bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinal reflex evoked by a pair of opposing pulsed magnetic fields
Authors: Ueno S. , Hiwaki O.
Published: July 2002

A noninvasive method of magnetic stimulation of the spinal roots was designed. The basic idea is to concentrate induced eddy currents in a target by a pair of opposing pulsed magnetic fields. A figure-eight coil was positioned outside the median of the back so that time varying magnetic fields pass through the body in opposite directions around the target. Magnetic stimulation of the spinal roots of human and a rabbit was carried out. It was found that each spine level can be stimulated selectively, producing electromyographic waves related to both the H-reflex and M-wave. The results indicate that the M-wave can be produced by currents flowing either in the rostral or caudal direction, whereas the H-reflex is only generated by currents flowing in the caudal direction. The H-reflex elicited by magnetic stimulation of nerves in the vicinity of the spine becomes a new tool in diagnosis of neuromuscular system diseases.
Magnetic properties of manganese tartrate (abstract)
Authors: Paduan-Filho A. , Carlin Richard L.
Published: July 2002

The susceptibility of single crystals of Mn (L-tartrate)⋅3H2O was measured down to 0.5 K. At high temperatures, the susceptibility follows the Curie–Weiss law with ϑ=−4 K. The data along the c axis decrease below 2 K and extrapolate to zero for T→0 as expected for measurements parallel to the easy axis of a typical antiferromagnet. In the two perpendicular directions, the data show a sharp peak at Tc=1.85 K, indicative of a weak ferromagnetic moment. Part of the magnetic phase diagram has been determined: there is a spin-flop transition at Hc=4.2 kOe and a spin-flop para transition at about 32 kOe. For H⊥c, Hc is slightly higher. These data allow HA and HE to be calculated. Measurements of the specific heat are in progress.
Mechanism of orientation of stimulating currents in magnetic brain stimulation (abstract)
Authors: Ueno S. , Matsuda T.
Published: July 2002

We made a functional map of the human motor cortex related to the hand and foot areas by stimulating the human brain with a focused magnetic pulse. We observed that each functional area in the cortex has an optimum direction for which stimulating currents can produce neural excitation. The present report focuses on the mechanism which is responsible for producing this anisotropic response to brain stimulation. We first obtained a functional map of the brain related to the left ADM (abductor digiti minimi muscles). When the stimulating currents were aligned in the direction from the left to the right hemisphere, clear EMG (electromyographic) responses were obtained only from the left ADM to magnetic stimulation of both hemisphere. When the stimulating currents were aligned in the direction from the right to the left hemisphere, clear EMG signals were obtained only from the right ADM to magnetic stimulation of both hemisphere. The functional maps of the brain were sensitive to changes in the direction of the stimulating currents. To explain the phenomena obtained in the experiments, we developed a model of neural excitation elicited by magnetic stimulation. When eddy currents which are induced by pulsed magnetic fields flow in the direction from soma to the distal part of neural fiber, depolarized area in the distal part are excited, and the membrane excitation propagates along the nerve fiber. In contrast, when the induced currents flow in the direction from the distal part to soma, hyperpolarized parts block or inhibit neural excitation even if the depolarized parts near the soma can be excited. The model explains our observation that the orientation of the induced current vectors reflect both the functional and anatomical organization of the neural fibers in the brain.
Bismuth rare-earth iron garnet composition for a magneto-optical wheel rotation rate sensor
Authors: Gualtieri D. M. , Emo S. M. , Kinney T. R.
Published: July 2002

A magneto-optical garnet composition has been developed for use in a multimode, two-port, fiberoptic wheel rotation rate sensor for aerospace applications. The sensor utilizes a layer of (Bi, Y, Gd, Tm, Lu, Ca)3(Fe, Si)5O12 grown on a (111)-oriented substrate of Gd3Ga5O12 by standard liquid-phase-epitaxy techniques. The sensor has an integral biasing magnet and lensless coupling of multimode glass fibers to a polarizer/garnet/analyzer sandwich. The sensor operates at a signal channel of 725 nm and a reference channel of 850 nm, convenient wavelengths for semiconductor emitters and detectors. The (Bi, Y, Gd, Tm, Lu, Ca)3 (Fe, Si)5O12 layer is grown to 25-μm thickness on one side of the substrate. It has a saturation field of 500 Oe, Curie temperature of 530 K, and the following approximate room-temperature optical properties at 725 nm: a Faraday rotation of 15°, an optical attenuation of 5 dB, a specific rotation of 0.65°/μm, a specific attenuation of 0.25 dB/μm, and a figure of merit of 2.5°/dB. The low figure of merit is a consequence of the strong optical absorption of iron cations in the near infrared, but it is sufficient for this device. Gadolinium and thulium incorporation onto dodecahedral lattice sites serves the dual purpose of reducing the saturation magnetization and reducing the temperature dependence of magnetization. Device operation is specified over a temperature range of −65 to 450°F (−54 to 232°C), but layers of slightly higher Curie temperature allow operation to an upper temperature limit of 550°F (288°C).
Magnetic properties of 1% Al-iron and its applications
Authors: Omori T. , Suzuki H. , Sampei T. , Yako K. , Kanero T.
Published: July 2002

A study was carried out to improve permeability and coercivity of pure iron without decreasing its saturation magnetization. It was found that about 1-wt % addition of aluminum in combination with a high-temperature annealing process greatly increases its permeability (μm) up to 60 000, which is close to that of Permalloy B, and reduces its coercivity (Hc) to 0.2 Oe without decreasing the high-saturation magnetization of pure iron. This marvelous effect of the 1-wt %-Al addition can be attributed to a stabilization of the ferrite phase which enables ferrite grains to coarsen drastically due to abnormal grain growth during the high-temperature annealing. The ferrite stabilization also helps to avoid both residual strain and grain refining due to the austenite-ferrite phase transformation, which are thought to be undesirable for soft magnetic properties. In the present paper, the performance of this Fe–1-wt %-Al soft magnetic alloy, and an example of its practical application to the magnetic shielding, will be described.
Integrated ferromagnetic MR sensors
Authors: Konno H. , Kataniwa H.
Published: July 2002

