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Erbium-doped GaN (Er:GaN) quasi-bulk crystals are emerging as a promising novel gain medium for high energy lasers emitting at the retina-safe wavelength window of 1.5 μm. We report the polarization-resolved photoluminescence (PL) emission spectroscopy studies, which revealed that the pumping efficiency with the excitation polarization parallel to the c-axis of GaN (E ⇀ | | c ⇀) is significantly higher than that with the excitation polarization perpendicular to the c-axis of GaN (E ⇀ ⊥ c ⇀). This phenomenon is a direct consequence of the inherent polar wurtzite GaN lattice, giving rise to a net local field, surrounding each Er ion, along the c-axis of GaN. The temperature dependent behaviors of the PL emission spectra were explained in terms of the Boltzmann population distributions among sublevels within the 4I15/2 ground state and the 4I13/2 first excited state of Er3+ in GaN, thereby providing an improved understanding regarding the origin of the dominant emission lines observed near 1.5 μm. The results suggested that the polarization field in GaN can be exploited to enhance the effective Er excitation cross section by manipulating the polarization of the excitation light source. [ABSTRACT FROM AUTHOR]

Research describing the characteristics of polymer films irradiated by an excimer laser is presented. In particular the electron field emission properties are investigated.

Amorphous carbon films containing iron were studied to determine their surface energy.

Filtered cathodic vacuum arc methods were used to deposit titanium-containing tetrahedral amorphous carbon films.

The electron field-emission properties of diamond-like nanocomposite films were studied to determine the annealing effect.

The Raman spectroscopy of phenylcarbyne polymer films under pulsed green laser irradiation is reported.

A new study uses micro-Raman spectroscopic analysis to investigate the structure of tetrahedral amorphous carbon films deposited under a variety of conditions.

The minimization of the remanent magnetization of ferromagnetic materials is a prerequisite for a reproducible low magnetic field inside shields. To realistically describe this so-called magnetic equilibration procedure, this paper proposes two approaches for the calculation of time- and space-dependent fields in the presence of ferromagnetic materials like permalloy. The first method is based on the Jiles-Atherton model and also takes into account frequency dependent effects. The second method is the newly developed empirical phase shift model, tailored specially for the simulation of the equilibration procedure. Both approaches are compared to experimental tests and show good quantitative agreement. [ABSTRACT FROM AUTHOR]

We report on the origin of the anomalous temperature dependence of coercivity observed in some soft ferromagnets by studying the magnetic and electronic properties of FeZr films doped using ion implantation by H, He, B, C, and N. The anomalous increase of the coercivity with temperature was observed only in the C- and B-doped samples. Using x-ray photoelectron spectroscopy, we show that the anomalous behavior of the coercivity coincides with the occurrence of an electron charge transfer for those implanted samples. The origin of the anomaly is discussed in terms of (i) magnetic softness, (ii) nature of the Fe-C and -B covalent bonds, and (iii) large charge transfer. [ABSTRACT FROM AUTHOR]

The formation dynamics of periodic ripples induced by femtosecond laser pulses (pulse duration τ=50 fs and central wavelength λ=800 nm) are studied by a collinear pump-probe imaging technique with a temporal resolution of 1 ps and a spatial resolution of 440 nm. The ripples with periods close to the laser wavelength begin to appear upon irradiation of two pump pulses at surface defects produced by the prior one. The rudiments of periodic ripples emerge in the initial tens of picoseconds after fs laser irradiation, and the ripple positions keep unmoved until the formation processes complete mainly in a temporal span of 1500 ps. The results suggest that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples. [ABSTRACT FROM AUTHOR]

We have performed the study on the dependence of laser beam induced current (LBIC) spectra on the temperature for the vacancy-doped molecular beam epitaxy grown Hg1-xCdxTe (x = 0.31) photodiodes by both experiment and numerical simulations. It is found that the measured LBIC signal has different distributions for different temperature extents. The LBIC profile tends to be more asymmetric with increasing temperature below 170 K. But the LBIC profile becomes more symmetric with increasing temperature above 170 K. Based on a localized leakage model, it is indicated that the localized junction leakage can lead to asymmetric LBIC signal, in good agreement with the experimental data. The reason is that the trap-assisted tunneling current is the dominant leakage current at the cryogenic temperature below 170 K while the diffusion current component becomes dominant above the temperature of 170 K. The results are helpful for us to better clarify the mechanism of the dependence of LBIC spectra on temperature for the applications of HgCdTe infrared photodiodes. [ABSTRACT FROM AUTHOR]

