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Recent progress on (Si)GeSn optoelectronic devices holds great promise for photonic integration on Si substrates. In parallel to the development of bulk devices, (Si)GeSn-based quantum wells (QWs) have been investigated, aiming to improve device performance. While multiple QW structures are preferred for the device applications, a single quantum well (SQW) is more suitable for optical property studies. In this work, a comprehensive study of an SiGeSn/GeSn SQW was conducted. The calculated band diagram provided band alignment and energies of possible transitions. This SQW features a direct bandgap well with L–Γ valley energy separation of 50 meV, and barrier heights for both electron and hole are greater than 80 meV. Using two continuous-wave and two pulsed pumping lasers, the analysis of PL spectra allows for identifying different transitions and a better understanding of the SQW optical properties. This study could provide guidance for advancing the future QW design toward device applications. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a versatile candidate for photonic devices due to its highly efficient optical emission. However, for pumping of ZnO photonic devices UV-sources are required. Here, we investigate the alternative usage of widely available pulsed near-infrared (NIR)-sources and compare the efficiency of linear and nonlinear excitation processes. We found that bulk ZnO, ZnO thin films grown by molecular beam epitaxy, and ZnO/SiO2 microdisk devices exhibit strong nonlinear response when excited with NIR pulses (λ ≈ 1060 nm). In addition, we show that the ZnO/SiO2 microdisks exhibit sharp whispering gallery modes over the blue-yellow part of the visible spectrum for both excitation conditions and high Q-factors up to Q=4700. The results demonstrate that nonlinear excitation is an efficient way to pump ZnO photonic devices. [ABSTRACT FROM AUTHOR]

Cr-dosed FePt thin films are grown in an ultrahigh vacuum at room temperature and are analyzed by using the surface magneto-optic Kerr effect, scanning electron microscopy and x-ray magnetic circular dichroism. The segregation of Cr during annealing is responsible for the formation of round FePt islands and the separation of the [L1.sub.0] islands and planar A1 phase.

A study is conducted on structural, optical and nonlinear optical properties of photonic crystals (PC) that are based on porous n-Si. The fabrication of one-dimensional photonic crystals based on porous n-Si is reported.

The exchange-spring behavior found in Sm-Co (20nm)/Fe epitaxial bilayer films was investigated by analyzing major hysteresis and recoil curves as a function of anneal conditions. The Sm-Co thickness was fixed at 20 nm while the Fe thicknesses of 10 and 20 nm were studied with ex situ annealing carried out in evacuated, sealed silica tubes at different temperatures.

Research into the magnetic field and temperature dependence of the magnetic susceptibility for the ferromagnetic layered manganites SrO(La(sub 1-x)Sr(sub x)MnO3)2 in the composition range x = 0.32-0.40 is presented. It is concluded that the paramagnetic phase in these ferromagnetic layered manganites shows a reduced ferromagnetic exchange coupling.

The normal magnetic modes in spiral ferromagnetic structures are analyzed theoretically and experimentally. The bilayer system is made up of Fe layers (25, 50, 100 and 200 angstrom) which are exchange coupled to 200 angstrom thick SmCo films with roughly 200 kOe anisotropies. The Fe spiral, which is induced by an external magnetic field, leads to a structure similar to that of a Block domain wall. Experimental and theoretical results showed good agreement.

A study was conducted to fabricate epitaxial, (100)-oriented GdN/W/NbN/W and NbN/W multilayers. Coexistence of the superconductivity and magnetism in the nanometer limit was obtained. NbN/W multilayers were found to exhibit smooth and well-defined layering. They also showed coupling of superconductivity layers. Results suggest the possibility of obtaining coupling between ferromagnetic layers across a superconducting spacer.

Two layered Ruddlesden-Popper phase SrO(La(sub1-x)SrxMnO(sub3))(sub2) with x=0.3 and 0.4, shows colossal magnetoresistance, magnetic anisotropy, and an anomalous low-field magnetization (M) plateau between the Curie temperature (Tc) and T-300K. Intergrowths show two-dimensional magnetic behaviour in both 0.3 and 0.4 compositions.