Ferromagnetic magnetoresistive (MR) sensors are magnetic devices developed for the purposes of detecting rotation or position of magnetized objects. These are distinguished theoretically from Hall elements, Hall IC, and other semiconductor magnetoresistive elements which utilize the Hall effect. Formerly, several papers were reported concerned with integration of MR elements with IC. Usuki reported on a Ni-Co integrated MR sensor and Honeywell Inc. have already commercialized such a product. We have developed integrated ferromagnetic sensors by adopting our own approach. The sensors consist of IC parts fabricated using a bipolar process, permalloy (Ni-Fe) thin films of 0.03 μm thickness, and ion-implanted feedback resistors. These sensors have excellent electrical characteristics.
Iron loss of the multilayered CoZrMo core
Authors: Okuno H. , Kirita T. , Sakaki Y.
Published: July 2002

In this paper the iron loss of the magnetic thin-film core is investigated with the intention of applying it to power transformers for high-frequency use. The multilayered CoZrMo core was prepared by a facing-targets-type rf magnetron sputtering system. The core consisted of alternate CoZrMo and SiO2 layers. The coercive force was small and had a value of 2.8 A/m (0.035 Oe). The hysteresis loss at the maximum flux density of 0.1 T was 0.74 J/m3 and was 0.06 times the value of 12 J/m3 for the multilayered NiFeMo core. The iron loss of the multilayered CoZrMo core at 1 MHz and 0.1 T was 3.4 J/m3, which was 0.09 times the value of 38 J/m3 for the multilayered NiFeMo core. Magnetic domains were observed using a magneto-optical Kerr microscope. The shape and configuration of domains differed with frequency and place in the core. The process of magnetization is considered to be accomplished by nucleation of zigzag domains at the edge, followed by their growth and fusion and by rotation.
High-field magnetization processes in actinide intermetallics (invited)
Authors: Franse J. J. M. , de Boer F. R. , de Chatel P. F. , Frings P. H. , Menovsky A. A.
Published: July 2002

In magnetically ordered intermetallics of uranium with d transition elements, the magnetic moment on the uranium site is often limited to values below 0.1μB, with, in some cases, extremely large magnetic anisotropies. Several approaches are followed for explaining these small uranium moments: opposite directions and almost compensation of the spin and orbital moments, reduction of the uranium 5f moment by strong hybridization effects between the 5f and conduction electrons, and very weak itinerant magnetism of the 5f electrons. In the Laves-phase compounds UFe2 and UNi2, the magnetic data have been explained in terms of opposite spin and orbital moments on the uranium sites. In the heavy-fermion compounds UPt3 and URu2Si2, on the contrary, a Kondo approach is followed, although coherence effects largely complicate a proper description. The experimental evidence for these different approaches will be reviewed.
Magnetic ordering in triangular antiferromagnets: A neutron scattering study (abstract)
Authors: Visser D. , McIntyre G. J. , Harrison A.
Published: July 2002

Recent much theoretical interest has been shown in the magnetic ordering process of triangular antiferromagnets. Such a magnetic lattice type should exhibit strong frustration effects. The hexagonal ABX3 ternary halides and the AX2 metal halides are good candidates for studying the frustration effects on the triangular lattice. We discuss neutron scattering studies of the magnetic ordering process in the Ising-like antiferromagnets CsCoCl3, CsMnI3, and the XY-like antiferromagnets CsMnBr3, CsVCl3. The effects of magnetic as well as diamagnetic doping were studied for the systems CsMn1−xMgxBr3 and CsMn1−xFexBr3. Asymmetric line profiles were observed which corresponds to frustration behavior in the magnetic ordering of this type of compound. A release of frustration is observed for the modified triangular antiferromagnet.
Study of Sm(Co,Fe,Cu,Zr)7.1 magnets produced using a combination of hydrogen decrepitation and ball milling
Authors: Kwon H. W. , Harris I. R.
Published: July 2002

The magnetic properties of Sm(Co,Fe,Cu,Zr)7.1 sintered magnets produced using a combination of hydrogen decrepitation (HD) and ball milling have been investigated. The powder for the sintered magnets was produced by exposing the as-cast material to hydrogen at a slightly elevated temperature and then ball milling the friable material which resulted from the HD treatment. It was found that the combination of HD and milling is an effective means of production of 2:17 type sintered magnets.
Domain stability of multilayered CoZrCr/Ti stripes
Authors: Kanamine M. , Kanai H. , Kobayashi K.
Published: July 2002

The narrow-track perpendicular magnetic heads with multilayered CoZrCr/Ti main-pole films developed here reproduce output signals having increased stability as the number of pairs of CoZrCr layers increases. To see why, a Kerr-effect apparatus was used to measure the relationship between dynamic domain behavior and the number of pairs of CoZrCr layers for multilayered narrow CoZrCr/Ti stripes of different widths. Increasing the number of pairs of CoZrCr layers suppressed wall displacement and stabilized the domain structure. The domain stability agreed fairly well with the stability in perpendicular heads having multilayered CoZrCr/Ti main-pole films.
Magnetization distributions in thin film Permalloy strips
Authors: Hill E. W. , Heyes N. A. E. , Tomlinson S. L.
Published: July 2002

