bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstract: A quarter of a century of magnetism: Personal reminiscences
Authors: Goldman J. E.
Published: February 2003

The 25 years that have elapsed since the first Magnetism Conference constitute a virtual history of magnetism in the U. S. At the first post-war International Conference on Magnetism held in Grenoble in 1950 (four years prior to the first of the regular U. S. Conferences on Magnetism that were the joint creation of the Physics and Electrical Engineering communities) fewer than ten Americans participated. Then, as two years later at the Maryland Conference, the focus was on ferromagnetism, the magnetization curve, domain wall motions and a brief nod to the then relatively new phenomena of ferrimagnetism, nuclear magnetism and neutron diffraction. The only concession to theory at Maryland was an evening symposium on ferromagnetic exchange that will be remembered by those who attended primarily for the controversy engendered therein. The explosive growth of the field in the subsequent decade is probably as much a consequence of the technological emphasis on applications principally in computers as it is a result of the new theoretical powers made available by those same computers. In an aesthetic sense, the impact that magnetism research has had on kindred fields of science and engineering from lasers to DNA is testimony to the unboundedness of scientific inquiry whatever the initial motivation. It is probably in its impact on the rest of the world of science and engineering that magnetism research today holds its greatest potential.
Abstract: Magnetic phase diagram of iron-rich iron-aluminum alloys: A microscopic model
Authors: Shukla P. , Wortis M.
Published: February 2003

Iron-aluminum alloys with less than 50 atomic percent aluminum are known to exhibit an interesting phase diagram, including paramagnetic, ferromagnetic, and spin-glass regions. We present a microscopic model of this behavior, involving competition between direct ferromagnetic Fe-Fe interactions and indirect antiferromagnetic Fe-Al-Fe superexchange interactions. The model incorporates the experimentally observed fact that only Fe atoms with four or more Fe nearest neighbors have fully developed magnetic moments. By performing an approximate decimation-type pretransformation, we are able to map this model onto an equivalent nearest-neighbor simple-cubic bond-random Ising model, the properties of which have been previously studied by mean-field and renormalization-group methods. We are, thus, able to derive theoretical phase diagrams in the temperature-concentration plane based on three model parameters: the two elementary interaction strengths (Fe-Fe and Fe-Al-Fe) and the (weak) moment of a triply coordinated iron atom. Assignment of physically reasonable values to these parameters leads to a phase diagram in semi-quantitative agreement with experiment. We treat alloys with both Fe3Al and FeAl-type structure. Research supported in part by NSF grants DMR-77-23999 and DMR-75-22241.
Abstract: Magnetic susceptibility and electrical resistivity of Gd(Cu1−xGax) pseudo binary alloys
Authors: Mydosh J. A. , van Dongen J. C. M. , Buschow K. H. J.
Published: February 2003

We have measured at low temperatures the ac differential susceptibility and the electrical resistivity for a series of Gd(Cu1−xGax) pseudo binary alloys for x between 0.10 and 0.22. The Gd(CuGa) system is particularly interesting in this concentration region since high temperature susceptibility measurements have shown a zero paramagnetic ϑ for x?0.15. The intermetallic compound GdCu is antiferromagnetic TN?140 K while GdGa is ferromagnetic Tc?210 K. It was hoped by randomly mixing the Cu and Ga in the x region where Tc and TN→0, a spin glass-like state could be formed. The susceptibility exhibits a broad maximum around 38 K for all alloys which is relatively concentration independent. At very low temperatures (1–10 K) a shoulder develops in the susceptibility which does vary with x. The resistivity shows an x dependent minimum at high temperatures 80–120 K, followed by a lower temperature maximum at 45–80 K. These behaviours indicate that a simple spin glass freezing is absent and that a complicated form of long range magnetic order is present.
Abstract: Measurement of order parameter in CuMn spin-glass
Authors: Nagata Shoichi , Keesom P. H.
Published: February 2003

There exists in the literature a large number of experiments involving the basic characteristics of spin-glass materials. Much less information is available on order parameters and critical properties of spin-glass. The present work is motivated by a desire to study these properties and is concerned with the low-dc-field susceptibility of CuMn spin-glass containing 1.08 and 2.02 at. %Mn, using a superconducting quantum-interference device (SQUID). The zero-field cooled initial susceptibility shows a cusplike peak at Tg, the transition temperature to a spin-glass state. After field cooling from T≳Tg (even for H=2 Oe), the susceptibility below Tg is nearly independent of temperature with the constant value of ∼0.97χ (Tg). The high temperature susceptibility follows a Curie-Weiss law until just above Tg; the value of the Weiss constant is very small. Sherrington and Kirkpatrick obtained a spin-glass solution characterized by the Edwards-Anderson type order parameter q(T). The susceptibility χ provides an experimental probe of q(T), since χ (T) ={C(T)[1−q(T)]}×{T−ϑ (T)[1−q(T)]}−1. In the mean-field theory, C(T) and ϑ (T) are constants, corresponding to the Curie constant and Weiss constant, respectively. Using this theory, the order parameter q(T) as a function of temperature is extracted from the susceptibility data. A critical index β?1 is obtained assuming a power law for q(T) ∝ (1−T/Tg)3. The value of β is in agreement with the prediction of the mean-field theory: β=1. It appears however to exclude the renormalization-group method prediction, obtained by Harris et al. They derived expansions for the exponents in power of ε=6−d, d is the dimension of the system, which leads in first order of ε to β=2.5 for the Ising model, 1.75 for the X-Y model and 1.6 for the Heisenberg model. It also excludes the prediction of the percolation theory by Kirkpatrick, which gives β=0.39.
Comparison of spin anisotropy and exchange alternation
Authors: Bonner Jill C. , Blöte Hendrik W. J. , Johnson J. D.
Published: February 2003

