bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic viscosity in MnAlC
Authors: Gaunt P. , Kenning G. , Ram U. S.
Published: February 2003

Magnetic viscosity has been measured in aged MnAlC alloys having an intrinsic coercive force of 1.44 kOe at 295 K rising to 1.97 kOe at 77 K. The measurements are used to estimate the derivative (∂E/∂H) of the activation energy E which must be supplied thermally to move segments of domain wall through coherent jumps. This derivative is found to vary linearly with the reciprocal of the effective applied field. These results are consistent with a domain wall pinning model which allows a range parameter 4b to be deduced, from the viscosity results, as 44 Å. This result is close to the estimated wall width of 49 Å.
Magnetic and crystallographic properties of substituted Ce2Co17−xTx compounds (T = Ti, V, Cr, Mn, Fe, Cu, Zr, and Hf)
Authors: Fujii H. , Satyanarayana M. V. , Wallace W. E.
Published: February 2003

The ternary Ce2Co17-based systems in which Co is replaced by Ti, V, Cr, Mn, Fe, Cu, Zr, and Hf have been studied to ascertain the effect of substitution on their magnetic and crystallographic properties. X-ray diffraction experiments indicate that Mn and Fe stabilize the rhombohedral Th2Zn17 structure, while Ti, V, Cr, Cu, Zr, and Hf stabilize the hexagonal Th2Ni17 structure. The unit cell volume is found to increase by introducing substituents for all the systems. The Curie temperatures TC decrease monotonically with increasing x, in the order Fe<Hf<Cu<Zr<Ti<Mn<Cr<V. The saturation magnetizations Ms increase with increasing x for the Fe system with x?10 and the Mn system with x<2. It is found that Ms decreases sharply with x in the Mn system with x?2 and in the other systems, the magnitude of the effect being in the order Hf≳V≳Cr≳Mn≳Zr≳Ti≳Cu. The rate of decrease is larger than that expected as a simple dilution except for the Cu system. The anisotropy field HA shows a maximum around x = 2 for the Cr, Mn, and Fe systems, indicating that T atoms substitute preferentially for the dumbbell cobalts in Ce2Co17−xTx with x?2. The magnitude of the effect of substitution on HA is found to be in the order Zr≳V≳Hf≳Ti≳Cr≳Mn≳Fe≳Cu in the range of x?1.0. Crystallographic and magnetic characteristics suggest that all substituents replace Co when the ternaries are formed.
Demagnetization curves of four rare-earth-cobalt magnet types at temperatures 300–1000 K
Authors: Liu S. , Mildrum H. F. , Strnat K. J.
Published: February 2003

Intrinsic demagnetization curves and the temperature dependence of specific magnetization states were measured with a dc magnetometer on four types of sintered rare-earth-cobalt permanent magnets at temperatures from 300 to 1000 K. All magnetic properties vary reversibly with temperatures up to limits of 650–850 K, depending on the alloy. Precipitation-hardened magnets of the 1–7 or the 1–5 types and the common sintered SmCo5 all exhibit quite different temperature characteristics. The MHc of 1–7 type magnets decreases gradually with increasing temperature. Its temperature dependence can be well described by a simple exponential function. The MHc of SmCo5 drops sharply with increasing temperature and becomes very small at about 750 K. The cerium magnet shows a distinct kink in MHc versus T at 550 K, separating two temperature regions in which clearly different mechanisms are responsible for the coercivity.
A study of magnetic hardening in Sm(Co0.69Fe0.22Cu0.07Zr0.02)7.22
Authors: Hadjipanayis G. C. , Yadlowsky E. J. , Wollins S. H.
Published: February 2003

Magnetic hardening has been examined in the commercial Sm(Co, Fe, Cu, Zr)7.22 permanent magnet by correlating the magnetic properties with the microstructure of the sample. The shape of the initial magnetization curve and magnetic domain observations indicate that there is more than one magnetic hardening process involved in this magnet. This is consistent with microstructure studies which show the existence of nonmagnetic Cu-rich precipitates and 1:5 phase lamellae distributed in a 2:17 rhombohedral matrix. The presence of the lower Tc 1:5 ferromagnetic phase in the higher Tc 2:17 phase is responsible for the peak observed in the M(T) curve around 870 K and in the change of slope in the Hc(T) curve around 800 K.
Self-consistent recording model for perpendicularly oriented media
Authors: Beardsley I. A.
Published: February 2003

We describe modifications to the fully two-dimensional self-consistent recording model which make it more applicable to perpendicularly oriented media such as cobalt chromium alloys. Writing and reading with a thin-film head are modeled at a separation of 0.2 μm and results are compared with experiment.
Simulation of perpendicular recording on Co-Cr media with a thin Permalloy film-ferrite composite head
Authors: Shinagawa K. , Fujiwara H. , Kugiya F. , Okuwaki T. , Kudo M.
Published: February 2003

Numerical analyses of thin film head-medium system for perpendicular recording are performed using a two-dimensional model. The formulation is based on Poisson’s equation for magnetic vector potential in the head-medium system. The following conclusions are drawn: (1) Magneto-motive force needed for producing a sufficient perpendicular field in the medium is about 1/10 that of the SPT (single pole type) head proposed by Iwaski et al. (2) There is an optimum spacing between the magnetic layer and the ferrite of the head that lies 5–20 times the distance between the main pole and the underlayer. (3) The conductor should be placed in the very tip portion of the magnetic layer. (4) Simulation confirms that recording of densities as high as 100 kBPI is possible using a thin film head-Co-Cr medium system.
Noise and overwrite characteristics for perpendicular magnetic recording on a sputtered Co-Cr medium
Authors: Okuwaki T. , Koizumi M. , Uesaka Y. , Fujiwara H.
Published: February 2003