A novel hybrid electrode structure using Ag nanowires (NWs) to create surface plasmons to enhance light trapping is designed and applied on the front surface of hydrogenated amorphous silicon (a-Si:H) solar cells on steel substrates, targeting broad-band absorption enhancements. Ag NWs were synthesized using a soft and self-seeding process. The produced Ag NWs were deposited on indium tin oxide (ITO) glass substrates or the ITO layers of the as-prepared flexible a-Si:H solar cells to form Ag NW-ITO hybrid electrodes. The Ag NW-ITO hybrid electrodes were optimized to achieve maximum optical enhancement using surface plasmons and obtain good electrical contacts in cells. Finite-element electromagnetic simulations confirmed that the presence of the Ag NWs resulted in increased electromagnetic fields within the a-Si:H layer. Compared to the cell with conventional ITO electrode, the measured quantum efficiency of the best performing a-Si:H cell shows an obvious enhancement in the wavelength range from 330 nm to 600 nm. The cell based on the optimized Ag NW-ITO demonstrates an increase about 4% in short-circuit current density and over 6% in power conversion efficiency under AM 1.5 illumination. [ABSTRACT FROM AUTHOR]

The local structure of copper nanoparticles grown in organic solution by reducing Cu(II) hexafluoroacetylacetonate [Cu(hfac)2] was studied as-grown by the Cu K-edge x-ray absorption near-edge structure (XANES). Comparison of the experimental XANES spectra with reference materials indicated small copper clusters are formed by ligand-exchange with oleylamine and subsequent reducing by diphenylsilane. The multiple-scattering (MS) calculation for various model clusters consisting of 13-135 atoms suggests that small (13-19 atom) Cu clusters are stabilized without a large deformation. [ABSTRACT FROM AUTHOR]

We investigate plasmon-enhanced upconversion (UC) fluorescence in Yb3+-Er3+-Gd+3 codoped sodium yttrium fluoride (NaYF4:Yb/Er/Gd) nanorods using gold nanoparticles or nanoshells. A simple method was proposed for the preparation of core/shell NaYF4/Au structures, with dispersed Au nanoparticles or uniform Au coating on the surface of the UC nanorod. Pure hexagonal-phase NaYF4:Yb/Er/Gd nanorods were synthesized via a liquid-solid reaction in oleic acid and ethanol solvent. A one-step approach was introduced to modify the hydrophobic surfaces of the as-deposited NaYF4:Yb/Er/Gd nanorods. After this surface modification, Au nanoparticles or nanoshells were successfully attached on the surfaces of NaYF4:Yb/Er/Gd nanorods. The as-deposited UC nanorods showed a strong UC emission in green and red bands under 980 nm laser excitation. The attachment of Au nanoparticles onto NaYF4:Yb/Er/Gd nanorods resulted in a more than three-fold increase in UC emissions, whereas the formation of continuous and compact Au shells around the nanorods suppressed the emissions. The related interaction mechanisms of the UC emission of NaYF4:Yb/Er/Gd nanorods with plasmon modes in Au nanostructures are analyzed and discussed. [ABSTRACT FROM AUTHOR]

The energy band structure and optical properties of C-doped and C/H-codoped anatase TiO2 are investigated using the first-principles based on density-functional theory. The obtained results indicate that the structure of C/H-codoping is more stable than that of C-doping. For C-doped anatase TiO2, the band gap narrowing is small, and the high visible-light catalytic ability originates from the isolated C 2p states above the valence-band maximum. With the same carbon doping level, the C/H-codoping produces significant bandgap narrowing, which leads to higher visible-light photocatalytic efficiency than the C-doping does. [ABSTRACT FROM AUTHOR]