Quasi-1-D magnetic systems with on the one hand an Ising-Heisenberg type spin anisotropy and on the other hand an alternating (dimerized) character have many interesting features in common and a few interesting differences in their phase behavior and general magnetic properties. This report reviews results rather scattered in the literature in addition to presenting new results. These rather complex quantum models present a theoretical challenge. It is also hoped that this work will be helpful to magnetochemists interested in identifying the underlying magnetic character of their systems, and to experimentalists in general.
The optimum design of magnetic bubble propagation circuits
Authors: Ishak W. S. , Torre E. Della
Published: February 2003

This paper describes a procedure for the optimal design of field access bubble propagation circuits. Each type of propagation circuit is described by the assignment of a set of parameters. An objective function of these parameters is formulated to describe the ideal to be achieved. An optimization procedure is applied to the objective to compute the set of optimum parameters. Various objectives can be used, one such is: maximizing the speed of the device by maximizing the propagating potential-well gradients, and minimizing bubble size fluctuations by adjusting the potential-well profile. The optimization package used permits the application of constraints on the circuit parameters such as the assuring of propagation past critical points in the circuit and limiting the parameters to realistic ranges. An example is given to show the results of optimizing the performance of a T-I propagation circuit.
Testing and defects of bubble memory devices
Authors: Iwasa S. , Orihara S. , Matsuyama S. , Kaneko Y. , Nogiwa K.
Published: February 2003

A computer-controlled bubble memory wafer test system has been developed and more than 5,000 chips of 83 kbit and 300 kbit major-minor loop design have been tested. Throughout the testing, various types of defects have been found, including defects sensitive to bubble population, start-stop operation and in-plane holding field. These defects are found to be caused by small defects in permalloy patterns or garnet films. An effective way to detect these defects has been developed.
Abstract: Thermoelectric power of Nd1−xLax and Ce1−xLax alloys
Authors: Petersen T. S. , Legvold S. , Gschneidner K. A. , McMasters O. D. , Moorman J. O.
Published: February 2003

The thermoelectric power of polycrystalline dhcp samples of Nd1−xLax and Ce1−xLax has been measured from 2–300K. Single crystals of Nd have also been measured. (AIP)
Magnetooptical rotation in a transverse field in D
y3A
l5O12(D
A
G)
Authors: Chen E. Yi , Dillon J. F. , Blount E. I. , Van Uitert L. G.
Published: February 2003

As part of a study of the role of the two order parameters M and Ms in the magnetic birefringence of DAG we have found the case with applied field parallel to [110] and light propagating along [001] surprising and interesting. An analysis for this case shows that the dielectric tensor contains imaginary off diagonal terms proportional to MsM2, this means that the normal modes of propagation may be elliptical or even circular when Ms is finite. In such experiments on DAG at 1.40 K it was found that the normal modes of propagation in the antiferromagnetic state are nearly circular; in the paramagnetic state they are linear. Just below the metamagnetic transition the magnetooptical rotation in a transverse field is about 32% cm. This rotation is observed to be odd in Ms, even in M.
Theory of the speromagnetism phase transition
Authors: Lai Wu-yan , Wang Thien-si , Shem Jue-lian
Published: February 2003

A new type of spin structure, called speromagnetism, has recently been observed in some amorphous materials. Preliminary theoretical studies on the basis of a random distribution molecular field model (RMF) have been carried out. In order to analyze such a system within the framework of Landau theory, a method of stochastic functions has been used. While the result of the calculations implies a scattered distribution of orientations of the spins in space, the sum total of the spins does not vanish. Additional calculations demonstrate that the susceptibility of any system with RMF does not diverge at the second-order phase transition point.
Stress-induced playback loss and switching field reduction in recording materials
Authors: Flanders P. J.
Published: February 2003

When a magnetized tape in an oppositely directed field is rubbed, the stress σ reduces the switching field by an amount ΔHσ so as to produce a partial reversal of the magnetization ΔMH,σ. This inverse magnetostrictive effect leads to the playback loss ΔL that is observed in a recorded tape. The loss depends on ΔHσ, the coercive force Hc, the demagnetizing field and the shape of the hysteresis loop. The parameter ΔHσ is proportional to σ and is related to the magnetostriction constants. It can exceed 300 Oe or greater than one half the coercive force in a 3.5% Co-doped γ-Fe2O3 sample when σ=500 kg/cm2. When Co is adsorbed on the surface of γ-Fe2O3 particles the saturation magnetostriction ‖γs‖, ΔHσ and ΔL are all smaller than for a Co-doped tape with an equivalent Hc. The small ΔL for CrO2 is due to its low λs whereas low stress related losses in Fe are due primarily to a high Hc.
A self-consistent calculation of the transition zone in thick particulate recording media
Authors: Ortenburger Irene B. , Potter Robert I.
Published: February 2003

