bluuebunny/crossref_metadata_2025 huggingface dataset:
A system of three Josephson junctions
Authors: Strenski P. N. , Doniach S.
Published: July 2002

A system of three Josephson junctions driven by a direct current is modelled and studied both numerically and with a perturbative approach. The results are compared and the relation with experiment is discussed. Hysteretic behavior is observed and predicted with the perturbation. Chaotic behavior is also observed and analyzed. Extensions of the approach to other models is discussed.
Double scattering by randomly oriented long cylinders
Authors: Cohen Ariel , Cohen Leonard D. , Haracz Richard D. , Egert Smadar
Published: July 2002

Double scattering lidar events involving long cylindrical particles are discussed. The scatterers are allowed to be randomly oriented and the geometry required in the scattering solution is described in detail. The geometry is general, made to be applicable to any type of particle for which the single scattering matrix is provided, relative to the main axis of the scatterer. Results of the double scattering calculations are presented for the penetration of the lidar light into clouds of different optical depth τ (τ≤0.5).
Measurement of central nickel density in Doublet III plasmas with a soft x-ray diode array
Authors: Groebner R. J. , Jahns G. L. , Ejima S. , Hsieh C. L.
Published: July 2002

An array of soft x-ray diodes has been used to obtain central nickel densities for discharges in the Doublet III tokamak, during operation with an inconel primary limiter, in which nickel L-line radiation dominated the diode signals. The nature of the diode signals is determined primarily by comparison with soft x-ray spectra. The contribution of the continuum portion of the spectra to the central diode signal can be calculated and compared to the observed signal. When the diode signal is dominated by nickel L-line emission, the observed signal is considerably larger than the calculated continuum contribution. Chordal data from the array of diodes are inverted to provide the spatial profile of soft x-ray emission. Because the diodes are absolute detectors of radiation, the soft x-ray emission profile is used to obtain the absolute nickel concentration and density profile in the center of the plasma. A computer code, including over 100 nickel L-line transitions, has been developed to obtain the nickel density. The nickel L-line cooling rate, calculated with the code, is presented. The nickel density obtained by this technique agrees well with that obtained from the Kα line intensity measured with a soft x-ray spectrometer and that obtained from a bolometric measurement of central radiated power coupled with a coronal equilibrium model of the radiation.
Determination of the frequency spectrum of a quartz crystal and oscillator
Authors: Koehler D. R.
Published: July 2002

An alternative explanation for the reported behavior of a tuned L-C quartz-crystal oscillator is given. This explanation is based on the nonlinear behavior of electronic oscillators. Controlled coupled mode behavior is possible in a single stage allowing precision harmonic and subharmonic frequency generation.
The effect of metal work function on current conduction in metal-insulator-semiconductor tunnel junctions
Authors: Camporese D. S. , Pulfrey D. L.
Published: July 2002

The effect of metal work function on current conduction in metal-insulator-semiconductor (MIS) tunnel junctions has been investigated both experimentally and theoretically. MIS junctions on 2 and 10 Ω cm silicon substrates have been fabricated with both aluminum and magnesium contacts. It is shown that in the region of tunnel-limited current conduction, device characteristics are dependent on the metal work function. The results are in good agreement with predictions from a comprehensive analytical model. The implication of this result for MIS-inversion layer solar cells, where contact current densities are much larger than in transparent metal MIS devices, is examined.
Effect of Coulomb scattering in n-type silicon inversion layers
Authors: Manzini S.
Published: July 2002

Experimental results of surface mobility (effective mobility) in n-channel metal-oxide-semiconductor field-effect transistors subjected to high electric field stress are presented. The electron mobility limited by Coulomb scattering is extracted from the experimental data comparing the measured effective mobility before and after the stress. The low-temperature data (T=77 K) are discussed in terms of the Stern–Howard two-dimensional Coulomb scattering theory in the electric quantum limit approximation.
Thermal gradient distributions in trapped energy quartz resonators
Authors: Valentin Jean-Pascal
Published: July 2002

An improved thermal model of bulk acoustic wave quartz resonators, which is different from the ‘‘infinite plate’’ model, is proposed. It takes into account the actual boundary conditions and energy trapping. Inside the resonator, three parts are distinguished: an internal source part, a transfer part, and an exchange part. The thermal steady state is studied, the model validity limits being pointed out. Three typical parameters are proposed to specify the resonator thermal state. Principal results for coated and electrodeless quartz resonators are given. Especially, the value of thermal radial gradient is computed and its share in the oscillator’s frequency shifts due to transient thermal phenomena is pointed out.
Annealing of zinc-implanted GaAs
Authors: Barrett N. J. , Grange J. D. , Sealy B. J. , Stephens K. G.
Published: July 2002

A study of ion-implanted zinc in GaAs has been made using three annealing techniques: e-beam, graphite strip heating, and furnace annealing in an arsine ambient. The highest hole concentrations, 7–8×1019 cm−3, were obtained using electron-beam annealing. Graphite strip heating and electron-beam annealing were able to electrically activate 100% of the implanted dose. The effect of strain on the activation of the zinc has been demonstrated by comparing chemical-vapor-deposited Si3N4 with reactively evaporated AlN encapsulants.
New injection mode infrared detector
Authors: Coon D. D. , Gunapala S. D.
Published: July 2002

