Magneto-optic polar Kerr and Faraday effects in magnetic superlattices

Magneto-optic (MO) effects in magnetic multilayers with periodic regions are discussed assuming normal incidence of polarized waves and polar magnetization (Faraday and polar Kerr effects). From the (4 × 4)-matrix formalism simplified analytical expressions linear in the off-diagonal permittivity tensor element are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions are given for the case when the thickness of magnetic layers is much smaller than the radiation wavelength. The procedure is illustrated on superlattices consisting of symmetric sandwiches of ultrathin magnetic and non-magnetic metallic layers. Partial support from the Grant Agency of Czech Republic # 202/00/0761 is acknowledged.     

Magneto-optical effects in ultrathin structures at transversal magnetization

Procedures based on the Yeh’s 4 × 4 matrix formalism for the treatment of the electromagnetic interactions in multilayers at transversal magnetization and at an arbitrary angle of incidence are described. With the restriction to the magneto-optical effects linear in the magnetization the characteristic matrix for magnetic layer is derived. The reflection and transmission coefficients are obtained in the case of magnetic ultrathin film on substrate. The magneto-optical thin film waveguides at transversal magnetization are analysed in details and the dispersion relations for guided modes in a single layer, a bilayer, a sandwich and the approach to expand this way for waveguiding conditions in multilayers are presented. Work partially sponsored by Grant Agency of the Czech Republic, reg. No. 202/98/0235 and Ministry of Education in the frame of KONTAKT program, reg. No. ME 175/1998.     

“Elastic” fluctuation-induced effects in smectic wetting films

The Li-Kardar field theory approach is generalized to wetting smectic films and the “elastic” fluctuation-induced interaction is obtained between the external flat bounding surface and distorted IA (isotropic liquid-smectic A) interface acting as an “internal” (bulk) boundary of the wetting smectic film under the assumption that the IA interface is essentially “softer” than the surface smectic layer. This field theory approach allows calculating the fluctuation-induced corrections in Hamiltonians of the so-called “correlated” liquids confined by two surfaces, in the case where one of the bounding surfaces is “rough” and with different types of surface smectic layer anchoring. We obtain that in practice, the account of thermal displacements of the smectic layers in a wetting smectic film reduces to the addition of two contributions to the IA interface Hamiltonian. The first, so-called local contribution describes the long-range thermal “elastic” repulsion of the fluctuating IA interface from the flat bounding surface. The second, so-called nonlocal contribution is connected with the occurrence of an “elastic” fluctuation-induced correction to the stiffness of the IA interface. An analytic expression for this correction is obtained.     

Dependence of the magnetization on the interface morphology in ultra-thin magnetic/non-magnetic films: Monte Carlo approach

Using Monte Carlo simulations, we have studied the dependence of magnetic properties on interface morphology in magnetic/non-magnetic (M/NM) multilayers. Our aim is to relate macroscopic magnetic properties of the multilayers to their concentration profile at the interface. Our model consists of an alternate staking of magnetic and non-magnetic layers with disordered interfaces. We have considered different concentration and the existence of local magnetic domains at the interface. The results indicate the crucial dependence of magnetization amplitude with interface multilayers atomic composition and the spatial arrangement of magnetic atoms. In particular, we show that isolated islands at the interface leads to the apparition of super-paramagnetic behavior.     

Lubricated sliding dynamics: Flow factors and Stribeck curve

We study the fluid flow at the interface between elastic solids with randomly rough surfaces. We derive (approximate) analytical expressions for the fluid flow factors which enter in the equation describing the fluid flow, and for the frictional shear stress factors which enter in the equation for the frictional shear stress. Numerical results for a rubber cylinder with surface roughness sliding on a flat lubricated substrate, under “low” and “high” pressure conditions, are presented and discussed. Finally we discuss the role of the fluid-induced elastic deformations of the surface roughness profile.     

Conformational properties of poly(p-Phenylene vinylene)

We investigate the quasiparticle conformational defects (excitons, polarons and bioplarons) in the phenylene vinylene oligomers. The conformations are determined by means of the minimization of the total Hartree-Fock energy calculated at 3–21G level. The infrared vibrational transitions are calculated and the types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental vibrational spectrum of poly(p-phenylene vinylene). Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic, 26–30 May 1997. The quantum mechanical calculations were performed on the following computers: Power Challenge XL at Prague Supercomputing Centre, Charles University, IBM Power 2 at Supercomputing Centre of the Czech Technical University and Power Challenge XL at Supercomputing Centre Brno. The work is supported by Projects No. 202/94/0453 and 202/97/1016 of the Grant Agency of the Czech Republic and by Project No. 155/96 of the Grant Agency of the Charles University.     