We describe a fully two dimensional self-consistent calculation of an isolated transition in a thick particulate magnetic recording tape. The calculation includes relative motion between the tape and head, as well as a vector magnetic hysteresis model.
Abrasive wear in magnetic disc recording
Authors: Weiss Ronald D.
Published: February 2003

Recent developments in disc recording have made use of low flying ferrite heads which make sliding contact with the discs during starts and stops. The disc media, comprised of finely dispersed γ-Fe2O3 in a polymer matrix, generates abrasive wear at the head and disc interface. Physical measurements concerning the nature of the wear mechanism and magnetic recording anomalies are reported. Both the head and disc wear were studied respectively and related to flight mechanics, the air bearing, component geometry and structures. The role of boundary lubricants has been investigated and their effect on magnetic and physical performance criteria are discussed.
Magnetic interaction in small iron-copper clusters
Authors: Montano P. A. , Talarico M. A.
Published: February 2003

In this work we report a Mössbauer study of iron-copper clusters isolated in a rare gas solid. For the FeCu dimer we were able to determine the electronic ground state. The samples were prepared in a liquid-helium cryostat evacuated to a pressure better than 10−7 torr. The Cu and (90% enriched) 57Fe atomic beams were produced in alumina crucibles contained in resistance heated tantalum furnaces and codeposited with a stream of argon gas at 4.2K onto a Be disk. In this study very dilute samples were used (Ar/metal ?500) in order to identify correctly the FeCu dimer. From the Mössbauer parameters we were able to identify the molecule as 2π with a spin at the iron atom of 1/2. A concentration dependence study of the iron-copper multimer was carried out. It was observed that by increasing the number of copper nearest neighbors the isomer shift approaches the value obtained for iron in a copper matrix. For very high concentrations the Mössbauer parameters are similar to those of pure iron multimer. It seems that the presence of a large number of copper nearest neighbors produces a drastic change in the electronic structure of the iron atom.
Study of Fe-rich superparamagnetic clusters in olivine, (Mg,Fe)2SiO4 by Mossbauer spectroscopy
Authors: Rao V. U. S. , Huggins F. E. , Huffman G. P.
Published: February 2003

Mossbauer spectra of olivines of composition (MgxFe1−x) 2SiO4 (x?0.3 to 0.9) have been examined in the temperature range 4.2 to 300 K, and found to exhibit superparamagnetic relaxation effects originating from clusters of Fe2+ ions. Relaxation times were determined by comparison with theoretical relaxation spectra calculated from the stochastic model of Blume and Tjon, which was modified to include the asymmetry parameter and general orientations of the hyperfine field direction with respect to the crystal axes. From the variation of the relaxation time with temperature, the mean cluster-size diameters of the Fe-rich regions were found to be in the range 20 to 40 Å, and to increase with increasing Fe content. The distribution of cluster diameters was asymmetric, with higher probabilities for small diameters. Potential applications with regard to the determination of the thermal histories of rocks containing olivine are discussed.
Shock induced magnetic effects in fine particle iron dispersions
Authors: Wasilewski P. J.
Published: February 2003

In order to understand the role of shock waves in modifying existent remanent magnetization and in inducing magnetization via 1st and 2nd order shock transitions in iron and iron-nickel alloys a model system has been adopted. Dilute iron in copper (1.5 wt % Fe solutions can be annealed arbitrarily to produce a near ideal dispersion of spherical fcc precipitates having diameters ≲2000 Å. The size range is arbitrarily specified by the anneal. These spherical iron (antiferromagnetic-fcc) particles are then transformed to the ferromagnetic state (bcc) during a shock pulse in controlled external fields (≲1 Oe). The axial vector always takes on the sign of the external field indicating that on the microsecond time scale of the transformation the particles record the field sense. The amount of fcc iron transformed depends on both precipitate size and the peak input pressure. The observed deformation induced anistropy is dependent on particle size and shock level, but the 400 Å–600 Å particles show the maximum degree of anisotropy at all shock levels. Different sizes of precipitates support different degrees of magnetic hardening (i.e., response to alternating field demagnetization). Anisotropy in magnetic hysteresis, using hysteresis ratios - RI (ratio of saturation remanence to saturation magnetization) and RH (ratio of remanent coercive force to coercive force) indicate a shock induced weak field remanence anisotropy. Measurement of the angular variation of coercive force (HC) and remanent coercive force (HR) and the computed RH clearly identifies the direction of the shock, RH being a minimum and HC a maximum parallel to P. Unique properties observed in hysteresis behavior are related to the narrow iron particle size distribution, orientation, and mean particle spacing. These unique properties include discrete switching fields for magnetization reversal, and separation of region of hysteresis from region of shape response.
The increasing of the coercivity of γ-Fe2O3 powder by epitaxial Co-doping
Authors: Lo Ho-Let , Gung Wei
Published: February 2003