The impact of uniaxial deformation on the giant magnetoresistance (GMR) effect in cobalt-copper (Co-Cu) ribbons are examined in an experiment. Samples of free-standing ribbons created using the melt-spinning technique are used for the study. Test results show that the GMR effect is affected by the structural disorder and the resistivity of mechanical processing. In addition, it was observed that Co particles are not affected by postprecipitation deformation.

Experimental studies using the surface magnetooptic Kerr effect help analyze the magnetic and related structures of ultrathin Fe films present as wedge structures onto Ag(100) and Cu(100). Thermal fluctuations in an isotropic two-dimensional Heisenberg system inhibit the long-range order and/or generate domain structures exhibiting unusual properties. Film thickness and temperature exert significant influence on spin-reorientation transition for Fe/Ag(100) and Fe/Cu(100).

Analysis of the effect of lithium doping on the electrical and optical properties of LiNbO3 and LiBO2 thin films reveals that lithium doping enhances the ionic conductivity of the films to high levels with a maximum conductivity of 4.5 times 10 to the power of -6 S per cm. The films display high level transmission in the 350 to 2500 nm spectral region. The simultaneous increase in transmission and conductivity enables the use of lithium doping for designing ion conductors for transmissive solid-state electrochromic systems.

Ferromagnetic resonance was observed in sputtered Fe/FeSi films subjected to temperatures below 100 Kelvin. These films exhibited antiferromagnetic interlayer coupling at ambient temperature and also at low temperatures when the films were exposed to visible light. Charge carriers in the FeSi spacer layer, which carried spin information between the Fe layers, contributed to this phenomena.

The optical characteristics of a gelatin film with a very low concentration of silver particles was investigated. The results showed that the gelatin film featured isotropic properties and well-separated and noninteracting silver particles. An apparent blue shift in the plasma resonance absorption was observed with the loss function when the silver particles varied in size from 22 to 10 nm.

The magnetic behavior of Fe/Mo/Fe and Co/Cu/Co sandwiches epitaxially grown on Mo(100) and Cu(100) single crystals were investigated using electron diffraction and in situ magneto-optic Kerr effect measurements. The results showed that there was an oscillatory behavior between ferromagnetic and antiferromagnetic coupling. This behavior originated from the interface between the magnetic and the spacer layers.

The exchange coupling behavior of the epitaxial Sm-Co(1100)/Nd-Co exchange-spring bilayers is studied. The results indicate that the exchange field H(sub ex) and the maximum size of the soft phase for the effective exchange-spring coupling can be enhanced by tailoring the magnetic anisotropy of the soft phase.

The stochastical theory was applied to fluctuating hyperfine interactions in perturbed angular correlation (PAC) spectroscopy in order to describe experimental data on Fe/Cr(100) superlatticies. The results show the existence of fluctuating magnetic moments in the Cr layers and the correlation of interlayer coupling with the temperature dependence of the fluctuation rates.

The method for analysis of temperature and field dependent magnetization data near the Curie temperature is described. The width of the intrinsic Curie temperature is found to be larger than the field-induced effect yet critical exponents beta = 0.3682 plusmn 0.0033 and delta = 4.76 plusmn 0.32 is observed in inhomogeneous La2/3Ca1/3MnO3 films.

It has been possible to obtain images of the magnetic domain structure in a 1600 angstrom thick buried SmCo layer of a Fe/SmCo spring magnet. This work allowed the determination for the first time of the orientation of magnetic domains in a SmCo layer buried beneath another ferromagnetic layer of Fe.

Research into the magnetic stability in exchange-bias and exchange-spring systems during repeated reversal of the pinned layer is presented. It is suggested that the strong initial decay in uniaxial samples is the result of the reversal of local inhomogeneities.

Research into the impact of magnetic disorder on the magnetization reversal process in thin Co/CoO films is presented. It was possible to establish the existence of a disorder-driven critical point in the nonequilibrium phase diagram.