This paper describes noise, overwrite, and pattern peakshift characteristics for a Co-Cr medium that is used in perpendicular magnetic recording by means of a ring head. Uniform Co-Cr (20 wt% Cr) films of about 1 μm thickness were formed by rf sputtering on A1 disk substrates, whose saturation magnetization and coercive field were 205 emu/cc and 700 Oe, respectively. Magnetic recording tests were performed for them using a Mn-Zn ferrite ring head of 0.28-μm gap length and 100-μm track width at a relative speed of 2.5 m/s. The maximum D50 recording density was 70 kBPI, with a signal-to-noise ratio of 40 dB at 60 kBPI. Overwrite characteristics were measured by writing a 66 kBPI signal over a 35 kBPI signal that had previously been written in. The ratio of the output of the 66 kBPI signal to that of the remaining 35 kBPI signal was 24 dB. The peakshift for the worst pattern in MFM coding was 50% of the detection window at 60 kBPI. From these results, it was deduced that the Co-Cr medium described above is feasible for the 60 kBPI/1 kTPI disk storage device.
Static and dynamic magnetic studies of compositionally modulated thin films
Authors: Flevaris N. K. , Ketterson J. B. , Hilliard J. E.
Published: February 2003

New data on the magnetic behavior of compositionally modulated Pd-Ni and Cu-Ni thin films are presented. The room temperature magnetization density (M) and first-order uniaxially anisotropy constant (K) were determined by using a torque magnetometer. The temperature dependence of K was obtained from ferromagnetic resonance experiments. For the Cu-Ni system measurements were also performed on a SQUID magnetometer and the results of the three experiments were in agreement. It was found that, for the Pd-Ni system, the moment per Ni-atom for different films with various asymmetric wavelengths may exceed that of pure Ni, in contrast to the Cu-Ni films. For the later ones it is shown that, when ∼3 atomic planes of Ni are isolated between ∼6 Cu planes, the ferromagnetic behaves as a two-dimensional ferromagnetic.
Computer analysis of Arrott plots of compositionally modulated materials
Authors: Jones Walter R.
Published: February 2003

We investigated the field and temperature behavior of the magnetization for a simple model of a compositionally-modulated (CM) material. Our aim is to determine the value of the Curie temperature (TC) for a material which has a large composition modulation. We use Arrott plots to find TC. Our model neglects the exchange interaction between layers and is applied to copper-nickel CM films. In this model the fraction of nickel along the film can be represented by a sinusoidally varying function. Then, the magnetization at any point along the film normal depends on the nickel fraction at that point. Thus, for any temperature and field, the magnetization can be determined at any position along the film normal. By integrating these magnetizations over a wavelength, we obtain the magnetization of the film for any temperature and field. The Curie temperature obtained from the Arrott plot curves of these data shows that TC of these films arises essentially from TCmax and that only the upper 40% of the compositions contribute to TCmax. Since our model neglects exchange, we did not expect our results to be applicable to films with short-wavelength modulations. However, TC measured on a 8 Å Cu-8 Å Ni film agrees closely with the model presented here.
Magnetic properties of RAlGa compounds
Authors: Sill L. R. , Hitzman C. J.
Published: February 2003

The magnetic moments of the series of intermetallic compounds RAlGa (where R is Nd, Sm, Gd, Tb, Dy, Ho, Er, or Tm) have been measured at temperatures from 4.2 to 300 K in applied fields up to 26 kOe. These compounds form in a trigonal crystal structure and are isostructural with CeCd2 (a distorted AlB2-type structure). At higher temperatures the reciprocal susceptibility for each compound except the Sm one follows a Curie-Weiss law; the effective paramagnetic moments are in approximate agreement with those calculated for free tripositive earth ions. The asymptotic Curie temperatures are mostly negative; they do not exhibit de Gennes-type behavior. The Gd, Tb, Dy, and Ho compounds order antiferromagnetically. No magnetic order is observed for the other compounds.
CEMS characterization of ion-implanted bubble garnets
Authors: Picone P. J. , Morrish A. H.
Published: February 2003

Conversion-electron Mössbauer spectroscopy (CEMS) applied to the study of the implanted region of garnet bubble films is described; both the advantages and limitations of this technique are discussed. After comparing some earlier work, CEMS results on annealed and etched bubble films are presented. The hyperfine parameters provide information on the paramagnetic phase present, the depth profile, the damage to the superexchange coupling, and the stress effects.
Strain profiles in ion-implanted bubble devices investigated by transmission electron diffraction
Authors: Omi T. , Bauer C. L. , Kryder M. H.
Published: February 2003

Selected area electron diffraction has been used to obtain strain profiles around unimplanted disks in thin (<2000 Å) films of (111) oriented garnets. Measurements of in-plane lattice constant were made as a function of position in (SmYGdTm)3Ga0.4Fe4.6O12 films implanted with oxygen (120 KeV, 1×1014/cm2) and helium (80 KeV, 4×1015/cm2). In most cases the data show a relaxation of stress normal to and near to the implanted boundary. These results are consistent with models suggesting that stress relaxation normal to an implanted boundary is critical to the formation of charged walls. In addition, effects of the nonuniform stress field on the local anisotropy in the underlying bubble layer of an ion-implanted contiguous disk device are considered. It is shown that under the edge of an implanted region, there is a tensile stress perpendicular to the film plane which reduces the perpendicular anisotropy, causing reduced bubble-nucleation thresholds in bubble materials with large negative values of λ111.
Resonant oscillations of magnetic bubble domains with vertical Bloch lines
Authors: Jantz W.
Published: February 2003

