bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum fluctuations in the vicinity of the spin–flop transition in large-spin clusters
Authors: Zvezdin A. K. , Dobrovitski V. V. , Harmon B. N. , Katsnelson M. I.
Published: July 2002

If a single-spin possessing an easy-axis anisotropy is subjected to an external field perpendicular to the easy axis, the susceptibility exhibits a peculiar peak. We establish that the specific spectral properties of quantum fluctuations give rise to this peak. We predict that this effect takes place in real many-spin systems, such as Mn12 clusters, and can be studied at finite temperatures in real experiments with attainable resolution. For studying quantum fluctuations in magnetic molecules, this offers an approach as an alternative to relaxation rate measurements.
Relations of slow relaxation of ferromagnets to saturating and recoiling fields
Authors: Hsu Shau-Wei
Published: July 2002

Systematic experiments on the Nd–Fe–B, Sm–Co, and Sr–Ferrite samples were performed to study the measuring-process dependent magnetic slow relaxation (magnetic viscosity). The relaxation coefficient (S) is proportional to the magnetic susceptibility (χ) for the Sr–Ferrite sample as the saturating field (Hs) and demagnetization field (Hd) are relatively large. The S–χ data for the Sm–Co sample are confined between two lines, which are related to the magnitudes of Hs and Hd. S is proportional to a specific magnetization difference (ΔM1) for the measurements along recoil curves. The proportional constants of the Nd–Fe–B sample are 0.163 and 0.171 for the applied field parallel and perpendicular to the c axis, respectively.
Ferromagnetic resonance as a probe of anisotropy in giant magnetoresistance structures
Authors: Lubitz Peter , Cheng Shu-Fan
Published: July 2002

The ferromagnetic resonance spectra of thin alloy films, which are often used as components of giant magnetoresistance structures, were observed. Face-centered-cubic films with Cu underlayers and single magnetic layers of permalloy, permalloy containing Co; or Co rich CoFe alloys were deposited by magnetron sputtering. The magnetic field position of the resonance provides information about the magnetic moment and the growth induced anisotropies of the films, and was affected by magnetostriction when stresses were induced. Linewidths and coercivity increased rapidly as a function of the total (Cu+magnet) layer thickness above about 20 nm. The linewidth is sensitive to the damping parameter for the thinner films and to magnetocrystalline anisotropy and crystallographic texture for the thicker Co containing films in which the grains become large. Based on observations of the resonances in stressed films, several nonmagnetostrictive compositions were determined.
Scanning microscopy of magnetic domains using the Fe 3p core level transverse magneto-optical Kerr effect
Authors: Friedrich J. , Rozhko I. , Voss J. , Hillebrecht F. U. , Kisker E. , Wedemeier V.
Published: July 2002

We demonstrate the feasibility of the vacuum ultraviolet analog to visible-light magneto-optical imaging of magnetic structures using the resonantly enhanced transverse magneto-optical Kerr effect at core level thresholds with incident p-polarized radiation. The advantages are element specificity and a variable information depth. We used the scanning x-ray microscope at HASYLAB capable of obtaining about 1 μm resolution by means of its focusing ellipsoidal ring mirror. The p-polarized component of the reflected light was selected using multilayer reflection at an additional plane mirror downstream to the sample. Micrographs of the optical reflectivity were taken in the vicinity of the Fe 3p core level threshold at 53.7 and 56.5 eV photon energy where the magneto-optical effect is of opposite sign. Magnetic domains are visible in the difference of both recorded images.
Method for expanding the uniformly shielded area in a short-length open-ended cylindrical magnetic shield
Authors: Oshita K. , Sasada I. , Naka H. , Paperno E.
Published: July 2002

A compensation method is proposed by which the uniformly shielded area of the axial magnetic field in a relatively short, open-structure axial magnetic shield can be extended. An open-ended cylindrical magnetic shield of 120 cm in length, 52 cm inner diameter, and a ∼0.5 mm total thickness of the shielding material is used to demonstrate the idea. The shield axis is oriented along the horizontal component (∼320 mG) of the Earth’s magnetic field. A simple way to increase the axial shielding factor is to use a pair of compensating coaxial ring coils set at both open ends of the shield. This increases, however, the radial gradient of the shielded field since the axial compensation field is stronger towards the shield axis. In order to decrease the radial gradient, an additional ring coil is wound around the middle part of the outer surface of the shield. The compensating field generated by this central ring coil is stronger towards the inner surface of the shield, and it helps, therefore, to unify the axial resultant field over a wider area inside the shield. The axial shielding factor obtained with this compensation according to the proposed method is 128, in contrast to only 16.4 obtained with compensation by a set of two ring coils. The field gradients observed are 1.2 μG/cm along the length direction and 2.7 μG/cm along the radial direction, in contrast to the 14 μG/cm axial and 78 μG/cm radial gradients obtained with compensation by a set of two ring coils.
Magnetocrystalline anisotropy of Ce2Co17−xAlx compounds with x=0–3
Authors: Shen Bao-gen , Wang Jing-yun , Zhang Hong-wei , Zhang Shao-ying , Cheng Zhao-hua , Liang Bing , Zhan Wen-shan , Lin Chin
Published: July 2002