The colossal magnetoresistance of La(sub 1-x)Ca(sub x)MnO(sub 3) are reported in many experiments. The sign reversal is discussed in terms of band structure and the coexistence of hole-like and electron-like conduction.

The basic building block is the voltage-controlled rotation (VCR) element that consists of four-layer structure-two ferromagnetic layers separated by both nanometer-thick insulator and metallic space layers. The interlayer exchange coupling between the two ferromagneticlayers oscillates as a function of applied voltage.

The origin of the 18 angstrom period of the Fe/Cr system is determined by studying the period of the oscillatory exchange coupling of Fe/Cr(sub 1-x)V(sub x) (x = 0.085, 0.20)(100) and (211) superlattices. Results show that the period of oscillation decreases slightly with increasing V doping. This indicates that the N-centered ellipse is the origin of the 18 angstrom period in Fe/Cr superlattices.

A study was conducted to analyze the magnetic characteristics of ultrathin iron films prepared on stepped W(001) and Pd(001) substrates. The substrates were mechanically polished with diamond-paste finish. Experimental results indicated that improvements in the Curie temperature correlated with the step-induced Pd moments that is supported by the increased surface magneto-optic Kerr effect signal on the stepped surface.

Face-centered cubic Fe was grown onto a novel Cu(110) substrate with ordered Cu-O stripes. Results showed that the growth mode was layer-by-layer and was better than either clean or oxygen-saturated Cu(110). It was postulated that the Fe films grow conformationally onto the original striped substrate. Lateral long-range ordering of the stripe-like structure on Fe was retained up tp 6-7 ML. These films were ferromagnetic with in-plane magnetic anisotropy.

A study was conducted to analyze expressions for the resonant magnetic x-ray scattering from rough surfaces. Four formulas were utilized to examine the structural and magnetic roughness, including the correlation between them. The effects of magnetic domain structure and magnetic dead layers on the surface scattering was then discussed. Experimental results indicated that the leading contribution to the diffuse component is nonzero if the magnetic and structural roughness are correlated.

The magnetic reversal process in epitaxial Sm-Co(1100)/TM bilayer films prepared through magnetron sputtering onto Cr-buffered single-crystal MgO substrates, is reported. The coercive field of the hard layer was found to become much less than that of a single layer, with increasing soft layer thickness. Experimental results were compared with model simulations, and suggest that bilayer film exchange-spring behaviour, can be understood from the parameters of the hard and soft layers.

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and, consequently, no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast, conventional annealing under appropriate conditions leads to an increase in the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements. [ABSTRACT FROM AUTHOR]

Cr-dosed FePt films with total thicknesses of 1.8 and 3.6 nm were grown in an ultrahigh vacuum at room temperature and studied by means of the surface magneto-optic Kerr effect, scanning electron microscopy, and x-ray magnetic circular dichroism. After annealing at 550 °C, the L10 and A1 phases are spatially separated. In the L10 phase, round nanoparticles form that are 15±4.8 nm in diameter and possess out-of-plane magnetic easy axes. An addition of <0.01 nm Cr enhances the coercivity (∼0.9 T), which then decreases with additional Cr, and a spin reorientation transition occurs near 0.3 nm Cr dosage as the L10 islands disappear. Segregation of Cr during annealing is believed to be responsible for the formation of round FePt islands and the separation of the L10 islands and planar A1 phase. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles coated with biochemical ligands are enabling many biological and medical applications. In particular biomagnetic sensors have potential advantages of simplicity and rapidity. We demonstrate a substrate-free biomagnetic sensing approach using the magnetic ac susceptibility of ferromagnetic particles suspended in a liquid. The magnetic relaxation of these particles is mainly due to Brownian rotational diffusion, which can be modified by binding the particles to the intended target. This scheme has several advantages: (i) it requires only one binding event; (ii) there is an inherent check of integrity; and (iii) the signal contains additional information about the target size. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of NiMnSb films, 5–120 nm thick, grown on InGaAs/InP(001) substrates by molecular-beam epitaxy, were studied by x-ray diffraction, transmission electron microscopy (TEM), and ferromagnetic resonance (FMR) techniques. X-ray diffraction and TEM studies show that the NiMnSb films had the expected half-Heusler structure, and films up to 120 nm were pseudomorphically strained at the interface, greater than the critical thickness for this system, about 70 nm (0.6% mismatch to InP). No interfacial misfit dislocations were detected up to 85 nm, however, relaxation in the surface regions of films thicker than 40 nm was evident in x-ray reciprocal space maps. TEM investigations show that bulk, planar defects are present beginning in the thinnest film (10 nm). Their density remains constant but they gradually increase in size with increasing film thickness. By 40 nm these defects have overlapped to form a quasicontinuous network aligned closely with <100> in-plane directions. The associated strain fields and or compositional ordering from these defects introduced a reduction in crystal symmetry that influenced the magnetic properties. The in-plane and perpendicular FMR anisotropies are not well described by bulk and interface contributions. In thick films, the in-plane uniaxial and fourfold anisotropies increased with increasing film thickness. The lattice defects resulted in a large extrinsic magnetic damping caused by two-magnon scattering, an increase in the coersive field with increasing film thickness, and a lower magnetic moment (3.6 Bohr magnetons) compared to the expected value for the bulk crystals (4 Bohr magnetons). [ABSTRACT FROM AUTHOR]