A new injection pulse phenomenon is reported which may have a variety of applications including the detection of infrared (IR) radiation. Injection current pulses were observed in simple circuits containing forward biased silicon p-i-n diodes at liquid-helium temperatures. Under exposure to IR radiation, the pulse rate was observed to increase approximately linearly with increasing incident IR intensity. The substantial voltage, current, and power output may eliminate the need for on-chip amplifiers in many applications. Figures of merit are discussed, although the performance of the devices has not yet been optimized.
Optical properties and photovoltaic effect in Pb2CrO5 thin films
Authors: Toda Khoji , Morita Shinichi
Published: July 2002

Optical properties and the photovoltaic effect in Pb2CrO5 thin films, which are prepared by an electron-beam evaporation technique, are investigated. From the main peaks of the x-ray diffraction (XRD) patterns, which depend on the preparation condition, thin films are classified into three types: (1) (020), (2) (310), and (3) (200). The sample with a (310) main reflection has a similar XRD profile to that of the bulk material. A device to measure the photovoltiac response in the thin films has one pair of semitransparent Au electrodes on the same surface. All the Pb2CrO5 thin films had a photovoltaic response. The (310) sample shows the largest photosensitivity. In this sample the saturation photovoltage is 1.16 V at a light intensity of 23.25 mW/cm2. The absorption constant (α) of thin films in the visible region ranges between 4×103 and 1×105 cm−1. A band-gap energy of 2.3–2.4 eV is obtained from both plots of α2 and photovoltage as a function of photon energy.
Characterization of GaAs films grown by metalorganic chemical vapor deposition
Authors: Swaminathan V. , Van Haren D. L. , Zilko J. L. , Lu P. Y. , Schumaker N. E.
Published: July 2002

We studied undoped GaAs films grown by metalorganic chemical vapor deposition in a vertical geometry atmospheric pressure reactor. Our results on the surface morphology, carrier concentration and conductivity type and low-temperature photoluminescence spectra of the films, studied as a function of substrate temperature and As/Ga flux during growth, are generally in agreement with previous studies. In addition, we also report the effect of rotation speed of the substrate during growth. It is found that lower speeds give higher defect density and less n-type films and most notably enhance a defect exciton line at 1.5119 eV. From the free-to-bound transitions and from the dependence of the intensities of the exciton lines on growth temperature and As/Ga flux we inferred that the acceptors in our films are C, Zn, Mg and donors are those substituting on Ga sites.
Model experiments describing the microcontact of ZnO varistors
Authors: Schwing Ulrich , Hoffmann Bernd
Published: July 2002

A macroscopic model of the microcontacts in ceramic ZnO varistors was prepared by using ZnO single-crystal plates and a layer of the usual oxide additives. The electrical properties of these model contacts are very similar to those of the microcontacts. Measurements on one-sided macrocontacts require the assumption of a ‘‘buried’’ potential barrier underneath the surface of the ZnO, the formation of which is explained by the distribution of the atomic defects and the dopants in the ZnO. Based on this idea, the I-V characteristics in the prebreakdown region and the breakdown voltage have been calculated.
Recording and reproducing process of a perpendicular magnetic head
Authors: Tanabe S. , Iwasaki S.
Published: July 2002

The results from a finite-element analysis of perpendicular magnetic recording are presented. The mechanism responsible for a striking improvement of recording and reproducing sensitivity by the addition of a Ni-Fe soft magnetic underlayer to the Co-Cr medium is described. We have calculated the flux flow for perpendicular recording using a main pole/auxiliary pole head. In the presence of an underlayer, flux density in the main pole is enhanced about ten times in both the recording and reproducing processes. Another feature of the auxiliary-pole-driven head with double-layer media is that flux density is highest at the tip of the main pole. Results for main pole flux as a function of head to medium spacing are also presented.
Ring head recording on perpendicular media: Output spectra for CoCr and CoCr/NiFe media
Authors: Stubbs D. P. , Whisler J. W. , Moe C. D. , Skorjanec J.
Published: July 2002

The recording density response for sputtered CoCr (thickness=0.5 μm) and CoCr/NiFe (t=0.25 μm/0.5 μm) as well as evaporated CoNi (t=0.12 μm) and Co surface-doped iron oxide particulate media has been measured by reading and writing with Mn-Zn ferrite heads (gap length=0.375 μm, track width=37 μm) in contact with the media. Measurements to 200 kfc/i (thousand flux changes per inch) show a gap null around 115 kfc/i. The data have been normalized by dividing out the head sensitivity to obtain the value of spacing plus transition width (d+a) for the various media. For the CoCr media this value varied from 0.075–0.088 μm; for CoNi, 0.100 μm, and for the particulate medium, 0.163 μm. In addition, testing with a larger gapped Mn-Zn ferrite head (g=2.43 μm) shows that the head fields are distorted by the soft magnetic underlayer in dual layer CoCr/NiFe samples when the gap length is large compared to the distance to the underlayer.
Epitaxial growth of Co-Cr films and their characterization
Authors: Leu C. , Chen G. , Sivertsen J. M. , Judy J. H.
Published: July 2002