Thin film Permalloy strips are used extensively for magnetoresistive sensors both in magnetometry and magnetic recording. A determination of magnetization distributions is vital to allow optimization of sensor performance. Results from a previously described scanning laser microscope (SLM) unambiguously determine magnetization distributions to submicron resolution. Operating the SLM in a mode sensitive to magnetization angles about the long axis of the strip shows typical closure domains. If the mode is sensitive to fluctuations about the strip short axis then light and dark bands are observed. These results indicate that the magnetization is not parallel with the strip edges within the domains as normally considered for closure domains. The SLM images are compared with results from a previously described numerical micromagnetic model. Results from the model compare well with those from the SLM, confirming the ability of the model to reliably predict domain activity in Permalloy strips. Results are shown for Permalloy strips of approximately 15 μm×50 μm and 250 Å thick in the presence of dc and ac magnetic fields.
Magnetoelastic and magnetovolume effects in ternary Cr-Mo-Si alloys
Authors: Smit P. , Alberts H. L.
Published: July 2002

The temperature dependence of the elastic constants and the thermal-expansion coefficient of (Cr1−xMox)0.986Si0.014 for 0<x≤0.12 and (Cr0.97Mo0.03)1−ySiy for 0≤y≤0.05 was measured. Well-defined anomalies were observed at the Néel temperature giving rise to large magnetic contributions to the thermal expansion and elastic constants making these alloys suitable to be analyzed and parametrized in terms of existing theories.
A 3D anisotropic rotation model for magnetization and magnetostriction in Tb0.3Dy0.7Fe1.9 (abstract)
Authors: Jiles D. C. , Thoelke J. B.
Published: July 2002

The highly magnetostrictive alloy Tb0.3Dy0.7Fe1.9 orders with its magnetic moments aligned along the 〈111〉 axes. When a magnetic field is applied along one of the 〈112〉 axes it has been shown in recent work that the principal magnetization mechanism is domain rotation. In order to produce higher magnetostriction at lower field strengths the initial domain orientations should be configured with high population of the [1̄1̄1] and [111̄] axes at right angles to the field direction. This paper is concerned with the determination of these population densities from magnetization and magnetostriction data using the domain rotation model in the presence of anisotropy. We have developed a three-dimensional anisotropy model for the domain rotation mechanism.1 This enables the direction of magnetization of domains originating along each of the 〈111〉 axes to be found as a function of magnetic field. The change in magnetization ΔM is calculated from: ΔM=∑piMs(cos θi − cos Ωi), where Ms is the saturation magnetization, Ωi is the initial orientation of a domain with respect to the field, and θi is the final orientation. The change in magnetostriction is calculated from: Δλ =3/2λ100Σi[(cos2 θf,j −cos2 θi,j)cos2 φj]Δλ= 3/232λ100Σi [(cos2 θf,j−coscos2 θi,j)cos2 φj] +3λ111Σ3j=1[(cos θf,j cos θf,j+1 −cos θi,j cos θi,j+1)cos φj cos φj+1]pi. The population densities pi of the domain in the various 〈111〉 axial directions determine the amplitude of the magnetostriction. From the model it is possible to determine the bulk magnetization and magnetostriction from the occupancies of these directions.
Magnetization and spin correlation in a single crystal of YFeMnO4
Authors: Iida Junji , Tanaka Midori , Funahashi Satoru , Nakagawa Yasuaki
Published: July 2002

Magnetization and neutron-diffraction measurements were carried out on a single crystal of hexagonal YFeMnO4, a two-dimensional Heisenberg triangular antiferromagnet. The Fe3+ and Mn2+ are randomly distributed on equivalent triangular sites, producing the system with both frustration and randomness. The thermomagnetization curve in 50 Oe shows that a field-cooling effect is observed below 60 K, where the susceptibility along the c axis has a cusplike peak. Neutron-diffraction measurements reveal that a two-dimensional (1/3,1/3,l) magnetic rod is observed in the whole temperature range instead of three-dimensional Bragg points, and the magnetic correlation in the c plane does not become long range even at the lowest temperature. It also shows that spins fluctuate largely at room temperature, and this fluctuation still remains at low temperatures. This magnetic property is similar to that of spin-glass system. Some type of spin freezing occurs below 60 K, and a slight increase of the correlation length down to the lowest temperature suggests that this freezing is imperfect even at the lowest temperature. The temperature and cooling field dependence of thermoremanent magnetization can be explained by assuming a domain structure which is divided into microdomains by random fields induced by the disorder.
Frustrated spherical spin model and walk statistics on Bethe lattices
Authors: Cassi Davide , Pimpinelli Alberto
Published: July 2002

It is known that the free energy of the spherical model of Berlin and Kac [Phys. Rev. 86, 821 (1952)], with nearest-neighbor couplings on an Euclidean lattice, can be expressed in terms of generating functions of walks on the same lattice. We show that this relationship is valid on any discrete geometrical structure (graph) and can be exploited to solve the model on non-Euclidean lattices, such as a variety of infinite tree graph. We show next that this technique of solution can be employed even when interactions are extended beyond nearest neighbors and frustrated, provided one defines distance in terms of shortest path on the graph between two sites. Implications of this definition for Euclidean lattices is discussed. We then compute the phase diagram of the spherical model with next-nearest-neighbor competing interactions on the usual Bethe lattice, and the thermodynamical behavior of ferromagnet and antiferromagnet on Bethe cactuses, that is, trees whose branches are symplexes.
Long-wavelength spin waves in structures with large out-of-plane anisotropies
Authors: Stamps R. L. , Hillebrands Burkard
Published: July 2002