γ-Fe2O3 powder of acicular shape was modified by reaction with Co2+ and Fe2+ ion containing solution or Co(OH)2 to obtain a cobalt ferrite layer of various cobalt content on the surface of each particle. It was found that this epitaxial Co-doping raised the coercivity of γ-Fe2O3 from 420 (Oe) to 770 (Oe). The coercivity of such epitaxial Co-doped γ-Fe2O3 powders depends on the packing density in the same manner as the acicularly shaped γ-Fe2O3 powder. The dependence of the coercivity of the powders on temperature, the chemical composition and preparation technique were also studied. The effective uniaxial anisotropy constants were measured. The shapes of the powders were observed by electron microscopy. On the basis of these studies, we are of the opinion that the development of a surface anisotropy of the epitaxial layer is the most probable cause of the increasing coercivity.
Abstract: High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film
Authors: Chen Tu , Charlan G. B.
Published: February 2003

The correlation between the magnetic properties and microstructures of sputtered pure Co and Co-Re alloy thin films have been investigated. Magnetic properties were investigated via hysteresis loop measurements while microstructure was determined using TEM. (AIP)
Evoked neuromagnetic fields of the human brain
Authors: Williamson S. J. , Kaufman L. , Brenner D.
Published: February 2003

Detectable magnetic fields are associated with electrical activity in the brain that may be evoked by sensory stimuli. Neuromagnetic fields as weak as 20 femtotesla can be studied with modern SQUID detectors without recourse to magnetic shielding. Studies in our laboratory and elsewhere reveal that the field patterns may be sharply localized near the appropriate area of the cortex for visual, somatosensory, or auditory stimuli. The temporal features of the magnetic response to visual stimuli reveal aspects of the organization of the visual system of the brain.
Magnetic and metallurgical properties of directionally solidified eutectic Bi/MnBi composites: The effects of annealing
Authors: Pirich Ron G. , Larson D. J.
Published: February 2003

Eutectic Bi/MnBi (97.8 a/o Bi) samples have been plane-front directionally solidified. The resultant microstructures consist of elongated, aligned particles of MnBi dispersed in a Bi-matrix. Magnetization as a function of temperature (4.2 to 300 K) and applied field (up to 220 kG) has been used to evaluate solidification parameters and magnetic properties. At room temperature, in addition to the diamagnetic contribution of Bi, one finds a superposition of the ferromagnetic, low temperature (LTP) MnBi phase and paramagnetic phases. At cryogenic temperatures, one of the room temperature paramagnetic phases is ferromagnetic with an intrinsic coercivity of 120 kOe while the other remains paramagnetic for low fields and orders ferromagnetically at high fields in a complicated way. Annealing of as-grown samples was found to produce significant changes in magnetic properties. The origins of the paramagnetic phases and their relation to the mechanisms which control the coercive field of the hard magnetic LTP MnBi phase are discussed.
Phonon spectroscopy and forbidden transitions in rare earths and transition metal ferromagnets
Authors: Blackstead H. A.
Published: February 2003

Conventional pulse-echo techniques and spin-phonon spectroscopy have been employed to examine magnetoelastic excitations in films of Fe, Ni, Gd, Er, and crystals of Gd. With perpendicular rf and dc fields, transverse magnetoelastic excitations are observed with intensities appropriate to a coupled mode model. Recent experiments on Er, with parallel rf and dc fields applied in the film plane, demonstrate the excitation of longitudinal phonons with signal intensities which increase monotonically with an applied field, varying from 0–24 kOe at 10K. Experiments on Gd, Ni, and Fe films with the same field configuration also yield longitudinal phonons at applied fields sufficiently large to magnetize the specimens. Experiments on Gd crystals give similar results. In all cases, the phonon signal is at the rf frequency and the signal intensity varies linearly with the rf field intensity. The data support the conclusion that a first order transition is responsible for the signals; however, with this so-called ’’parallel-pumping’’ configuration of the rf and dc magnetic fields, first order transitions are forbidden. An addition to the conventional Hamiltonian, which may reconcile these difficulties, is discussed.
Anomalous transmission of microwave power at FMR through nickel crystals at 4.2°K
Authors: Dewar G. , Heinrich B. , Cochran J. F.
Published: February 2003

We have observed an unexpected increase in the transmission of 24 GHz microwave power through thin pure, nickel slabs at liquid helium temperatures, and at an applied static magnetic field value corresponding to ferromagnetic resonance (FMR). This increase in power at FMR was particularly unexpected because our specimens were very thick compared with the anomalous skin depth at FMR, d/δ∼100 to 1000. The nickel crystals were prepared from a boule having a residual resistance ratio in excess of 2000. The transmission amplitude ratio was found to be ca. 10−6 for a specimen 8.2 μm thick, and having the static field oriented along the hard axis (100). The transmission ratio was approximately six times smaller when the static field was oriented along the easy axis (111). The anomalous transmission amplitude decreased rapidly with increasing temperatures, and was no longer observable at 25 °K in a specimen 8.2 μm thick. Numerical calculations using a non-local conductivity and the assumption of specular scattering of the current carries at the specimen surfaces did not show any field dependence of the transmission at FMR. The origin of this effect is unknown, but is clearly related to the large mean free path at low temperatures (l∼d), since it was not observed in polycrystalline specimens having a residual resistance ratio ∼16.
Magnetoelastic excitations and ferromagnetic resonance
Authors: Alexandrakis G. C. , Allen J. W. , Privorotskii I. A.
Published: February 2003