An investigation of the structure and magnetocrystalline anisotropy of Ce2Co17−xAlx (x=0, 1, 2, and 3) compounds has been performed by means of x-ray diffraction and magnetization measurements. It is observed that the unit-cell volume, Curie temperature, and saturation magnetization of Ce2Co17−xAlx compounds are anomalously low in comparison with the values obtained from a simple extrapolation by the other R2Co17−xAlx compounds, such as R=Pr and Nd. These anomalies may be an evidence of a mixed-valence behavior of the Ce ion. X-ray diffraction measurements on magnetically aligned Ce2Co17−xAlx powders with x=0–3 exhibit an easy-axis type of magnetic anisotropy at room temperature. Substitution of Al for Co leads to a change of the magnetocrystalline anisotropy of the Co sublattice from the basal plane to c axis and strongly increases the uniaxial anisotropy of Ce2Co17−xAlx. The magnetocrystalline anisotropy field HA is found first to increase and then decrease with increasing Al concentration, attaining a maximum value of 18 kOe at x=2. The magnetocrystalline anisotropy constant K1 shows a small decrease with increasing temperature and K2 is almost a constant.
Anomalous thermal expansion in Nd2Fe17−δGaδ (δ=0–2)
Authors: Girt Er. , Altounian Z. , Swainson I. P. , Krishnan Kannan M. , Thomas G.
Published: July 2002

In Nd2Fe17−δGaδ (δ=0, 0.5, 1, 1.5, 2), Ga substitutes for Fe without changing the crystal structure. Neutron diffraction measurements show that Ga preferentially substitutes for Fe in the 18h sites only. The magnetic moments in Nd2Fe17−δGaδ, below the Curie temperature, Tc, are found to be in the basal plane. Below Tc the unit cell constant, c, decreases with increasing temperature for Nd2Fe17−δGaδ (δ⩽1). For Nd2Fe17−δGaδ (δ>1), the thermal expansion coefficient changes sign and becomes positive for Nd2Fe15Ga2. The relative decrease in the Fe(6c)–Fe(6c) distance is twice as large as the decrease in the c axis below Tc. Below Tc, the Fe(6c)–Fe(6c) distance decreases with an increase in the Ga concentration, while above Tc the Fe(6c)–Fe(6c) distances are found to be independent on Ga concentration indicating that the presence of Ga decreases the negative exchange coupling between Fe atoms.
Structural and magnetic properties of Sm2Fe17−xTxM (T=Co, Ti; M=Al, Si) compounds
Authors: Ren Z. Y. , Lee W.-Y. , Qin C.-D. , Ng D. H. L. , Ma X-Y.
Published: July 2002

The structural and magnetic properties of off-stoichiometric 2:17-type compounds Sm2Fe17−xTxM (T=Co, Ti; M=Al, Si; x=0–4) were studied by x-ray powder diffraction, thermomagnetic analysis, and magnetic measurements. All these compounds were of the Th2Zn17 type. The substitution of Co or Ti for Fe, and the addition of Si or Al into the Sm2Fe17 did not alter the rhombohedral structure. The Co replacement increased the Curie temperature Tc due to the strong coupling between Fe and Co. A small substitution of Ti also led to an increase of Tc. However, when x>3, the exchange coupling became less effective as the separation between the Fe atoms became large, and Tc decreased. The maximum Tc=713 K was found in Sm2Fe17−xCoxSi when x=4. As for the saturation magnetization Ms, Sm2Fe17−xTixAl had its Ms decreased monotonically with increasing Ti, while Ms of other compounds increased first and then decreased with the content of Co or Ti. The maximum Ms=159 emu/g was recorded in Sm2Fe15Co2Al. To make use of these compounds as permanent magnets, Sm2Fe15Co2Si is preferred because it has Tc=641 K and Ms=142 emu/g. The dual substitutions of Fe by using Co or Ti, and by Al or Si to improve Tc and Ms of Sm2Fe17, are more effective than using single substitution.
Study of nonlinear dibit interactions
Authors: Glavinas Elias , Indeck Ronald S. , Muller Marcel W.
Published: July 2002

We investigate isolated dibit interactions by varying the intradibit spacing and observing position fluctuations using a magnetic force microscope. We see that the measured dibit spacing deviates at a recording density that depends on the remanence–thickness product Mrδ of the medium. The increased dibit separation may be partially due to the demagnetization fields during write: we find that partial erasure annihilates the narrower crosstrack parts of the dibit, effectively inducing an increase in dibit separation.
Magnetic properties of RTSb3
Authors: Leonard Michael , Saha Shibaji , Ali Naushad
Published: July 2002

Magnetization, electrical resistivity, and thermal expansion measurements have been performed on polycrystalline RTSb3 (R=La, Ce, Pr, Nd, Gd, Tb, and Dy; T=Cr, V) samples in order to study their magnetic properties. Depending on the rare-earth element, RTSb3 has been found to have either a purely ferromagnetic (or antiferromagnetic) phase or combination of antiferromagnetic (lower-temperature) and ferromagnetic (higher-temperature) phases. The antiferromagnetic order evolves from the ferromagnetic order as a result of the competition between R3+ and Cr3+ ions. As R is changed from La to Dy, the antiferromagnetic ordering of the R3+ ions becomes more prominent and predominate over the ferromagnetic ordering of Cr3+ for R=Gd, Tb, and Dy. Thermal expansion measurements show that the antiferromagnetic transition accompanies a drop in the sample dimension. The order of the ferromagnetic transition is found to be of the second order.
Determination of the magnetic structure of hexagonal manganites RMnO3 (R=Sc, Y, Ho, Er, Tm, Yb) by second-harmonic spectroscopy
Authors: Fröhlich D. , Leute St. , Pavlov V. V. , Pisarev R. V. , Kohn K.
Published: July 2002