In recent years, much attention has been devoted to the study of Co-Cr thin films. There are mainly two different models of magnetization mechanisms which have been proposed in the literature, typified by the work of Iwasaki et al. and that of Wielinga et al. To further clarify this matter, epitaxial Co-Cr films have been grown by rf sputtering onto (001) MgO single-crystal substrates. The cleanliness of the substrate and target were found to be the most critical parameters. The substrate bias and too high a substrate heating temperature were also found to be unfavorable for epitaxial growth of Co-Cr films. These epitaxial films were characterized by x-ray diffraction, electron diffraction, Auger spectroscopy, VSM, and torque magnetometer. It is found that low argon pressure ranging from 1 to 2 mTorr favors the epitaxial growth of Co-Cr films. The values of Ku, K1 and Hk of the epitaxial films are higher than those of the polycrystal Co-Cr films.
Use of ion-beam sputtering in the production of thin-film magnetic heads (abstract)
Authors: Hughes Bill
Published: July 2002

Tests have been run using Commonwealth Scientific Corporation equipment to determine the advantages of ion-beam sputtering over reported electroplating, EB vapor deposition, and RF sputtering in the production of thin-film magnetic heads. Advantages of ion-beam sputtering relate to stronger adhesion of films achieved at lower substrate temperatures. One relative disadvantage is the impurity content inherent to the sputtering process. Variables which were adjusted to achieve optimal results (permeability, anisotropy, magnetic strength, internal stress of the film) were the substrate to target angle, temperature, target (Ni, Fe) content and a magnetic depositional field. Sputtering was preceded by base pressures below 2×10−6 Torr. Ar ions at 1 keV were used at 1 ×10−4 Torr pressure. The substrate was rotated at 10 rpm while deposition rates of 250 Å/mm were recorded. A permanent magnet was affixed to the underside of the substrate holder to provide an orienting magnetic field to induce uniaxial magnetic anisotropy of the film. Substrate angles of greater than 35° exhibited the best uniaxial anisotropy while increasing the substrate surface temperature. Increasing substrate surface temperature decreased the internal stress of the film. Substrate angle can also be varied to create films with good anisotropy from targets of varied Ni-Fe content. Good uniaxial anisotropy was obtained from high Ni content at smaller substrate angles while lower Ni content was deposited with similar results at greater substrate angles. Deposition in a magnetic field (along the axis of difficult magnetization) proved effective in increasing the permeability of the film.
Usage of Laplace transform for analysis and synthesis of magnetic heads (abstract)
Authors: Minuhin V. B.
Published: July 2002

In the two-dimensional approximation, the field of a magnetic head is described by a potential function, which is either the imaginary V or the real U part of an analytic complex potential W=U+jV. In the first case the field vector is H̄=jdw/dz (H̄ is the conjugate of H), in the second case, H̄=−dw/dz. An analytical function dw/dz can be called the system function of the head. According to the Laplace transform theory, an analytical function is the image of some (complex) original. We show that the original for dw/dz is the aperture of the head (the playback wavelength response with a chosen head and a thin layer of magnetic media), provided we modify (semantically) the definition of the spectrum, so that it contains only the positive wave-number components. Now, we have at our disposal the powerful tool of operational calculus. Usage of it for head analysis is straightforward. For example, having found dw/dz for some head which is the product of two functions (the original is known for each, example is provided), we can find the aperture of the head as a convolution of the two known originals (the rule of image multiplication). The problem of head synthesis is more complex, because the criteria of physical realization of dw/dz (which are presented) must be also met. For the simplest cases, the Laplace transform of the desired aperture provides the distribution of the poles of dw/dz in which each pole corresponds to the thin current conductor of a physical head. More sophisticated cases which result in magnetic cores and distributed windings of synthesized heads are also presented.
Motional eddy currents in a nonmagnetic conducting laminate backed with an iron substrate
Authors: Zmood R. B.
Published: July 2002

This paper discusses the eddy currents induced in a nonmagnetic conducting laminate on an iron substrate. These results are applicable to the analysis of linear induction motors, ordinary induction machines with sleeve rotors, and eddy current couplings. Under appropriate assumptions it is shown that the boundary conditions and Ampere’s circuital law reduce the problem to eight linear simultaneous equations. Simple algebraic expressions for the current density and power dissipation in the laminate are obtained in terms of the solutions of the above simultaneous equations. Numerical results for typical situations are presented, and a brief discussion of the experimental verification of the analysis is presented.
Computation of high-frequency TM eddy-current losses in magnetic materials
Authors: Fawzi T. H. , Ahmed M. T. , Burke P. E.
Published: July 2002

The paper deals with the computation of eddy-current losses in linear magnetic materials due to time-harmonic transverse magnetic fields. The variations of the losses in magnetic cylinders with circular and rectangular cross sections are examined over the whole frequency range. The results are generated analytically or by a boundary-elements analysis. Four distinct ranges are identified. It is shown that over a wide frequency range an impedance boundary condition (impedance BC) prevails at the boundary. The magnetic field however is still strongly influenced by the demagnetizing fields. In this range the losses can be approximately evaluated by solving one singular boundary integral equation.
Infrared absorption spectra and crystal-field effect of TbIG (abstract)
Authors: Hau Nguyen Hy , Porcher Pierre , Vien Tran-Khanh
Published: July 2002

