bluuebunny/crossref_metadata_2025 huggingface dataset:
Lorentz microscopy studies of magnetization patterns recorded on a real disk
Authors: Byun C. , Rauch G. C. , Greggi J. , Messinger C. , Ng P.
Published: July 2002

In this paper we describe a new method for producing samples with large thin areas for Lorentz TEM observation of recorded magnetic domain patterns in production-quality thin-film rigid disks. In this method, as applied in this paper to the study of electroplated Co-Ni-P media, a strippable metal layer is introduced beneath the magnetic layer, along with plated Ni-P which provides a sublayer for magnetic film growth comparable to the normal polished electroless nickel substrate. In this way one can produce a magnetic layer identical to that on a real disk, write data on the disk with a flying head, and then remove the magnetic layer for TEM analysis. We also describe some typical applications of the new method, including a comparison of magnetic domain structure at recorded transitions in high- and low-noise media, and an illustration of the effect of head pole geometry on bit-cell shape.
Magnetism and bonding in light actinide and rare earth systems (invited)
Authors: Eriksson Olle , Brooks M. S. S. , Johansson Börje , Albers R. C. , Boring A. M.
Published: July 2002

The importance of including all of Hund’s rules in self-consistent electronic-structure calculations in solids is pointed out. We present a scheme that accounts for the interactions that lead to these rules, and we give examples of when these interactions become important. Calculated ground state properties (chemical bonding, magnetic moment, magnetic form factor) of actinide and rare earth systems are found to agree better with experiment when all Hund’s rules are accounted for. On the other hand, but also in agreement with experiment, we find that Hund’s second and third rule contributions for Fe, Co, and Ni are small.
Recording and tribological properties of CoNi magnetic films on chemically textured aluminum rigid disk substrates (abstract)
Authors: Tsuya N. , Tokushima T. , Hirayama Y. , Oka Y.
Published: July 2002

In a rigid disk a very smooth surface is desirable for high density recording, while it tends to stick to the magnetic head. To avoid this difficulty, the mechanical texturing (M/T) is widely used. Unfortunately very low flying height can’t be achieved with the M/T. To improve the flying height, authors have developed a new texturing process using anodically oxidized aluminum substrates named chemical texturing (C/T).1 Aluminum anodic oxide films have a regularly arranged honeycomb structure and uniform and roughness-controlled surfaces were formed by etching process of chemical texturing. In the present research, the relation between the recording and tribological properties and the etching conditions were investigated. On C/T substrates Cr, a longitudinal magnetic layer CoNi, C were sputtered in an inline sputtering equipment. The surface of the sputtered layer was flat (Ra<5 Å) and uniform. Magnetic and electrical properties (coercive force, squareness, over write, modulation and so on) were examined. In spite of isotropy on the disk surfaces, the modulation caused by the inline sputtering was not observed, and high coercive force of 1200 Oe was obtained. Tribological properties (gride height, CSS, friction) were measured. Gride height was lower than 0.1 μm, and CSS more than 30 000 cycles. In semi-pilot plant production, thousands of C/T disks were prepared. Yield of disks having less than 5 missing and/or extra pulses was higher than 95%.
Wear properties of yttria-stabilized hafnia overcoats (abstract)
Authors: Miller M. S. , Crist J. , Narayan P. B. , Skelcher W. L.
Published: July 2002

Yttria-stabilized hafnia is shown to be another transformation toughening ceramic with good tribological properties. The hafnia was rf-diode sputtered over a 300 nm chromium underlayer on textured aluminum-NiP 130 mm diameter substrates. Wear properties of the hafnia overcoat were evaluated, via contact start-stop (css) testing, as a function of oxygen partial pressure, substrate bias potential and argon pressure. Depending on deposition conditions, a wide range of wear properties were observed. Lower oxygen partial pressures <1×10−4 Torr, produced the lowest average friction levels of 0.4–0.5 after 30 000 css. Use of simultaneous substrate bias during deposition, produced hafnia overcoats with relatively high friction levels of 0.7–0.9 after 30 000 css. TEM micrographs revealed some microcracking of the overcoats along texture lines.
A hybrid recording scheme for high-areal-density information storage (abstract)
Authors: Hintz M. B.
Published: July 2002

A novel recording scheme which combines optical-recording track widths with magnetic-recording linear transition densities is conceptually described. The system uses a magnetic transducer to both record and read information, but track width definition and track following are accomplished with a focussed laser beam, as in optical recording. Area recording densities of (1–3)×108 bits/cm2 appear possible. Several possible implementations of the method are presented and their advantages and disadvantages are discussed.
Evidence of the existence of a line of multicritical Lifshitz points in the phase diagram of manganese phosphide (abstract)
Authors: Brumatto H. J. , Becerra C. C. , Oliveira N. F.
Published: July 2002

Experimentally pure Lifshitz critical behavior has only been reported in the orthorhombic magnetic system MnP which exhibits uniaxial Ising-type Lifshitz points LP (d=3, n=1, m=1). Two LPs have been previously identified in MnP.1,2 One when the external magnetic field H was applied along the intermediate b axis, the other when H was along the hard anisotropy axis a. Both LPs occur roughly at the same temperature (T1∼121 K) but at different values of H due to the difference in anisotropy. In this work we report on measurements made with H applied within the ab plane. The observed phase diagram obtained using an ac susceptibility technique shows, near the confluence of the modulated and ferromagnetic phases with the paramagnetic phase the same characteristics of the phase boundaries found for H along a and b. The temperature at the multicritical point is ∼121 K. A preliminary analysis of the crossover exponent φ, obtained from the shape of the phase boundaries give φ≂0.6, a value that is consistent with that found for H along the a and the b axes. These data suggest that there is a line of LPs connecting the multicritical points found when H is along the b and a axes.
A strong pinning model for the coercivity of die-upset Pr-Fe-B magnets
Authors: Pinkerton F. E. , Fuerst C. D.
Published: July 2002