The anomalous transmission of the electromagnetic energy through thick ferromagnetic films has been discovered. The effect is observed when the static magnetic field is either parallel or perpendicular to the sample surface and perpendicular to the r.f. field. In order to explain the new effect, the spectrum and the attenuation of coupled sound-spin waves was calculated. The attenuation of the sound-like waves is rather small and thus sound waves can carry electromagnetic energy through the sample.
Magneto-optical characterization of thin films of Fe1−xBx, Fe1−xSix and Fe-overcoated permalloy
Authors: Krebs J. J. , Prinz G. A. , Forester D. W. , Maisch W. G.
Published: February 2003

The optical and magneto-optical constants of several magnetically soft thin film alloys have been determined for λ=6328Å using the transverse Kerr effect and ellipsometric techniques. The coercive force and magnetization were also measured. The alloy systems Fe1−xBx (0.15?x?0.5) and Fe1−xSix (0.1?x?0.3) and iron-overcoated permalloys were studied as were Fe, Co and permalloy for reference. When used as transverse Kerr effect mirrors for ring laser gyros, the Fe-rich Fe-Si alloys and iron-overcoated permalloys have the best calculated performance.
The magnetic properties of R3Pt4 intermetallic compounds
Authors: Gamari-Seale Helen , Yakinthos J. K.
Published: February 2003

The magnetic behaviour of the series of intermetallic compounds designated by the formula R3Pt4 in which R represents Nd, Cd, Tb, Dy, Ho, Er and Tm was investigated over a range of temperature extending from 4.2 to 160 K and at field strengths ranging from 500 Oe to 20 kOe. Curie-Weiss behaviour was observed at high temperatures for all compounds. Effective moments were obtained which are in agreement with those expected from theory for the free tripositive ions. The Curie paramagnetic temperatures of the heavy rare earth compounds follow de Gennes law. At low temperatures the compounds order ferro- or ferrimagnetically. The R3Pt4 compounds are isostructural to the series R3Pt4 [1], both series have very closed crystallographic parameters, but different magnetic behaviour. The obtained results for the R3Pt4 are compared with those obtained for the R3Pd4 compounds.
Electron spin resonance of Nd+3 in d band cubic intermetallic compounds
Authors: Barberis G. E. , Davidov D. , Donoso J. P. , Rettori C. , Suassuna J. F.
Published: February 2003

ESR of Nd+3 in various d band cubic AB2 compounds is reported. The measurements yield information about (a) the exchange parameters, (b) the crystalline field, (c) the hyperfine constants, (d) the superconducting state of the type II superconductors CeRu2 and ThRu2.
Evidence for easy axis rotation in Dy1−xGdxAl2 alloys from nuclear hyperfine field measurements
Authors: Berthier Y. , Devine R. A. B.
Published: February 2003

We have studied the nuclear magnetic resonance of 163Dy in ferromagnetic Dy1−xGdxAl2 alloys (0?x?0.99). The observed behaviour of the resonance frequencies of the various resonances observed is anomalous and does not follow simple molecular field arguments. Quadrupolar splitting measurements suggest that within a given Dy environment of 0, 1, 2, 3 or 4 Gd nearest neighbours the Dy moment is independent of concentration of Gd. These results lead us to believe that the easy axis of magnetization rotates gradually from (100) to (111) in these compounds and that we in fact sense the Dy moment through nuclei in the domain wall edge. From enhancement factor measurements we conclude that the Dy single ion anisotropy is very small and that the predominate term, establishing domain wall stiffness, is the Dy-Dy interaction anisotropy.
Effects of substitution of chromium and nickel on the magnetic properties of Er2Co17 and Sm2Co17
Authors: Satyanarayana M. V. , Wallace W. E. , Craig R. S.
Published: February 2003

Ternary Er2Co17- and Sm2Co17-based alloys in which Co is replaced by Ni or Cr have been studied to ascertain the effect of alloying on their magnetic properties. The systems are single phase for 0?x?7 in the case of Er2Co17−xNix and for 0?x?2 for the Cr-substituted ternaries. Directions of magnetization, saturation magnetizations (Ms), anisotropy fields and intrinsic coercive forces (IHC) are reported for 300 and 78 K along with the measured Curie temperatures (Tc). All systems were found to be uniaxial except Er2Co13.6Ni3.4 which has planar anisotropy. Replacement of Co by Ni or Cr results in a decrease in Ms and Tc. IHC values for Er2Co17−xNix are small at room temperature but increased to ∼4 kOe at 78 K. The IHC values for Cr-containing ternaries rise dramatically between 300 and 78 K, from ∼0 to ∼15 kOe for Er2Co15Cr2 as an example. Anisotropy fields are significantly increased by Cr substituting, reaching in the case of Sm2Co15Cr2 ∼400 kOe at 78 K. Ni is considerably less effective than Cr in enhancing HA in these ternaries. At low concentrations Ni decreases anisotropy presumably because it produces shrinkage in the c-spacing and brings the dumbbell cobalts closer together.
Magnetic anomaly in superconducting TmRh4B4
Authors: Smith J. L. , Huang C. Y. , Tsou J. J. , Ho J. C.
Published: February 2003