The frequencies of long-wavelength spin wave modes are calculated for single and multilayer structures composed of ferromagnetic films with strong out-of-plane surface and interface anisotropies. The properties of these modes are examined from the point of view of possible Brillouin light-scattering studies and the evaluation of exchange constants and interface anisotropies. The frequencies of the collective modes on multilayer structures as well as their degree of localization to the surface of the stack are strongly affected by perpendicular anisotropies. This is demonstrated by studying the spectral density function obtained from an effective medium theory for semi-infinite superlattices.
Evidence for collective exchange modes in Co/Pd multilayers observed by Brillouin light scattering (abstract)
Authors: Hillebrands B. , Harzer J. V. , Güntherodt G. , England C. D. , Falco C. M.
Published: July 2002

Recently, exchange-dominated collective spin-wave excitations have been predicted for multilayered structures consisting of alternating magnetic and nonmagnetic layers.1 These types of collective excitations exist for nonzero propagation wave vectors if the magnetic layers are exchange coupled across the spacer layers.1 The modes are the collective counterpart to the optic dipolar-exchange mode observed in magnetic double layers by Vohl, Barnás and Grünberg.2 For a multilayer with N periods of bilayer thickness Λ there exist N modes which, in the absence of exchange coupling, form the well-known band of dipolar collective spin-wave excitations. The modes are dominantly surface-mode-like at the upper band edge and mostly bulk-mode-like at the lower band edge. With the onset of exchange coupling the stack bulk modes are shifted to higher frequencies and become exchange-mode-like in character. In the full exchange coupling limit these modes become the so-called standing spin waves of the total multilayer stack, and their frequencies depend on the stack thickness NΛ.

The stack surface mode in this limit becomes the surface Damon–Eshbach mode of a single film of thickness NΛ. Brillouin light-scattering experiments have been performed on magnetron-sputtered Co/Pd multilayers.3,4 The number of atomic layers (AL) is the same in each Co and Pd layer. The number of periods was chosen to be N=8 and 30, with Λ varying between 4 and 140 Å. In the case of N=30 a strong increase of spin-wave frequencies for all but the stack surface mode is observed for d<8 AL. Decreasing d0 increases the interlayer exchange coupling and the band of collective bulklike modes increases in frequency to become a band of exchange-dominated modes. Depending on the strength of the coupling (i.e., spacer layer thickness), this band can have frequencies higher than that of the stack surface mode. From the crossing regime the maximum exchange coupling length is estimated to be 10 Å. For samples with N=8, collective exchange modes were not observed. Model calculations show that for N=8 the expected frequency increase near the onset of interlayer exchange coupling is much steeper than in the N=30 case, which might prohibit their experimental observation. Also, the cross section is reduced by a factor of 4 due to the smaller total stack thickness.
Memory implications of the spin-value effect in soft multilayers
Authors: Pohm A. V. , Comstock C. S.
Published: July 2002

New multilayer permalloy materials with thin separation layers that have significantly increased M-R coefficients at room temperature have the potential for substantially increasing both the speed and density of M-R memories. An analysis in the following discussion shows that the bit density at a given performance level is related to the product of M-R response and sheet resistivity when operating at the current-density limit. With a doubling of both sheet resistivity and M-R response over existing materials, the bit area can be reduced by about a factor of 4. Alternatively, if the bit area is kept the same, signal output is increased by a factor of 4 and circuit time constants can be reduced by a factor of 16.
Structure and magnetic properties of FeRuGaSi multilayer thin films
Authors: Jagielinski T. M. , Zeltser A. M. , Brucker C. F.
Published: July 2002

The structure and magnetic properties of FeRuGaSi thin films used in very-high-frequency (150 MHz) recording head has been studied. The best soft magnetic properties, viz., coercivity of 0.2–0.3 Oe, permeability of 2000 at 1 MHz and 400–500 at 150 MHz, and magnetostriction of less than 10−6, were obtained after annealing at 450–500 °C. This magnetic behavior was attributed to the phase transformations and the increase in the grain size of the films occurring during the annealing process. Transmission electron diffraction revealed that B2 and/or DO3 ordered phases were formed in the films depending on the annealing temperature. However, good soft magnetic properties were associated with the formation of the B2 phase with low crystal anisotropy and saturation magnetostriction. These results are somewhat in contrast to what has been observed in Sendust, where magnetic softness is usually attributed to the formation of the DO3 phase.
Polycrystalline ferrite for 150-MHz recording applications
Authors: West B. , Yang D. , Jeffers F.
Published: July 2002

As recording frequencies are increased above 50 MHz, the permeability of conventional Mn-Zn ferrites becomes prohibitively small with high losses. A material with low losses in this frequency range is needed. Ferrites with the general formula Ba2Me2Fe12O22, referred to as ferroxplana, have a large negative crystalline anisotropy resulting in a flat in-plane permeability spectra beyond 200 MHz. Unfortunately, single-crystal ferroxplana is difficult to use, owing to its poor machinability. Processes to fabricate highly oriented polycrystalline ferroxplana have been developed. Coprecipitation and molten salt firing were used to synthesize the starting materials. Powders were oriented, sintered, and hot isostatically pressed to theoretical density. A highly oriented polycrystalline sample was successfully fabricated, which had flat permeability spectra up to 200 MHz and a μ′=54 at 150 MHz. This is the highest reported value for polycrystalline ferroxplana.
Epitaxial growth and magnetic properties of RM5 thin films (R=rare earth, M=Ni,Co,Fe) prepared by laser ablation deposition (abstract)
Authors: Gavigan J. P. , Givord D. , Lienard A. , Rebouillat J. P. , Souche Y.
Published: July 2002