Hexagonal manganites RMnO3 (R=Sc, Y, Ho, Er, Tm, Yb) are compounds in which a ferroelectric and an antiferromagnetic order may coexist. The ferroelectric crystal structure is well known but theoretical studies show that there are different possibilities for the spin structure. By means of polarization- and temperature-dependent second-harmonic spectroscopy it is possible to determine the magnetic structure of RMnO3 compounds.
Effect of grain size and crystalline orientation on magnetic switching
Authors: Zheng Youfeng , Zhu Jian-Gang
Published: July 2002

The effect of crystalline orientation and grain size on the switching behavior for patterned face-centered-cubic Co film elements has been investigated through micromagnetic modeling. It is found that the switching field of the Co film element exhibits significant dependence on crystalline orientation and grain size. Large grain results in large switching field for polycrystalline Co film element. The switching fields of (001) and (110) oriented single crystal elements are much higher than that of the (111) oriented single crystal elements. It is also found that the effect of crystalline anisotropy on the switching behaviors strongly depends on the magnetization reversal mode.
Molecular magnetism: Noncollinear ordering and spin dynamics
Authors: Ivanov O. , Antropov V. P.
Published: July 2002

We have developed a new approach for the calculation of electronic structure and magnetic properties in the framework of spin density functional theory for arbitrary magnetic systems. This approach is based on the wavelets technique. We present test calculations and compare with previously published results. As an application of the general formalism to the noncollinear case we consider the two limiting cases of itinerant and localized magnetic moments. The development of this method is a first step to perform ab initio spin dynamics for finite atomic systems.
Electrical characteristics for solid C60/GaN heterojunctions
Authors: Chen K. M. , Sun W. H. , Wu K. , Li C. Y. , Qin G. G. , Zhang Q. L. , Zhou X. H. , Gu Z. N.
Published: July 2002

Solid C60/n-GaN heterojunctions have been fabricated and their electrical properties have been studied. It has been found that the heterojunction is a strongly rectifying contact with a rectification ratio greater than 106 and with an ideality factor close to 1. The current–temperature measurement shows an exponential decrease of current with increasing reciprocal temperature, from which the effective barrier height is determined to be 0.535 eV. The series resistance measured decreases with increasing forward voltage and finally tends to be constant.
Electroluminescence simulation of multiquantum well silicon structures
Authors: Kholod A. N. , Danilyuk A. L. , Borisenko V. E. , Bassani F. , Ménard S. , d’Avitaya F. Arnaud
Published: July 2002

A model of electroluminescence from the multiquantum well structure formed by alternated nanosize layers of silicon (Si) and calcium fluoride (CaF2) is proposed. Electron and hole tunneling through the CaF2 barriers is supposed to occur via Wentzel–Kramers–Brillouin mechanism. Carrier interband recombination in the Si wells is considered to produce photons. A simulation of current–voltage characteristics and luminescence properties is performed taking into account the geometry of the structure and the fundamental physical parameters of the materials involved. The electroluminescence is found to be characterized by a maximum intensity depending on the number of periods in the multiquantum wells. The electroluminescence intensity shows also a nonmonotonous dependence on the recombination coefficient and carrier concentration at the contacts.
Large Kerr rotation in ordered CrPt3 films
Authors: Cho Jaekyong , Park Moonki , Kim Hyung-Sik , Kato Takeshi , Iwata Satoshi , Tsunashima Shigeru
Published: July 2002

CrPt 3 films have been prepared by depositing Cr/Pt multilayers using a magnetron sputterer followed by heat treatment. Small and wide angle x-ray diffraction diagrams, magnetic hysteresis loops, and Kerr rotation angle spectra of the films have been investigated. The films had AuCu3 type ordered alloy structure and strong and weak preferred orientation of {111} and {100} planes parallel to the film surface. It was found that CrPt3 films showed the perpendicular magnetic anisotropy to the film surface, large coercivity of 3.7 kOe, and maximum Kerr rotation angle of 0.65 degrees at about 1100 nm. The origin of the large Kerr rotation was discussed.
Complementary analysis techniques for the morphological study of ultrathin amorphous carbon films
Authors: Lemoine P. , Lamberton R. W. , Ogwu A. A. , Zhao J. F. , Maguire P. , McLaughlin J.
Published: July 2002

This article presents experimental results for morphological assessment of sub-50-nm thick hydrogenated amorphous carbon (a-C:H) overcoats. The films were grown by rf plasma enhanced chemical vapor deposition using Ar/C2H2 gas mixture onto heterogeneous (Al2O3–TiC) ceramic substrates. They were analyzed using complementary information from scanning electron microscopy, energy dispersive x-ray analysis and atomic force microscopy. We found that the bias deposition voltage and the nature of the substrate (Al2O3 or TiC regions) adversely affect both growth rate and microstructure. Argon inclusion in the C2H2 plasma during the first stage of growth is responsible for the observed effects. These results suggest that the amorphous carbon layer is denser on the TiC than on the Al2O3 region.
Detection of defects in metal interconnects by the nonbias-optical beam induced current technique
Authors: Koyama Tohru , Sonoda Kenichiro , Komori Junko , Mashiko Yoji , Umeno Masataka
Published: July 2002

