bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of ceramic thin films on Si(100) using an in situ laser deposition technique
Authors: Tiwari P. , Sharan S. , Narayan J.
Published: July 2002

We have investigated the formation of MgO and yttria-stabilized ZrO2(YSZ) thin films on Si(100) substrates using laser (wavelength 248 nm pulse duration 40 ns, and repetition rate 5 Hz) physical vapor deposition method. The films were deposited from solid targets of MgO and polycrystalline YSZ in appropriate ambient with the substrate temperature optimized at 650 °C. The absorption coefficient in the MgO target was enhanced by Ni doping. The films were characterized using scanning and transmission electron microscopy (plan and cross section), x-ray diffraction, and Rutherford-backscattering spectrometry. The films were found to be polycrystalline with a texture. The thin films of MgO exhibited 〈111〉 texture, while the YSZ films contained both 〈111〉 and 〈200〉 textures.
Analysis of charge control in Si delta-doped field-effect transistor
Authors: Chen Qiang , Willander Magnus
Published: July 2002

The Schrödinger’s equation for two-dimensionally quantized electrons in a V-shaped well and Poisson’s equation including three-dimensional hole distribution have been self-consistently solved. Based on this model we have analyzed the charge control process at room temperature in the Si delta-doped field-effect transistors. It was found that the electron density of the channel as a function of the applied gate voltage could be well approximated by a quadratic expression. The influences of the device structure parameters on the charge control process have been studied. From the calculated gate capacitance-voltage behavior, the device performance has been estimated.
Post-growth process-induced degradation in thin gate oxides
Authors: Mehta Rajesh , Bhattacharyya A. B. , Singh D. N.
Published: July 2002

The mechanism of degradation in thin gate oxides due to postoxidation processing steps has been investigated using charge to breakdown QBD as a diagnostic tool. The QBD degradation is also correlated with trap generation rate in thin gate oxide. Controlled annealing experiments show that the gate oxide degradation is not related to the diffusion of phosphorous or other mobile ion impurities from the polysilicon film into the gate oxide. The degradation is caused by stress build up in silicon dioxide film with high-temperature annealing, due to viscous shear flow of the gate oxide at polysilicon/silicon dioxide and silicon dioxide/silicon interfaces. In another experiment, where the thickness of polysilicon was taken as a parameter, it is shown that degradation has a direct correlation with the polysilicon thickness which may be related to the mechanical stress.
Investigation of Se+-implanted GaAs layers by temperature-dependent dechanneling
Authors: Bachmann T. , Wesch W. , Gärtner K. , Bartsch H.
Published: July 2002

Semi-insulating GaAs wafers were implanted with 300-keV Se+ ions, Ni=1×1014 cm−2, at different temperatures (300 to 513 K). Weakly damaged layers were produced in the case of implantation at elevated temperatures. Channeling measurements at different temperatures showed the existence of displaced lattice atoms with low distances ra from the string dominating. The influence of the damage present in the as-implanted state on the resulting electrical sheet properties after annealing by means of a graphite strip heater is discussed.
Preparation of a high-J
c Y-Ba-Cu-O film at 700 °C by thermal chemical vapor deposition
Authors: Yamane Hisanori , Hirai Toshio , Watanabe Kazuo , Kobayashi Norio , Muto Yoshio , Hasei Masaharu , Kurosawa Hideyuki
Published: July 2002

A high-Jc Y-Ba-Cu-O superconducting film was successfully prepared at 700 °C on a SrTiO3(100) single-crystal substrate without postannealing by thermal chemical vapor deposition under a low-oxygen partial pressure of 0.036 Torr in the total gas introduced into a hot-wall-type reactor (total gas pressure: 10 Torr), using 1% O2 balanced with Ar as a reactant gas. The sources for the elements of Ba, Y, and Cu were β-diketone metal chelates. The film mainly consisted of YBa2Cu3Ox with c-axis orientation perpendicular to the substrate plane and included small amounts of a-axis oriented and randomly oriented grains. The film showed the superconducting transition temperature defined by zero resistivity at 89 K. The critical current density based on a 2 μV/cm criterion was 2.2 × 106 A/cm2 at 77.3 K and 0 T.
Cadmium telluride films by metalorganic chemical vapor depositiona)
Authors: Chu T. L. , Chu Shirley S. , Ferekides C. , Britt J. , Wu C. Q.
Published: July 2002

Polycrystalline films of cadmium telluride (CdTe) have been deposited on glass and SnO2:F/glass substrates at 350–400 °C by the reaction of dimethylcadmium (DMCd) and diisopropyltellurium (DIPTe) in a hydrogen atmosphere. The DMCd/DIPTe molar ratio in the reaction mixture is an important factor affecting the deposition rate, conductivity type, and photoluminescence of deposited films. Photoluminescence measurements indicate that CdTe films deposited at 400 °C are of better quality than films deposited at 350 °C. The films deposited at 400 °C are p-type at DMCd/DIPTe molar ratios of 0.51 or less and are n-type at higher ratios. The structural, optical, and electrical properties of CdTe films have been characterized.
Beam quality measurement of a narrow band KrF excimer laser with stimulated Brillouin scattering phase conjugate double-pass amplifier at 100 Hz operation
Authors: Ohta Kei , Yagi Takashi , Saito Hideaki , Obara Minoru
Published: July 2002