Correlation between the elastic modulus (B) and the Raman shift (Δω) of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature have been established as a function depending on the order, length, and energy of a representative bond for the entire specimen. In addition to the derived fundamental information of the atomic cohesive energy, binding energy density, Debye temperature and nonlinear compressibility, theoretical reproduction of the observations clarified that (i) the size effect arises from the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth; (ii) the thermally softened B and Δω results from bond expansion and bond weakening due to vibration; and, (iii) the mechanically stiffened B and Δω results from bond compression and bond strengthening due to mechanical work hardening. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantitative information as such from any single measurement alone. [ABSTRACT FROM AUTHOR]

We investigate magnetization reversal in a system of two Stoner particles with uniaxial anisotropies both subject to a static and antiparallel magnetic field, and taking into account their mutual dipolar interaction. We identify an interesting regime of stable synchronized magnetic dynamics where the two particles are implementing a single information bit. Here a modified Stoner-Wohlfarth limit occurs which results in a dramatically lower critical switching field Hc (including Hc=0) and also a substantially shorter reversal time. Our analytical results are verified by numerical simulations and offer new technological perspectives regarding devices for information storage and/or fast magnetic response. [ABSTRACT FROM AUTHOR]

Strong magnetic fields e.g., 10 T are now frequently used during materials preparation. In the present paper, a method of metal-ceramics graded materials preparation is proposed by applying a strong magnetic field with a high gradient. Experimental and theoretical analyses are performed to investigate the effect of the strong magnetic field on the migration and interaction behavior of diamagnetic oxide particles in a liquid metal. The migration of micrometer or sub-micrometer sized particles is clearly enhanced by the magnetic field gradient. After being treated by the strong magnetic field, a self-assembly structure of the particles is achieved. Various factors such as the magnetic dipole-dipole interaction and chain-chain interaction, are governing the particles assembly. The present results provide direct evidence that nonmetallic particles of micrometer size or less can be manipulated in a conductive melt by applying a strong magnetic field and as a consequence graded materials can be prepared. [ABSTRACT FROM AUTHOR]

The electronic structure and electrical transport properties of the cubic perovskite (E21) oxide barium manganese (BaMnO3) and the BaMnO3/BaTiO3 superlattice are investigated by the density-functional theory in this report. The results show that the cubic BaMnO3 exhibits half-metallic properties with an integral magnetic moment of 3.000 μB per unit cell in its metastable state, while the BaTiO3/BaMnO3 superlattice also shows a stable half-metallic ground state with an integral magnetic moment of 12.000 μB per unit cell. In conclusion, we show that the construction of a BaMnO3/BaTiO3 superlattice could stabilize the cubic metastable phase of the BaMnO3 and provide a stable half-metallic material for potential applications in spintronic devices. [ABSTRACT FROM AUTHOR]

With the help of first-principles GGA+U calculations, the origin of the deviation between the experimental and theoretical data for Cr2AlC was revealed. The structural, electrical and elastic properties of Cr2AlC were well described by considering the Cr 3d on-site Coulomb energy. The temperature effect on the bulk moduli of Cr2AlC was also studied within the quasiharmonic Debye model. Based on the present work, we propose that the electron correlation effects in Cr-containing MAX phases cannot be ignored. [ABSTRACT FROM AUTHOR]

Although the physics behind the bulk modulus, B(T,P), as a function of temperature (T) and pressure (P), has been intensively investigated, an atomic scale understanding of this attribute remains a high challenge. Here, we show that the B(T,P) for BaXO3 (X=Ti,Zr,Nb) can be established by connecting the B directly to the bond length and bond energy and their response to the applied T and P in the form of binding energy density, B[E/d3(T,P)]. Besides an estimation of the Debye temperature and single bond energy, outcomes clarified that the thermally softened B arises from bond expansion and bond weakening due to lattice vibration and the mechanically stiffened B results from bond compression and bond strengthening due to mechanical work hardening. [ABSTRACT FROM AUTHOR]

We investigated the resonance and antiresonance effects in electronic transport through several-quantum-dot combinations by using the nonequilibrium Green’s function method. All distinctive quantum-dot (QD) arrangements with one to three QDs and with different architectures were studied systematically. The theoretical and numerical results show that a peak in the current-voltage spectrum can be attributed to the resonance effect, whereas a dip is due to the antiresonance effect. The results will help experimenters to better understand their electronic measurements. [ABSTRACT FROM AUTHOR]