Rare-earth iron garnets (RIG) are well known for their numerous interesting magnetic properties, but few works have been done on their optical behavior, especially at low temperatures. This paper studies the optical properties of TbIG, one of the most anisotropic RIG at low temperatures, showing large magnetic and magneto-optical effects, in relation with its magnetic properties. For this purpose, polarized and unpolarized spectra of oriented single crystal of TbIG have been recorded at low temperatures (77, 4.2, and 2 °K) and in external magnetic fields up to 5 T, applied along the principal axis of a (110) plane. Transitions were observed from the ground level 7F6 to other states of the 7FJ multiplets of Tb3+ ions (between 2000 and 5500 cm−1). From the derived energy-level scheme, a set of crystal-field parameters was derived, within the D2 point symmetry. These parameters as well as the energy levels show no noticeable difference with those of Tb3+ ions in paramagnetic TbAlG. Correlations between polarized absorption spectra and magnetic effects will be discussed.
Photomagnetic effects in calcium and germanium substituted yttrium iron garnets (abstract)
Authors: He Y. Q. , Yuan S. H. , Wigen P. E. , DeGasperis P.
Published: July 2002

Photoinduced changes in the coercivity of uncompensated calcium and germanium substituted yttrium iron garnet epilayers have been observed. The experimental results indicate that there exists a ‘‘critical’’ temperature below which coercivity of the sample increases by up to 20% under illumination of low intensity red light. Around this same temperature range the measured temperature dependence of the magnetization M(T) and anisotropy field display significant anomalies. The theoretical simulations for M(T) curves have been performed by using a molecular field approach. Since the measured temperature dependence of the magnetization of the uncompensated films could not be explained by the usual two sublattice model, a third contribution proportional to the deviation of the magnetization from bulk values was introduced. These results demonstrate the possibility of a weakly bound hole at the Ca site which contributes to the magnetic properties of these materials.
Interpretation of hysteresis measurements for perpendicular double-layer media
Authors: Bloomberg Dan S.
Published: July 2002

A method is given for the extraction, from VSM measurements, of saturation magnetization, coercivity, thickness, and squareness of perpendicularly oriented double-layer media. The CoCr coercivity in double-layer films is found to be less than that in similarly prepared single-layer films. The importance of coil balancing, sample centering, and sample alignment is discussed. For ideally square loops with demagnetizing factor 4π, all properties of each layer can be determined. The literature on CoCr, although conflicting, suggests these ideal conditions are not met. An independent measurement of thickness is required to determine the intrinsic squareness and demagnetizing factor. The degree of sensitivity of the results to these two parameters is derived.
Ferritic Fe-Ni magnetic sensor wires with end-to-end voltage-generating characteristics
Authors: Jin S. , van Dover R. B. , Sherwood R. C. , Tiefel T. H.
Published: July 2002

The magnetic switching behavior and voltage-generating characteristics of microduplex-structured, plastically twisted ferritic Fe-6∼12% Ni alloys have been investigated. Relatively large voltage pulses (and large currents due to the low resistance of the short magnetic wires) are obtained from properly processed wires, e.g., 0.1–1 V from the ends ∼0.025-cm diameter and 2–10-cm-long wires switched by external ac fields (60 Hz–100 kHz) of 40–200 Oe. It is shown that the residual stress in the plastically twisted wire may not be needed and may even be undesirable since a similarly large voltage is obtained in a sample that has been stress-relief annealed after plastic twist. Various other factors that affect the voltage generation are discussed. This type of magnetic sensor is free of pickup coils and may conveniently be used as proximity/displacement/rotation sensors or triggering/switching devices. The possibility of biomedical applications as remotely controllable, implanted electrodes for stimulation of nerves or muscles will also be discussed.
Microwave measurement of saturation magnetization and magnetic crystalline anisotropy of polycrystalline ferrites
Authors: Zhu Sheng-chuan , Zhao Li-qun , Wen Fan-ping
Published: July 2002

On the basis of the expression for the microwave permeability of completely demagnetized states given by E. Schlömann, we suggest a method of simultaneous determination of saturation magnetization and magnetic crystalline anisotropy of polycrystalline ferrites by measuring this microwave permeability. This permeability has been measured on a number of a frequencies for polycrystalline ferrite materials, and the saturation magnetization and the magnetic crystalline anisotropy can be obtained by using computer methods. The experimental results are in agreement with the data obtained by other experimental methods.
Magnetic thin films produced by sol-gel processes
Authors: Kordas G. , Weeks R. A. , Arfsten N.
Published: July 2002

Iron oxide films on borosilicate glasses were produced with the sol-gel method. The ESR spectra of the as-produced films exhibit two signals, one at g about 4.2 and the other at g about 2. A ferromagnetic signal was detected by heat-treating the samples in hydrogen atmosphere between 500 and 800 °C. Angular variation of the ferromagnetic resonance signals revealed an internal field parallel to the plane of the films. The internal field was about 3500 G in the film heat treated at 620 °C for 120 min. Scanning electron microscopy was also used for detailed surface characterization. Before treatments the film is characterized by a fine texture and a few voids whose dimensions are about 5×15 μ. After treatments the film contains particles about 15 μ in size.
Measurement of the adiabatic temperature change in ferromagnetic intermetallic compounds (abstract)
Authors: Zimm C. B. , Barclay J. A.
Published: July 2002