A narrow band KrF excimer laser device which consists of an oscillator and a double-pass amplifier with a stimulated Brillouin scattering phase conjugation (SBS-PC) mirror (double-pass self-compensation scheme) was operated with the constant reflectivity of phase conjugation at 100 Hz repetition rate, by vibrating the SBS cell. The dependence of the beam quality on the operating frequency was evaluated for every shot by using a beam profiler. The beam divergence was less than 100 μrad and the fluctuation at the far-field peak position was less than 10 μrad at 100 Hz with the spectral bandwidth less than 0.2 cm−1.
Passive wavelength stabilization in the 1.5-μm region of wide gain spectrum lasers by Er3+-doped materials
Authors: Auzel F. , Zhou B. W. , Meichenin D. , Jean-Louis A. M.
Published: July 2002

Er3+-doped materials, either crystals or glasses, are shown to act as passive stabilizers for wide gain spectrum lasers of the F-center NaCl: OH− type and of the InGaAsP semiconductor type. The wavelength is demonstrated to be stabilized against perturbations originating from pumping intensity and temperature variations. A thermal stability coefficient of 0.14 Å/°C is demonstrated. In the InGaAsP laser case, single-mode operation, independent of possible extra Fabry–Perot etalon modes, is achieved, with rejection of adjacent modes by 25 dB. The possibility of active stabilization in the case of an inhomogeneous gain spectrum laser is discussed.
Removal of end-of-range defects in BF+2 implanted (111)Si by the grain growth of thin NiS2 overlayer
Authors: Chen W. J. , Chen L. J.
Published: July 2002

A significant reduction in the density of end-of-range (EOR) defects was achieved in BF+2 implanted (111)Si by the formation and growth of a polycrystalline NiSi2 overlayer in samples annealed at 850–900 °C. In contrast, no apparent reduction in the density of EOR defects was found in BF+2 implanted silicon with no NiSi2 layer or with an epitaxial NiSi2 overlayer, subjected to the same heat treatment. The significant reduction in density of the EOR defects was correlated to the grain growth of thin polycrystalline NiSi2 overlayer. The availability of both polycrystalline and epitaxial NiSi2 on BF+2 implanted (111)Si made a direct comparison of the effects of different structures of the same silicide on the removal of the EOR defects possible.
Oxide charge accumulation in metal oxide semiconductor devices during irradiation
Authors: Lee Der-Sun , Chan Chung-Yu
Published: July 2002

An analysis of a simple physical model for radiation induced oxide charge accumulation in the SiO2 layer of metal oxide semiconductor (MOS) structure has been developed. The model assumes that both electron and hole traps exist in the oxide layer. These traps can capture electrons as well as holes during irradiation. Using this model, final oxide charge distributions in the oxide layer of MOS capacitors exposed to a total dose radiation can be predicted. The resulting charge distribution is calculated to yield the midgap voltage shifts as functions of total dose, bias voltage, and oxide thickness. The results are shown to agree well with the experimental data. Furthermore, the model successfully analyzes the radiation-induced negative oxide charge distribution in an ion-implanted, radiation-hard MOS capacitor. These negative oxide charge distributions not only partially compensate the effects of trapped positive oxide charges but also reduced the density of positive oxide charges trapped near the Si/SiO2 interface. We found the reduction of the positive oxide charge density near the Si/SiO2 interface is due to internal electric field modification in the oxide layer.
Magnetic properties and Mössbauer spectra of sputtered Fe-Al-Si-Ni supersendust films
Authors: Miyazaki Masahiro , Ichikawa Masashi , Komatsu Takayuki , Matusita Kazumasa , Nakajima Kensuke , Okamoto Shoichi
Published: July 2002

Fe-Al-Si-Ni supersendust films containing 2.7 at. % Ni atoms with a thickness of 1 μm were deposited on crystallized-glass substrates by rf planar magnetron sputtering, and the changes in magnetic properties and structure due to the sputtering conditions and annealing were examined. The films with excellent soft magnetic properties and high magnetic-flux density which are good candidates for new recording-head materials were obtained by annealing as-deposited films at 500 °C. It was found through conversion electron Mössbauer spectroscopy (CEMS) that the disordered structure of α type in as-sputtered films transformed into the ordered structure consisting of a mixture of B2 and DO3 types at the temperature of 500 °C. The CEMS studies also revealed that Ni atoms are located at the corner in the bcc structure.
Compensation mechanism in undoped, semi-insulating GaAs
Authors: Suemitsu Maki , Nishijima Masaaki , Miyamoto Nobuo
Published: July 2002

Concentrations of neutral and ionized deep donor EL2 in undoped, semi-insulating GaAs crystals were obtained using the near-infrared photoabsorption method. By varying the carbon content in the crystal in a range of 1015–1016 cm−3, it was verified that only 30% of the total carbon acceptors take part in compensation of EL2, i.e., [EL2+]=0.3[C]. This contradicts with either the conventional two-level model which demands [EL2+]=[C] or the recent findings of electron paramagnetic resonance measurements indicating [EL2+]≫[C]. A model is presented to moderate these contradictions, which includes presence of indirectly carbon-related donor and electrically active and inactive two types of EL2. An evidence to support the model is given by a recent nuclear-magnetic resonance measurement by the same author [Appl. Phys. Lett. 57, 398 (1990)].
The effects of thermal history on electrical properties and microdefects of dislocation-free liquid-encapsulated Czochralski GaAs
Authors: Yamada Kohji , Osaka Jiro , Hoshikawa Keigo
Published: July 2002