Resonant domain wall oscillations of bubbles are investigated with special attention to the dynamic behavior of Bloch lines and Bloch points. It is found that the localized inertial masses associated with these structures result in localized resonant oscillations at frequencies that are characteristic for the structures. The amplitude is concentrated near the respective structure, resulting in oscillatory wall flexure. Bubbles containing different wall structures (e.g. Bloch lines with and without a Bloch point) oscillate at two different frequencies.
High density recording characteristics of sputtered γ-Fe2O3 thin-film disks
Authors: Yoshii S. , Ishii O. , Hattori S. , Nakagawa T. , Ishida G.
Published: February 2003

Sputtered γ-Fe2O3 thin films are attractive in practical application to high density magnetic recording. This paper presents basic processes of γ-Fe2O3 thin-film fabrication, magnetic properties, and high density recording characteristics of the films. The film is prepared by reactive sputtering of an iron alloy containing a small amount of Co, Ti, and/or Cu in an Ar-O2 atmosphere on anodized Al alloy substrates and successive heat treatment. The film shows a high coercivity of 1000 Oe and a coercive squareness of 0.84 with the reduced thickness. The anodized Al alloy provides hard, smooth, and chemically stable substrates. The continuous γ-Fe2O3 thin films show high recording density with an excellent signal to noise ratio (SNR). First, the recording characteristics of the film employed in practical disk storage with the areal recording density of 24 000 bit/mm2 are described. SNR improves as the average crystallite size decreases. It is shown that 35 dB can be obtained at the linear density of 1000 flux reversals/mm with the track width of 10 μm. Finally, the density D6dB of 2600 flux reversals/mm is experimentally shown by using a Mn-Zn ferrite head with the small gap length of 2g = 0.15 μm operated at the heat-medium spacing of 0.1 μm.
Rotational hysteresis in recording materials measured with a gas turbine
Authors: Flanders P. J.
Published: February 2003

Magnetic properties in recording particles are assessed in terms of their rotational hysteresis WR measured using a low power gas turbine. Values for the peak rotational hysteresis WRp divided by π/M2s and the field at the peak Hp divided by 2πMs are consistent with a model for magnetic reversal by curling. Rotational hystereis measurements within different planes of a sample give the magnetic orientation and the magnitude of the shape demagnetizing fields. From the profile for the curve of WR versus field, the distribution of mixtures which contain components with distinctly different coercive forces is determined, giving this method potential as a technique for magnetic tagging.
Noise characteristics in plated Co-Ni-P film for high density recording medium
Authors: Tanaka H. , Goto H. , Shiota N. , Yanagisawa M.
Published: February 2003

Noise characteristics on continuous plated thin-film media have been studied, using plated disks and Mn-Zn ferrite heads. It was found that the magnetic medium noise was influenced by magnetic medium underlayer properties and magnetic properties of the magnetic medium itself. The influence from the underlayer is considerably decreased by a gold film (0.1-μm thick) inserted between the underlayers. Medium noise power N2 from the magnetic medium itself is linearly proportional to half pulse width W50 and recording density 1/L (N2∝k⋅W50⋅1/L; k: constant; L: bit length). Noise in the γ-Fe2O3 particulate medium appears mainly in regions outside magnetic transition. However, the experimental result shows that noise in a continuous thin-film medium itself is caused by magnetic transition regions.
Superconductivity and magnetism in the Ho1−xErxRh4B4 alloy system
Authors: Mook H. A. , Koehler W. C. , Sinha S. K. , Crabtree G. W. , Hinks D. G. , Maple M. B. , Fisk Z. , Johnston D. C. , Woolf L. D. , Hamaker H. C.
Published: February 2003

We have used neutron scattering techniques to examine the magnetic transitions in the Ho1−xErxRh4B4 pseudoternary system. A wide variety of behavior is found, ranging from mean-field behavior for HoRh4B4 to complicated behavior for ErRh4B4, where superconductivity and long-range ferromagnetic order coexist between 0.7 and 1.2 K. Long-range ferromagnetic order is found at the lowest temperatures for all alloy compositions. Alloys with more than about 30% Ho order magnetically along the c axis and superconductivity is destroyed in these alloys in a sharp transition coincident with magnetic ordering. Alloys near the ErRh4B4 composition order in the basal plane but undergo a complex ordering process through a sinusoidally modulated state. Because Ho and Er have competing orthogonal magnetic anisotropies, compounds near the composition Ho0.25Er0.75Rh4B4 are near a multicritical point in the magnetic phase diagram.
Magnetic field induced superconductivity
Authors: Fuller W. W. , Wolf S. A. , Huang C. Y. , Harrison D. W. , Luo H. L. , Maekawa S.
Published: February 2003

The electrical resistance R and magnetic susceptibility χ of the pressure induced superconductors SnxEu1.2−xMo6S8 have been investigated as a function of magnetic field H up to 17 T and at pressures up to 18 kbar. Anomalous behavior is observed both in R versus H and χ versus H. The resistive behavior at p = 14 kbar at low temperatures is consistent with field enhanced superconductivity resulting from a large exchange field that compensates the applied field.
57Fe Mössbauer spectroscopy on hydrogenated ScFe2
Authors: Smit P. H. , Donkersloot H. C. , Bushchow K. H. J.
Published: February 2003