The mechanism for detecting defects by the nonbias-optical beam induced current technique is clarified by examining images and conducting simulations. This technique, using an electromotive current as a result of optical laser irradiation with no application of voltage, is very useful for analysis of metal interconnect failure in ultra large scale integrated devices. The characteristic images obtained by this technique, consisting of pairs of bright and dark regions, reveal point defects, such as voids in metal stripes and vias. It is found, by examining the characteristic images of defects, that the electromotive current generated near the defects originates as a result of the thermoelectromotive effect. Furthermore, it is confirmed by thermal simulations and transient current simulations, that the asymmetric temperature profiles near the defects generate the electromotive current and show the characteristic images.
Density difference related to humidity during dry oxidation for ultrathin silicon oxide films
Authors: Yamada Hiroshi
Published: July 2002

The densities of 3.5–6.5-nm-thick silicon oxide films grown on p-type Si(100) at humidities during dry oxidation of 0.5–1.0, 10–100 ppb and 200–500 ppm were determined by charged-particle activation analysis. It was confirmed that the density increases with decreasing humidity and its level is separated into two groups: an ultradry oxidation group that includes the films oxidized at a humidity of less than 100 ppb and a conventional dry oxidation group at a humidity of more than 200 ppm. Since similar humidity dependence was confirmed for several fundamental structural and electrical evaluations, the oxide becomes a homogeneous stoichiometric SiO2 compound and its quality approaches an intrinsic level by dehydrating. These strong similarities also suggest that all the humidity dependence possibly originates from a common cause—the slight microscopic structural change in the oxide near the interfaces. By dehydrating, therefore, its atomic arrangement may be efficiently transferred to a more stable state, and then consequently, the earlier humidity dependence would be confirmed.
Diagnostic measurement of ion implantation dose and uniformity with a laboratory-based positron probe
Authors: Coleman P. G. , Knights A. P. , Gwilliam R. M.
Published: July 2002

The development of a sensitive, depth-tuneable probe, with mapping capability, for low-energy ion implantation dosimetry, is described. The technique is based on the dependence of the extent of Doppler broadening of the positron annihilation linewidth upon the concentration of open-volume defects produced by the implanted ions. By varying the incident positron energy one can ensure that most of the annihilation events occur near the damage peak. A series of diagnostic measurements have been performed which demonstrate that the positron response lies on an almost universal curve, independent of ion mass and energy. The probe is highly sensitive, with a dose threshold in the 10−9 cm−2 range for many implants, and has the potential to measure dose/dose uniformity to better than 1×1011 cm−2 in the 1011−1012 cm−2 range in run times of a few seconds. Considerations underlying the development of a practical instrument based on these findings are discussed.
Ferrimagnetic resonance excitation by light-wave mixing in a scanning tunneling microscope
Authors: Gutjahr-Löser Th. , Krieger W. , Walther H. , Kirschner J.
Published: July 2002

Ferrimagnetic resonance is measured in a scanning tunneling microscope. The infrared light of two lasers is focused into the tunneling junction and a difference-frequency signal in the microwave region is generated. This microwave signal is used to excite spin waves in an yttrium–iron–garnet film with a thin Au capping. The coupling of the light to the tunneling junction is explained by an antenna mechanism. Characteristic antenna patterns of the angle-dependent receiving efficiency are obtained. The mixing of the two laser frequencies is due to the nonlinearity of the tunneling junction. The microwave signal obtained is absorbed in the ferromagnetic sample if the resonance condition is fulfilled. This method might allow the measurement of magnetic properties with a lateral resolution down to the nm scale.
Phase formation and ferroelectric characteristics of nonfatigue barium bismuth tantalate thin films
Authors: Lu Chung-Hsin , Wen Cheng-Yen
Published: July 2002

The phase formation and ferroelectric properties of new nonfatigue BaBi2Ta2O9 thin films prepared by the metal-organic decomposition method on Pt/Ti/SiO2/Si substrates have been investigated. After annealing at 700 °C, BaBi2Ta2O9 films become fully crystallized. On further higher temperatures, an unknown phase is formed by the interaction between the coated films and titanium species diffusing outward from the underlying substrates. A series equivalent-circuit model is successfully applied to analyze the dielectric properties of the unknown phase and BaBi2Ta2O9 films. The intrinsic dielectric constant of BaBi2Ta2O9 thin films is calculated to be 198. In the polarization-electric analysis, BaBi2Ta2O9 thin films exhibit saturated polarization hysteresis curves, which demonstrates their ferroelectric characteristics. The remnant polarization of BaBi2Ta2O9 thin films increases with increasing annealing temperatures. Adding excess amount of bismuth contents (10 mol %) in BaBi2Ta2O9 thin films substantially further improves their ferroelectric properties. However, adding bismuth species more than 10 mol % leads to the formation of Bi2O3, thereby inducing high leakage current. Adding 10 mol % excess bismuth in BaBi2Ta2O9 thin films, the resultant films exhibit a high remnant polarization (2Pr=14 μC/cm2), a low coercive field (2Ec=45 kV/cm), and a fatigue-free characteristic up to 109 switching cycles.
Degradation and hard breakdown transient of thin gate oxides in metal–SiO2–Si capacitors: Dependence on oxide thickness
Authors: Lombardo S. , La Magna A. , Spinella C. , Gerardi C. , Crupi F.
Published: July 2002

We have investigated the dynamics of hard intrinsic dielectric breakdown of gate oxide layers with thickness between 35 and 5.6 nm in n+ polycrystalline Si–SiO2–Si metal/oxide/semiconductor capacitors after constant voltage Fowler–Nordheim stress. The buildup of defects in the oxide during the degradation phase was monitored by quasi static C–V measurements. The dynamics of the final breakdown event was followed with high time resolution, allowing to measure voltage, current, and power versus time during the breakdown transient. Transmission electron microscopy data quantifying the damage produced during this transient are reported. Finally, we propose a phenomenological model concerning the dynamics of breakdown with model parameters adjusted on the basis of the experimental data.
Strain optimization for high differential gain and low current operation in 1.55 μm InGaAs/InGaAsP quantum well lasers
Authors: Gilard O. , Lozes-Dupuy F. , Vassilieff G. , Bonnefont S. , Arguel P. , Barrau J. , Le Jeune P.
Published: July 2002