Different experimental methods have been developed in recent years for the preparation of metallic thin films and multilayers in which the individual layers consist of a simple element. We are developing another method, laser ablation deposition, which permits the congruent evaporation and deposition of almost any target to be obtained and is thus well suited to the preparation of thin films of intermetallic compounds. A major obstacle in the development of this technique in the past has been the formation of droplets, expelled from the target which pollute the prepared films. This has been solved recently with the use of a velocity selector to eliminate the droplets. YNi5 thin films, of thicknesses between 50 and 200 Å, have been found to grow epitaxially on sapphire substrate, with the [0001] and [101̄0] sapphire directions being parallel, respectively, to the [0001] and [112̄0] YNi5 directions. YCo5 thin films, with thicknesses between 20 and 200 Å, have been subsequently grown on YNi5. Their magnetic properties have been studied using a SQUID magnetometer. Finally, test experiments to grow Y-Fe compounds on such substrates will be reported.
Magnetic viscosity studies of Nd16Fe77B7 permanent magnets
Authors: Liu Jinfang , Luo Helie , Pan Shuming
Published: July 2002

The intrinsic energy barriers 31rb2, as well as the lgHc–lgHf plot, were calculated from a localized weak domain wall pinning model which fit the experimental data well. These results support the localized weak domain wall pinning model in NdFeB sintered magnets.
Some magnetic properties of as-cast Re4Fe1 (Re=Pr,Nd,Sm) alloys and corresponding hydrogen-rich phases (abstract)
Authors: Bozukov L. , Apostolov A.
Published: July 2002

The aim of this work is to discuss some magnetic data of as-cast Re4Fe1 alloys (Re=Nd,Pr,Sm) as well as to study the influence of hydrogen absorption on their structural and magnetic properties. The pallets of 1 g were prepared by arc melting Nd,Pr,Sm, and Fe (purity 99.9%) under Ar. Structural analyses were performed using a standard x-ray diffractometer. The high-temperature magnetization was studied by a vibrating sample magnetometer in the temperature range of 300–1200 K and permanent magnetic fields up to 7 kOe. The high-field magnetization studies in fields up to 140 kOe in the temperature range from 4.2 to 300 K were performed by an extraction magnetometer. The hydrogen absorption processes were studied by a volumetric apparatus within the hydrogen pressure range of 10–4×103 kPa in the temperature range of 270–573 K. The x-ray and the magnetic measurements were performed on the samples of alloys and hydrides with H concentration of 2.8 at. %/mol. x-ray diffractograms for parent Re4Fe1 alloys showed the presence of two allotrope-hexagonal P6mmc and cubic structures. The existence of a small amount of amorphous phase cannot also be excluded. X-ray patterns of Re4Fe1H2.7 (Re=Pr, Nd) showed well-defined first and second diffuse haloes and the presence of some smeared diffraction peaks corresponding to the bcc structure, typical for Re-H3 systems.

Magnetic ordering temperatures were determined to be 515 and 502 K for Nd4Fe1 and Pr4Fe1, respectively. Formation of the hydride phases results in decreasing of the coercivity Hc. At room temperatures Hc was found to be 4.5 kOe and 60 Oe for as-cast Nd4Fe1 and its hydride, respectively. It should be noted that absorption of hydrogen increases the net magnetic moment. A strong thermomagnetic effect was observed in the magnetic fields up to 60 kOe for the alloys. In the case of zero-field cooling of the Nd4Fe1 sample the value of magnetization at 25 kOe is 3.4 μB/mol (4.2 K) and 5.0 μB/mol when the sample is cooling in the same field. The last observation as well as the presence of a minimum in the temperature dependence of magnetization around T=60 K at a field 25 kOe for Nd4Fe1 and Pr4Fe1 showed the strong influence of the anisotropy on the magnetic moments of the iron sublattice.
Molecular fields in Gd2Fe14B determined from inelastic neutron scattering
Authors: Loewenhaupt M. , Sosnowska I. , Taylor A. , Osborn R.
Published: July 2002

By means of inelastic magnetic neutron scattering, we have determined the molecular field acting on the Gd3+ ions in Gd2Fe14B. This field is due to the Gd-Fe exchange interaction and amounts to 2μBHm/kB = 435 K for the average value of f and g sites. From the width of the magnetic response, a maximal ratio of 1.3 for the molecular fields on f and g sites is deduced.
The degradation of polymer-bonded Nd-Fe-B magnets (abstract)
Authors: Mazany Anthony M. , Dickens E. Douglas
Published: July 2002

The susceptibility of Nd-Fe-B magnet powders to oxygen and chloride ions is well known, however, the interactions between magnet alloy powders and polymeric binders in bonded magnets can also lead to severe irreversible losses. The losses observed for polymer-bonded Nd-Fe-B magnets in some cases can be more substantial than the losses due to oxidation or corrosion alone. The aging characteristics of polymer-bonded magnets have been examined with respect to time, temperature, alloy treatment, particle size, molding method, and polymer composition. Each sample was evaluated for magnetic properties after thermal aging. The chemical effects of oxygen, chloride ions, and various polymers on Nd-Fe-B alloys and the resulting changes in magnetic properties can be very different, but all can lead to significant losses and each degradation process (oxidation, corrosion, or polymer-alloy interactions) exhibits a different magnetic hysteresis ‘‘signature.’’ The irreversible losses stemming from these processes can be alleviated through the use of passivating coatings.
Thermal stability of Nb-doped (NdDy)(FeCoAl)B magnets (abstract)
Authors: Rao Xiao-Lei , Liu Ying-Lie , Cao Yun-jin , Lin Wen-gui , Feng Ming-ying , Dong Xiao-Lin , Ji Shong-quan
Published: July 2002