The plastic deformation and fracture behavior of individual a- and c-domains of (001) oriented BaTiO3 single crystal are studied with nanoindentation and atomic force microscopy. Consistent with previous observations in rocksalt and perovskite crystals, square-shaped pileups directly surround the residual indents, and rosette arm patterns extend beyond these pileups. These features have been ascribed to dislocation activities on the {110}<110> slip systems induced by nanoindentations. We observed rosette screw arms only in c-domains, inside which 90° ac-domain switching is confirmed. We conclude that indentation-induced cracks on {110}90 planes most likely nucleate by dislocation pileups on two neighboring {110}45 planes, which create a sessile dislocation. Significantly shorter cracks in the c-domain under the same indentation load suggest a higher apparent toughness of the c-domain. However, we attribute the different crack lengths to the lower crack driving force resulting from indentation-induced plasticity in c-domains rather than an inherent difference in the crack growth resistance. [ABSTRACT FROM AUTHOR]

Molecular statics simulations combined with an embedded-atom method potential were performed to calculate the distributions of energy and bulk stresses in crystalline and amorphous Cu slabs and to examine the effect of surface relaxation on the distributions of energy and bulk stresses in the surface region. The results reveal that a release of energy and bulk stresses in the surface region occurs upon surface relaxation. The profile of energy release upon surface relaxation of a crystalline Cu slab exhibits oscillatory damping from the topmost layer to the interior layers, while that of an amorphous Cu slab exhibits monotonic decreasing. A great diversity of patterns was observed in the profiles of bulk stresses released upon surface relaxation, which may exhibit anisotropy according to the symmetry of the surface considered. Both the profiles of energy release and bulk stress release exhibit surface-orientation dependence. The present results may provide useful information to analyze different phenomena at Cu surfaces. [ABSTRACT FROM AUTHOR]

Eu3+-doped TiO2 films were prepared on silicon substrates by sol-gel method. Anatase and rutile phases appear when the samples were heat treated in oxygen atmosphere at 500 and 900 °C, respectively. Photoluminescence (PL) properties were investigated under the excitation of 325 nm He–Cd laser. Visible PL peaking at 543, 598, 620, 665, and 694 nm are founded which are ascribed to 5D1→7F1, 5D0→7Fj(j=1,2,3,4) transitions of Eu3+ ions and the PL intensities reach maximum when the sample was heat treated at 700 °C. Compared with the PL spectra of pure TiO2, energy transfer from self-trapped exciton state to rare-earth ions is considered to exist in Eu3+-doped TiO2 system. After the sample was heat treated at higher temperatures than 700 °C, the PL intensity of Eu3+ ions decreases obviously, while near-infrared PL (815 nm) was detected which is due to the defect states associated with Ti3+ ions. Through the analysis of excitation and emission mechanism, we conclude that visible and near-infrared PLs are two competitive processes and energy back transfer from Eu3+ ions to TiO2 host is responsible for the decrease of visible PL intensity and the increase of near-infrared PL intensity. [ABSTRACT FROM AUTHOR]

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Néel transition temperature at about 42 K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46 K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the peculiar dielectric relaxation peaks induced by Ce substitution have been discussed in detail. [ABSTRACT FROM AUTHOR]

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Néel transition temperature at about 42 K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46 K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the peculiar dielectric relaxation peaks induced by Ce substitution have been discussed in detail. [ABSTRACT FROM AUTHOR]

Neodymium-doped GeO2/γ-glycidoxypropyltrimethoxysilane hybrid planar waveguide films were prepared by a low-temperature sol-gel technique from an organic-inorganic hybrid system for photonic applications. Optical properties such as refractive index, thickness, propagation modes, and attenuation coefficient of the hybrid planar waveguides were investigated by using a prism coupling technique. An intense room-temperature yellow-to-violet up-conversion emission at 397 nm (4D3/2→4I13/2) was measured from the hybrid planar waveguide film heated at a low temperature of 100 °C upon excitation with a xenon lamp at the wavelength of 580 nm. In addition to this intense violet emission, a relatively weak ultraviolet emission at 376 nm and a blue emission at 468 nm were also observed. The mechanism of the up-conversion emission is proposed, and they indicate that the excited-state absorption process originating from the long-lived 4F3/2 excited state should be responsible for the up-conversion process. [ABSTRACT FROM AUTHOR]