The effect of strain on threshold current and differential gain in 1.55 μm InGaAs/InGaAsP quantum well lasers is reviewed. A constant decrease in the threshold current with increasing stress is predicted if a conventional model of Auger recombination is used. We propose a more realistic model based on an accurate method for the derivation of the Auger recombination rate in quantum wells. Unlike the conventional theory, a realistic valence band structure along with Fermi–Dirac statistics and analytic expressions of the transition matrix element for both bound–bound and bound-unbound Auger processes are employed. Contrary to conventional modeling, computation results show an optimal compressive strain of approximately 1% that minimizes the threshold current and maximizes the differential gain. These results are in good agreement with the experimental results reported in the literature.
Temperature dependence of recombination processes of photogenerated carriers in a quantum-well structure
Authors: Ishitani Yoshihiro
Published: July 2002

Time-resolved photoluminescence (PL) measurements are performed on an Al0.53In0.47P/Ga0.52In0.48P/Al0.53In0.47P quantum-well (QW) structure in a temperature range of 5–398 K. The radiative and nonradiative carrier recombination rates are obtained from the PL decay rates and the time-integrated PL intensities. It is found that the radiative recombination rate decreases rapidly as the temperature increases, and becomes constant at temperatures higher than 275 K. The nonradiative recombination rate increases rapidly at temperatures higher than 300 K. The dependence of the PL intensity on the temperature is expressed by a formula, which consists of the terms expressing the nonradiative recombination or recombination via deep levels of carriers which are free from localized states, the carrier transfer from QWs to barriers, and the temperature-dependent radiative recombination. The carrier localization energy is found to be 4–10 meV. The apparent barrier height for the carrier transfer from QWs is found to be 350–600 meV.
Optical properties of the γ-phase yttrium trihydride YH3−δ
Authors: Lee M. W. , Shin W. P.
Published: July 2002

The transmission spectra of thin films of γ-phase yttrium trihydride YHx, x≅2.87, are measured in the energy range 0.05–6 eV at room temperature. The measured quantities are used to determine the frequency-dependent index of refraction, extinction coefficient, dielectric function, and optical conductivity. In the energy range (E=0.2–6 eV), interband transition and impurity-related transitions dominate the optical properties. In the low-energy range (E=0.05–0.2 eV), hydrogen vibration modes dominate the optical properties. In addition, strong absorption due to free carriers is observed. This work also evaluates several parameters such as plasma frequency, effective carrier density, and donor ionization energy. The possible sources for optical features observed in the spectra are also described.
Study of carrier transport in metal/porous silicon/Si structures
Authors: Martı́n-Palma R. J. , Pérez-Rigueiro J. , Martı́nez-Duart J. M.
Published: July 2002

Electrical contacts to porous silicon were formed by depositing various metals such as aluminum, gold, and titanium onto its surface. Low temperature current–voltage measurements were performed, which allowed us to identify the contact as a metal–insulator–semiconductor (MIS) structure. The parameters which characterize the MIS structure: the mean barrier height presented by the insulating film (χ), the barrier height presented to the electrons in the metal by the semiconductor itself (VB0), the ideality coefficient (n) and the series resistance (Rs), were determined for each type of contact studied. All of these contacts show fairly high values of the ideality coefficient, which are explained by the presence of a large concentration of interface states.
Effect of a chemical modification on growth silicon dioxide films on gallium arsenide prepared by the liquid phase deposition method
Authors: Huang C. J. , Houng M. P. , Wang Y. H. , Wang H. H.
Published: July 2002

This article presents a chemical modification process to grow silicon dioxide (SiO2) on a gallium arsenide (GaAs) substrate using liquid phase deposition (LPD) at extremely low temperature (∼40 °C). In this process, pretreatment of the wafer by ammonia solution with buffer kept at pH=11–12 enriches OH radical formation on the GaAs surface, enhancing SiO2 deposition, providing good film quality, and reliability. The LPD SiO2 deposition rate on GaAs substrate is up to 1303 Å/h. The refractive index of the LPD SiO2 film on GaAs substrate is about 1.423 with growth at 40 °C. When the LPD SiO2 film on GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor, the surface charge density (Qss/q) is about 3.7×1011 cm−2 and the leakage current is 43.3 pA at −5 V. A mechanism for the deposition of silicon dioxide on a GaAs substrate is proposed.
Transport properties of NdNiO3 thin films made by pulsed-laser deposition
Authors: Catalan G. , Bowman R. M. , Gregg J. M.
Published: July 2002

Pulsed-laser deposition was used to make thin films of NdNiO3 on a variety of substrates. The films were found to be single phase perovskite in all cases. However, the transport behavior varied strongly as a function of the substrate used: the films were semiconducting on MgO, but showed a metal-semiconductor phase transition on SrTiO3 and NdGaO3. The best electrical-switching properties corresponded to films grown on NdGaO3, with the resistivity changing abruptly by more than two orders of magnitude at TMI∼185 K. Very thin films (∼35 nm) were also grown on NdGaO3 substrates to investigate the epitaxial strain effect on the transition. It appears that biaxial tensile strain stabilizes the high temperature metallic phase, thus lowering TMI.
Raman measurement of vertical conductivity and localization effects in strongly coupled semiconductor periodical structures
Authors: Pusep Yu. A. , Silva M. T. O. , Galzerani J. C. , Rodrigues S. C. P. , Scolfaro L. M. R. , Lima A. P. , Quivy A. A. , Leite J. R. , Moshegov N. T. , Basmaji P.
Published: July 2002