We have measured the temperature dependence of the intrinsic coercivity Hci(T) between 5 and 565 K in a die-upset Pr-Fe-B magnet. Over a very wide temperature range up to 477 K, Hci(T) is in excellent agreement with a model for strong domain-wall pinning by a random array of pinning sites proposed by Gaunt [P. Gaunt, Philos. Mag. B 48, 261 (1983)]. The model includes both the temperature dependence of the intrinsic magnetic properties of the Pr2Fe14B phase and the effects of thermal activation of domain walls over the pinning barrier. The pinning sites are modeled as nonmagnetic planar inhomogeneities at the boundaries between platelet-shaped Pr2Fe14B grains. We develop an expression for the maximum pinning force per site, f, and derive the model prediction that (Hci/γHA)1/2 varies linearly with (T/γ)2/3, where HA and γ are the magnetocrystalline anisotropy field and the domain-wall energy per unit area of the Pr2Fe14B phase, respectively. Significant deviations from the model are observed only at high temperature, suggesting that the strong pinning model is no longer valid very close to the Curie temperature (565 K). The present result agrees with the model fit obtained for a die-upset Nd-Fe-B magnet.
Oscillations in the Stokes–anti-Stokes ratio in Brillouin scattering from magnons in thin permalloy films
Authors: Moosmüller H. , Truedson J. R. , Patton C. E.
Published: July 2002

A Brillouin light-scattering study of surface magnons in permalloy thin films shows a distinct oscillation in the Stokes–anti-Stokes intensity ratio as a function of the in-plane wave number in the 0– 2.5×105 cm−1 range. This result differs from the previously reported monotonic dependence for thin iron thin films.
Direct observation of dynamic strain bifurcations and chaos in magnetostrictive amorphous ribbons
Authors: Vohra S. T. , Bucholtz F. , Dagenais D. M. , Koo K. P.
Published: July 2002

Period doubling, quasiperiodicity, phase locking, and chaos are observed in the strain dynamics of a magnetically driven magnetostrictive ribbon (Metglas 2605S-2). The dynamic strain response of the ribbon was measured with a fiber-optic Mach–Zehnder interferometer. The predicted universal behavior was characterized with power spectral density measurements and by phase-space flow. The nonlinearity responsible for observing universal behavior in the system does not involve the ΔE effect.
The head crash induced by liquefaction of gases
Authors: Kurokawa K. , Takahashi M. , Shinohara M.
Published: July 2002

The most frustrating type of head crash is one that wipes out data on one track after thousands of hours of stable operation. Analysis of debris gives few clues as to its cause. This paper explains this type of head crash and identifies the liquefaction of organic gases on the taper section of the head slider as its primary cause. Both theoretical considerations and experimental results are presented.
Brillouin spectroscopy of spin waves in sputtered CoPt alloy films and Co/Pt/Co multilayered films
Authors: Murayama A. , Miyamura M. , Nishiyama K. , Miyata K. , Oka Y.
Published: July 2002

Sputtered Co1−xPtx (x=0–0.14) alloy films have been studied by Brillouin scattering of spin waves and compared with results on Co/Pt/Co multilayered films. Brillouin spectra of the surface spin waves in the sputtered alloy films are remarkably broadened as an increase of the Pt content. The in-plane coercivity of the films also increases as the increase of the Pt content, which indicates larger and better oriented grains with proper separations that result from higher Pt content. The broadening of the spin-wave spectra is caused by the magnetic inhomogeneity due to the grains in the film. The exchange stiffness constant of the CoPt alloy films is determined from the magnetic field dependence of the frequency shifts of the surface and standing spin waves. To investigate the exchange interaction in the inhomogeneous alloy films, Co/Pt/Co multilayered films with the Pt interlayer of thickness of 0–40 Å have been fabricated as a model material. From the analysis of the frequency shifts of the spin waves, the exchange interaction between Co layers through the Pt interlayer is evaluated.
Magnetism instability under pressure in RMn2 compounds
Authors: Voiron J. , Ballou R. , Deportes J. , Galera R. M. , Lelievre E.
Published: July 2002

Magnetic properties of the Nd-, Gd-, Y-, TbMn2 intermetallic cubic Laves phases have been studied under applied pressure. Large effects of pressure are observed on the ordering temperatures and on the magnetization curves. In all cases the ordering temperatures decrease and the Mn magnetic moment tends to be suppressed with increasing pressure. Results confirm the existence of a critical distance between Mn atoms, for the appearance of a Mn magnetic moment.
Magnetic anisotropy and soft magnetism of iron nitride thin films prepared by facing-target sputtering
Authors: Morisako Akimitsu , Matsumoto Mitsunori , Naoe Masahiko
Published: July 2002