We investigated the field emission properties and resistivity of polymer-based carbon films prepared from poly ethyl-co-phenyl carbyne polymer precursors after treatment at different temperatures. As the heat-treatment temperature increased from 40 to 1200 °C, the emission threshold field decreased from 12.4 to 2.1 V/μm, the emission current density increased from 0.1 to 6.1 mA/cm2, and the film resistivity decreased from 108 to 102 Ω cm. The structural changes of the polymer films during the heat-treatment process were analyzed by Raman spectroscopy and atomic force microscopy. Raman analysis of these polymer-based carbon films suggests that the hydrogen content decreased while the sp2 carbon phase increased as the heat-treatment temperature increased. The dependence of the field emission properties of the polymer-based carbon films on the film structures (such as sp3, sp2 phases), film surface morphology and film resistivity is discussed. The enhancement of field emission from polymer-based carbon films was related to the increase of sp2/sp3 ratio, film conductivity, and surface roughness with the heat-treatment temperature. [ABSTRACT FROM AUTHOR]

The effect of ion implantation including ion species (N[sub 2][sup +] and C[sub 3]H[sub 8][sup +]) and the fluences (1×10[sup 14]–5×10[sup 15] ions/cm[sup 2]) on the surface energy of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The total surface energy increases significantly after implanting with the fluence of 1×10[sup 14] ions/cm[sup 2] regardless of ion species, then, the total surface energy slightly increases for N[sub 2][sup +] implanted UHMWPE and decreases slightly for C[sub 3]H[sub 8][sup +] implanted UHMWPE with a further increase of fluence. The structural changes of UHMWPE with different fluence for different ion species are very similar. The linear chains of UHMWPE are damaged and cross linking is generated after implantation. As the fluence increases, the polymer surface becomes more disordered, and the surface becomes hydrogenated amorphous carbon when the fluence exceeds 1×10[sup 15] ions/cm[sup 2]. The surface roughness increases with the increase of the fluence regardless of ion implantation species. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetic properties of Nd[sub 60-x]Y[sub x]Fe[sub 30]Al[sub 10] (x = 0, 10, 30) melt-spun ribbons were studied. The ribbons contain two amorphous magnetic phases characterized by their Curie temperature T[sub C1] and T[sub C2]. The Y atoms may be unevenly distributed in the two magnetic phases. The Y atoms prefer to substitute Nd in the low T[sub C1] phase. Thermo-history effects are found in the thermomagnetic curves for field-cooled and zero-field-cooled samples. The bifurcation temperature T[sub b] decreases with Y addition, suggesting a decrease of the anisotropy energy and the coercivity. The room-temperature coercivity and remanence ratio also strongly decrease with Y addition. The apparent coercivity μ[sub 0]H[sub C] for x = 0 first increases with decreasing temperature, reaching a maximum at about 60 K, near the Curie temperature of the T[sub C1] phase, then strongly decreases in the two-magnetic phase region. The coercivity mechanism is assumed as domain-wall pinning effect. [ABSTRACT FROM AUTHOR]

Presents a study which deposited diamond-like carbon films by a plasma chemical vapor deposition system. Properties of the carbon films; Results; Conclusions.

The magnetism of ultrasmall Co:CoO core-shell nanoclusters is examined. The proteretic behavior and its particle-size dependence have reflected a subtle interplay between various anisotropies and exchange interactions in the Co and CoO phases and at the Co-CoO interface.

The single molecule magnets with high frequency electron paramagnetic resonance (HFEPR) and study of two isomeric forms of an Mn12 molecule are presented. Computed simulations of the experimental HFEPR data yield spin Hamiltonian parameters for both complexes.