We have investigated the magnetic and superconducting properties of TmRh4B4 (which becomes superconducting at 9.6 K) by means of ac and dc magnetic susceptibility and specific heat measurements. At 10.7 K, an ac susceptibility peak similar to those found in spin glasses has been observed. In addition, a pronounced specific heat peak has been observed at 11.4 K. The susceptibility peak is essentially unaffected by substitution of 1% Lu or Er for the Tm, but it diminishes when much larger amounts of Er are substituted. The physical origin of this anomalous peak will be discussed.
Itinerant metamagnetism in rare earth-transition metal compounds
Authors: Cyrot M. , Lavagna M.
Published: February 2003

Intermetallic compounds of rare-earth and transition metals present the possibility of using the large magnetic moment of the first with the high Curie temperature of the second. We first discuss the nature of the coupling between the spin of the rare-earth and transition metal. We assume that it happens within the d band coming from the 5d and 3d levels and describe it using the Van Vleck model for ferromagnetism. We then consider the particular case of Cobalt compounds where Cobalt can be magnetic or not depending of the rare-earth metal. We describe the appearance of magnetism as a collective metamagnetism due to the position of the Fermi level in these compounds in a steep decrease of the density of states. Calculation of the density of states confirms this hypothesis.
Abstract: Susceptibility measurements on (La, Ce)Al3
Authors: Majewski R. E. , Edelstein A. S. , Dwight A. E.
Published: February 2003

Susceptibility measurements using a SQUID magnetometer on CexLa1−xAl3 where x=.01, .02, 0.1, 0.2, 1.0 over a temperature range from 1.5 K to 20 K are reported. (AIP)
Rare earth–cobalt permanent magnets with improved mechanical properties
Authors: Sagawa M. , Yamagishi W. , Okada M. , Henmi Z.
Published: February 2003

A rare earth–cobalt permanent magnet with improved mechanical strength has been developed. Sm1−uCeu(Co1−x−yCuxTmy)z with Tm=Fe or a combination of Fe with other transition metals were prepared by powder-metallurgical means. Mechanical strength was evaluated by flexural strength testing for sintered permanent magnet rods. The compositional dependence on flexural strength σf as well as the influence of the different parameters, as for instance particle size and sintering temperature, were investigated. For z ≳ 5, σf increases with increasing z and other substitution parameters u, x and y. For instance, fine grained magnet of Sm0.8Ce0.2(Co0.785Cu0.15Fe0.05 Cr0.015)7.6 shows σf of 290 MPa, iHc of 360 kA/m and Br of 0.85 T.
Coercive force of pseudobinary R(Col−xCux)5 compounds
Authors: Maeda H.
Published: February 2003

The coercive field of rare earth compounds of the general formula R(Col−xCux)5, with R=Pr and Nd, has been investigated both experimentally and theoretically. Homogeneous single-phase specimens with compositions from x=0 to 0.6 were prepared and measured. Compounds with x?0.3 have coercive fields greater than 5 kOe at low temperatures, both in bulk single crystal and in powder form. The coercive field increases steeply with decreasing temperature, and the temperature dependence is stronger for larger x. The spin structure and energy of domain walls in R(Col−xCux)5 have been calculated using a discrete spin configuration model, and are found to be more sensitive to short-range fluctuations of the exchange interaction than of the anisotropy. Short-range exchange fluctuations can account for pinning fields of the same order as the measured coercive fields. The exchange fluctuations may arise from fluctuations in the distribution of the non-magnetic Cu atoms in the compounds.
Abstract: Rare earth cobalt permanent magnet applications overview
Authors: Parker R. J.
Published: February 2003

In this paper permanent magnet property interrelationships are placed in two categories and energy storage principles are reviewed. Several new device concepts are described and the energy density of these new magnets is shown to be of great importance in rearranging magnetic circuits, inverting components and placing permanent magnets in heretofore restrictive regions in magnetic circuits. (AIP)
Abstract: Magnetocrystalline anisotropy, magnetostriction and saturation magnetization of SmCo5 single crystals
Authors: Trout Stanley R. , Graham C. D.
Published: February 2003

The saturation magnetization, magnetocrystalline anisotropy and magnetostriction of SmCo5 have been measured on single crystal samples from 4.2 K to room temperature and above. (AIP)
Abstract: The effects of V and V+Ti on the magnetic and mechanical properties of Fe-Cr-Co hard magnets
Authors: Belli Y. , Kubarych K. , Okada M. , Mishra R. , Thomas G.
Published: February 2003

The microstructure and magnetic properties of the Fe-Cr-15 (wt%) Co hard permanent magnetic alloys with and without V and V+Ti are studied using transmission electron microscopy and transmission Lorentz microscopy. (AIP)
Effect of solute oxidation on the magnetic properties of nonoriented electrical sheet steel
Authors: Huffman G. P. , Stanley E. B.
Published: February 2003