Study of the thermodynamics of magnetic refrigeration cycles that use the magnetocaloric effect in ferromagnetic materials requires, as a minimum, knowledge of the zero-field heat capacity C0 and the equation of state of the magnetization, M= f(B,T), for each material. However, refrigerator design calculations are easier to make if the field-dependent heat capacity CB and adiabatic temperature change ΔTS are known. The field-dependent heat capacity can either be directly measured or be derived according to CB(B,T) =CB(B=0,T) + ∫B0  (∂2M/∂l2)dB. The adiabatic temperature change can be obtained in three ways: by direct measurement, from field and temperature dependent entropy curves, or from dT=−T ∫B0  (1/CB) (∂M/∂T)dB. The time required for measurement, the complexity of the apparatus, and the quality of the resultant data differ considerably among the above methods. We have measured the magnetization, heat capacity, and adiabatic temperature change for several ferromagnetic intermetallic gadolinium compounds. Using these data an analysis of the different methods of obtaining CB and ΔTs will be presented. The accuracy, precision, and pitfalls of each approach will be discussed.
Method of the super-highly precise measurement of strong magnetic field (abstract)
Authors: Sheng Ye
Published: July 2002

This article describes the method of measuring a strong magnetic field with a nuclear magnetic resonance (NMR) magnetometer using flowing water. In the apparatus, the strong magnetic field measured is taken as the sample of polarizing magnetic field, and frequency synthesizer generator as the source of radio frequency exciting resonance transitions. The apparatus is different from the precise field averaging NMR magnetometer (precision:10−7) for low and high fields using flowing water developed by J. M. Pendlenbury etc., and the wide-ranged NMR magnetometer (precision:10−5) using flowing water developed by V. M. Simonov and colleagues. The minimum step of the frequency alterations of the synthesizer is 0.01 Hz. The stability of frequency is extremely high. The apparatus can quite accurately measure the proton absorption spectrum of the measured field. This provides possibilities for the super-high precision measurement of resonance central frequency. The method of taking the arithmetic mean of frequencies  f1 and  f2 measured at the half-height of spectrum lines to be the measurement of the central frequency  f0 is demonstrated in this paper as well. The precision of measuring results is higher an order of magnitude than that of the direct measurement of  f0. The precision of the measuring results of the value 8.455 T of NMR spectrum superconducting magnetic field reaches 0.7×10−9. This technique can be used to precisely measure the strong magnetic field over 0.5 T. So far as the measurement of the distribution of NMR spectrum superconducting field is concerned, it shows its significant advantages.
Hybrid boundary-volume Galerkin’s method for nonlinear magnetostatic problems
Authors: Mayergoyz I. D. , Doong T.
Published: July 2002

The paper describes a new technique for the solution of nonlinear magnetostatic problems. It is based on the reduction of field equations to two coupled boundary and volume Galerkin’s forms. A hybrid finite-quasifinite element discretization of these Galerkin’s forms is proposed. It leads to sets of simultaneous equations with symmetric matrices. This technique is also free from the other difficulties encountered in the mutually constrained differential-integral equation approach. Some numerical results obtained by this technique are reported.
Nonlinear analysis of a permanent magnet synchronous machine with nonsinusoidal stator winding currents
Authors: Chari M. V. K. , D’Angelo J. , Bedrosian G. , Neumann T. W.
Published: July 2002

Permanent magnet synchronous machines and induction motors are often required to operate on-line starting or inverter-fed systems, which results in nonsinusoidal stator currents. These, in turn, give rise to undesirable harmonics and power losses which degrade motor performance. In this paper a time-domain analysis is presented for evaluating the magnetic field distribution in the two-dimensional cross section of the machine under load conditions. The analysis is applied to a permanent magnet synchronous machine under locked rotor conditions. Although for purposes of this analysis, the iron permeability has been assumed a constant, the method can be easily extended to include iron saturation.
Macroscopic dynamic effects in an amorphous ferromagnet
Authors: Yan Li , Bhagat S. M. , Mazumdar P. , Moorjani K. , Kistenmacher T. J.
Published: July 2002

dc magnetization data on amorphous Fe60Al28B12 show that it is a soft ferromagnetic material. However, magnetic resonance measurements indicate that a single set of conventional parameters is not adequate at all fields when T≲200 K. It is suggested that, because of exchange fluctuations and random anisotropy fields, ferromagnetic resonance in amorphous materials needs additional macroscopic variables for an adequate description.
Muon spin rotation study of V2O3
Authors: Denison A. B. , Boekema C. , Lichti R. L. , Chan K. C. , Cooke D. W. , Heffner R. H. , Hutson R. L. , Leon M. , Schillaci M. E.
Published: July 2002

Muon spin rotation (μSR) measurements have been made on V2O3 as a function of temperature and externally applied magnetic field. V2O3 is an insulating antiferromagnet below about 155 K, while above this temperature it is a high-resistivity metal. The conduction arises from the band mechanism where the density of states is quite sensitive to temperature and doping. The local magnetic field, sensed by the positive muon, has been measured from room temperature down to 10 K, with emphasis on the transition region. Clear evidence of the onset of magnetization is provided by a jump in the muon precession frequency. From experiments using an externally applied magnetic field the directions of the internal fields at the muon stop sites are found. This information can be used to determine the muon stop site since the field at this site should be determined primarily by the magnetic dipoles of the V3+ ions. Dynamic effects are observed through the muon spin depolarization. The results obtained for V2O3 are discussed in the light of similar magnetic-oxide μSR studies and of the electric and magnetic properties of V2O3.
Theoretical model of the Raman intensities of localized and magnon modes in CoxMn1−xF2
Authors: Quazza J. , Labbe J.
Published: July 2002