Synchrotron radiation photoemission study showed that the energy level alignment at the interface between N, N'-bis(naphthalene-1-y1)-N, N'-bis(phenyl) benzidine (NPB), a typical hole transport material, and Al could be adjusted by precovering a thin C60 layer on Al. The interface dipoles so formed could shift both the highest occupied molecular orbital level of NPB and the secondary electron cutoff measured at the early stage of the NPB deposition. The barrier height for hole injection from Al to NPB could thus be lowered by as much as 0.98 eV, and the optimal thickness of the inserted C60 layer was found to be 8-12 Å. [ABSTRACT FROM AUTHOR]

Exchange biaslike phenomenon is observed in the Zn doped spinel polycrystalline CuCr2O4. The magnetic hysteresis loop shifts in both horizontal and vertical directions at 5 K after the samples are cooled down to 5 K in a magnetic field. The nature of this magnetic anisotropy arises from the freezing properties of the local anisotropy in the cluster glass system. The magnetic shifts along both directions can be observed directly under the principle that the spins of a cluster are frozen in random orientations upon zero field, and aligned to the field direction upon field cooling. [ABSTRACT FROM AUTHOR]

Nanoclusters of rocksalt TiO, anatase TiO2, and rutile TiO2 were produced by cluster deposition and examined with transmission-electron microscopy, x-ray diffraction, and magnetization measurements. The clusters are all magnetic at room temperature, but the magnetization is structure- dependent. The hysteresis loops show coercivities that are of the order of 100 Oe and all films show a preferential in-plane magnetization direction. The size dependence of the magnetization was investigated for rutile clusters with average sizes from about 15 to 40 nm. The analysis of the measurements indicates that the magnetism is predominantly located near the surface of the clusters and characterized by a nominal value of 7.6 μB/nm2. [ABSTRACT FROM AUTHOR]

The current-voltage characteristics of a silicon nanochain is investigated. The nanochain is viewed as a superlattice structure of quantum dots (QDs), where silicon cores in a chain act as QDs while silicon dioxides covering the cores act as potential barriers. It is found that the whole nanochain structure can display the negative differential conductance (NDC) feature as the tunneling current through each barrier has the NDC property individually. Importantly, large peak-to-valley ratios of the current are observed and tunable by the number of QDs involved. This feature will be useful in device design. [ABSTRACT FROM AUTHOR]

Fast magnetization reversal of uniaxial Stoner particles by spin-transfer torque generated by the spin-polarized electric current is investigated. It is found that the critical current required to reverse a magnetization can be dramatically reduced if a current with a properly designed time-dependent polarization direction is used. Under the condition that the magnitude of the current does not vary with time, the optimal time-dependent electron polarization is obtained such that the magnetization reversal is the fastest. [ABSTRACT FROM AUTHOR]

Polycrystalline Cd0.7Fe0.3Cr2S4 has been prepared by a solid state reaction. A crystalline structure study shows that the x-ray diffraction pattern can be indexed successfully in a cubic spinel phase. Its magnetic and dielectric properties have been investigated. A ferrimagnetic phase transition of the material was identified at 123 K. Larger permittivity and loss tangent are observed than those of CdCr2S4 in the frequency range 300 Hz–1 MHz. An anomaly cusp induced by the internal magnetic field on [variant_greek_epsilon]-T and tan δ-T curves is observed near its magnetic transition point, implying an existence of magnetodielectric effect. At low temperature T

Polycrystalline Cd0.7Fe0.3Cr2S4 has been prepared by a solid state reaction. A crystalline structure study shows that the x-ray diffraction pattern can be indexed successfully in a cubic spinel phase. Its magnetic and dielectric properties have been investigated. A ferrimagnetic phase transition of the material was identified at 123 K. Larger permittivity and loss tangent are observed than those of CdCr2S4 in the frequency range 300 Hz–1 MHz. An anomaly cusp induced by the internal magnetic field on [variant_greek_epsilon]-T and tan δ-T curves is observed near its magnetic transition point, implying an existence of magnetodielectric effect. At low temperature TN, the permittivity variation Δ[variant_greek_epsilon] depends on magnetization M and shows clearly a linear relationship between Δ[variant_greek_epsilon] and M2, indicating an interplay of permittivity and magnetism. Furthermore, compared to CdCr2S4, Cd0.7Fe0.3Cr2S4 exhibits smaller values of dielectric relaxation time and activated energy above TC due to Fe2+ doping. [ABSTRACT FROM AUTHOR]