The intermetallic compound ScFe2 is capable of absorping large amounts of hydrogen, which can be derived from the measured absorption isotherm and from the lattice constant before and after charging. The magnetic properties of ScFe2 are sensitive to small variations in the stoichiometry and are changed significantly after hydrogen absorption. Magnetization measurements and 57Fe Mössbauer spectroscopy have been performed on the stoichiometric composition and a composition somewhat excessive in iron. The increase in magnetic moment and hyperfine field at the iron nuclei are much smaller for the off-stoichiometric compound. From the temperature dependence of the Mössbauer spectra it is concluded that this effect is due to a difference between the two compositions in the occupation of the various interstitial holes by the hydrogen atoms. In the stoichiometric compounds an efficient shielding of the iron sublattice from the scandium sublattice results from a preferential, symmetric filling of the interstitial holes. In the off-stoichiometric composition the shielding is much less effective, since a fraction of the iron atoms occupy scandium positions and thereby affect the occupation of many interstitial holes.
Magnetostatic wave devices and applications (invited)
Authors: Sethares J. C.
Published: February 2003

Microwave magnetics technology is faced with two challenges: the development of an analog signal processing capability directly at microwave frequencies, and development of electronically tunable nanosecond time delays for phased array antennas. The focus is on these two problems from the point of view of magnetostatic wave (MSW) technology in thin films such as liquid phase epitaxy yttrium iron garnet. An assessment is made of MSW devices, their role in realizing wideband phased arrays, and how MSW stacks up against competing technologies. Important devices include oscillators, signal to noise enhancers, frequency separators, filters, tunable time delays, and compressive receivers. One MSW device, a simultaneous pulse separator, is now scheduled to be incorporated into an existing system. This is a first for MSW. Although it is encouraging, much work remains in the areas of materials research, dispersion control, nonuniform biasing fields, and improved theory. The largest payoff may well be in phased array antennas due to the large number of elements involved. Some of the requirements for phased array antennas, including solid state transmit/receive modules and adaptive antennas, are addressed.
Ion-implanted magnetostatic wave reflective array filters
Authors: Carter R. L. , Owens J. M. , Smith C. V. , Reed K. W.
Published: February 2003

Ion-implanted bars have been used in fabricating magnetostatic surface wave normal incidence reflective array filters at 3.0 GHz. A theory is presented, based on a dispersion relation derived from a four layer model, and data taken agrees well with the theory. The ion-implanted bars provide a solution to problems previously associated with etched grooves and metal bars.
Magnetostatic wave precursors in thin ferrite films
Authors: Stancil D. D.
Published: February 2003

Precursors, or forerunners, are characteristic features of wave propagation in dispersive media. Magnetostatic wave precursors have the feature that their time of arrival does not depend on the center frequency of a propagating microwave pulse but can depend on the dc bias field. In the case of forward volume waves in an infinite, isolated slab, the arrival time depends on neither the frequency nor the bias field. This fact may prove to be of use in the physical characterization of thin films. A phenomenological theory for these precursors based on the approach taken by Sommerfeld and Brillouin is briefly described. In addition, experimental precursors due to forward volume waves, backward volume waves, and surface waves are reported. The qualitative and semiquantitative agreement between theory and experiment is very good.
Abstract: Correlation of Mössbauer studies on Metglas 2605 alloys with magnetomechanical coupling
Authors: Bucci C. A. , Methaseri T. , Clark A. E. , Savage H. T.
Published: February 2003

The present work correlates the direction and spread of the magnetization measured by 57Fe Mössbauer absorption with the magnetoelastic coupling factor k for amorphous field-annealed ribbons of the 2605 Metglas family: 2605Co and 2605SC with k = 0.71 and ≳0.9, respectively. The absorption line intensities measured for different orientations of the ribbons relative to the γ-rays allow us to determine the direction of M relative to the ribbon. In particular, the component of the magnetization in the direction of the annealing field ma is maximum for the same annealing temperatures (360 °C for 2605Co and 400 °C for 2605SC) that induce the maximum coupling coefficient. In both cases the in-plane magnetization is maximum along the direction of the annealing field, and ma is as high as 0.95 for 2605SC, while it is 0.75 for 2605Co, thus indicating that the overall spread of magnetization directions in the sample is quite small for the SC ribbon. This implies that the dependence of k on bias field can be understood in terms of a simple moment-rotation model. In studying the effect of higher annealing temperatures, the Mössbauer spectra also show that, for SC ribbons, surface crystallization is produced near 420 °C followed by bulk crystallization near 440 °C, whereas for CO ribbons, bulk crystallization is first observed at 370 °C. In both cases the correlation between the decrease in k and the onset of either surface on bulk crystallization is clear. In addition to the previous results on k, a direct determination of (1−k2) is independently performed by using frequency-dependent ac susceptibility measurements in the range between 1 kHz (constant stress regime) and 1 MHz (near constant strain regime). Although the high-frequency side of the data requires accurate corrections for Eddy-current losses, the kCo and kSC values so far determined are 0.7 and 0.92, respectively.    a)Metglas is a registered trademark of the Allied Chemical Corporation.  b)Associated with American University.  c)Associated with Naval Surface Weapons Center.  1C. Modzelewski, H. Savage, L. Kabacoff, and A. Clark, IEEE Trans. Magn., MAG−17, 2837 (1981).
Magnetic susceptibility of antiferromagnetic nickel diglycine dihydrate
Authors: Calvo R. , Nascimento O. R. , Fisk Z. , Suassuna J. , Oseroff S. B. , Machin I.
Published: February 2003