Iron nitride thin films have been prepared at various nitrogen-gas pressures (PN2) on a heated substrate by using a facing-target sputtering (FTS) system, and their crystallographic characteristics and magnetic properties have been investigated. Total gas pressure (PN2+PAr) was set at 2 mTorr. MS for the films prepared at PN2 below 0.05 mTorr was slightly higher than 1700 emu/cc with scattering and did not show apparent dependence on PN2. These films exhibited a bcc structure, and the lattice constant was about 2.875 Å, which was larger than that of bulk iron. Large values of compressive stress were observed in these films. The films prepared with pure argon gas exhibited isotropic magnetic properties in the film plane, while the films with PN2 above 0.07 mTorr exhibited magnetic anisotropy in the film plane. The direction of the easy axis was parallel to the magnetic stray field in the FTS system. The films with soft magnetism were prepared at PN2 around 0.1 mTorr, which corresponded to the onset of the growth of γ′-Fe4N. A minimum Hc of 0.5 Oe in the hard axis and Ms of 1700 emu/cc were obtained in these films.
Structure sensitivity of magnetization processes at the spin-reorientation transition in Nd2Fe14B
Authors: Foldeaki M. , Koszegi L. , Dunlap R. A.
Published: July 2002

Calculations based on different micromagnetic models were carried out in order to describe the behavior of the ac susceptibiIity in the temperature range of the spin-reorientation transitions in hard magnets. It was found that the rotational susceptibility shows a sharp cusp at the transition temperature, while the contribution due to an increase in the domain- wall mobility is less significant. As well, there is a significant contribution of domain- wall processes to the overall susceptibility over the entire range of temperatures studied (80– 180 K). For randomly oriented bulk samples, the susceptibility cusp has been experimentally observed. The susceptibility of randomly oriented powders shows only a moderate temperature dependence below the transition, followed by a sharp decrease at the transition temperature. The frequency dependence of the susceptibility showed the behavior expected for conducting samples, proving that domain-wall dynamics (e.g., aftereffects, lattice-defect–domain-wall interactions, etc.) do not play a role in the observed temperature dependence of the susceptibility.
Field-induced transitions in Ho2Co17 studied in fields up to 50 T
Authors: Tomiyama F. , Ono M. , Date M. , Yamagishi A. , Verhoef R. , de Boer F. R. , Franse J. J. M. , Zhong X. P.
Published: July 2002

High-field magnetization studies have been performed at 4.2 K on single-crystalline Ho2Co17 in the high-field facilities of the Universities of Amsterdam and Osaka up to magnetic fields of 38 and 50 T, respectively. Several magnetic transitions have been observed for field directions in the easy hexagonal plane in the field range between 20 and 50 T. The transitions reflect field-induced changes in the configuration of the holmium and cobalt magnetic moments and are a measure for the intersublattice-coupling parameter.
Trends of hybridization-induced magnetism in cerium monochalcogenides
Authors: Kioussis N. , Swearingen D. , Cooper B. R. , Wills J. M.
Published: July 2002

A synthesis of ab initio linear-muffin-tin-orbital (LMTO) electronic structure calculations and a phenomenological model of orbitally driven magnetic ordering has been applied to investigate trends of the effect of hybridization of moderately delocalized f electrons with band electrons on the diverse magnetic behavior across the cerium monochalcogenide series. The parameters entering the Anderson lattice model Hamiltonian are determined from total-energy supercell warped-muffin-tin LMTO calculations with zero, one, and two electrons in the cerium 4f core state. The origins, in the electronic structure, of the variation of the density of states at the Fermi energy, the f-state resonance width, the hybridization potential, the hybridization-dressed crystal-field splitting, and the hybridization-mediated exchange interactions with the chemical environment (anion size) on going down the chalcogen column have been investigated systematically, increasing thus the degree of f-electron localization as the cerium-cerium separation increases.
Evaluation of sintered and reground Nd-Fe-B alloys with Co, Dy and Al substitutions for use in bonded magnets
Authors: Li M. , Strnat K. J. , Mildrum H. F.
Published: July 2002

Crushing sintered Nd-Fe-B into coarse powders quickly destroys their coercivity and alignability in a magnetic field, making them useless for bonded magnets. But a double anneal of 890 °C/1 h plus 570 °C/1 h can largely restore these properties for particles ≳200 μm. Alloys modified with two or more of Co, Dy, and Al additions suffer much lower Hci and Hk losses during grinding. They also respond favorably to annealing, but less than the ternary alloy. Sintered magnets of four compositions were prepared in many size fractions between ∼50 and 1600 μm and demagnetization curves measured as-crushed, after single and double anneals. Powders of alloys (Nd0.88Dy0.12)(Fe0.8−xCo0.12B0.08 Alx)5.5, where x=0.012 and 0.036, retain Hci values above 10 kOe down to ∼200 μm and could be quite useful in bonded magnet fabrication. This paper reports detailed results for two selected compositions: the six-component alloy with x=0.012 and ternary Nd-Fe-B.
Hydrogen induced radial anisotropic R-Fe-B magnet (R=Pr,Dy)
Authors: Lin C. H. , Chen C. J. , Liu T. Y. , Chang W. C. , Wu C. D.
Published: July 2002