The recombination property of nitrogen (N)-related acceptor-bound states in ZnO has been investigated by photoluminescence (PL), time-resolved PL, and selective PL. Several possible recombination processes were discussed by analyzing the relaxation and recombination properties under large Coulomb interaction. It is strongly suggested that bound exciton emission dominates the recombination process related to the N acceptor. The recombination lifetime is 750 ps and the binding energy is 67 meV for N-acceptor-bound exciton at low temperature. [ABSTRACT FROM AUTHOR]

Isotropic nanocomposite magnetic structures were produced via cluster assembly routes with energy products reaching 18 MG Oe. Gas aggregation produces Fe clusters with an average size less than 10 nm with a very narrow size distribution, and these were embedded in a hard magnetic matrix by cosputtering of FePt. Structures produced were crystallographically isotropic with Fe cluster phase content ranging from 0 to 30 vol %. The coercivity decreased from 13 kOe as Fe cluster content increased. Single-phase-type hysteresis loops indicating excellent exchange coupling at low Fe cluster content give way to a stepped demagnetization loop at an Fe cluster content greater than 20%. The energy product initially increased with Fe cluster content, then decreased. [ABSTRACT FROM AUTHOR]

The effects of Co addition on the structure and magnetic properties of melt-spun Nd[SUB60]Fe[SUB30-x]Co[SUBx]Al[SUB10] (x = 0, 2, 5, 10, 20, and 30) ribbons have been investigated. Except an amorphous matrix, nanocrystalline Nd was found in the Fe-containing alloys. Its relative amount decreases with increasing Co addition, and a fully amorphous structure was observed for x530, indicating that glass-forming ability increases with Co addition. The room-temperature coercivity and magnetization are found to decrease sharply with increasing Co content. Thermomagnetic measurements show two magnetic transitions occurring at about 50 K and 480 K, respectively. Combining the isothermal differential scanning calorimetry measurement, it demonstrated that the amorphous phase in the Fe-contained alloys further separates into Nd-rich regions and Fe-rich regions. The relative amount of each phase is estimated by the magnetization of each phase. [ABSTRACT FROM AUTHOR]

A sputtering gas-aggregation technique has been used to prepare FePt and FePt:Ag nanocluster films. The cluster size was controlled in a range from 3 to 6 nm. FePt cluster films were directly deposited onto Si substrate; FePt:Ag cluster films were fabricated by depositing a FePt cluster layer between a Ag underlayer and overlayer. Nanostructure and magnetic properties of the samples were characterized by x-ray diffraction, transmission electron microscopy, and magnetometry. The high magnetic anisotropy L1[SUB0] fct phase was realized in the films annealed at a temperature of 550°C and above. The orientation of clusters is random. The coercivity increases with an increase of annealing temperature; high in-plane and out-of-plane coercivities, exceeding 10 kOe, were achieved in both FePt and FePt:Ag cluster films after annealing. For FePt:Ag films, the coercivity increases with Ag underlayer thickness, t[SUBAg], and reaches about 17 kOe at room temperature for t[SUBAg] = 5 nm after annealing at 650°C for 10 min. The high coercivity is closely correlated with the degree of L1[SUB0] ordering and nanostructure of the films. [ABSTRACT FROM AUTHOR]

Pr[sub 8]Fe[sub 88]B[sub 4] ribbons prepared by melt spinning have been investigated by x-ray diffraction, differential thermal analysis, thermomagnetic analysis, atom force microscopy, and superconducting quantum interface device magnetometer. The results show that the annealed ribbons consist of the Pr[sub 2]Fe[sub 14]B and α-Fe phases. The magnetization of soft α-Fe phase remains parallel to the magnetization of the hard Pr[sub 2]Fe[sub 14]B phase for fields less than the exchange field (H[sub ex]). The exchange field in exchange-spring magnets, determined from the demagnetization curves measured at various temperatures, increases with decreasing grain size and measure temperature. The temperature dependence of exchange field was analyzed qualitatively by the expression H[sub ex]=(AK)[sup 1/2]/(M[sub s]t). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hot-filament chemical vapor deposition of diamond films on ZnO:Al thin-film silica substrates and their ultrasonic irradiation results in an increase in the diamond nucleation density on the substrates. Growth rate and nucleation density of the film are higher on ZnO:Al thin films than on silica. Peak frequency Raman line shift and stress in the diamond and ZnO:Al films causes the formation of cracks, indicating that diamond films have a compressive stress value.