The effects of thermal history on the electrical properties and microdefects of In-doped dislocation-free liquid-encapsulated Czochralski GaAs are investigated. The EL2 concentration ([EL2]) and sheet-carrier concentration of an implanted Si layer both increase as the cooling rate of the crystal during growth is decreased. Postgrowth annealing at 1000 °C eliminates changes in these concentrations due to the various cooling rates, but could not eliminate the differences associated with boron concentrations or stoichiometry of the crystal. It is also found that the effects of thermal history on the microdefects, which may be minute arsenic precipitates, are similar to those on [EL2]. In other words, the average volume of the microdefects increases but their density decreases with decreasing cooling rates. While postgrowth annealing at 1000 °C reduces these variations, it cannot eliminate them. Based on the results, the relation between [EL2] and the microdefects is discussed and it is suggested that the dense distribution of the microdefects contributes to microscopic [EL2] homogeneity. High-temperature postgrowth annealing at 1200 °C with subsequent 1000 °C annealing can achieve high [EL2] and dense microdefect distribution which is independent of the thermal history in the as-grown crystals. The material uniformity of such annealed dislocation-free crystals should be excellent.
Parametric dispersion and amplification of acoustohelicon waves in piezoelectric semiconductors
Authors: Neogi A. , Ghosh S.
Published: July 2002

Assuming that the origin of the nonlinear interaction lies in the second-order optical susceptibility arising from the nonlinear induced current density and using the coupled-mode theory, the parametric dispersion and amplification of acoustohelicon waves is analytically investigated in a longitudinally magnetized piezoelectric semiconductor of noncentrosymmetric nature. The relevant experiments have not been reported. The threshold value of the pump electric field E0th and its corresponding excitation intensity is obtained. The longitudinal magnetic field decreases the required magnitude of E0th for the excitation of parametric amplification. The phenomenon of self-defocusing of the signal in the prevailing case is found to be a consequence of the negative dispersive characteristics exhibited by the acoustohelicon waves. Numerical analyses are performed for an InSb crystal at 77 K, duly irradiated by frequency-doubled pulsed 10.6-μm CO2 lasers. The parametric gain constant is observed to be maximum when the cyclotron frequency ωc attains the magnitude equal to that of ω0, the incident laser frequency (=1.78×1014 s−1 ).
Magneto-optical properties and temperature dependence of SmCoDy films with perpendicular magnetic anisotropy (abstract)
Authors: Lee Z. Y. , Miao X. S. , Wang C. G. , Hu Y. S. , Zhu P. , Lin G. Q. , Wan D. F. , Dai D. W.
Published: July 2002

Amorphous LRE-TM SmCo perpendicular magnetic film provides a promising candidate for perpendicular magnetic recording media.1 In order to improve the magneto-optical properties of SmCo films, we have studied the ternary system: Smy(Co100−xDyx)100−y films which were prepared by rf magnetron sputtering system. Because the Dy moment is antiferromagnetically coupled to the Co moment and Dy has a larger magnetic anisotropy, Dy addition will increase Ku and decrease Ms of LRE-TM films. With the Dy addition content increased from 0 to 10 at. %, the perpendicular anisotropy constant K⊥ (K⊥ = Ku(K⊥=Ku− 2πM2s) increased to improve the magneto-optical properties of SmCo films. The torque curve measurement and Kerr hysteresis loop of SmCoDy film had proved it was perpendicular magnetic film. In order to prevent RE metal selective oxidation of SmCoDy films, a protective layer AlN was used. AlN films were prepared by rf reactive sputtering.2 The temperature dependence of AlN/SmCoDy/glass were studied. Hc decreased rapidly when temperature increased while its Kerr angle decreased slightly. When the sample was cooled to room temperature, Hc and θk returned to its original value. The results show SmCoDy films may become new material of magneto-optical recording media. The long-term stability and microstructure of SmCoDy films have also been studied.
T=0 magnetization and susceptibility curves for Heisenberg-like and other spin-1 chains (abstract)
Authors: Bonner Jill C.
Published: July 2002

Recently there has been extensive theoretical interest in the remarkable Haldane prediction that spin-1 antiferromagnetic Heisenberg-like chains should display an energy gap between singlet ground state and excited continua. This behavior has been confirmed numerically, and it has been shown that the energy gap is of a magnitude to be observable experimentally. The phenomenon has captured the interest of experimental groups in neutron scattering and magnetism. A recent experimental study obtains very good experimental agreement with the theoretical T=0 magnetization curve obtained numerically by Parkinson and Bonner.1,2 An explanation will be provided for the unusual phase diagram and other anomalous features observed by the authors of Ref. 2. Numerical susceptibility studies of Heisenberg antiferromagnetic and general XXZ spin-1 chains will be presented, and discussed in terms of a novel quantum-classical cross-over phenomenon.2 Finally, a comparison will be made of T=0 magnetization isotherms for several spin-1 chains, including the Takhtajan–Babujian chain and the chain with pure biquadratic interactions.
Orbital polarization transition metal oxides (invited) (abstract)
Authors: Norman M. R.
Published: July 2002

One of the most controversial topics in condensed matter physics concerns the nature of the electronic structure of transition metal oxides. Unpolarized band structure calculations predict metallic ground states for these oxides, whereas experimentally they are insulating. This led to the development of the Mott insulator picture for these materials fifty years ago. Later, though, Slater’s group showed that by taking into account spin polarization, one could produce insulating gaps from band theory for MnO and NiO. The gaps are too small, the size of the gap actually being determined by the Mott-Hubbard U, but this led to a hope that on symmetry grounds one could also obtain gaps for the other two metal oxides, FeO and CoO. In these two cases, there is an unquenched orbital moment, which might be important for this purpose. Recently, a theory has been developed by Erickson, Brooks, and Johansson for including an orbital polarization correction to local spin density theory.1 The author in turn showed that such a correction can lead to insulating gaps for CoO and FeO.2 A discussion of these results, including the calculated sizes of the moments, as well as related work on insulating mixed valent TmSe, will be presented in this paper.
Cu-added Nd-Fe-B anisotropic powder for permanent magnet use
Authors: Sakamoto H. , Fujikura M. , Mukai T.
Published: July 2002