The effect of alloying concentration of Dy and the absorption amount of hydrogen on the magnetic properties of PrFeB magnets have been studied in this work. Experimental data show that the easy direction of magnetization (EDM) of the Pr-Fe-B-H system is determined by hydrogen concentration. Radial anisotropic magnets can be obtained from hydrogenated Pr15Fe79B6 powders with hydrogen of 4500 ppm. A slight decrease of hydrogen content down to 4250 ppm leads to a uniaxial anisotropic magnet. Partial replacement of Pr by Dy significantly influences the anisotropy of the Pr-Fe-B-H system with saturated hydrogen. A 0.9 at. % Dy substitution for Pr changes the anisotropy of hydrogen decrepitated powders from planer to cone, thus resulting in an isotropic magnet. As the amount of Dy substitution increases to 1.35 at. %, the EDM of magnets persist in the field direction during alignment compaction.
Magnetic hardening in melt-spun Fe-rich Fe-Mo alloys
Authors: Wan H. , Zhang Y. J. , Hadjipanayis G. C.
Published: July 2002

The change in magnetic properties corresponding to the structural changes that occur during aging at temperatures in the range 500–900 °C have been studied in melt-spun Fe-Mo alloys using magnetometry, x-ray diffraction (XRD), and transmission electron microscopy (TEM). The as-spun ribbons were found to be magnetically soft with a coercivity smaller than 180 Oe. After a heat treatment at temperatures in the range of 600–670 °C, the coercivity was found to increase to 600 Oe and the magnetization decreased. It is suggested that Mo clustering takes place with heat treatment and this may explain the decreased magnetization and increased coercivity of the samples. Mo-rich clusters can act as domain-wall pinning centers and therefore can lead to an increased coercivity.
Parametric excitation of magnetostatic modes in thin yttrium iron garnet films (invited)
Authors: McMichael R. D. , Wigen P. E.
Published: July 2002

Recently, equations of motion for the normal modes of normally magnetized thin films have been successful in predicting experimental auto-oscillation frequencies and onset pumping powers in circular yttrium iron garnet films under ferromagnetic resonance. These results have now been extended to include ‘‘hidden’’ modes, modes that do not couple directly to the pumping field. Using the equations of motion derived for this system, hidden modes are shown to be parametrically excited through processes analogous to the second-order Suhl instability. Through excellent agreement with experimental results, parametrically excited hidden modes are shown to be involved in features of the domain of auto-oscillation that were not previously understood. Numerical studies of the effects of degeneracy breaking in pairs of hidden modes show how small perturbations can fix the phases of parametrically excited modes. The random-phase approximation is shown to have a significant effect in simulations of the experiment.
Anomalous composition dependence of anisotropy in amorphous Tb-Fe and Ho-Fe (abstract)
Authors: Hellman F. , Gyorgy E. M. , van Dover R. B. , Felder R. J.
Published: July 2002

The magnetic anisotropy Ku of magnetron cosputtered amorphous Tb-Fe has been found to drop precipitously when the composition is within several at. % of 22 at. % Tb, a composition which is the room-temperature compensation point. The samples showing this low value for Ku are magnetically saturated (fields up to 100 kOe were used) and torque curves have the expected uniaxial behavior. The unexpected decrease is correlated with a previous finding of anomalous, nonuniaxial anisotropy for films prepared with less than 22 at. % Tb when nonperpendicular incident angles are used for the deposition. We hypothesized that an undetected phase separation was occurring in these Fe-rich samples. The present study examines films prepared on rotating substrates, essentially eliminating the effect of incident angles. As previously predicted, with no incident angles the phase separation is unobservable by magnetic anisotropy, but presumably is still present and may account for the observed drop in Ku. Analogous results have been seen in amorphous Ho-Fe; the relevant composition is far from magnetic compensation, supporting the conclusion that the coincidence of compensation with the anomalies in Tb-Fe is accidental. This behavior of the anisotropy is inconsistent with simple models for the atomic structure and the source of Ku. The effect of deposition temperature will also be discussed.
Magnetic characteristics of amorphous CoDyZr films with well-defined in-plane uniaxial anisotropy (abstract)
Authors: Suran G. , Sztern J.
Published: July 2002

Results are reported upon the process of formation, the magnitude, and physical origin of in-plane uniaxial anisotropy Ku in Co1−α−β(Dy)α(Zr)β layers. The film was studied for the concentration range of 0.05≤α≤0.15 and 0.05≤β≤0.12. The in-plane anisotropy was formed by applying a field of 0.1 T in the film plane during the rf sputter deposition. The results show without any ambiguity that the magnitude and the direction of Ku is essentially related to the pressure of the sputtering gas PAR. For the lowest pressure used an extremely well-defined in-plane uniaxial anisotropy field Hk is obtained with practically no detectable dispersion. Ku is fairly large and is in the range of 1.2 < Ku<3×105 erg/cm3 (250 < Hk<700 Oe) for the concentration range studied. Along the in-plane easy axis a rectangular hysteresis loop is detected which exhibits a rather small coercive field of 3 < Hc<10 Oe. With increasing PAR the magnitude of Ku increases largely and when PAR exceeds a critical threshold (PAR)c a film with a biaxial structure is obtained having an in-plane and a perpendicular anisotropy Kp. (PAR)c is related to the Dy content of the films and decreases for higher Dy concentrations. The basic mechanism of the formation of Ku and its change with PAR is similar to that observed in amorphous Co nonmagnetic transition-metal-type layers and can be explained by a progressive change of the local structure.1 For the lowest PAR, Ku is the result of pseudodipolar-type anisotropy while with increasing PAR a contribution of the structural anisotropy occurs. The formation of Kp is essentially related to the effective deposition temperature.
Modeling of horizontal magnetoresistive recording heads
Authors: Mountfield K. R. , Guzman J. I. , Kryder M. H. , Jones R. E.
Published: July 2002