We analyze two excited modes due to the presence of Co++ ions embedded as impurities in MnF2. The Raman scattering is not observed in the pure crystal of MnF2 for there is no spin-orbit coupling in the ground state of the Mn++ ion. But the magnon modes become activated by the presence of Co++ ions and the intensity of these magnetic excitations is of the same order of magnitude as that of the localized ones. We calculate separately the scattered intensities of those two types of modes. They depend on the amplitude of the two excited wave functions on the impurity sites. The wave functions are calculated with the help of the Green function formalism and using the Lippman–Schwinger equation. (Here it is not necessary to know the density of magnon states.) Our main assumptions are that the energy level of the localized mode is near the edge of the magnon band and that the concentration of impurities is low enough to treat them as separated scattering centers. So, after explicit calculations of the Green function of the pure crystal we find that the variation of the spin-wave intensity is quadratic in the concentration whereas it is linear for the localized modes. Thus our model yields their ratio in terms of the concentration, the two exchange integrals, the two effective spins, and the distance in energy between the localized and magnon modes, relative to the magnon bandwidth.
Incommensurable magnetic structure and soft mode behavior in CsFeCl3 (abstract)
Authors: Knop W. , Steiner M.
Published: July 2002

The class of 1-D ferromagnetic chain systems AFeCl3 (A=Rb,Tl,Cs) are of special interest in the group of 1-D magnets of the type ABX3. This is because of the strong single-ion-anisotropy D, which favors a nonmagnetic singlet-ground state. If however the exchange interaction J is large enough, with d=D/J<1 the system has a magnetic ground state with easy plane anisotropy. While RbFeCl3 has a magnetic ground state, CsFeCl3 has not; it is however possible to induce a magnetic moment through the Zeeman splitting of the first excited state. We have therefore studied CsFeCl3 by neutron scattering experiments in external magnetic fields, H̄∥c̄. Such experiments yield a strong quasi-elastic scattering around Q=(0.294,0.353,0) and Q=(0.353,0.294,0) at H≥4 T, due to the dynamical behavior of the correlated clusters of spins in the easy plane. At higher fields or lower temperatures true elastic scattering occurs at incommensurable positions with Q̄=(1/3−x,1/3−x,0). Further increase of fields or decrease of temperature leads to discrete changes of x, which finally lock in at the commensurate 120 spin structure. We explain the incommensurate phases as a result of the competition between dipole- and exchange-interaction. In addition we performed inelastic measurements in fields up to 5.4 T, which cannot be explained by spinwave theory. These inelastic results are discussed on the basis of the exciton model using the RPA decoupling.
Neutron scattering investigation of magnetic excitations at high energy transfers (invited)
Authors: Loong C.-K.
Published: July 2002

With the advance of pulsed spallation neutron sources, neutron scattering investigation of elementary excitations in magnetic materials can now be extended to energies up to several hundreds of meV. We have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO2, UO2, BaPrO3, and CeB6 we observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 meV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce0.74Th0.26, on the other hand, no sharp crystal-field lines but a broadened quasielastic magnetic peak was observed. The line width of the quasielastic component is thought to be connected to the spin-fluctuation energy of the 4f electrons. The significance of the neutron scattering results in relation to the ground state level structure of the magnetic ions and the spin dynamics of the f electrons is discussed. Recently, in a study of the spin-wave excitations in itinerant magnetic systems, we have extended the spin-wave measurements in ferromagnetic iron up to about 160 meV. Neutron scattering data at high energy transfers are of particular interest because they provide direct comparison with recent theories of itinerant magnetism.
‘‘Collapsing’’ versus ‘‘noncollapsing’’ empty band states in iron (invited; abstract)
Authors: Kirschner J. , Glöbl M. , Dose V. , Scheidt H.
Published: July 2002

We report on the behavior of unoccupied exchange split bands in iron on approaching the Curie temperature at different points in the Brillouin zone. We use spin-polarized isochromat spectroscopy, which allows to identify the spin-character of the bands. Near the H point in bcc Fe we observe minority and majority states to merge with increasing temperature, providing evidence for a ‘‘collapsing’’ band state at this point of the Brillouin zone. The flat empty minority band of Fe is sampled at two other points in k space by using different crystal surfaces and/or different angles of incidence. At these locations the energetic position of the minority peak remains unchanged, indicating the existence of ‘‘noncollapsing’’ band states. These findings are compared to the predictions of the ‘‘local band’’ theory and the ‘‘disordered local moment’’ theory.
Surface spin waves in thin-film antiferromagnets and at interfaces (abstract)
Authors: Camley R. E. , Stamps R. L.
Published: July 2002

We discuss antiferromagnetic bulk and surface spin waves, in the long-wavelength region, on a finite thickness slab geometry. Implicit dispersion relations for both surface and bulk modes are derived, along with numerical calculations for MnF2 and GdAlO3. In the absence of a magnetic field the magnetic scalar potential has either pure even or pure odd symmetry. We find that the application of a magnetic field strongly localizes the surface spin wave to either the top or bottom surface of the film. In addition we will discuss the propagation of spin waves localized at the interface between a ferromagnet and an antiferromagnet.
Magnetic surface anomaly in high purity YIG
Authors: Bush Gary G. , Rodrigue G. P. , Legg K. O.
Published: July 2002