Raman scattering was applied to a study of collective plasmon–LO phonon excitations polarized normal to the layers in strongly coupled GaAs/AlAs and δ-doped GaAs superlattices. Thus, the corresponding (vertical) motion of electrons and their localization were studied and compared in both types of superlattices. The localization of the collective excitations caused by the localization of the electrons at the top of the miniband was found in the GaAs/AlAs superlattices. Much stronger localization effects were observed in the δ-doped structures than in the GaAs/AlAs superlattices. Our results reveal evidence of the formation of a miniband structure in the δ-doped structures even in the case of complete localization of electrons inside one period.
Paramagnetic centers in Al-doped 6H–SiC: Temperature and concentration effects
Authors: Gerardi Gary J. , Poindexter Edward H. , Keeble David J.
Published: July 2002

The electron paramagnetic resonance of Al-doped 6H–SiC was investigated over a range of temperature and concentration. The resonance signals attributed to Al substituting for Si (AlSi) were found to decrease sharply with temperature between 3.4 and 6.0 K. Impurity-band conduction accounts for the anomalous temperature behavior better than other mechanisms. Variable temperature measurements of the AlSi resonance provide activation energies for hopping conductivity that increase with the free-carrier concentration. The g map of AlSi was observed to vary with [Al]. Additional resonance signals were found which increase with Al doping level. The temperature and saturation dependence of these signals differ from those of the neutral AlSi center. One resonance having g∥=2.08 is detectable below 38 K, while the AlSi signal is observed below 7 K. For free-carrier concentrations near 1019 cm−3, all the resonances are superimposed on a broad anisotropic signal that exhibits complex intensity and linewidth changes with temperature. These additional Al-related signals were not assigned to specific models.
Analysis of bistable noise from microfabricated field emission cathodes
Authors: Olson R. T. , Condon G. R. , Panitz J. A. , Schwoebel P. R.
Published: July 2002

Field emission current fluctuations from microfabricated cathodes have been investigated. Time-correlated noise measurements and field emission electron microscope images indicate that the dominant current fluctuations are bistable in character and are emitted from a few localized sites on the cathode surface. Apertured bistable current transitions from these emission sites are often significantly larger than the percent change in total emitted current. Analysis of bistable pulse lengths has shown that the dwell time in a particular bistable emission state decays exponentially with time. Current autocorrelation measurements indicate that bistable noise at ⩽300 K is generated by adsorbates switching between emission states and not by adsorbate diffusion.
Multiline visible emission from a barium low-pressure discharge
Authors: Curry J. J. , Anderson H. M. , MacDonagh-Dumler J. , Lawler J. E. , Lister G. G.
Published: July 2002

A multiline visible emission spectrum, yielding “white” light, has been observed from a low-pressure Ba discharge. A five atomic level numerical model reproduces the observations qualitatively, suggesting that a low-pressure Ba discharge light source is capable of a significantly better color rendering than previously thought.
Magnetotransport in the low carrier density ferromagnet EuB6
Authors: Süllow S. , Prasad I. , Bogdanovich S. , Aronson M. C. , Sarrao J. L. , Fisk Z.
Published: July 2002

We present a magnetotransport study of the low-carrier density ferromagnet EuB6. This semimetallic compound, which undergoes two ferromagnetic transitions at Tl=15.3 K and Tc=12.5 K, exhibits close to Tl a colossal magnetoresistivity (CMR). We quantitatively compare our data to recent theoretical work, which, however, fails to explain our observations. We attribute this disagreement with theory to the unique type of magnetic polaron formation in EuB6.
Novel soft magnetic composites fabricated by electrodeposition
Authors: Yu R. H. , Ren L. , Basu S. , Unruh K. M. , Parvizi-Majidi A. , Xiao John Q.
Published: July 2002

Soft magnetic composites have been fabricated by electrodepositing FeNi and FeCo onto W fibers with a diameter of 20 and 100 μm. Structural and compositional characterizations indicate that FeNi and FeCo-based composites are of fcc and bcc structure, respectively. The mechanical strengths are significantly improved depending on the volume fraction of W fibers. To further improve the mechanical properties of these composites, we have codeposited soft magnets and Al2O3 powders, resulting in an increase in Vickers hardness of more than 100%. Magnetic measurements show that as-deposited fibers are not magnetically soft. After proper thermal annealing, the samples exhibit excellent soft magnetic properties.
Magnetoelastic waves in spin glass with remanent spontaneous magnetization
Authors: Janutka A. , Rusek P.
Published: July 2002

The magnetoelastic interaction in spin glass with remanent spontaneous magnetization (SGRSM) has been investigated. The phenomenological Lagrangian of the interaction of the SGRSM with the lattice has been constructed. Well defined magnetoelastic waves have been found. The dispersions and damping coefficients of these waves have been evaluated.
Surface spin wave in canted antiferromagnets
Authors: Albuquerque E. L. , Costa Filho R. N. , Cottam M. G.
Published: July 2002