In this contribution a model for the elastic relaxation of Al0.5 Ga 0.5 As and ZnSe wire structures, respectively, is presented. The wire structures extend along 1¯1 0 and were characterized by high resolution x-ray diffraction experiments. Based on Monte Carlo simulations, the wire structures, which have been simulated at atomic resolution, were relaxed to reduce the strain caused by the lattice misfit. The x-ray diffraction patterns calculated for the final structures reproduce the observed data. The structures display a two dimensional strain gradient and curved lattice planes. Hence the introduced modeling is a powerful method in particular to resolve the atomic structure of a wet chemically etched or molecular beam epitaxial grown wire by giving a microscopic picture on an atomic scale. [ABSTRACT FROM AUTHOR]

We have studied superparamagnetic behavior of ultrathin Fe films grown on an Al[sub 2]O[sub 3](0001) substrate at various growth temperatures. It is demonstrated that 1-nm-thick Fe films are in the superparamagnetic state, and the blocking temperature is strongly dependent on the growth temperature. The blocking temperature has a minimum value of 30 K for a growth temperature of 473 K, while it is ∼70 K at other growth temperatures. In order to clarify the behavior, we consider the Fe growth mechanism and the magnetic interactions between Fe particles. Fe grows as three-dimensional islands at all temperatures studied and forms particles. The volume of the particles is observed via atomic force microscopy to increase with increasing growth temperature. In the case of growth at 323 and 373 K, Fe forms small particles that are close together and that interact with each other. For growth at 673 and 773 K, Fe forms relatively large particles and the magnetic properties are dominated by the individual particles. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

X-ray emission and absorption spectroscopy (XES and XAS, respectively) are important and powerful techniques for determining the electronic properties of materials. Both are used to study magnetic circular dichroism (MCD) which is especially useful for analyzing the magnetic properties of materials. We present XAS and XES measurements and a MCD model study of two thin film layered samples containing SmCo layers in order to report on the applicability of soft x-ray spectroscopic techniques to determine the composition, layer thickness, and electronic structure of such materials. Using a transmission by fluorescence attenuation (TFA) technique we determined the composition and thickness of the SmCo layer to be consistent with the intended composition and thickness. We also confirmed the thickness of the other layers by comparing the XES from the thin film with that of a bulk sample. We showed by a model study that TFA could be used to obtain MCD, and thus the anisotropy of the sample, for film thicknesses between about 400 and 800 Å. [ABSTRACT FROM AUTHOR]