The magnetic susceptibility χ of nickel diglycine dihydrate has been measured between 0.6 and 120 K. The high-temperature data were taken in powder and follow a Curie law behavior with μeff = 3.189 μB and an antiferromagnetic Curie temperature TC = 2.47 K. At low temperatures the χ vs temperature curves for powder and oriented single crystals deviate from the Curie law; they show a maximum χ at about 2.21 K and an abrupt decrease at lower temperatures. The observed behavior of χ for nickel diglycine dihydrate indicates dominating antiferromagnetic interactions between Ni ions. A phase transition to an antiferromagnetic phase occurs below 2.2 K.
Random field effects in diluted anisotropic antiferromagnets
Authors: Belanger D. P. , King A. R. , Jaccarino V.
Published: February 2003

Linear birefringence has been used to study the effects of random dilution on the critical behavior near TN in the anisotropic antiferromagnetic systems MnxZn1−xF2 and FexZn1−xF2. In the critical region the temperature derivative of the birefringence is almost entirely magnetic in origin and is proportional to the magnetic specific heat. Measurements were made in magnetic fields 0⩽H0⩽20 kOe applied parallel to the easy axis. Such an applied field is expected to couple with the random magnetization generating effective random fields which cause large changes in the critical behavior. With increasing field, dramatic effects on the shape of the magnetic specific heat occur within a crossover region. Large shifts in TN were observed as a function of the applied field for several concentrations. The observed effects are in qualitative agreement with the theoretical predictions.
Nuclear relaxation study of the randomly diluted antiferromagnets MnxZn1−xF2 and FexZn1−xF2
Authors: Yasuoka H. , Vernon S. P. , Jaccarino V.
Published: February 2003

The nuclear spin-lattice (1/T1) and spin-spin (1/T2) relaxation rates have been measured for 19F nuclei with no magnetic near neighbors (F0) in diluted antiferromagnetic MnxZn1−xF2 and FexZn1−x F2, for x between 0.1 and 0.8. For T≫Tn, 1/T1 in FexZn1−xF2 varies nearly as x1/2. This result indicates that the relaxation process is dominated by the electron-nuclear dipole interaction with electronic spins in exchange-coupled clusters. In contrast, 1/T1 in MnxZn1−xF2 is independent of x, for x greater than 0.5. As x decreases, 1/T1 increases until a maximum is observed at x≃0.1. The departure from x1/2 behavior is found to be proportional to x(1−x)8, indicating that the exchange-isolated Mn electronic spins dominate the nuclear relaxation for x less than 0.4. The absence of the exchange-isolated electronic spin contribution 1/T1 in FexZn1−xF2 is attributed to the rapid electronic spin-lattice relaxation rate (τsl)−1 of the Fe2+ ion at elevated temperatures. However, this contribution has been observed at 77 K where the dependence of 1/T1 on x is virtually identical to that observed in the Mn-Zn system. The temperature dependence of 1/T1 in FexZn1−xF2 exhibits a critical-like divergence near the Néel temperature, for x above the percolation limit.
Single crystal growth and magnetic properties of YIG:Pr4+
Authors: Ostorero J. , Marais A. , Makram H. , Villers G. , Porte M. , Tighezza M.
Published: February 2003

Single crystals of Y3−x−zCaxPr4+xPr3+z−xFe5 O12 have been successfully grown. Their magnetic moments have been measured and interpreted on the basis of Néel’s model. Cubic magnetocrystalline anisotropy and growth induced uniaxial anisotropy have been obtained on spherical samples using torque measurements.
Neutron diffraction study of the umbrella structure on holmium iron garnet
Authors: Guillot M. , Marchand A. , Tchéou F. , Feldmann P.
Published: February 2003

In Ho3Fe5O12, canting of the rare-earth magnetic moments is evidenced by neutron diffraction. Assuming the garnet to be cubic, analytic expressions of the superstructure lines are given as simple combinations of both components (parallel and perpendicular to [111]) of the Ho3+ moments. New parameters of the ’’umbrella structure’’ are given.
Abstract: A numerical model for Barkhausen coercivity
Authors: Della Torre E.
Published: February 2003

The well-known Barkhausen effect occurs when a domain wall moving through a crystal gets ’’hung up’’ at imperfections. A numerical model is described here that gives a possible mechanism for this effect. It is assumed that the imperfection is a spherical nonmagnetic inclusion in an otherwise perfect ferromagnetic material. The equilibrium wall shapes, as the applied field is slowly increased, are successively computed. When the wall ’’touches’’ the hole, the induced pole strength decreases and a sudden irreversible change is triggered. The field strength at which this takes place is the coercive force. A new numerical techique is introduced to overcome the ’’stiff’’ equations encountered. A discussion of these techniques will be included in this presentation.     a) Work supported by National Science Foundation grant.
Ultrasonic velocity measurement in conductive magnetic fluids
Authors: Chung D. Y. , Lin J. X. , Funderburk W. A. , Popplewell J.
Published: February 2003

The propagation of ultrasonic waves in iron-in-mercury magnetic fluids has been studied by a continuous wave (CW) method. The CW method proved to be adequate for studying the velocity change (ΔV) due to an external magnetic field. The magnitude of ΔV was about 0.3% for field of 100 G. ΔV was also measured at two field angles, when the direction of ultrasonic propagation is either perpendicular or parallel to the magnetic field directions. The characteristic time was found to be about 60 sec, which is of the same order as found from other magnetic measurements in the same sample. This fact indicated that there are aggregates of the size 104 Å in the fluid.
Manometric measurement of susceptibility of liquids in high magnetic fields
Authors: Meservey R. , Tedrow P. M. , Brooks J. S. , Zimmerman G. O.
Published: February 2003