The effect of internal solute oxidation during annealing in H2-N2-H2O atmospheres on the magnetic properties of nonoriented Si-steel electrical sheet has been investigated, using standard magnetic tests, electron and x-ray re-emission Mossbauer spectroscopy, metallography, and scanning electron microscopy. A significant correlation was found between the extent of internal oxide penetration into the steel and the degradation of magnetic properties. Permeability was observed to decrease linearly with increasing fayalite content, as determined by Mossbauer spectroscopy.
A study on AlN in high permeability grain-oriented silicon steel
Authors: Sakai T. , Shiozaki M. , Takashina K.
Published: February 2003

We report the results of studies on AlN which precipitates during the γ-α phase transformation in high permeability grain-oriented silicon steel (HI-B). We examined the behavior of AlN in each stage of the process by means of chemical analysis, electron microscope observation and hydrogen hot extraction technique. The AlN observed by the electron microscope in each stage of the HI-B production process can be classified into three types: A type: fine needle-like precipitate; B type: fine plate-like precipitate of irregular shape; C type: larger agglomerate plate-like precipitate. The B type AlN, the most important nitride, precipitates during the γ-α phase transformation which occurs continuously on cooling after hot band annealing. This irregularly-distributed fine AlN is believed to play an important inhibiting role in the secondary recrystallization process.
Improving the magnetic properties of high induction boron silicon-iron by adding boron to the coating
Authors: Fiedler H. C.
Published: February 2003

The presence of boron, nitrogen and sulfur provides strong inhibition to normal grain growth in heavily cold-rolled 3% silicon-iron, which permits the development of a precise (110) [001] secondary recrystallization texture during the final anneal. The addition of boron to the magnesia coating, which results in the diffusion of boron into the alloy, has a marked effect on the grain growth behavior during the final anneal of silicon-iron containing these elements for grain growth inhibition. Alloys initially deficient in either boron or sulfur experience more extensive secondary recrystallization, and therefore achieve a higher induction, as a result of boron being added to the coating. While small additions of boron are helpful, larger additions decrease the induction, the optimum boron addition to the coating being related to the nitrogen content.
Control of bias field profiles in bubble memory devices
Authors: Craik D. J. , Cooper P. V.
Published: February 2003

The field profiles in the central planes between pairs of rectangular magnets, bearing thin sheets of highly permeable material on their inner faces, are investigated theoretically and experimentally. Particular attention is paid to measures which affect the degree of uniformity of the field and the relative extent of the uniform region, by optimizing the geometrical parameters and, to a limited extent, by shaping the magnets. Theoretical and experimental results show good correlation, verifying the simple method of calculation used.
Abstract: The design and characterisation of single chip bubble memory packages
Authors: Adamson S. J. , Cooper P. V. , Fairholme R. J. , Phillips R. J.
Published: February 2003

We will report our experience in the design and characterization of a second generation dual-in-line single chip package currently in production was designed to contain a 0.250 inch square chip and to dissipate less than 350 mW in continuous operation. The package operates in external fields up to 100 Oe and shows no irreversible changes over the range −25°C to 100°C; the overall package size is 0.8×0.8×0.35 inches and it fits a 0.9\ pitch socket. (AIP)
Influence of planar anisotropy on the domain structure in amorphous and garnet magnetic films
Authors: Puchalska I. B.
Published: February 2003

Domain structure in materials with shape anisotropy and ’’skin’’ anisotropy is shown. The influence of the shape anisotropy in Co-P amorphous film is discussed and the similarity between the domains in amorphous film and non-amorphous materials such as Permalloy and YIG single cyrstals is pointed out. The influence of the ’’skin’’ anisotropy in the garnets and amorphous material with perpendicular anisotropy is shown. Some examples of domains in garnet with implanted layer, garnet with Permalloy layer and annealed YCo3 films are presented.
Specific properties of ion implanted bubble circuits
Authors: Jouve H.
Published: February 2003

Stress measurements using the beam cantilever method have been performed on ion implanted garnet films for bubble applications. A maximum average stress of 6.109 ergs/cc is obtained for a nuclear energy loss density of about 1ev/Å3. A very fast decrease occurs for higher dosages. Ion implanted circuits for bubble propagation are shown to be formed by alternated portions of convex and concave squares. A bubble rotates in one period of the external drive field around a concave square and in three periods around a convex square. The latter has strongly anisotropic properties as determined by bubble collapse field measurements. Consequently the propagation on ion implanted patterns is also anisotropic and occurs with different velocities. The magnetocrystalline anisotropy is revealed by measuring the collapse and run out fields of free bubbles, and the nucleation field of bubbles on the edge of a disk. The conjunction of these two anisotropies leads to bias field margins which are dependent on the loop orientation with respect to the crystallographic axis. The comparison between ion implanted and permalloy coated garnets suggests the importance for successful propagation of the three following properties: adherence of bubbles along the propagation patterns, sample homogeneity and three fold symmetry.
Orientation dependence of propagation margin of 1-μm bubble contiguous-disk devices—Clues and cures
Authors: Lin Y. S. , Almasi G. S. , Dove D. B. , Keefe G. E. , Shir C. C.
Published: February 2003