To improve the poor thermal stability of NdFeB magnets, we add Dy, Co, Al, and Nb into the magnets with nominal composition (Nd0.9Dy0.1)17FebCo5Al1.7B7Nbx (x=0.3–1.5 at. %). We have measured their Hcj at room temperature. The data of irreversible loss (IL) of open-circuit flux density at different temperatures are also obtained using cylinder samples with L/D=0.7 (P=2). We have also compared the IL of the same sample with different P. The results show that Hcj increases linearly with Nb content in average 4.8 kOe/Nb at. %. The higher the Hcj and/or the longer the sample is, the lower the absolute value of IL is. The IL of sample with x=1.5 at. % and L/D=0.7 is less than 5% even at 150 °C. Nb effectively achieves the thermal stability of the magnets. The SEM has been used to observe the microstructure of the surface and cross section of a typical sample.
Superconductivity of UPt3 studied by μ+SR and neutron scattering (abstract)
Authors: Broholm C. , Aeppli G. , Kleiman R. N. , Harshman D. R. , Bishop D. J. , Bucher E. , Williams D. Ll. , Ansaldo E. J. , Heffner R. H.
Published: July 2002

The magnetic field penetration depth λ in single-crystalline UPt3 has been measured by muon spin relaxation ( μ+SR). The temperature dependence of λ−2 is nonexponential and anisotropic decreasing from its T=0 value proportional to T when measured perpendicular to the c axis but with a higher-power ∥c. Our data can be accounted for in detail by a superconducting gap with a line of nodes in the basal plane and axial point nodes. By neutron scattering we furthermore show that the antiferromagnetic order parameter of UPt3 is perturbed by the development of superconductivity. We discuss the implications of these results on the symmetry of the superconducting states of UPt3.
Low temperature magnetic properties and microstructure of rapidly solidified Nd-Fe(-Co) and Sm-Co(-Fe) Laves compounds
Authors: Yang C. J. , Choi S. D. , Lee W. Y.
Published: July 2002

Laves phases of NdFe2, Nd(Fe0.5Co0.5)2, SmCo2, and Sm(Fe0.5Co0.5)2 stoichiometries were prepared using a rapid solidification technology. Low temperature magnetic properties show ferromagnetic behavior for Nd(Fe0.5Co0.5)2, SmCo2, and Sm(Fe0.5Co0.5)2. Laves compounds, while a sort of antiferromagnetism has been suggested for the supposed NdFe2 compound. This rapidly solidified NdFe2 alloy is believed to consist of an unstable rhombohedral NdFe7 phase plus fine particles of a Nd-rich phase. Some evidence of a phase transition from the mixture of unstable NdFe7 compound plus Nd-rich to Nd2Fe17 plus Fe-Nd-O phase are obtained after annealing the NdFe2 alloy. The ternary Laves compound, Sm(Fe0.5Co0.5)2, exhibits a high coercivity of 4 kOe at room temperature with a Curie temperature of 400 °C, while the Nd(Fe0.5Co0.5)2 compound shows a magnetic moment of 3.0–3.5 μB.
Correlation of magnetic properties and local atomic structure observed by electron-yield EXAFS in amorphous Co74Fe6B15Si5 thin films
Authors: Harris V. G. , Oliver S. A. , Nowak W. B. , Vittoria C. , Kim K. H. , Elam W. T.
Published: July 2002

Thin-film specimens of amorphous Co74Fe6B15Si5 were subjected to heat-treatment procedures followed by room-temperature magnetic and structural characterization in an effort to quantitatively correlate magnetic property changes to local atomic structure. Fourier transforms of electron-yield extended x-ray-absorption fine structure spectra show second and higher atomic shell ordering about transition-metal ions to occur at Tann≊300 °C. This ordering evolves to a body-centered atomic structure with heat treatments at higher temperatures. Accompanying this structural evolution is an expansion of the nearest-neighbor distance, disruption of the spin-wave-resonance spectra, and general deterioration of the soft magnetic properties.
Distribution of iron moments in a-Fe glass by first-principles spin-polarized calculations
Authors: Xu Yong-Nian , He Yi , Ching W. Y.
Published: July 2002

We have studied the electronic structure and the distribution of magnetic moments in amorphous Fe metallic glass by means of first-principles calculations. Large periodic models containing 100 and 200 atoms in a cubic cell are constructed using the Monte Carlo technique. The electronic structures are calculated within the real-space OLCAO scheme using the spin-polarized potentials obtained from the crystalline calculation. Results are presented for the spin-projected density of states (DOS), the partial DOS, and spin magnetic moments. It is shown that spin moments in a-Fe is mainly determined by the minority spin band because the Fermi level is located near the middle of this band. The site-specific distribution of Fe moments in an amorphous environment is analyzed as a function of local short-range order such as the number of nearest-neighbor atoms and the average nearest-neighbor distances. Extension of similar calculations to a-Fe1−x–Bx metallic glasses is also discussed.
Effect of a distribution of exchange parameters within a simple localized-itinerant model (abstract)
Authors: Iannarella L. , Guimarães A. P. , da Silva X. A.
Published: July 2002

The magnetic behavior at T=0 K of a system consisting of conduction electrons coupled to localized electrons is studied in the molecular-field approximation with a simple exchange parameter distribution. The localized electrons are also submitted to an axial crystal field. We define an average ionic magnetic moment and obtain a condition for the spontaneous magnetic order involving the crystal field, the width, and the center of the exchange distribution. We also study the magnetic behavior in the para- and ferromagnetic regions of the phase diagram. In a previous study1 the same model was applied to a system containing a crystal-field distribution.
The economics of amorphous core power transformers for induction heating applications at 20–50 kHz
Authors: Dughiero F. , Lupi S. , Nunes M. F.
Published: July 2002