A two-dimensional finite-element method was used to model a horizontal magnetoresistive head in order to test the fabrication design parameters. The device consists of two magnetoresistive elements placed closely together and parallel to the plane of the media, following a design of Chapman, Heim, and Williams [IEEE Trans. Magn. MAG-25, 3689 (1989)]. A single transition in the media was moved, in steps, past the head. The electrical signal strength and pulse width, due to this transition, were studied as a function of the shield permeability, thickness and shield gap, the sensor-sensor distance, the flying height, and sensor-shield distance. The width of the pulse did not show appreciable change with shield thickness, permeability, or shield gap size, although the signal strength changed significantly. A thin shield (1000 Å) of moderately low permeability (2000) is therefore preferred. The signal fell off almost exponentially with flying height and sensor-shield separation. The situation where no shield was present was also simulated and showed a reasonably narrow pulse with a large undershoot and a long tail. These results indicate the horizontal head suggested by Chapman and co-workers may in fact provide good readback resolution with a thin shield or perhaps no shield whatsoever.
Planar inductors with a new coil configuration (abstract)
Authors: Sasada I. , Inoue I. , Yamaguchi T. , Harada K.
Published: July 2002

High-frequency (f≥1 MHz) magnetic power devices are key elements for developing compact and low-profile switching power supplies. Planar inductors with a flat coil are investigated,1–3 however, a problem arising from the use of a flat coil is not addressed. The problem is that normal components to the magnetic plate inevitably exist in the exciting fields from a flat coil and that those components induce severe in-plane eddy currents. The problem is most typical in the case of a spiral coil. In this paper, a new flat coil is proposed (see Fig. 1) for planar inductors which greatly improves the problem because paths of eddy currents are chopped up corresponding to the mesh size of the coil. It is obvious that density of eddy currents becomes small when the mesh size becomes fine. Sandwich planar inductors with a proposed coil (mesh coil) and a meander one were prepared for preliminary tests using pairs of Metglas 2705M amorphous ribbons of 50×50 mm2 and 100-μm copper wires, where the mesh size was 3 mm, equal to the pitch of the meander coil. Inductances at 1 MHz were 1.85 μH for the mesh coil and 2.25 μH for the meander one, whereas Qmax=5 at 6 MHz for the mesh coil and 4.5 at 2 MHz for the meander one. Advantages of the mesh coil may further become clear when it is made on the magnetic plates with thin insulating layer in between by IC or thick-film process.
Quasiperiodical effects of the Bloch lines distribution (abstract)
Authors: Krotenko E. B. , Kuzin Yu. A.
Published: July 2002

The purpose of this work is to clear out the reasons of Bloch lines (BL) clustering in plane 180° domain boundary (DB) of the standard ferromagnet with the quality factor Q≫1. The reason for that may be the complicated orthorhombic anisotropy b(θ,φ), caused by the growth particularities of the sample defects and nonhomogeneities due to local changes of the lattice constant and the composition. Here θ, φ are spherical coordinates of the magnetization vector. The exact (in this approximation) analytical decisions for an isolated BL in DB as well as the number of Bloch lines were obtained. In the last case the sections with increased BL’s density may appear. In this place DB is narrowed and its density increased. For the other side, this situation is modeled for the case when Bloch lines are spaced on the Gauss law: Sn= S0[1 − exp( − n2/2p)], where S0 is the distance between periodically spaced BL, from 1l, S0=4.51, here l is Bloch line’s width; n is BL’s number. In this model the magnetization distribution and energy density of DB were calculated numerically. In particular, it was found out that the energy density near the cluster’s center from the BL’s quantity N increases in accordance with the complicated law similar to N2, and the average DB energy density approximating 2.2E0 value, where E0is DB without BL energy density. There N∼2(2p)1/2.
Interface quality and magnetic properties of Co/Au multilayers investigated by Brillouin light scattering
Authors: Krams P. , Hillebrands B. , Güntherodt G. , Spörl K. , Weller D.
Published: July 2002

The magnetic properties of ion-beam-sputtered Co/Au multilayers have been investigated by Brillouin light scattering. Annealing the samples enhances the perpendicular anisotropy and also gives evidence for perpendicularly magnetized domains. Upon annealing the saturation magnetization is reduced. The spin-wave properties and the obtained magnetic parameters are discussed with respect to interface sharpness and roughness.
Synchrotron x-ray diffraction studies of the lattice and magnetic structure of epitaxial Dy films in LaF3/Dy/LaF3 sandwiches (abstract)
Authors: Farrow R. F. C. , Toney M. F. , Hermsmeier B. D. , Parkin S. S. P. , Wiesler D. G.
Published: July 2002

Lattice and magnetic x-ray diffraction from a 2000 Å thick film of Dy, sandwiched by LaF3 films on a GaAs(111) substrate, are reported. The structure was grown by molecular beam epitaxy with the c axis of the Dy parallel to the LaF3 c axis and GaAs [111] axis. We find that the c-axis lattice constant of the Dy has a similar temperature dependence to bulk Dy from room temperature to about 110 K, but below this, the film is different from bulk. The transition to ferromagnetic ordering at ∼86 K exhibits temperature hysteresis which is also evident in the magnetic x-ray scattering and SQUID magnetometry data. This hysteresis may arise from a combination of the strain-energy barrier accompanying the transition and magnetic inhomogeneities in the film. The temperature dependence of the magnetic wave vector is qualitatively similar to bulk, although a weaker dependence is observed below ∼110 K, which is possibly caused by magnetoelastic effects. The magnetic coherence length (310 Å) is significantly shorter than the structural coherence length (730 Å).
Magnetic anisotropy energy of antiferromagnetic coupled Fe/Cr/Fe layers (abstract)
Authors: Williams C. M. , Krebs J. J. , Prinz G. A. , Chaiken A.
Published: July 2002