A packed-rolling method has been applied to fabricating Nd-Fe-B anisotropic powder from melt-spun ribbons; the method involves packing the ribbon materials in a steel container under a vacuum and rolling the pack at around 700 °C. The hot-rolled materials, which form a bulk in a plate-shape, exhibited a strong deformation-induced magnetic anisotropy with the easy magnetization axis parallel to the plate-thickness direction. The anisotropic powders can be obtained by pulverizing the hot-rolled materials. Hot rolling to an 82% reduction in ribbon thickness produced the following magnetic properties: iHc = 12.3 kOe, Br = 12.3 kG, and (BH)max = 36.8 MGOe for a conventional Nd14Fe80B6 alloy. We have found that additions of Cu increase the coercive force up to 19 kOe and result in a remarkable improvement in thermal stability of the anisotropic powders. The result is interpreted in terms of the suppression of grain growth by Cu additions.
Magnetic hardening in as-cast Nd-rich Nd-Fe-B magnets
Authors: Singleton E. W. , Tsoukatos A. , Zhang Y. , Hadjipanayis G. C.
Published: July 2002

The microstructure of as-cast Nd-rich Nd-Fe-B alloys has been studied in detail and correlated with their magnetic hysteresis behavior. A hard magnetic phase with a Curie temperature around 250 °C and a coercivity of 5.2 kOe has been observed in an arc-melted Nd80Fe15B5 sample. Annealing at around 600 °C led to a transformation of this phase to Nd2Fe14B which is present in the form of small crystallites randomly disbributed in a nonmagnetic Nd-rich matrix, resulting in coercivities greater than 14 kOe. The Stoner and Wohlfarth model of single domain particles has been used to discuss the large coercivities.     
Magnetoelastic properties of terbium-dysprosium-iron compounds
Authors: Jenner A. G. , Lord D. G. , Faunce C. A.
Published: July 2002

Microstructure, magnetic, and magnetoelastic behavior measurements under varying conditions of compressive stress have been carried out on as-cast samples of the alloy system TbxDy1−xFe1.9 (x=0.27, 0.3, and 0.5) prepared by a contained float-zone growth technique.
Characterizing chaos in magnetostatic modes
Authors: Carroll T. L. , Pecora L. M. , Rachford F. J.
Published: July 2002

The nonlinear behavior seen in ferromagnetic resonance experiments in yttrium iron garnet (YIG) has long proven difficult to model. Time series analysis techniques from nonlinear dynamics have been applied to characterize chaos seen in an experiment involving an YIG film. It is found that this characterization reveals possible shortcomings in some of the common models.
Cohesion and promotion energies in the transition metals: Implications of the local-density approximation
Authors: Watson R. E. , Fernando G. W. , Weinert M. , Wang Y. J. , Davenport J. W.
Published: July 2002

The accuracy of the local-density (LDA) or local-spin-density (LSDA) approximations when applied to transition metals is of great concern. Estimates of the cohesive energy compare the total energy of the solid with that of the free atom. This involves chosing the reference state of the free atom which, as a rule, will not be the free atom’s ground state in LDA or LSDA. Comparing one reference state versus another, e.g., the dn−1s vs dn−2s2 for a transition metal, corresponds to calculating an s-d promotion energy Δ, which may be compared with experiment. Gunnarsson and Jones (GJ) [Phys. Rev. B 31, 7588 (1985)] found for the 3d row that the calculated Δ displayed systematic errors which they attributed to a difference in error within the LSDA in the treatment of the coupling of the outer-core electrons with the d versus non-d valence electrons. This study has been extended to relativistic calculations for the 3d, 4d, and 5d rows and for other promotions. The situation is more complicated than suggested by GJ, and its implications for cohesive energy estimates will be discussed.
Deposition of Fe-N films by means of an opposed targets sputtering type plasma source
Authors: Hoshi Y. , Naoe M.
Published: July 2002

Synthesis of Fe-N thin films were attempted by means of an opposed targets sputtering type plasma source. In this film preparation technique, both ions and neutral particles which are extracted from the plasma source are deposited on the substrate directly. Film deposition rate changes with substrate bias voltage Vs and takes a maximum value at a Vs around −30 V. This is mainly due to the increase in the amount of incident ions as the Vs decreases from 20 V to −30 V. The ion ratio in the deposited particles is estimated to be about 1/3 from the changes in the deposition rate with Vs. The increase in the amount of incident ions and in their energy suppresses the growth of the crystallites in the film significantly, which results in the decrease in coercive force of the films. The films deposited at a proper condition has a saturation magnetization of about 1700 emu/cc, coercive force below 0.8 Oe, and permeability at 1 MHz above 3000.
Surface doping with Al in Ba-hexaferrite powders (abstract)
Authors: Turilli G. , Paoluzi A. , Lucenti M.
Published: July 2002

