively. It was observed that |ΔTad|≈1 K for relatively small field changes (ΔH=1 T) for both types of transitions. The results indicate that these materials should be further explored as potential working materials in magnetic refrigeration applications.

Extraordinary Hall effect (EHE) of ferromagnetic composites in the effective medium approximation

Abstract The expression for the EHE coefficient R s of ferromagnetic composites is derived in the framework of the effective medium approximation. In the case of a composite ferromagnetic metal-dielectric, R s increases monotonically as the concentration of the magnetic component c decreases and in the dielectric region (c ≤ 1 3 ) R s = 9R s 1 (1 − c) , where R s 1 is the EHE coefficient of the ferromagnetic component. The dependences of R s on composition are calculated for composites ferromagnetic-paramagnetic metals, ferromagnet-ferromagnet. The typical relation R s ∼ρ 2 for uniform ferromagnets, where ρ is electroresistivity, is not fulfilled in all the cases considered.

Recent results on the giant magnetoresistance in magnetic multilayers (anisotropy, thermal variation and CCP-GMR)

Abstract We present some recent results obtained on the electrical transport properties in magnetic multilayers. Three points are addressed. The first one is an experimental demonstration of the existence of an intrinsic anisotropy of the giant magnetoresistance (GMR). The experiments have been carried out on spin-valve samples for which there is no contribution of the usual anisotropic magnetoresistance to the observed magnetoresistance. The GMR amplitude is found to be larger (lower) in the direction perpendicular (parallel) to the sensing current. The second point concerns a quantitative analysis of the thermal variation of the CIP (current-in-plane) GMR in magnetic multilayers. This analysis is based on a semi-classical theory including the spin-intermixing due to spin-flip scattering by magnons. This approach allows quantitatively evaluation of the respective weights of the various contributions to the thermal decrease in GMR: (i) scattering by magnons in the bulk of the ferromagnetic layers; (ii) phonon scattering in the non-magnetic spacer layer; and (iii) interfacial scattering by paramagnetic interfacial layers which may form as the temperature is increased. The third point is a theoretical investigation of the CPP (current perpendicular to the plane) electrical transport through an interface between two semi-infinite metallic materials. It is shown that when a potential step U exists at such an interface, this step gives rise to an interfacial resistance proportional to U 2 . It also leads to the existence of large oscillations in the electric fields on both sides of the interface.

High-frequency giant magneto-impedance in multilayered magnetic films

We present the results of experimental and theoretical investigations of giant magneto-impedance (GMI) in the thin-film multilayer structure of F/SiO2/Ti/Cu/Ti/SiO2/F, where F stands for the ferromagnetic alloy having a composition of Fe73.5Cu1Nb3Si16.5B6. The layers were deposited under a transversemagnetic field Hp = 200 Oe applied in the plane of the sample perpendicular to its long side and were annealed at 280°C under Hp = 420 Oe for 2h. The GMI effect was measured at frequencies ranging from 0.5 to 1250 MHz using a waveguide methhod. An external magnetic field with a strength of up to 130 Oe was applied along the direction of the alternating current. The GMI is shown to exist in the multilayer structure even if the skin depth in the ferromagnetic layers is of the order of their thickness. Both real and imaginary parts of the impedance vary significantly under external magnetic field. A maximum GMI sensitivity of 10–35%/Oe was achieved at high frequencies.

The features of GMI effect in amorphous wires at microwaves

A new waveguide method is used to investigate high frequency GMI and magnetic permeability in Co-rich amorphous wire. The GMI spectra at microwaves are quite different from those measured at relatively low frequency. The amplitude of magnetic permeability decreases with increasing frequency, however, its relative change under external magnetic field is still large which enables a high sensitivity of GMI sensors of up to 1000 MHz.