Thin films of Fe with interleaved Cr have generated considerable interest because of the antiferromagnetic coupling between the Fe layers. This coupling has been examined using ferromagnetic resonance and other measurements. The results have been explained on the basis of the phenomenological expression for the magnetic free energy. We have determined the magnetic free energy for a single-crystal Fe/Cr/Fe(001) sandwich grown by molecular beam epitaxy using torque magnetometry. At fields below the anisotropy field, both the torque and free energy show a complex switching of the antiferromagnetically coupled Fe moments (Fig. 1). Preliminary calculations show that the exchange and the angle between the antiferromagnetically coupled Fe moments can be determined directly from these curves. We shall discuss our measurements and calculations and compare our results with the earlier ferromagnetic resonance results.
Domain structure of as-cast and annealed FeSiB amorphous wires
Authors: Letcher M. , Jones G. A. , Lord D. G. , Wun-Fogle M. , Savage H. T.
Published: July 2002

The domain structures of amorphous FeSiB wires have been studied as a function of applied field. The main features of as-cast wires are: the proliferation of surface closure domains; a distinction between core and sheath domain behavior; and a reproducible switching behavior. Transverse magnetically annealed wires have larger domains, show little sign of a sheath and a greater variety of domain displacement mechanisms.
Amorphous TM1−xBx alloy particles prepared by chemical reduction (invited)
Authors: Linderoth So/ren , Mo/rup Steen
Published: July 2002

Amorphous transition-metal boron (TM-B) alloy particles can be prepared by chemical reduction of TM ions by borohydride in aqueous solutions. ln the last few years systematic studies of the parameters which control the composition, and, in turn, many of the properties of the alloy particles, have been performed and are reviewed in the present paper. The most important preparation parameters which influence the composition are the concentration of the borohydride solution and the pH of the TM salt solution. By controlling these parameters it is possible to prepare amorphous alloy samples with boron contents from about 9 up to about 40 at. %.
Generalized flux states and the quantum Hall effect (abstract)
Authors: Zimanyi Gergely T. , Nori Franco , Abrahams Elihu
Published: July 2002

We investigate certain generalized flux phases arising in a mean-field approach to the t-J model. First we establish that the energy of noninteracting electrons moving in a uniform magnetic field has an absolute minimum as a function of the flux at exactly one flux quantum per particle. Using this result we show that if the hard-core nature of the hole bosons is taken into account, then the generalized flux states in the mean-field approximation constitute a solution where both the spinons and the holons experience an average flux of one flux quantum per particle. We elaborate the relation to the integer and fractional quantum Hall effect. Based on this analogy one expects that only states with certain fractional fillings (ν=1/odd integer) are stable against the fluctuations of the (gauge) field. We speculate that at arbitrary fillings the system minimizes its energy by phase separating into these stable states. Finally we work out the ground state energy for nonuniform (staggered) flux phases and establish that the often claimed equivalence of frustration and doping does not hold for these states.
Magnetic anisotropies in Fe(110) films on W(110) (abstract)
Authors: Elmers H. J. , Gradmann U.
Published: July 2002

Magnetic anisotropies in epitaxial Fe(110) films on W(110) were analyzed using torsion oscillation magnetometry (TOM) in situ in UHV. Films with clean surfaces and films coated by Cu, Ag, and Au were analyzed. Out-of-plane anisotropies were determined by standard TOM methods, in-plane anisotropies from hard-axis magnetization loops. All anisotropies showing a clear linear dependence on reciprocal film thickness, a straightforward separation of volume- and surface-type anisotropies could be performed. Volume anisotropies can be explained as a superposition of standard fourth-order magnetocrystalline and of strain anisotropies, caused by residual strain of a Fe coincidence lattice on W. Surface anisotropies, both in-plane and out-of-plane, are connected by Néel’s model with bulk magnetoelastic constants, to a surprisingly good approximation.
Magnetic properties of fine Fe-Co-B particles prepared by chemical reduction
Authors: Yiping L. , Hadjipanayis G. C. , Sorensen C. M. , Klabunde K. J.
Published: July 2002

The effect of chemical composition and particle size on the magnetic properties of Fe-Co-B fine particles has been studied. The powders were produced by chemical reduction of aqueous solutions of ferric chloride and cobalt chloride with sodium borohydride. The structure of the initially reduced powders varied from amorphous to crystalline bcc depending on the boron concentration. Chemical composition analysis showed a boron content in the range 5–30 at. %. The particle size was found to be 25 nm. The magnetization and coercivity of as-made powders were relatively low. After annealing, the maximum values of magnetization and coercivity obtained were about 160 emu/g and 1940 Oe, respectively. The temperature coefficient of coercivity varied from negative to positive with sample composition and packing fraction.
The Hopkinson effect in BaFe12O19 fine particles (abstract)
Authors: Popov O. , Sanchez J. L. , Rachev P. , Leccabue F. , Mikhov M.
Published: July 2002