We have adapted a classical nonresonance method to measure the magnetic susceptibility of liquid 3He at low temperature. With modern instrumentation the method has sufficient sensitivity to measure the nuclear susceptibility and nuclear relaxation time of 3He. The technique is based on the fact that for two locations on the free surface of a liquid in equilibrium, the height difference is given by h2−h1 = χ(H22−H21)/2g, where H2 and H1 are the local values of the magnetic field at the liquid surface, χ is the magnetic susceptibility per unit mass, and g the acceleration of gravity. Change in the liquid level between closely spaced parallel electrodes changes their capacitance, which is used to obtain h2−h1. Differences in χ as small as 10−10 emu/gm were easily detected in these measurements. The method can be applied to other weakly magnetic liquids and, in modified form, to solids.
Static magnetic and Mössbauer spectroscopic measurements on Fe-N thin films
Authors: Lo C. , Krishnaswamy S. V. , Mulay L. N. , Diffenbach R. A.
Published: February 2003

Discrete Fe-N phases which are difficult to prepare by common chemical methods have been synthesized by rf sputtering. Some of these phases are relevant in the Fischer-Tropisch synthesis of synfuels. Single Fe-N phases as well as the desirable mixtures have been synthesized by a careful control of various sputtering parameters. These films showed varied columnar microstructure with the columns perpendicular to the film plane. Magnetic anisotropy measurements for selected samples containing pure Fe4N, ε-Fe3N, and Fe4N+αFe have been carried out. The anisotropy components when the field (H) is perpendicular or parallel to the columns show significant differences in the magnetization versus H curves up to fields of 8 kOe at room temperature and evidence for superparamagnetism. These results are explained on the basis of structural anisotropy of the columnar structure of the films. Mössbauer results for the ε-nitride film are compared with those reported in the literature and again related to the microstructure.
Stress operated random access, high-speed magnetic memory
Authors: Schröder Klaus
Published: February 2003

The memory consists of a checkerboard pattern of transducers. Each transducer is connected to two lines of electrical conductors which form two grids of parallel lines. The grids are placed perpendicular to each other. A magnetic block is placed on top of each transducer. A magnetic field is applied to the system of magnetic blocks. It is slightly smaller than the coercive field H(c). One transducer generates a stress wave which will travel into the magnetic block adjacent to it. Its dipoles will line up parallel to the applied field if the stress is high enough. This corresponds to the writing process. If a stress wave interacts with a magnetic block which is magnetized antiparallel to the applied field, the block will reverse its magnetization direction. This leads to stress waves, which will induce a voltage in the transducer. No magnetic energy release and no generation of new stress waves is expected if the field is applied parallel to the magnetization direction of the block. This is the readout process.
The concept and initial studies of a crosstie random access memory (CRAM)
Authors: Schwee L. J. , Hunter P. E. , Restorff K. A. , Shephard M. T.
Published: February 2003

The crosstie-Bloch line memory elements which were used in the serial crosstie memory can be reconfigured into a random access memory. The new approach decreases the access time, eliminates complexity, increases reliability, and is straightforward. The five-level nonvolatile device is intended to be integrated on a silicon chip with decoders and drivers on the chip. It is expected that some of the five levels will be folded in with the levels used to connect the transistors needed for decoding and driving.
Electrostatic TEM studies of twisted domains in thin iron films
Authors: Karamon H. , Rempfer G. F. , Dash J. , Takeo M.
Published: February 2003

The Lorentz and Foucault methods have been used to study twisted domains in thin (∼200 Å) iron films (made by evaporation) in an electrostatic transmission electron microscope (TEM). Twisted domains have been observed to occur spontaneously, as well as during and after the application of an in-plane magnetic field. We have found that twisted domains consist of alternate sections separated by roughly 90° domain walls. Between these sections and the surrounding domain the wall is alternately 90° and 180°. The ripple structure in the micrographs provides further evidence as to the directions of magnetization. When Blochline-crosstie pairs are present, they occur on the 180° walls but not on the 90° walls.
Observations of stimulated Brillouin scattering and enhanced ion wave damping in a z-pinch plasma
Authors: Walsh C. J. , Meyer J. , Hilko B. , Bernard J. E. , Popil R.
Published: February 2003

The backscattered spectrum from short CO2 laser pulses incident upon an overdense z-pinch plasma has been measured. A clear red shift and an exponential growth in the reflectivity to a saturated value of approximately 4% has been observed. The results suggest the presence of strong damping on the scattering ion wave in the saturation region, consistent with predictions of an ion trapping model.
Power losses in a conducting sheet with bar domains. I. Eddy currents due to Barkhausen regions
Authors: Lorenz B. E. , Coren R. L.
Published: February 2003

Energy loss in magnetic steels is generally taken to consist of two parts: static loss, associated with Barkhausen switching and assumed independent of drive frequency, and eddy current loss due to wall motion. Little effort has gone into analyzing the Barkhausen contribution. We consider a model of a magnetic sample in which the Barkhausen volumes are represented as a distribution of sites which reverse their moments at a uniform rate and only along a single axis. Using Green’s function the current distribution of symmetrically placed regions is determined subject to the boundary conditions of periodic bar domains in a thin sheet. In subsequent reports this is used to calculate losses.
Abstract: Power losses in a conducting sheet with bar domains. III. Complete solution for cyclic losses
Authors: Lorenz B. E. , Coren R. L.
Published: February 2003