Barium M-hexaferrites were intensively studied in order to improve their magnetic characteristics for application as permanent magnets using different ion substitutions. However, substitutions that improve the BHmax energy product have not been found. We propose a new method in order to modify the extrinsic magnetic characteristics of Ba-hexaferrite powders without reducing drastically the magnetization and the magnetic anisotropy. This method consists in the surface doping of the hexaferrite particles, giving as a result a modification of the energy pinning of the domain walls at the grain boundary. Ba ferrite powders having a mean diameter of 3.2 μm have been dry mixed with Al2O3 powders with a diameter <0.5 μm. From the mixed powder a series of 10 cylindrically shaped samples was obtained by isostatically pressing the powders. The samples were thermically treated from 900 to 1200 °C, together with 10 cylindrical samples of pure hexaferrite, for 1 h each. For all the samples we have measured the Curie temperature (Tc), the anisotropy field (HA), the coercive field (Hc), and the saturation magnetization σ. The main results are that up to 1000 °C the Al diffusion is mainly localized at the surface of the grain so that the main part of the grain is undoped as confirmed by the Tc and HA values that are the same as those found in pure hexaferrites. From 900 to 1000 °C the saturation magnetization decreases of the 3% while Hc increases of the 9% with respect to the pure hexaferrite. This result seems to confirm the validity of the proposed method. Above 1000 °C Al begin to diffuse in the grain and above 1200 °C it is possible to say, from thermomagnetic analysis, that Al has diffused uniformly throughout the grain. In this last temperature range the Al substitution leads to a 10% reduction in σ as expected1 while Hc only increases 12%. These preliminary results suggest that the method of surface doping of the powders could be used in order to increase or decrease the H values without strongly influencing the σ values.
Magnetization of Ce0.8La0.2Ru2Si2 single crystal under pressure (abstract)
Authors: Voiron J. , Haen P. , Lapierre F. , Lejay P. , Flouquet J.
Published: July 2002

Magnetization measurements performed on a single crystal of Ce0.8La0.2Ru2Si2 with H parallel to the tetragonal c axis are reported. This alloy exhibits a long-range modulated order below 5.6 K. Below this temperature, anomalies are observed in both the M-vs-H curves at constant T and the M-vs-T curves at constant field. These anomalies agree with the multiphase (H,T) diagram recently determined by neutron experiments. On applying a hydrostatic pressure (P) a rapid decrease of TN is observed, in agreement also with neutron data, and the evolution of the (H,T) phase diagram can be determined. For P≳3 kbar, the M-vs-H curves measured above TN show an inflection (maximum of dM/dH at a field HM similar to that observed in the nonordered compound CeRu2Si2 and to those observed above TN in Ce1−xLaxRu2Si2 alloys containing a small concentration of La (x≤0.13). This effect is certainly related to the existence of short-range correlations. The variation of the value of M at HM with P (validity of the scaling previously observed for CeRu2Si2) is discussed.
High-resolution electron microscopy analysis of Nd-Fe-B-type sintered magnets
Authors: Liu Jinfang , Luo Helie , Pan Shuming , Sun Yuan , Shi Guoshun
Published: July 2002

Transmission electron microscopy (TEM) analysis showed that the grain-boundary thin layer is a kind of Nd-rich phase. The high-resolution micrographs of the grain-boundary thin layer were obtained. The lattice constant c of the matrix phase is measured as 12.2 Å. The grain-boundary thin layer is coherent with the matrix.
Effect of the coupling agent on the properties of NdFeB injection molding magnets (abstract)
Authors: Chen L. K. , Hung Y. C. , Ko W. S.
Published: July 2002

In the manufacturing of injection molded magnets made from NdFeB (MQ) powder and nylon-12, coupling agents are normally added to prevent NdFeB powders from oxidation in the period of injection processes. The reheological behavior of NdFeB pellets related to the quantities and kinds of coupling agents. The effects of coupling agents on the NdFeB injection molded magnets are seldom presented in literature1 and will be the sub-seldom presented in the literature1 and will be the subject of this work. Five coupling agents (two belong to silane series, two belong to titanate series, and one belongs to the zircoaluminate series) have been investigated and evaluated. Differential scanning calorimetry (DSC) data show that 0.5 wt. % of isopropyle tri(dioctyl)-pyrophosphate titanate has the best result for oxidation resistance. On the other hand, the compression strength and reheological behavior of the bonded magnets are dependent on the kinds of coupling agents. The zircoaluminate coupling agent induces 30% enhancement of compression strength better than other coupling agents. Titanate coupling agents have a lower injection temperature. It demonstrated that the titanate coupling agent can effectively reduce the relative viscosity of the compounds. In the meantime, we did a 100-h environmental test at 80 °C, 90% RH. Experimental results also show that the titanate coupling agents have best anticorrosion ability. Magnetic properties of bonded magnet Br=5.7 kG, Hc=4.5 kOe, iHc=8.4 kOe, and (BH)max=6.7 mGOe can be obtained. Results suggested the titanate coupling agent is the best choice in this study.
Self-organized criticality in magnetic domain formation (invited) (abstract)
Authors: Suhl H.
Published: July 2002

Certain large dissipative systems prepared in an unstable state or subject to destabilizing forces do not necessarily settle in the lowest, most ordered state. Frequently such systems have a huge number of metastable states available to them, and in cascading down from the unstable configuration, they tend to ‘‘get stuck’’ in an ‘‘only just’’ metastable state with characteristics sufficiently distinctive to justify the name ‘‘self-organization.’’ Such a configuration is critical in the sense that deviations from it die out according to a power law without time or length scales, and with a critical exponent. Magnetic domain structures seem to furnish excellent examples of this behavior; two of these will be discussed in detail. A major advantage of this state is that it can be successfully computed using only the simplest cellular automata algorithms to crudely mimic the physics. The significance to some aspects of the magnetic recording process will be discussed.
Molecular-dynamics simulation of structural anisotropy in glassy metals and its relationship to magnetic anisotropy
Authors: Tomida T. , Egami T.
Published: July 2002