Mössbauer-effect studies of multilayers and interfaces

The usefulness of Mössbauer spectroscopy for the investigation of magnetic multilayer systems is described. By applying ⁵⁷Fe Mössbauer spectroscopy, the behavior of ultrathin magnetic layers, such as FCC-like Fe films on Cu(0 0 1), is studied. Position-specified (depth-selective) information is available by preparing samples in which monatomic ⁵⁷Fe probe layers are placed at specific vertical positions, e.g. at interfaces or at the surface. As demonstrated for epitaxial chemically ordered Fe₅₀Pt₅₀ alloy films and polycrystalline nanostructured Tb/Fe multilayers, the Fe-spin structure can be determined directly, and a site-selective Fe-specific magnetic hysteresis loop can be traced in very-high-coercivity materials. For the studies of non-magnetic layers, on the other hand, hyperfine field observations by ¹⁹⁷Au and ¹¹⁹Sn probes are worthwhile. Spin polarizations in Au layers penetrating from neighboring ferromagnetic 3D layers are estimated ¹⁹⁷Au from Mössbauer spectra and are also studied by inserted ¹¹⁹Sn probes in Au/3D multilayers. In the Sn spectra for Cr/Sn multilayers, it was found that remarkably large spin polarization is penetrating into Sn layers from a contacting Cr layer, which suggests that Cr atoms in the surface layer have a ferromagnetic alignment.     

Formation and investigation of cobalt silicide ultrathin layers in Ti/Co/Ti-, TiN/Ti/Co-, and TiN/Co-on-silicon structures

The formation of ultrathin CoSi₂ layers in Ti(8 nm)/Co(10 nm)/Ti(5 nm), TiN(18 nm)/Ti(2 nm)/Co(8 nm), and TiN(18 nm)/Co(8 nm) systems magnetron-sputtered on the Si(100) surface is studied. The systems are subjected to two-step rapid thermal annealing. In between the annealing steps, the “sacrificial” layer is chemically removed and the second and third systems are additionally covered by a 17-nm-thick amorphous silicon (α-Si) layer. In the course of the fabrication process, the structures are examined using time-of-flight secondary-ion (cation) mass spectrometry, Auger electron spectroscopy, and scanning electron microscopy combined with X-ray energy dispersion microanalysis. It is shown that the above complex of analytical investigation provides efficient physical control of ultrathin silicide layer formation.     

Polar and longitudinal magnetooptical Kerr effects in magnetic film/spacer/magnetic substrate system

The paper deals with the electromagnetic theory of longitudinal and normal incidence polar magnetooptical Kerr effects (MOKE) in sandwich structures consisting of a magnetic film on a thick magnetic substrate separated by a nonmagnetic spacer. These structures are employed in fundamental studies of magnetic exchange coupling, tunnel magnetoresistance, spin polarized current,etc., as well as in the design of the magnetoelectronic devices,e.g., magnetic random access memories. The results are expressed in terms of the Jones reflection matrix. This makes the analysis of the observed MOKE in various experimental set-ups easier. To first order in off-diagonal elements of the permittivity tensor, the analytical expressions approximate the results obtained using rigorous matrix formalisms with a little loss in accuracy, provided the magnetooptical effects quadratic in the offdiagonal elements are negligible. The total MOKE is expressed as a a sum of components originating from magnetic film and magnetic substrate, respectively. The components enter the analytical expressions with different phases and may be identified separately by a proper control of the polarization state and photon energy of the incident radiation, angle of incidence, nonmagnetic spacer thickness, and radiation wavelength. The formulae are derived without any restriction on the magnetic film thickness. However, for a rapid evaluation of the trends the MOKE response is also treated under the assumption that the thickness of the magnetic film is much smaller than the radiation wavelength. This work has been partially supported by Grant Agency of the Czech Republic (#202/97/1180 and #202/00/0761), Barrande Project and Grant Agency of Charles University.     

The effect of the shear flow on directional solidification of SCN-3wt% Salol alloy

The directional solidification process of SCN-3wt% Salol transparent alloy is investigated in the presence of the shear flow at the liquid-solid interface. It is found that the shear flow induces a stabilizing effect on planar interface. At higher pulling rates, oscillation of the growth pattern together with fluctuation of the growth velocity takes place. With the increase of the pulling rate, the interface growth pattern transits from “planar-cellular” oscillation to “cellular-dendritic” oscillation, and the periodicity increases. The modification of the growth pattern is due to the effect of the shear flow on solute distribution, and the time and history dependent character of interface morphology evolution also plays an important role in the formation of the oscillating growth pattern. Supported by the National Natural Science Foundation of China (Grant Nos. 50331040 and 50702046)     

CVD diamond films for electronics

Mechanical, optical, thermal and electronic properties of diamond films and chemical vapour deposition (CVD) techniques are briefly reviewed. Some spectroscopical methods for the characterization of CVD diamond films are described (optical absorption, photothermal deflection spectroscopy, Raman spectroscopy and electron paramagnetic resonance), together with our recent results on investigation of electronic properties of the main defects in this material, relevant to the application of CVD diamond films for the future electronic devices. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant Agency of the Czech Republic, Grant No. 202/06/0446 and by the NATO Scientific Exchange Programme, HTECH.LG 940890 and NFWO (National Fonds voor Wetenschappelijk Orderzoek, Brussel) Project G.0014.96.     