LPE YIG films have been shown to exhibit variable magnetization and uniaxial anisotropy in the regions nearest the air/YIG and YIG/GGG interfaces. The change in magnetic properties has been modeled in terms of ΔHs=[(Hu−4πM)surf−(Hu−4πM)bulk] due to the difficulty in separating the uniaxial anisotropy and the magnetization within a region. FMR measurements of ΔHs indicate that homogeneous surface conditions can be restored by implantation of 1×1016 Ar/cm2 at energies of 60 or 123 keV and annealing for at least 2 h in an oxygen atmosphere at 915 °C. It is thought that the implantation destroys the crystalline order of the surface and facilitates regrowth of the prototype YIG structure from the high-purity YIG beyond the first few hundred angstroms.
Magnetic properties of consolidated glassy metal powder cores
Authors: Hasegawa R. , Hathaway R. E. , Chang C. F.
Published: July 2002

Magnetic properties of mechanically compacted glassy metal powder cores are presented. The powder size ranges from about 2 μm to 2 mm. The compositions of the powder materials are Fe78B13Si9, Fe40Ni38Mo4B18 and Co72.2Fe5.8Mo2B15Si5; the magnetostriction values of these are 30, 9, and 0.5 ppm respectively. The cores compacted with and without oxide binders are in a toroidal form. The effects of powder size, binder, value of magnetostriction and consolidation conditions on the properties are discussed. It is shown that cores made from near-zero magnetostrictive powders exhibit core loss of about 12 W/kg and permeability of about 1600 at f=5 kHz and Bm=0.2 T, which are comparable to those for Ni-Zn ferrite cores.
Sm-Co film magnet synthesized by rf sputtering (abstract)
Authors: Tada J. , Hayashi S. , Akihiro M. , Satoh T.
Published: July 2002

SmCo film magnet has been synthesized on a heated substrate by means of rf sputtering. In Sm1−xCox (0.6≤x≤0.98) films the saturation magnetization simply decreases with the increase in Sm content, while the other magnetic properties strongly depend on the crystalline phases. The film with 1 μm in thickness and x∼0.8 mainly consists of SmCo5 phase, which exhibits in-plane anisotropy. The films with the easy axis perpendicular to the film surface are obtained in the composition around x=0.75. It is the mixture of amorphous and crystalline SmCo3 phases.
Theoretical determination of surface magnetism (invited)
Authors: Weinert M. , Freeman A. J. , Ohnishi S. , Davenport J. W.
Published: July 2002

The theoretical determination of the magnetic structure of surfaces within the (local) spin-density formalism is briefly described. The feasibility of using such methods for determining delicate magnetic quantities is illustrated by calculation of (1) the Knight shift of the paramagnetic Pt(001) surface, (2) the magnetization of the clean and Ag-covered Fe(001) surface, and (3) the effect of a p(1×1) H overlayer on the magnetization of a Ni(001) surface. These results demonstrate that it is possible not only to make quantitative predictions for real systems, but more importantly, to gain insight into the underlying physics at surfaces.
Spin stiffness anomaly in the reentrant spin-glass (Fe0.25Ni0.75)0.75P0.16B0.06Al0.03
Authors: Erwin R. W. , Lynn J. W. , Rhyne J. J. , Chen H. S.
Published: July 2002

Low field magnetization measurements have shown that the amorphous alloy (Fe0.25Ni0.75)0.75P0.16B0.06Al0.03 becomes a demagnetization-limited ferromagnet below a Curie temperature Tc of 200 K, but that the spontaneous magnetization vanishes again below a reentrant temperature TR of 4 K. Inelastic neutron scattering measurements have been performed to study the spin-wave dynamics as the spin-glass state is entered from the ferromagnetic state. The observed spin-wave peak positions decrease in energy and the linewidths increase as the temperature is lowered towards TR. A detailed analysis based on both the double Lorentzian and damped harmonic oscillator forms of the spectral weight function shows that the spin-wave energies strongly decrease as the temperature is lowered and the excitations become heavily damped over the range of wave vectors (0.04 Å−1<q<0.18 Å−1) studied. An elastic component of the magnetic scattering, attributed to a spin-glass order parameter, is also observed.
ESR study of reentrant FexNi80−xP20 ribbons
Authors: Hou M. K. , Salamon M. B. , Pechan M. J.
Published: July 2002

Amorphous Fex Ni80−x P20 alloys in the ferromagnetic composition range (x=12,14,16) show progressive distortion of the ESR lineshape at temperatures well below the Curie temperature. We employ the Kubo–Toyabe model to analyze these ESR data which permits us to extract a freezing temperature Tf. There is a tendency for the relaxation rate to vanish as T is reduced toward Tf; below Tf an anisotropy energy K(T) appears that is proportional to (1−T/Tf). The magnetic phase diagram can now be constructed for x=12, 14, and 16 samples, showing them to be reentrant.
Magnetomechanical resonant losses in metallic glasses
Authors: Ramanan V. R. V. , Smith C. H. , Barberi L.
Published: July 2002