Creep-induced magnetic anisotropy in metallic glass was investigated using a molecular-dynamics simulation. A model binary glass structure of 2048 particles interacting via Lennard–Jones potentials was creep deformed below its glass transition temperature. Creep deformation resulted in the bond-orientational anisotropy (BOA) within the first nearest-neighbor shell with a large sixth-order spherical harmonic component. The magnetic anisotropy estimated on the basis of the point-charge model shows that a small two-fold component of the BOA can induce a sizable magnetic anisotropy in amorphous rare-earth alloys.
Effects of pressure on spin fluctuations and the exchange interaction in La2CuO4 as determined by two-magnon Raman scattering (abstract)
Authors: Dierker S. B. , Aronson M. C. , Dennis B. S. , Cheong S.-W. , Fisk Z.
Published: July 2002

We have measured the two-magnon Raman scattering spectrum of magnetic La2CuO4 at pressures of up to 100 kbar. Analysis of the moments of the two-magnon line shape indicates that the renormalization parameters resulting from spin fluctuations are essentially pressure independent in this pressure range. Our results provide the first direct determination of the pressure dependence of the in-plane exchange coupling constant J. The pressure dependence of J is compared with that of the Néel temperature and discussed in the context of recent theories for quasi-two-dimensional magnetic systems.
Dependence of magnetoresistive head readback characteristics on sensor height
Authors: Wallash A. , Salo M. , Lee J. K. , Heim D. , Garfunkel G.
Published: July 2002

The microtrack profile and bias point of a magnetoresistive (MR) head play a fundamental role in determining the full track response. In this paper the stripe height dependence of these properties is studied. The magnetic center of the MR head is found to approach the physical center, and microtrack side slopes become steeper and more equal as the stripe height is decreased. These experimentally observed trends can be understood using a simple model based on anisotropic flux propagation in the MR sensor.
The enhancement of Fe hyperfine field with Mn addition in a-Fe(80−x−y)NiyMnxB12Si8 alloys
Authors: Sharma Nirupama , Nigam A. K. , Prasad Shiva , Shringi S. N. , Chandra Girish , Krishnan R.
Published: July 2002

Amorphous Fe(80−x−y)NiyMnxB12Si8 alloys with 0≤x≤1 and 20≤y≤50, have been studied using Mössbauer spectroscopy at 77 K. It has been found that the sharp rise in the alloy magnetic moment for certain specific values of x and y can be best explained if both μFe and μNi increase for those particular samples. However, the increase in μNi (∼80%) is much larger than that in μFe (∼5%).
Zero-field muon-spin relaxation in (Y1−xPrx)Ba2Cu3Oy
Authors: Dawson Wayne K. , Lam John C. , Boekema C. , Lichti Roger L. , Cooke D. Wayne , Crow Jack E.
Published: July 2002

Results of zero-field muon-spin-relaxation (μSR) experiments of Y1−xPrxBa2Cu3Oy [(Y1−xPrx)1237; 0.5<x≤1.0, y=7; x=1, y=6] are examined in light of the observed magnetism and the candidate μ-probe site. A μSR frequency signal near 2 MHz (extrapolated to 0 K) has been found for 0.5≪x≤1, y=7, and z=0.08, y=7, representing a local magnetic field of about 0.15 kOe at the established B2 μ-probe site. For x near 1.0 (z=0), a shift in μSR frequency of about −0.4 MHz has been observed near TN2(x). Between TN2 and TN1, the magnetism is due to antiferromagnetic ordering of the Cu moments in the CuO2 planes. No frequency shifts have been observed for Pr1236 at its TN2. The anomalous frequency shift for (PrxY1−x)237 can be due to additional Cu-chain antiferromagnetism and/or attributable to additional Pr magnetism.
Long range magnetic order in nonpercolating granular Fe-SiO2 thin films (abstract)
Authors: Carey M. J. , Parker F. T. , Berkowitz A. E. , Leroux C.
Published: July 2002

Granular Fe-SiO2 thin films were prepared by low rate (∼0.3 Å) sputtering onto substrates rotating above separate Fe and SiO2 targets. Thin silicon nitride ‘‘windows’’ in the substrates permitted transmission electron microscopy measurements on the same films characterized by other techniques. Low Fe concentration, nonpercolating films contained well dispersed ∼40 Å spheres of pure Fe with a narrow size distribution, as previously reported for granular films prepared from separate sources.1 Although Hc showed a strong temperature dependence, as did films prepared at high sputtering rates from a single composite target, the other magnetic properties of these films were very different. The maximum Hc values at 4.2 K were much lower. The peak in Hc occurred at a significantly lower vol % Fe. The hysteresis loops were square with remanence ratios ≳0.90 at temperatures between 4.2 and 296 K. Furthermore, Lorentz micrographs taken at 296 K showed stable domain structures and ripple patterns. This strong evidence for cooperative magnetic behavior is difficult to reconcile with arrays of nonpercolating particles far above their nominal blocking temperatures. The possible role of dipolar and exchange interactions among these particles will be discussed.2
Magnetic properties of electrochemically produced Cu-X (X=Ni, Fe,and Co) artificial superlattices (abstract)
Authors: Bennett L. H. , Lashmore D. S. , Swartzendruber L. J. , Soltani E. , Beauchamp C. E.
Published: July 2002