A theory is presented for the study of surface spin waves in a two-sublattice, uniaxial antiferromagnet when there is an external magnetic field applied perpendicular to the easy axis of the material to induce a canting of the spins. Our theoretical model uses a microscopic canted Heisenberg magnetic Hamiltonian, treated within the RPA (random phase approximation) approach. Numerical results show, from the stability condition, that the convergence to the infinite-bulk canting angle θ can be over several layers (for MnF2) or almost localized in the surface layer (for FeF2 and CoF2). The bulk mode for the uniaxial case (θ=0) becomes split into two well-defined bulk regions in the spectrum for the canted materials. It is found that, between these branches, there is an acoustic surface magnon branch.
Vectorial second-harmonic magneto-optic Kerr effect measurements
Authors: Kabos P. , Kos A. B. , Silva T. J.
Published: July 2002

A significant modification of an existing experimental technique based on the second-harmonic magneto-optical Kerr effect (SH-MOKE) is introduced. With a p-polarized pumping optical wave incident upon a magnetic film, the transverse component of magnetization causes a change in the second-harmonic generation efficiency of the material and the longitudinal component of the magnetization produces a change in the polarization rotation and/or ellipticity of the second-harmonic signal. This permits simultaneous vectorial measurement of the in-plane magnetization components. Examples of measured hysteresis loops from 50 nm thick permalloy films and procedures for SH-MOKE signal calibration are presented.
Magnetoresistance and Hall magnetometry of single submicron ferromagnetic structures
Authors: Kubrak V. , Neumann A. , Gallagher B. L. , Main P. C. , Henini M. , Marrows C. H. , Hickey B. J.
Published: July 2002

We present measurements on hybrid ferromagnetic/semiconductor devices. Single, submicron ferromagnetic structures have been fabricated directly onto the surface of a semiconductor, which incorporates a near-surface two-dimensional electron gas (2DEG). The induced Hall resistance and magnetoresistance of the 2DEG are used to measure the magnetic properties of the stripes directly. The relative merits of these two techniques are compared using a device geometry in which both types of measurement can be made simultaneously.
New class of magnetic refrigerants based on the Cr(V) tetraperoxides
Authors: Cage Brant , Dalal Naresh
Published: July 2002

We have recently investigated a series of compounds based on the Cr(V) tetraperoxides (general formulas M3CrO8 where M=Li, Na, K, Rb, Cs) that exhibit novel magnetic and heat capacity properties. Chief among them is the promise of superior performance for magnetic refrigeration. Currently, adiabatic demagnetization refrigeration (ADR) compounds are generally limited in their effective cooling temperature range. These limitations are a function of the magnetic spin ordering temperature, which limits the lowest attainable temperature, and the spin concentration, which limits the refrigeration power. Our investigations indicate that the peroxychromates can be tuned to possess maximal refrigeration power at a desired operating temperature. Evidence for this claim is suggested by the heat capacity coefficient (b). The lower the magnitude of b, the greater the ADR potential. Experimental evidence shows introducing larger cations significantly lowers b, while basically maintaining the spin concentration. This paper focuses on explaining the trend in terms of contributions to the internal fields, which are tentatively assigned to the exchange and dipolar interactions. It is predicted that the controlled modification of these fields by molecular structural alterations tunes these compounds to have maximum refrigeration power over a broad range of temperatures, i.e., 0.010 to 20 K.
Substrate dependence of Kondo and local moment physics in thin metal films (invited)
Authors: Giordano N. , Jacobs T. M.
Published: July 2002

Recent experiments have revealed that Kondo behavior in reduced geometries can be quite different from that found in the corresponding bulk systems. For example, the Kondo contribution to the resistivity in thin metal films can be suppressed by reducing the film thickness. This behavior has been explained theoretically by Zawadowski and co-workers [O. Újsághy, A. Zawadowski, and B. L. Gyorffy, Phys. Rev. Lett. 76, 2378 (1996); O. Újsághy and A. Zawadowski, Phys. Rev. B 57, 11598 (1998); 57, 11609 (1998)]. in terms of a model involving a surface induced single ion anisotropy at the local moment site. Moments which are near a surface experience a splitting which can result in a nonmagnetic ground state. In this article we describe experimental observations regarding such surface effects, and in particular the influence of the substrate on the Kondo behavior. We find that with substrates of freshly oxidized Si or freshly prepared SiO coated glass, the Kondo effect can be much larger than when the same film is deposited on glass. This finding seems to resolve a long standing controversy in the field.
Crystallization and hard magnetic properties of Fe–Co–Nd–Dy–B amorphous alloys with glass transition
Authors: Zhang Wei , Inoue Akihisa
Published: July 2002

Glass transition followed by a supercooled liquid region was observed in the composition range of 4–56 at. %Co, 2–4.5 %Nd, 0–1.25 %Dy, and 18–30 %B in melt-spun Fe–Co–Nd–Dy–B amorphous alloys. The largest value in the supercooled liquid region (ΔTx) was 45 K for Fe66.5Co9.5Nd3.5Dy0.5B20. The crystallized structure consists of 2:14:1, Fe3B, and α-(Fe, Co) phases and their grain sizes after annealing for 420 s at 933 K are 15, 15, and 50 nm, respectively. The interparticle spacing of the 2:14:1 phase is less than 50 nm. The remanence (Br), coercivity (iHc), and maximum energy product (BH)max after an optimum annealing treatment (933 K, 420 s) are 1.24 T, 263 kA/m, and 92 kJ/m3, respectively, for the Fe66.5Co9.5Nd3.5Dy0.5B20 alloy. The rather good hard magnetic properties are interpreted to result from the exchange magnetic coupling among 2:14:1, Fe3B, and α-(Fe, Co) phases. The good hard magnetic properties in the crystallized state of the Fe–Co–Nd–Dy–B amorphous alloys with large ΔTx over 40 K are expected to enable the future fabrication of a bulk hard magnetic material by the simple process of the formation of a bulk amorphous alloy followed by optimum crystallization.
The effect of air-bearing surface roughness on avalanche test
Authors: Wang Geng , Li Yufeng , Lee Hyung J.
Published: July 2002