The total, temporally averaged, expected power density loss due to the combined actions of the Barkhausen (B) and Pry–Bean (PB) mechanisms is p̄ = (ρ/V)(JB+JPB)2 dV            (1)                = p̄ B+p̄ PB+2(ρ/V)JB⋅JPB dV   where p̄B is given by Eq. (II.15),b) p̄PB is the expression derived by Pry and Bean, multiplied by (1−K)2, and V is the domain volume. The last term in Eq. (1) is a result of the simultaneus occurrence of both currents. In evaluating p̄B it was noted in paper II that the B currents from each switching site/section only flow for the time τ so that it was appropriate to consider energies instead of power. In terms of Eq. (II.15): p̄B = fE(w)¯, where f = frequency. This consideration must also enter into the cross term in Eq. (1). Space in this abstract limits the discussion of this term, but one may estimate its behavior by taking the currents to be rms values. Then             p̄ = ̇p̄ B+p̄ PB+2(pB pPB)1/2.              (2)   Since pPB∝f2 and pB∝f, this cross term varies as f3/2; the energy density per cycle becomes             W = p̄ /f = ̇(A1+A2√f̄+A3f)C,     (3)   where the A’s are functions of the model parameters K and a, and C is a common function of the material properties. The middle term in Eq. (3) is new. Comparison with experiments and analysis of data available in the literature is difficult and unreliable because of the uncertain sample parameters and magnetic state relative to the assumptions entering Eq. (3). However, several works on 3.5% Si-Fe lead us to infer the values: a≊10 000/sec and K≊0.1. Similarly, direct comparison of Eq. (3) is inconclusive although some agreement is found in cases where the experimental magnetic parameters can be determined. The traditional view of magnetic reversal has large wall traps and smaller Barkhausen switches superimposed upon the continuous wall motion. These all may actually represent different regimes of a continuous distribution of behavioral properties. The present model separates and approximates the trapped regions and larger Barkhausen switches; the literature experiments on Barkhausen effect, from which the parameter values a and K were derived, probably also reflect this separation. More work is necessary to develop the full distribution properties.    a)This work will be reported more fully in the near future.  b)B. E. Lorenz and R. L. Coren, J. Appl. Phys. 53 XXXX (1982) (preceding paper).
Apparatus for adapting a high-pressure light scattering cell to density measurement
Authors: Abebe M. , Schoen P. E.
Published: February 2003

A new experimental method is presented here by which the density of water, glycerol, HIW (a mixture of isopropyl ammonium nitrate, hydroxyl ammonium nitrate, and water), and solithane 113 was measured at 25 °C and pressure up to 410 MPa.
Derivation of the current-potential equation for steady point-to-plane corona discharges
Authors: Henson Bob L.
Published: February 2003

The characteristic equation showing the dependence of the steady-state current for point-to-plane electrical corona discharges on the point-to-plane potential and other relevant parameters is derived. The mathematical model is based on hyperboloid point to plane geometry and assumes a constant charge-carrier mobility with a constant potential drop across the corona glow region. The equation is an exact relationship for this geometry in that no calculation approximations are used in its derivation.
Deep levels in Si-implanted and thermally annealed semi-insulating GaAs:Cr
Authors: Rhee Jin K. , Bhattacharya Pallab K. , Koyama Richard Y.
Published: February 2003

Deep levels in semi-insulating GaAs:Cr have been detected and characterized before and after Si implantation and thermal annealing. The measurement techniques used were current transients, photoinduced current transients, capacitance transients, and photocapacitance transients. Hole emission from the Cr centers with activation energy ΔET = 0.85±0.01 eV was recorded in the semi-insulating substrates as well as in the implanted layers. An electron trap level with ΔET = 0.52±0.01 eV and a hole trap with ΔET = 0.15±0.01 eV have been consistently observed in the implanted and annealed GaAs. The capture cross section of these traps and other traps detected in unimplanted and implanted GaAs:Cr have been determined.
Deep level transient spectroscopy study in n-type InP
Authors: Lim H. , Sagnes G. , Bastide G. , Rouzeyre M.
Published: February 2003

This paper reports the results of a Deep Level Transient Spectroscopy (DLTS) study on 14 InP diodes fabricated from five different crystals. From 16 observed DLTS peaks and corresponding Arrhenius plots, seven (or eight) trapping levels have been identified whose characteristics are as follows: Trapping levels Characteristics E1 = 210 meV S1 = 3×10−16 cm2 E2 = 190 mev S2 = 7×10−19 cm2 E3 = 330 meV S3 = 4×10−16 cm2 E4 = 500 meV S4 = 2×10−12 cm2 E5 = 410 mev S5 = 1×10−16 cm2 E6 = 630 meV S6 = 2×10−14 cm2 E7 = 330 meV S7 = 5×10−14 cm2
Effect of electron-electron scattering on mobility in GaAs
Authors: Chattopadhyay D.
Published: February 2003

The influence of electron-electron scattering on mobility in GaAs is studied over the temperature range 80–300 K using the variation principle. The mobilities limited by both polar optic and ionized impurity scattering are reduced more significantly due to electron-electron scattering than those limited by deformation potential acoustic and by piezoelectric scattering. For a carrier concentration of 1016 cm−3, the overall mobility is reduced by about 10% at 80 K.
Back surface field and vertical solar cell
Authors: Yang Yu-Tung
Published: February 2003