Recently it has been shown1 that electrochemically produced Cu/Ni artificial superlattices can exhibit magnetic properties comparable (or superior) to samples produced by traditional processing techniques. Measurements will be presented showing the relationship between the applied potential during nickel deposition and the curvature of the saturation magnetization versus temperature curve, and also linking the applied potential to the recently discovered2 magnetic aftereffect produced by rapidly switching the applied field from a value for which magnetic saturation is achieved to a value near the coercive force. Further data will be presented for the first time on magnetic behavior of artificial superlattices consisting of fcc copper and fcc cobalt.
Observations of magneto-optic phase contrast using a scanning laser microscope
Authors: Heyes N. A. E. , Wright C. D. , Clegg W. W.
Published: July 2002

A scanning laser microscope (SLM) has been built which is capable of observing magnetic structure via ‘‘conventional’’ Kerr imaging techniques and a ‘‘novel’’ magneto-optic phase contrast approach. This latter contrast mode highlights magnetic transitions, rather than domains themselves. In this paper we present results of observations in TbFeCo samples using this phase contrast technique and assess its possible application as a read-out mechanism for magneto-optic recording systems.
The effect of lamination on the domain structure of finely patterned amorphous thin films
Authors: Thiele Alfred A. , Bowman Chris C.
Published: July 2002

We have examined the domain structure of thin-film stripes of soft magnetic material of varying width using the Bitter pattern technique. Laminated and nonlaminated films on glass substrates and magnetic bubble films have been examined. The structures we observe occur only in the presence of an applied field in the plane generally growing in intensity according to the component of this field in the direction of the stripe. The structures appear at the narrow points of the stripes appearing to be due to flux leaving and reentering the stripes at these points. The results are in part explained qualitatively in terms of the theory of Van Den Berg as extended by Bryant and Suhl. When used as a magnetic bubble propagator, the presence of the observed domains explains features of the margin plots which are otherwise unexplained.
The process-controlled magnetic properties in nanostructured Fe/Ag composite films
Authors: Zhang Y. X. , Liou S. H. , DeAngelis R. J. , Lee K. W. , Reed C. P. , Nazareth A.
Published: July 2002

Nanostructured Fe/Ag composite films were prepared by magnetron sputtering using a single target. Correlations between the microstructure and magnetic properties, in particular the effects of cluster-size distribution in the films, are discussed. The cluster-size distribution was calculated by analyzing the width and shape of the x-ray-diffraction peaks. The average cluster size in the films increased from 42 to 295 Å and from 38 to 320 Å in the systems of 41 and 27 vol % of Fe, respectively, as the substrate temperature increased from 100 to 500 °C. The maximum magnetic coercivity, as high as 900 Oe, has been observed in the film with 27 vol % of Fe, which was prepared at a substrate temperature of 400 °C.
FMR studies of single Fe layers sandwiched by Ag (abstract)
Authors: Hurdequint H.
Published: July 2002

We report a systematic FMR study, at X band, of magnetic films constituted of (Ag‖single Fe layer‖Ag) sandwiches deposited by sputtering on heated mica substrates (base Ag layer 550 Å thick; top one 275 Å). The conditions of deposition used enable to get a polycrystalline Ag base layer with large lateral size (∼2000 Å) of the crystallites, as determined using scanning tunneling microscopy, and a preferred (111) orientation perpendicular to the film. The resonance spectrum is studied as a function of the orientation [θH=(N̂,Ĥ) with respect to the film normal N̂] of the applied dc field H in a plane perpendicular to the film: (i) for the ultrathin Fe layers (<100 Å) the angular variation Hres(θH) of the unique mode observed can be essentially accounted for in terms of (4πM−HA), i.e., the total component of perpendicular uniaxial anisotropy where HA=2K/M is a uniaxial anisotropy field (N̂ easy axis). From the observed proportionality of HA to 1/tFe it is deduced Ks≂1.45±0.1 erg/cm2 for the value of the effective interface-induced anisotropy of the (Ag/Fe) interface. (ii) Additional information on the interface pinning parameter is provided, in the ‘‘thick’’ Fe layers (≳400 Å), by the observation, besides the principal mode, of a higher field mode identified to a surface exchange mode. At low temperatures more complex phenomena are observed (shift of Hres and line broadening) which are interpreted, as already suggested,1 in terms of the dissipative part of the magnetic interfacial coupling at the Fe/Ag interface (to be associated to the diffusion of the microwave induced magnetization of the conduction electrons from one metal to the other).
Observability of a quasilinear temperature dependence of the magnetization in a semi-infinite ferromagnet (abstract)
Authors: Rado G. T. , Hicken R. J.
Published: July 2002

Current theory [G. T. Rado, Phys. Rev. B 40, 407 (1989)] shows that the existence of magnetic surface anisotropy leads to surface spin waves which can provide a mechanism for a quasilinear temperature dependence of the magnetization (MT) near the surface of a semi-infinite ferromagnet. Since volume spin waves as well as surface spin waves are excited thermally, we now generalize this theory in two ways. First, we include in the calculation the effects of both surface and volume spin waves, and second, we include the effects of both of the surface anisotropy constants Kss and Ks. The fractional magnetization deviation (M0−MT)/M0 caused by the volume spin waves competes, of course, with that caused by the surface spin waves. We find that, for all allowed values of Ks and Kss, it is mostly at very low temperatures that the contribution to (M0−MT)/M0 arising from surface spin waves is comparable to the contribution to (M0−MT)/M0 arising from volume spin waves. This result depends on the assumption that the material parameters are independent of position throughout the sample volume. A full account of this work will be published elsewhere.
Nonstationary dynamics in a two-dimensional spin glass
Authors: Schins A. G. , Arts A. F. M. , de Wijn H. W. , Leylekian L. , Vincent E. , Paulsen C. , Hammann J.
Published: July 2002