磁性多层膜的巨磁电阻随铁磁和非磁层厚度变化的唯象理论计算

根据唯象理论，并采用以铁磁─非磁混合层代替铁磁／非磁层界面的理论方法，计算了Ｆｅ／Ｃｒ多层膜的巨磁电阻随铁磁和非磁层厚度的变化关系与实验结果做了比较，发现它们符合得较好．还绘出了巨磁电阻随铁磁和非磁层厚度变化的二元函数图 关键词：     

Modeling interface trapping effect in organic field-effect transistor under illumination

Organic field-effect transistors (OFETs) have received significant attention recently because of the potential application in low-cost flexible electronics. The physics behind their operation are relatively complex and require careful consideration particularly with respect to the effect of charge trapping at the insulator–semiconductor interface and field effect in a region with a thickness of a few molecular layers. Recent studies have shown that the so-called “onset” voltage (V _onset) in the rubrene OFET can vary significantly depending on past illumination and bias history. It is therefore important to define the role of the interface trap states in more concrete terms and show how they may affect device performance. In this work, we propose an equivalent-circuit model for the OFET to include mechanism(s) linked to trapping. This includes the existence of a light-sensitive “resistor” controlling charge flow into/out of the interface trap states. Based on the proposed equivalent-circuit model, an analytical expression of V _onset is derived showing how it can depend on gate bias and illumination. Using data from the literature, we analyzed the I–V characteristics of a rubrene OFET after pulsed illumination and a tetracene OFET during steady-state illumination.     

Sensors measuring oxygen activity in melts: Development of impedance method for“in-situ” diagnostics and control electrolyte/liquid-metal electrode interface

An impedance method for periodic“in-situ” diagnostics of the solid electrolyte/liquid-metal electrode interface during the lifespan of yttria-stabilized zirconia (YSZ)-based sensors measuring oxygen partial pressure in melts was developed. It was found that the impact of polarization effects on YSZ, stipulated by corrosive measuring environments (molten alkaline metals), is increasing with increase of the working temperature, which may lead to the appearance blocking reaction layers at the electrolyte/liquid-metal electrode interface. The proposed impedance method allows obtaining necessary information about the electrolyte/liquid-metal electrode interface and about the character and the level of polarization of the liquid-metal electrode.     

A contribution to the characterization of laser-hardened steel surfaces

The article deals with the possibility to characterize the laser heat-treatment of steel surface by means of X-ray diffraction and microhardness measurements. For tensometric analysis the X-ray one-tilt method with no reference substance was used. It is shown that hardened surface layers of the carbon steel are affected by compressions reaching in the middle of the laser beam track up to ≈ 350 MPa. The microhardness increased by as much as 350 %. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This research is a part of the research project supported by Grant Agency of the Czech Republic (Grant No. 106/95/0080).     

Strained In x Ga1−x As/GaAs multiple quantum wells grown by MOVPE

Luminescence properties of strained In _x Ga_1−x As/GaAs multiple quantum wells of different thickness and In content, prepared by metal organic vapour phase epitaxy were studied. The influence of the quantum well material composition on the shape of luminescence spectra was investigated. The experimental results were fitted by the Model Solid Theory. This fit was improved by the use of adjustedQ parameter. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998. This work was supported by Grant Agency of Czech Republic under grants numbers 202/98/0074, 102/99/0414 and Grant Agency of Academy of Sciences No. A 10110807/1998.     

Preparation and properties of thick not intentionally doped GaInP(As)/GaAs layers for optoelectronic applications

We report on liquid phase epitaxial growth of thick layers of GaInP(As) lattice matched to GaAs. Layers with thicknesses up to 7 μm were prepared in multi melt bin, step-cooling, one-phase configuration. Unintentionally doped layers, grown from moderate purity starting materials show significant decrease in the residual impurity level when erbium was added into the melt. Fundamental electrical and optical properties of the layers were investigated. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998. This work was partially supported by the Grant Agency of the Acad. Sci. CR under contract GAAV No. A 1010807/1998.     

Microscopic properties of Co/Pd multilayers studied by ferromagnetic and nuclear magnetic resonance

The microscopic properties of Co/Pd multilayers were studied by ferromagnetic and nuclear magnetic resonance. The anisotropy of the layer is found to decrease for decreasing Co sublayer thickness and a switching of the magnetic preferential direction occurs below 8Å. The anisotropy is also a function of the Pd layer thickness: below 20Å it increases with decreasing thickness. This is attributed to a decrease in the Pd/Co interface contribution to the anisotropy. Hyperfine field spectra show the layers with [111] texture to be mainly polycrystalline fcc. The spectra shift to lower hyperfine fields upon decreasing Co sublayer thickness. This is attributed to a decrease in the magnetic moment caused by stretching of the Co lattice due to neighbouring Pd atoms. The results were checked by experiments on almost single phased [100] fcc Co/Pd multilayers. The similarity with the results on the [111] layers suggests that the expansion of the Co lattice is nearly isotropic.