Experiments show that a region of back surface field is also a region of strong light-to-electric-power conversion capability.
Metal-insulator-semiconductor diodes fabricated on InP, InGaAsP, and InGaAs
Authors: Kobayashi Takeshi , Shinoda Yukinobu
Published: February 2003

The compositional dependence of In1−x Gax Asy P1−y (y = 2.2x) MIS (metal-insulator-semiconductor) diode C-V characteristics was investigated for entire As fraction range (0⩽y⩽1). As the gate insulator, the pyrolytic Al2O3 film was employed. All n-type MIS diodes fabricated on InP, In0.76 Ga0.24 As0.55 P0.45 and In0.53 Ga0.47 As showed almost entire capacitance variation between the accumulation and high-frequency inversion capacitances. The compositional dependence of the C-V curve was clearly seen in its hysteresis and the surface state density distribution. The C-V curve hysteresis becomes less pronounced as the crystal composition is closer to InGaAs. The botton of the V-shaped surface state density distribution shifts toward the conduction band edge as As fraction (y) increases. Therefore, the surface state density near the conduction band edge was reduced to 1012/cm2 eV, compared to the value 1013/cm2 eV at InP surface.
Analysis of free-to-bound flourescence line shapes for a deep level in GaAs:Sn
Authors: Zemon S. , Vassell M. O. , Lambert G. , Bartram R. H.
Published: February 2003

Photoluminescence spectra and decay times have been measured in liquid-phase epitaxial GaAs:Sn as functions of temperature (T = 4.2–300 K) and carrier concentration (n = 6×1016–2×1018 cm−3). High-temperature, deep-level (DL) spectra are identified with conduction-band-to-deep-acceptor transitions and are analyzed in terms of a theory which incorporates both coupling to lattice vibrations and the distribution of initial electronic states. Parameters obtained from a configuration-coordinate model are in reasonable agreement with those derived from low T and decay time measurements. Shifts in the DL spectra with carrier concentration are attributed to band filling and impurity banding.
The interpretation of space-charge-limited currents in semiconductors and insulators
Authors: Gould R. D.
Published: February 2003

The specific current-voltage-temperature dependence of space-charge-limited conduction processes in semiconductors and insulators is largely determined by the distribution in energy of traps within the band gap. A linear dependence of current-density on the square of the applied voltage, may be alternatively interpreted in terms of either a single discrete trapping level, or of an exponential trap distribution. The two types of trapping behavior may be distinguished using measurements of the variation of current with temperature for a range of different constant voltages.
Electron backscattering from thin films
Authors: Niedrig H.
Published: February 2003

The basic principles of electron backscattering from atoms and solids in the energy range 10 to 100 keV are reviewed. The total backscattering from thin self-supporting films, from bulk solids, and from thin surface films on supporting bulk solids is discussed as well as the angular distribution of the backscattered electron intensity for normal and for oblique incidence of the primary beam. The results of theoretical models are compared with experimental results. Contrast mechanisms in scanning electron microscopy based on electron backscattering and the influence of diffraction effects are described. Finally the thickness determination of thin films by electron backscattering and by other methods is reviewed.
Weak- and strong-field magnetoresistance in (111)-oriented n-type PbTe epitaxial films between 1.8 and 300 K
Authors: Allgaier R. S. , Restorff J. B. , Houston Bland
Published: February 2003

Magnetoresistance measurements on epitaxial PbTe, covering a wide range of temperatures and magnetic field intensities, are reported. Nearly all of the results exhibit a common behavior which depends only on μHB, the product of the Hall mobility and magnetic field. The usual quadratic weak-field dependence is followed by a tendency towards saturation near μHB = 1, and by a linear range for μHB = 10–300. The relevance of sample inhomogeneities, boundary effects, and quantum-limit magnetoresistance theories is considered. None of these factors seems capable of explaining the general insensitivity of the results to temperature, scattering mechanisms, and sample profile.
HgTe/CdTe heterojunctions: A lattice-matched Schottky barrier structure
Authors: Kuech T. F. , McCaldin J. O.
Published: February 2003

HgTe-CdTe lattice-matched heterojunctions were formed by the epitaxial growth of HgTe on CdTe substrates using a low-temperature metal organic chemical vapor deposition technique. These heterojunctions combine features of the Schottky barrier structure, due to the high carrier concentrations found in the semimetallic HgTe, with the structural perfection present in a lattice-matched heterojunction. The measured Schottky barrier height varied from 0.65 to 0.92 eV depending on the details of the heterojunction growth procedure used. This dependence may be due to the formation of an inversion layer in the CdTe at the interface. Presence of such an inversion layer suggests that the valence band discontinuity between HgTe and CdTe is small, in agreement with previous theoretical estimates.
Slow and fast states induced by hot electrons at Si-SiO2 interface
Authors: Fischetti M. V. , Gastaldi R. , Maggioni F. , Modelli A.
Published: February 2003

The kinetics of formation of both fast and slow states at the Si-SiO2 interface during avalanche injection is carefully examined on Al gate, wet oxide metal-oxide-silicon capacitors. They are both found to approach exponentially a saturation value. The annealing behavior of fast and slow states is examined by means of isochronal heat treatments. They can be annihilated at temperatures lower than 600 °K with similar activation energies. Correlations between slow and fast states are discussed. The instability of flatband voltage after avalanche injection due to the presence of slow states is characterized at various temperatures and electric fields. A process involving thermal activated hopping (Continuous Time Random Walk Model) among the slow states may be invoked in order to explain the experimental data.