Aging is observed in the two-dimensional short-range Ising spin glass Rb2Cu0.78Co0.22F4 (Tc = 0 K) by means of low-frequency ac susceptibility and zero-field-cooled (ZFC) magnetization measurements. Below the freezing temperature (∼3.5 K), slow logarithmic relaxations are found in both the in-phase and out-of-phase ac susceptibility, and a waiting time dependence is observed in the relaxation of the zero-field-cooled magnetization. No saturation of the relaxations was found. The results suggest that the aging is governed by activated dynamics at length scales smaller than the equilibrium spin-glass correlation length.
Concentration dependence of the random field crossover scaling in FexZn1−xF2
Authors: Ferreira I. B. , King A. R. , Jaccarino V.
Published: July 2002

The proportionality between the field-induced shift ΔTc(H) of the transition temperature Tc(H) and the root-mean-square (rms) random-field hRF was studied over a wide range of concentration (0.31≤x≤0.84) in the nearly ideal random-field Ising model (RFIM) system FexZn1−xF2. Tc(H) was determined experimentally from the optical birefringence Δn, for which d(Δn)/dT exhibits a peak proportional to the magnetic specific heat. For all x studied, Tc(H) was found to shift from the H=0 transition at TN as ΔTc(H)ΔTc(H)= cTN h2/φRF as predicted, with φ=1.42±0.03 the universal random exchange to RFIM crossover exponent, after a mean-field correction bH2. The nonuniversal quantity c was found to be of order unity as expected, but slightly x dependent.
Frustration and short range magnetic correlations in the pyrochlore Y2Mn2O7 (abstract)
Authors: Reimers J. N. , Greedan J. E. , Subramanian M. A. , Kremer R. K. , Gmelin E.
Published: July 2002

The bulk magnetic susceptibility of Y2Mn2O7 is suggestive of ferromagnetic order, θc=+40 K, apparent Tc=25 K. However, both dc and ac susceptibility data show a broad maximum near 6 K which is frequency and field dependent. Heat capacity studies to 2 K show no evidence for long range magnetic order. Also, neutron scattering data indicate the presence of short range correlations. These results are compared to mean field theory predictions for the highly frustrated 16c sites in the pyrochlore lattice.
Concentration scaling of the specific heat in the d=3 random exchange Ising model system FexZn1−xF2
Authors: Ferreira I. B. , Cardy J. L. , King A. R. , Jaccarino V.
Published: July 2002

Linear magnetic birefringence Δnm was used to study the concentration dependence of both the total magnetic specific heat Cm and critical amplitudes in the random exchange Ising model (REIM) system FexZn1−xF2. We find the proportionality between Δnm and the magnetic energy Um is x independent for 0.24≤x≤1.0, since Δnm scales with x2 as does Um. However, the critical part of Cm is found to decrease with dilution very much faster than x2. To explain this, a scaling form is derived which describes the x-dependent crossover from pure Ising to REIM with a crossover exponent φ=α, the pure Ising specific heat exponent. The critical amplitudes A± of Cm = A±‖t − tn‖−α̃ are shown to scale as A±(x)A±(x)∼ (1 − x)(α̃−α)/(φ)∼ (1 − x)−1.9(3), using the experimental REIM value of α̃=−0.09(3), and theoretical value of α=0.105(7). Good agreement between theory and experiment is found.
Magnetic structures of actinide materials by pulsed neutron diffraction (invited)
Authors: Lawson A. C. , Goldstone J. A. , Huber J. G. , Giorgi A. L. , Conant J. W. , Severing A. , Cort B. , Robinson R. A.
Published: July 2002

We describe some attempts to observe magnetic structure in various actinide (5f-electron) materials. Our experimental technique is neutron powder diffraction as practiced at a spallation (pulsed) neutron source. We will discuss our investigations of α-Pu, δ-Pu, α-UD3, and β-UD3. β-UD3 is a simple ferromagnet: Surprisingly, the moments on the two nonequivalent uranium atoms are the same within experimental error. α-UD3, α-Pu, and δ-Pu are nonmagnetic, within the limits of our observations. Our work with pulsed neutron diffraction shows that it is a useful technique for research on magnetic materials.
A converter-type magnetometer using amorphous ribbon or wire
Authors: Kozak Marek Z. , Misiuk Eugeniusz , Kwiatkowski Waldemar
Published: July 2002

The accurate and quick-response magnetometer presented here is composed of a resonant circuit with an amorphous core, an operational amplifier, and a voltage-current converter. Nonmagnetostrictive amorphous ribbons or wires are used in the straight form for sensing strength and direction of the dc magnetic field. The range having good linearity strongly depends on the converter current and the demagnetizing field of the core. The maximum sensitivity was around 20 V/Oe and noise level around 10 mV/Oe depending on the alloy composition. A simple electrical model of the magnetometer also has been created. Experimental and analytical results obtained from this model proved to be comparable to that used in the computer-aided designing. A converter-type magnetometer is suitable for applications in the magnetic field and dc current sensors, in displacement transducers, and others.