The advantages of the use of amorphous magnetic cores in power transformers for induction heating applications in the frequency range 20–50 kHz are discussed. These advantages are pointed out presenting the characteristics and costs at different frequencies of a shell-type pancake coils power unit.
Phase changes in plasma-sprayed zinc-nickel ferrite
Authors: Dooling T. A. , Cook D. C.
Published: July 2002

The magnetic and crystalline properties of a plasma-sprayed coating of the microwave absorbing zinc-nickel ferrite, (Zn0.41Ni0.59 )Fe2O4 have been studied at 300 K using the Mössbauer effect and x-ray diffraction (XRD). Both techniques indicate that the plasma-sprayed material separated into two phases. The first is a nickel-rich phase with magnetic fields of 47.5 and 44.5 T at the tetrahedral and octahedral sites, respectively. The second is a zinc-rich phase, zinc meta-ferrite, having a small magnetic field of 4.2 T. The quadrupole splitting of this second phase is ΔE=0.34 mm s−1, which is the same as in pure nonmagnetic zinc ferrite. XRD analysis shows that the zinc-rich phase remains cubic with a0= 8.389 Å and the zinc meta-ferrite phase is tetragonal with the same lattice parameters as the cubic phase except for one elongated axis given by c0 =8.488 Å. This is much larger than the spacing for any of the series of zinc-nickel ferrites. The isomer shift of the zinc meta-ferrite is 0.710 mm s−1, which indicates that a large fraction of Fe3+ was reduced during the spraying process. Annealing the sprayed coating at temperatures less than 400 °C converted the zinc meta-ferrite into a magnetic phase that now exhibits magnetic fields close to those in the nickel-rich phase. However, the large isomer shift remains, indicating that the ferrous iron is still present. XRD shows that the phase is now cubic. Annealing up to 650 °C gradually oxidized all of the Fe2+ in the material and restored the magnetic and crystalline properties of the plasma-sprayed coating to very close to those of the unsprayed ferrite.
Soft magnetic characteristics of Co/Zr thin-film layered structures (abstract)
Authors: Valanju A. P. , Kim D. Y. , Walser R. M.
Published: July 2002

We have extended the stable amorphous phase of the Co1−xZrx system to 7<x<52 by compositionally modulating very thin (five to ten atomic layers) layers of Co and Zr by rf diode sequential sputtering from the elemental targets onto rotating, water cooled substrates. This extension was attributed to a stable, two-phase, hetero-amorphous state similar to that previously reported for Co/B layered structures (Ref. 1). The measured compositional variation of Ms of our Co/Zr layered structures indicated that, as expected, the composition of the stable Co-rich clusters in the heterogeneous state lies near the stable Co-rich eutectic of the CoZr system. The composition variation of the coercivity of the as-deposited Co/Zr structures was remarkably low (<1 Oe) over the entire composition range. The uniaxial anisotropies of 15–30 Oe were reduced to ≊2 Oe by a combination of bias sputtering and rotating field annealing. Although they have reduced Ms, the permeabilities of the Zr-rich films are ≳1200, and constant (to 10%) to ≊50 MHz. They also have high resistivities (≊190 μΩ cm), potentially increased hardness and stability, and could be useful for magnetic recording head applications.
S-wave pairing: A study of low-field dc magnetization in micrometer-sized HTSC powders
Authors: Shaw G. , Bhagat S. M.
Published: July 2002

An extensive study of the low-field (μ0H ≤ 8 mT) dc initial susceptibility χin has been performed using micrometer-sized HTSC powders of varying sizes and methods of preparation. It is found, as before, that χin(T) is essentially constant for T ≲ 0.4Tc. This supports s-wave pairing and implies no zeros of the gap on the fermi surface. Additionally, χin(T) finds reasonable description in a London model for superconducting spheres and a two-fluid model λ(T).
Magnetic properties of single-crystal Y-Ba-Cu-O containing Fe
Authors: McGuire T. R. , La Placa S. J. , Boehme R. F. , Shivashankar S. A. , Keane D. T.
Published: July 2002

A single-crystal of YBa2Cu2.85Fe0.15O7 was found to be tetragonal over the temperature range 10–300 K. The iron obeyed a Curie–Weiss law attributed to divalent Fe and showed a negative intercept indicating antiferromagnetic exchange. The presence of Fe degraded the superconducting properties such that critical currents are only 10%–20% of that in the best pure YBa2Cu3O7−δ crystals without Fe and the superconducting transition temperature has decreased from 90 to 60 K.
The crystalline electric field as a direct probe for charge transfer processes in high-temperature superconductors (abstract)
Authors: Allenspach P. , Mesot J. , Staub U. , Furrer A.
Published: July 2002

Charge fluctuations and charge transfer processes appear to be important mechanisms towards understanding high-Tc superconductivity.1 We describe the inelastic-neutron-scattering technique to observe the crystalline electric field (CEF) as a direct probe of the local symmetry and charge distribution at the rare-earth site. For RBa2Cu3Ox (R=Ho,Er; 6<×<7) we have succeeded to directly prove the oxygen-vacancy-induced charge redistribution in the CuO2 planes,2,3 which support the idea of charge transfer from the chains to the planes.4 An empirical relation between Tc and the observed charge transfer Δρ3 is derived which is highly nonlinear close to Tc=90 K.3 Charge transfer can also be realized by pressure and doping (at the Cu sites). Neutron spectroscopic CEF studies performed under pressure up to 10 kbar and with doped systems RBa2Cu3−xMxO7 (M=Ni,Zn) as well as CEF studies on RBa2Cu4O8 compounds can be consistently described within our picture. Similarly, we have analyzed the neutron spectroscopic data available for the recently discovered high-Tc cuprates Nd2−xCexCuO4 and found direct evidence for the electron doping process occurring in the copper-oxide planes.
Magnetic properties of MBE structures using fcc Co/Cu(001) and bcc Fe/Cu(001) (abstract)
Authors: Heinrich B. , Celinski Z. , Myrtle K. , Cochran J. F. , Kowalewski M. , Arrott A. S. , Kirschner J.
Published: July 2002