Excess core losses, attributable to mechanical resonances, are observed in tape-wound toroidal cores of two Fe-rich metallic glasses. In the absence of these resonances, the behavior of core loss as a function of frequency follows traditional models. The damping of the mechanical resonances is described in this paper. The reduction of the resonance losses is identified as due to externally supplied viscous damping forces.
Magnetic and electrical properties ascribed to the heterogeneous structure of new amorphous Fe-B-O system
Authors: Kudo T.
Published: July 2002

Ferromagnetic amorphous Fe-B-O films deposited by sputtering take a heterogeneous structure which consists of an amorphous Fe-B alloy and an oxide B2O3 glass. The large saturation magnetization originates from the ferromagnetic Fe-B alloy and the high electrical resistivity from the structure separated into metal and oxide phases. An anomalous change in the magnetic and electrical properties at about 46 at. % of Fe is due to changing of a continuous Fe-B matrix into many particles isolated by B2O3.
Magnetic properties and hyperfine interactions of amorphous Fe-Hf alloys
Authors: Liou S. H. , Xiao G. , Taylor J. N. , Chien C. L.
Published: July 2002

Alloys of FexHf100−x (20≤x≤100) were fabricated by a vapor-quench method. The amorphous state, as verified by x-ray diffraction, is realized over a wide composition range of 20≤x≤94. The magnetic phase diagram was determined. The variation with Fe content of the magnetic ordering temperature (Tc) in Fe-Hf amorphous alloys shows a maximum at xp≂87. In contrast, the effective magnetic hyperfine field and therefore the Fe moment increases monotonically with x. Amorphous pure Fe is likely to be magnetic (Tc ∼200 K) with a large magnetic moment. At higher Fe concentrations (x>95), the samples are crystalline alloys and strongly ferromagnetic. These sharp changes of the magnetic properties are consequences of structural differences, a fact which has been observed in every Fe-early transition metal alloy system reported thus far. In general, the magnetic properties and hyperfine interactions of amorphous Fe-Hf alloys are very similar to those of amorphous Fe-Zr alloys.
Effects of hydrogen on magnetic properties of amorphous zirconium alloys
Authors: Venturini E. L. , Bowman R. C. , Cantrell J. S.
Published: July 2002

The magnetic susceptibilities χ(T) of the amorphous ternary hydrides of the paramagnetic metallic glasses a-Zr2Pd and a-Zr3Rh have been measured between 7 and 300 K. It has been found that χ(T) of both a-Zr2PdHx and a-Zr3RhHx decrease substantially with increasing hydrogen content. This behavior is primarily attributed to reductions in the densities of the Fermi level electronic states. Although χ(T) for crystalline Zr2Pd (MoSi2 structure type) is smaller than the susceptibility of the a-Zr2Pd glass, χ(T) for a crystallized Zr3Rh sample was found to increase relative to the initial susceptibility for this glass.
Dependence of the magnetic properties of the spin-glass Ag-Mn on the addition of magnetic impurities
Authors: Tovar M. , Fainstein C. , Oseroff S. , Schultz S.
Published: July 2002

We have measured the dc magnetization, electron spin resonance (ESR) linewidth and ESR line shift δHr for the spin-glass Ag-Mnx (x=4 and 8 at. %) as a function of adding magnetic impurities (Er and Gd). We determine the anisotropy constant from the relation K=δHrM0, where M0 is the magnetization measured at the dc field corresponding to g=2 resonance. We find that the addition of Er systematically changes α, the slope of the linear dependence of the anisotropy constant, i.e., K(T)=K(0)(1−αT/Tc), such that α approaches unity at high-impurity concentration. The addition of Gd produces a reduction of M0 which results in values for K(T) which are nearly independent of concentration. We have measured the dependence of the dc magnetization cusp temperature Tg as a function of the concentration of the various impurities, and have also studied the remanent magnetization as a function of time, temperature, and field.
Suppression of spin-glass characteristics in a ‘‘reentrant’’ amorphous Fe-Zr alloy by the addition of Ni (abstract)
Authors: Rao K. V. , Goldfarb R. B. , Fukamichi K.
Published: July 2002

Amorphous, Fe-rich, Fe-Zr alloys containing 90–93 at. % Fe show low-temperature spin-glass behavior after acquiring ferromagnetic order at a higher temperature TC. From our measurements of the imaginary component of ac susceptibility, we have determined, for these alloys, the temperature Tfg at which a well-defined maximum is observed indicating the onset of spin-glass behavior upon cooling. We thus obtain a boundary line for the ferro-to-spin-glass transition in this region of the magnetic-phase diagram. In order to elucidate the loss of ferromagnetic order and the evolution of the spin-glass state at low temperatures, ac susceptibility measurements were made as a function of temperature on seven amorphous (Fe1−xNix)90Zr10 alloys with 0<x<0.08 and x=0.21. We find that Tfg, observed at 13 K for the x=0 alloy, decreases with increasing x and is completely suppressed for alloys with x>0.04, while concurrently, TC increases. In addition, while magnetization in the x=0 alloy does not saturate at 4.2 K, even in applied fields of 12 MA/m (150 kOe), substitution of Ni for Fe leads to easy saturation for alloys with x>0.04. These results indicate that, on substitution of Ni for Fe in these alloys, the local short-range order is modified to suppress the antiferromagnetic exchange coupling between the Fe atoms.