The traditional method of glide height measurement is used for avalanche height evaluation. The air-bearing surface (ABS) of the avalanche head is assumed to be perfectly flat. This assumption, however, is not appropriate for today’s drive. In addition, a glide avalanche head normally has a different surface finish than that of a real recording head. So what an avalanche head is “seeing” on the disk surface may not be what a real head “sees” in the drive. Therefore, it becomes extremely important that one can correctly report the true avalanche height. In this study, we proposed one possible way of doing so by correctly calibrating the flying height of a glide head and the defining glide avalanche contact as “0.02% bearing depth.”
Mn–Zn ferrite thin films fabricated on crystalline substrates using laser ablation technique
Authors: Nakano M. , Tomohara K. , Song J. M. , Fukunaga H. , Matsuo Y.
Published: July 2002

We report a fabrication of Mn–Zn ferrite thin films by a low temperature process. It was found that usage of crystalline substrates is an effective way to obtain crystallized Mn–Zn ferrite thin films at the substrate temperature of room temperature in laser ablation technique. The usage of crystalline substrates reduced the coercive force of the thin films by approximately 25% compared to that of the thin films fabricated on glass substrates.
Effect of a Ti seed layer on the magnetic properties of CoCrTa double-layered perpendicular media
Authors: Shimatsu T. , Komagome H. , Watanabe I. , Muraoka H. , Sugita Y. , Nakamura Y.
Published: July 2002

The effect of a Ti seed layer on the magnetic properties and microstructure of Co77Cr19Ta4 was studied in Co77Cr19Ta4/Ti/M (M=Co91Zr3Nb6, Fe, Co) double-layered perpendicular recording media. A thin Ti film of ∼5 nm enhanced the c-axis alignment perpendicular to the film plane, resulting in a large perpendicular anisotropy Ku and the best magnetic properties under the present experimental conditions. The coercivity at this Ti thickness (3–3.7 kOe) was approximately half of the magnetocrystalline anisotropy field Hk estimated from the Ku value, even with the present thick 50 nm CoCrTa. The recording performance using a single-pole-type writing head showed that media with a 5 nm Ti layer had higher recording sensitivity compared to media without Ti layers, and a higher SN value at densities greater than 200 kFRPI. No significant loss of recording resolution due to the nonmagnetic Ti space between the CoCrTa and the back layers was observed by the use of the 5 nm Ti film. Moreover, the results for media with Fe back layers indicated that a thinner back layer with a high flux density can be used without any reduction of recording sensitivity and resolution.
Cathode-induced luminescence quenching in polyfluorenes
Authors: Stoessel M. , Wittmann G. , Staudigel J. , Steuber F. , Blässing J. , Roth W. , Klausmann H. , Rogler W. , Simmerer J. , Winnacker A. , Inbasekaran M. , Woo E. P.
Published: July 2002

We investigate the impact of the deposition of low work function metals such as calcium on thin layers of fluorene-type polymers by time-of-flight secondary ion mass spectroscopy. An implantation process rather than a slow metal diffusion is found to be the most probable source of metal contamination within the polymer layers. This contamination extends to a range of several tens of nanometers in the organic layers. Photoluminescence and electroluminescence measurements are performed with varying calcium layer thicknesses. The luminescence efficiency exhibits a strong correlation with the depth profile of the calcium present within the polymer. The results are discussed with respect to the exciton diffusion length in the fluorene polymer. A numerical model including exciton formation, migration, and quenching is proposed in order to describe the observed phenomena.
Easy-axis changes in perovskite-type Fe–Ni nitrides γ′-(Fe1−xNix)4N: A Mössbauer study
Authors: Rechenberg H. R. , Diao X. G. , Scorzelli R. B.
Published: July 2002

Perovskite-type Fe–Ni nitrides γ′-(Fe1−xNix)4N have been investigated by Mössbauer spectroscopy in the 0⩽x⩽0.8 concentration range. Mössbauer spectra have been recorded at low temperatures and above the Curie temperature of each compound. The quadrupole splitting at the FeII (cube face center) site was large and increased upon Ni substitution, exceeding 1 mm/s. The low-temperature Mössbauer spectra were fitted with a full Hamiltonian model combined with a binomial distribution of Ni nearest neighbors. The fitting results indicated that the direction of the easy magnetic axis undergoes a continuous rotation from [100] to [111] for increasing Ni concentration. This result is discussed in terms of possible changes in the K1/K2 ratio upon Ni substitution.
Tb3+→Ce3+ energy transfer in Tb3+:Ce3+:YAG single crystalsa)
Authors: Shmulovich J. , Berkstresser G. W. , Brasen D.
Published: July 2002

An energy transfer from 5D3 and 5D4 levels of Tb3+ to 2D3/2 state of Ce3+ in Ce3+:Tb3+:YAG was studied using time resolved spectroscopy. It was found that the transfer from the Tb3+(5D3) level proceeds via (d–d) interaction and the critical distance is 18 Å. The transfer from Tb3+(5D4) state was consistent with the (d–d) interaction and with the critical distance of 15.4 Å, but could also be described in the framework of (d–q) interaction.