In the study of spin dependent magnetic tunneling junctions, the switching stability of the magnetically hard layer is a crucial issue for long-term use in magnetic random access memory. After N switching cycles of the soft layer, the hard layer would be demagnetized due to the stray field from the domain wall created during switching of the soft layer. Therefore, reducing the stray field from the soft layer is the way to increase switching stability. In this study, we propose a structure which replaces the usual soft layer (typically permalloy, Fe, or Co) with an artificial ferrimagnet to reduce the stray field. The artificial ferrimagnet consists of a trilayer with an interlayer that antiferromagnetically couples two ferromagnetic layers of unequal thickness. The total stray field from the artificial ferrimagnet structure can be approximated as the sum of the stray fields from the two ferromagnetic layers. Since the sign of the stray field of the two layers is opposite, due to antiferromagnetic coupling, the total stray field is reduced due to cancellation. Since the magnitude of the stray field depends on the magnetic properties and the thickness of each layer and the distance from the magnetic layer, we can tailor the two magnetic layers of the artificial ferrimagnet structure to minimize the total stray field. [ABSTRACT FROM AUTHOR]

Examination of the ferromagnetic and antiferromagnetic phases of the Fe wedges epitaxially grown on Cu(100) helps investigate the interaction between magnetic and structural instabilities. Fcc Fe films with 6-11 monolayer (ML) exhibit antiferromagnetic phase and a ferromagnetic surface. Antiferromagnetic phase is absent in films grown below 200 K, but they are ferromagnetic and undergo a spin-reorientation transition at about 6 ML. A new magnetic phase diagram based on thickness and growth temperature is developed for the growth of Fe/Cu(100).

Magnetron sputtering characterizes epitaxial Fe/Cr(100) and Fe/Cr(211) superlattices grown on MgO(100) and MgO(110) substrates magnetically and structurally. Fe/Cr(011)/MgO(001) is the epitaxial orientation of the Fe/Cr(211) superlattice with Mg(110) substrate. Fe/Cr(001)//Mg(011) is the epitaxial orientation of Fe/Cr(100) superlattice. The interlayer coupling in both orientations is 18 angstroms.

Thermally evaporated lithium borate films (LiBO2) are investigated to determine their optical and electrical properties. The investigation is used for the application of these films as conductors of lithium ions in electrochromic devices. A high degree of transmission in the solar spectral range is exhibited by LiBO2 films and lithium ion conductivity is about 10 to the power of -7 times S per centimeter. Such films possess high potential for use in electrochromic devices as ion conductors.

The characteristics of sputtered Fe/Si superlattices were investigated using x-ray analysis to study magnetic coupling between the ferromagnetic Fe layers. The results showed that the system as a whole was well-layered but the crystal structure was coherent only as long as the spacer layer thickness remained under 17 angstroms. This indicated that the Si layer was crystalline for spacer layer thicknesses below 17 angstroms.

The oscillatory interlayer magnetic coupling of sputtered Fe/Nb superlattices was investigated using neutron and x-ray measurements. The results showed that the material featured a magnetic ground state of the +-+- type. In addition, it was shown that the average lateral size of the crystallites and the magnetic domains were small despite the crystalline and antiferromagnetic order.

The fabrication process, magnetic behavior, as well as the surface modification of ferromagnetic microdisks suspended in aqueous solution is described. The method has helped in fabricating suitable magnetic carriers with excellent size tolerance and the particles have a magnetic core covered with gold on each side to provide stability at ambient conditions as well as biocompatibility and selective adhesion functions.

The effect of step-induced anisotropy is studied by examining the magnetic properties of Fe grown on a curved Pt(111) single crystal that has provided a continuous gradient in step density. The atomic steps of the vicinal surface have affected the magnetic properties of ultrathin Fe films and the anisotropy of Fe on the curved Pt(111) surface is related to the step density of the substrate.

A net moment is observed from Mn in a SrRu[O.sub.3]/SrMn[O.sub.3] (SRO/SMO) superlattice film by using element-specific x-ray resonant magnetic methods. The results have provided evidence for the presence of pinned SRO magnetization at the SRO/SMO interface and have also disclosed that the net Mn moment is due to a canted antiferromagnetic spin configuration in the SMO layers.

The effects of the patterned pinning profile on the magnetization dynamics of the exchange-biased magnetic vortices are examined. Micromagnetic simulations have shown that the frequency has scaled linearly with the magnitude of the local pinning field.