The samples are prepared by the coprecipitation method.1 The average particle size is 0.07 μm, which is less than critical single-domain size. Thermomagnetic curves (TMC) of thermally demagnetized samples are studied between 300 and 800 K in external fields up to 8 kOe by VSM. An experimental curve with a well-expressed maximum closely below the Curie temperature (so-called Hopkinson effect) is shown on Fig. 1 (curve 1). Curve 2 on the figure shows a TMC calculated on the basis of the Stoner–Wohlfarth model, following the method described in Ref. 2. There is a good agreement between the experimental and calculated curves. This agreement becomes better when the thermal activation processes are taken into account.3 These results can be considered as an experimental confirmation of the existence of the Hopkinson effect in systems of single-domain particles.
Magnetization study of the I-Al80Mn20 and T-Al78Mn22 quasicrystalline phases (abstract)
Authors: Yang D. P. , Hines W. A. , Clark W. G. , Machado F. L. A. , Azevedo L. A. , Giessen B. C. , Quan M. X.
Published: July 2002

The results of a magnetization study are reported for two phases of rapidly quenched Al-Mn that possess noncrystallographic rotational symmetry: icosahedral (I phase) I- Al80Mn20 and decagonal (T phase) T-Al78Mn22. The measurements were carried out over a temperature range from 1.7 to 300 K and for magnetic fields up to 50 kOe utilizing both VSM and SQUID magnetometry. The magnetic behavior of both phases is characterized by a small concentration of large moment ‘‘clusters’’ and spin-glass-like ordering.
Spin-glass behavior in the Al:Mn quasicrystalline alloys (abstract)
Authors: Machado F. L. A. , Montenegro F. C. , Rezende S. M. , Azevedo L. J. , Clark W. G.
Published: July 2002

Despite the large manganese concentration present in the quasicrystalline Al:Mn system (typically of the order of 20%), only a small fraction of unusually large magnetic moments are detected.1 Recently2 we performed a scaling analysis of the nonlinear magnetic susceptibility of the decagonal T-Al78Mn22 quasicrystalline alloy. The critical exponents obtained (β=0.6 and γ=4.4) are identical to those obtained for canonical spin glasses.3 In this work, we present new scaling results for the icosahedral I-Al80Mn20 alloy. A discussion on the dynamical scaling of the quasicrystalline alloys is also presented.
Magnetic properties of Fe deposited into anodic aluminum oxide pores as a function of particle size (abstract)
Authors: AlMawlawi D. , Moskovits M.
Published: July 2002

A combination of magnetic and electron microscopic measurements on iron deposited in chemically widened anodic aluminum oxide films has allowed us to relate the coercivity of these materials to the dimensions of the metal particles. The coercivity is found to be highly anisotropic and to depend on the aspect ratio of the metallic particles. The functional dependence of Hc on the aspect ratio fits the expression reported by Jacob and Bean [Phys. Rev. 100, 1060 (1955)] for magnetization reversal by symmetric fanning. This is likely due to the fact that in our unannealed samples the metal deposit consists of a cylindrical assembly of fused single-domain particles. Pore widening by chemical dissolution of the anodic oxide is found to depend quadratically on the time that the sample is soaked in the acid bath.
Characteristics of level and two-axis attitude detector A using magnetic fluid
Authors: Kanamaru Y. , Kojima A.
Published: July 2002

Level and attitude detector are required for the detection of level and angles, for controlling the attitude of robots, keeping solar cell panels directed toward the sun, and the parabola antenna constantly toward the manmade satellite in communication systems. The usual angle detector can detect an angle in one axis only, and cannot detect the level alone. The detector described in this paper is able to detect angles of orientation with respect to horizontal and vertical planes. In addition, the new detector can detect level by itself for using fluids, such as water levels. This detector has three tubes with the magnetic fluid placed inside with three coils. The tubes are sealed and the solvent of the magnetic fluid does not evaporate. Therefore, the life span of the detector is longer than the previous detector. Its structure is very simple, small, and robust. It is also a lightweight unit. The output signals are square waves, always in use with digital signal processes. The operating characteristics are described in this paper.
A rotating field automated measurement system for the characterization of ferromagnetic materials
Authors: Geirinhas Ramos H. , Silva Girão P.
Published: July 2002

This paper presents an automated measurement system which uses general purpose IEEE-488 controlled devices for the characterization, according to a Preisach-type model, of ferromagnetic materials subjected to magnetic fields of variable amplitude and direction. For that purpose, the measurement of component values in two orthogonal directions of both magnetic field and magnetic induction are required. The magnetic induction in the sample is obtained by using analog integration of the resulting induced electromotive forces in two test coils when the magnetizing current is changed. The magnetic field inside the sample is obtained by measuring the electromotive forces induced in two air core sensing coils placed on both surfaces of the sample. Besides hardware and software details, this paper presents results of tests conducted on ferromagnetic materials commonly used in electrical apparatus.
New optical magnetic field sensor with optional white light source (abstract)
Authors: Abe M. , Shimosato M. , Kozuka Y. , Imaeda M.
Published: July 2002