We have used ferromagnetic resonance and surface magneto-optic Kerr effect to investigate the magnetic anisotropies in face-centered-cubic fcc Cu/Co/Cu(001) structures. We have found that Cu/Co/Cu structures possess large magnetic anisotropies. The twofold perpendicular anisotropy results in a strong easy plane (4πMeff = 4πMs + Hu ∼ 40 kOe). The perpendicular uniaxial anisotropy is only weakly dependent on Co film thickness. Hu = 25.4, 23.7, and 17.7 kOe in 3-, 4-, and 10-ML-thick Co films, respectively. The twofold perpendicular anisotropy in fcc Co/Cu/Cu structures is caused by the lateral expansion and vertical contraction of fcc Co(001) ultrathin films. The in-plane fourfold anisotropy in fcc Cu/Co/Cu(001) structures has its easy axis along the [110] crystallographic direction. The fourfold in-plane anisotropy is large (2K1/Ms ∼ 1 kOe) and weakly dependent on Co film thickness. Fe(001) can be grown epitaxially on fcc Co(001) and results in a significant change in the magnetic properties. In Cu/4Co/3Fe/Cu(001) multilayer (integers describe the number of ML) the perpendicular anisotropy changes its sign and is very weak (Hu = −1.5 kOe). The in-plane fourfold anisotropy is also appreciably decreased (2K1/Ms = 0.4 kOe). Cu/4Co/6Cu/4Co/Cu(001) trilayers are coupled antiferromagnetically. However, this coupling is smaller (J=−0.07 ergs/cm2) compared to bcc Fe/Cu/Fe structures. The exchange coupling in Co/Cu/Co trilayers depends strongly on details of the total structure, e.g., the sample Cu/4Co/6Cu/4Co/3Fe/Cu is ferromagnetically coupled (J∼0.1 ergs/cm2). The exchange coupling in bcc Fe/Cu/Fe(001) trilayers oscillates with increasing Cu thickness (oscillatory period of 10 ML). However, no evidence of symmetric oscillations was found.
Contours of constant χSG in the H-T plane: Mean-field versus droplet theories of Ising spin glasses
Authors: Singh Rajiv R. P. , Huse David A.
Published: July 2002

One of the central features of the mean-field theory of Ising spin glasses is the de Almeida-Thouless phase transition line in the H-T plane, where the spin-glass susceptibility χSG diverges. Contours of constant χSG in the paramagnetic phase go to high fields as T→0 in mean-field theory. In contrast, in the droplet theory for short-ranged spin glasses, χSG remains finite in a field and the contours go to H=0 as T→0. We have investigated the constant χSG contours both in the SK model and for d-dimensional short-ranged spin glasses. For the latter we use transfer matrix methods in d=1 and high-temperature expansions and Monte Carlo simulations in higher d. The results are in good accord with droplet theory for d=1 and 2. For d=3 the evidence remains ambiguous, although extrapolations of high-temperature series are qualitatively different from d=2.
Magnetic-field dependence of T
g in bulk Cu:Mn and Cu:Mn/Cu multilayer systems
Authors: Kenning G. G. , Chu D. , Alavi B. , Hammann J. M. , Orbach R.
Published: July 2002

In order to ascertain the universality class of the long-range metallic spin glass Cu:Mn, extensive measurements of the longitudinal component of the zero-field-cooled (Mzfc) and field-cooled (Mfc) magnetization have been made. Measurements were made in both bulk Cu:Mn and Cu:Mn/Cu multilayer films in magnetic fields between 2 and 15 000 G. Mean field calculations of a Heisenberg spin glass with weak Dyzaloshinskii–Moriya-type anisotropy predict Ising-like behavior at low fields crossing over to Heisenberg behavior in high fields. Evidence consistent with crossover behavior in the transition temperature Tg (where Tg is defined by the onset of strong irreversibility in the magnetization, Mirr = Mfc − Mzfc) was observed at fields similar to previous magnetic-field-dependent studies. From the low-field extrapolation of Tg to H=0, the zero-field Ising-like transition temperature was obtained while from the high-field extrapolation to H=0 the zero-field Heisenberg transition temperature was obtained, the latter significantly lower than the former. This analysis, applied to the multilayer systems, suggests that the lower critical dimension of both Ising and Heisenberg spin glasses lies between two and three.
Rotational spin-glass properties of nearly ferromagnetic Tb0.15Y0.85Zn
Authors: Said M. R. , Kouvel J. S. , Brun T. O.
Published: July 2002

For this cubic pseudobinary compound, the bifurcation of the magnetization (M) vs temperature for warming and cooling in low fields (after zero-field cooling) indicates a spin-glass freezing point (Tg) of ∼20 K. Isotherms of M vs cooling field show zero spontaneous moments down to 4.2 K but an initial susceptibility that almost diverges below Tg. From rotational measurements of M as a vector in a fixed field (H) at 4.2 K, the anisotropy field produced by field cooling (HK) is found to turn rigidly with the sample for H below ∼1 kOe. At higher H, HK rotates up to some angle relative to H and then stays fixed as the sample continues to turn, thus exhibiting a frictional rotation relative to the sample. Nevertheless, HK remains sizeable in magnitude (∼12 kOe). Comparisons are made with analogous results for isostructural (Tb, Y) Ag, where spin-glass order coexists with antiferromagnetism, as well as for various prototypal spin-glass alloys.