A new type of magnetic field sensor which measures ac electric current utilizing Faraday rotation is proposed. On a Faraday element a stabilized dc bias magnetic field Hb is applied. Output signal is given by the ratio R = I2ω/Iω, where Iω and I2ω are fundamental and second harmonic signals generated by the field Hx which the ac current induces. Since R is calculated as R = Hx/4Hb, we can measure Hx independent not only of light intensity but also of the Verdet constant (and therefore its temperature dependence) of the Faraday element. This was supported by experiments performed at 20–100 °C for HeNe laser (λ=0.633 and 1.15 μm) light on Faraday elements of FR-5 paramagnetic glass and Bi-substituted YIG crystal. The bias field Hb was generated by a stabilized dc current in a coil and using a SmGdCo plastic magnet with very weak temperature dependence of remanent magnetization (<1% at T=20–120 °C). According to theory the equation holds even when broad spectrum polychromatic light is used. This was confirmed by experiments performed with a halogen-lamp white light transmitted through an optical fiber. Calculated signal-to-noise ratio of the sensor with a polychromatic light agreed with experiments.
Critical behavior in two reentrant N
iMn ferromagnets
Authors: Kunkel H. , Roshko R. M. , Ruan W. , Williams G.
Published: July 2002

The real and imaginary components of the low-field dynamic susceptibility of two reentrant NiMn ferromagnets containing 22.5 and 23 at. % Mn have been measured as a function of temperature in static magnetic fields up to 43.3 Oe. The real component χ′ exhibits a triple-peaked structure. A critical analysis confirms the highest temperature component of this structure as a manifestation of the critical fluctuations associated with the paramagnetic–ferromagnetic transition. The remaining double-peaked structure is localized in the vicinity of the reentrant transition and is accompanied by a complementary structure in the imaginary component χ″. A correlation is established between the reentrant susceptibility peaks and the reentrant phase boundaries predicted by vector spin models for bond disordered systems.
Study of hysteresis phenomena in Ising-like pseudospin systems with random local reversal fields and random spin-spin interactions
Authors: Bertotti G. , Pasquale M.
Published: July 2002

We study the hysteresis properties of a generalization of the Sherrington–Kirkpatrick spin-glass model, including, in addition to the random spin-spin coupling costants {Jij}, a random distribution {hci} of local spin coercive fields, hindering spin flipping. The system evolution is driven by the time-dependent external field H(t). We investigate numerically the behavior as a function of H of the average magnetization per spin, m(H), and of the spin internal field distribution P(h;H). A rich variety of m(H) hysteresis loops is obtained, whose properties are controlled by the parameters of the {Jij} and {hci} distribution. It is found that the contributions of {Jij} and {hci} to the coercive field of these loops simply add to each other. An approximate Fokker–Planck equation for P(h;H) is derived, which permits one to understand the main features of P(h;H). In particular, it leads to a natural interpretation of the fact, put in evidence by computer simulations, that P(h;H) is, for small h, a linear function of h, whose slope is independent of H and of the {hci} distribution.
Spin-resolved electronic band structure of fct-cobalt (100) (abstract)
Authors: Schneider C. M. , Schuster P. , Hammond M. , Ebert H. , Noffke J. , Kirschner J.
Published: July 2002

The spin-polarized electronic structure of the fcc high-temperature modification of cobalt has not been investigated yet, because of the experimental difficulties of photoemission at high temperature. We stabilized fcc Co by molecular-beam epitaxy on a Cu(100) substrate with large, atomically flat terasses (0.5–1 μm wide) as revealed by STM. The structure of the layers was studied by LEED and MEED, showing a tetragonal distortion of the fcc lattice perpendicular to the (100) surface plane. The dispersion of the exchange split bands perpendicular to the surface was determined for a 5-monolayer-thick sample (tetragonal distortion on average 4%–5%) by spin- and momentum-resolved photoemission. The results are compared to two relativistic spin-polarized band-structure calculations for fcc cobalt. Somewhat surprisingly, even a 5-ML-thick sample shows three-dimensional dispersion in good agreement with the calculations, as far as the average exchange splitting (1.2±0.2 eV), and the symmetry character of the bands is concerned. There are, however, some systematic deviations of minority bands near the Fermi energy which are attributed to the tetragonal compression.
Magnetic aftereffect and domain structure at spin reversal in ultra-thin ferromagnetic Co/Au (111) films (abstract)
Authors: Ferré J. , Pénissard G. , Meyer P. , Pommier J. , Bruno P. , Renard D.
Published: July 2002

We discovered giant magneto-optical effects in ultrathin ferromagnetic Co films of a few atomic planes (3–5) deposited on Au (111), showing square hysteresis loops.1 For the first time, and by Faraday rotation microscopy, we observed magnetic domains in such ultrathin films exhibiting strong perpendicular anisotropy, and confirmed a recent suggestion2 that field-induced magnetization reversal near the coercive field occurs via a nucleation–domain wall propagation mechanism. The associated magnetic aftereffect is well analyzed from the time dependence of the dendritic magnetic domain structure. Models of domain wall propagation developed for bulk ferromagnets still appear to be valid for ultrathin films. Our study allows to understand better the magnetization reversal process, a crucial effect in this promising magneto-optical storage medium.
Software model of an alternator under sudden short circuit
Authors: Hoole S. Ratnajeevan H. , Mahinthakumar G. , Kim Hoi Won , Karunananthan J. , Rigaud Herve
Published: July 2002

Today, sophisticated programs exist to model electromagnetic devices using finite elements under static conditions. In recent times, these models have been extended to the dynamic regime. In this paper, a software model of an alternator is constructed using finite elements and the model is used, for the first time, to simulate an alternator under dynamic sudden short-circuit conditions The pitfalls in constructing such models are also discussed.