The operating margins for bubble propagation along ion-implanted contiguous-disk devices are found to depend upon the orientation of the propagation track with respect to the tridirectional crystalline symmetry of the implanted garnet layer. Continuous disk propagation structures provide bubble tracks on each side of the structure. Depending upon orientation both tracks may have equally good propagation margin, or one track may be characterized as super while the other is bad. Studies of charged wall configurations using Ferrofluid colloid show distinct differences in wall behavior associated with the good, bad and super tracks. Annealing and removal of the implantation-protected Au patterns tend to improve, but not cure, the bad tracks. One solution is to orient the orthogonal major-minor loop tracks at 15° to an easy stripout direction so that all tracks propagate acceptably well; however, superior performance can be obtained by a parallelogram array with all tracks parallel to an easy stripout direction.
Micro-magnetic structures of planar charged walls
Authors: Shir C. C. , Lin Y. S.
Published: February 2003

The energy structure and internal magnetic field distributions for the cross section of a planar charged wall [1] have been calculated by direct numerical integration of the Landau-Lifshitz-Gilbert equation with minimal physical approximations [2]. Head-to-head (and tail-to-tail) charged wall structures have been computed for a wide range of material parameters. Results indicate that the charged wall structures depend on a non-dimensional film thickness D normalized by δo=π√ (A/K) which is the Néel or Bloch wall width for thin or thick film respectively. For thin films, the charged walls have features of the Néel wall in terms of wall width and energy. For thick films, the charged walls have complex structures with Néel wall features at the center, and Bloch wall features (Bloch spin) near the surfaces of the film. The Bloch spin increases with the film thickness D and is nearly independent of the value of Q. The charged wall width is equal to the Néel wall width δo for large Q and small D. The charged wall width increases rapidly with decreasing Q which causes some difficulties in defining the wall width and in estimating the wall energy. The charged wall energy is close to the Néel wall energy for large Q=5, and is constantly larger than that for small Q regardless of the value of D.
Abstract: Nucleation of 1-μm bubbles via charged walls
Authors: Almasi G. A. , Keefe G. E. , Lin Y. S.
Published: February 2003

This paper describes a novel bubble nucleator utilizing charged walls to provide a portion of the nucleation field and substantially reduce the nucleation current level. Compared to nucleators without charged wall assistance, the reduction in current level attributable to the charged wall is approximately 30–40%. (AIP)
Generation of high capacity, high density bubble domain patterns using electron beam technology
Authors: Reekstin J. P. , Potosky J.C. , Imerson R. G.
Published: February 2003

Three mask fabrication techniques capable of producing megabit capacity chip mask sets have been investigated: photocomposition, electron beam raster scan, and electron beam vector scan. Details of the technique used for photocomposition are described to illustrate the difficulties of obtaining 1 μm resolution over 1×1 cm2 chip areas with reasonable throughput. These difficulties may be circumvented by using electron beam pattern generation. Details of the experimental vector scan system used are presented and a comparison made of results obtained using the three techniques.
Improved propagation, stretching and annihilation of magnetic bubbles in current-access devices
Authors: Dekker E. H. L. J. , Wiegman N. J. , van Mierloo K. L. L. , de Werdt R.
Published: February 2003

New functional elements have been tested for 16 μm-period current-access circuits in single and double mask structures. Improved propagate patterns exhibit 15% operating margins at 1 MHz frequency and 20 mA current. Heat dissipation drops to 0.3 mW per conductor period. In conventional CaGe-garnet films it has been possible to increase the maximum frequency to 1.9 MHz at 60 mA. In the first orthorhombic films to be processed, 4 MHz has been reached already at 20 mA current. High-frequency current-access stretching of bubbles prior to detection is discussed. Operating margins of 10% are obtained up to 700 kHz in a pattern that stretches bubbles normal to their propagation direction. High-frequency writing is obtained by combining a number of field-access generators with an annihilator in the conductor track. A compact current-field-access swap gate allows the closest possible packing of the field-access minor loops. These elements have not yet been combined for the same conductor structure. In principle, however, the functions required for a field and current-access major-minor loop chip are now available.
Bubble propagation direction effects on high frequency bias margin
Authors: Matsutera Hisao , Hidaka Yasuharu
Published: February 2003

The bias margin dependence on propagation direction is observed at drive fields higher than 200 kHz, on YY-overlay propagation of 3 μm bubbles in (YSmLuCa)3 (FeGe)5O12 LPE film. This propagation direction effect of bias margin is found to depend on the bias field direction, drive field, bubble-Permalloy spacing and Permalloy pattern shape. These results are discussed in terms of the correlation between the bubble wall state (S=1) and propagation pattern induced bias field gradient on the bubble.
Wafer integrated bubble memory chip
Authors: Lee W. P. , Chen T. T.
Published: February 2003

A wafer level integration method is proposed for building large capacity bubble memory chips using present processing technology. A single cell pattern is stepped and repeated to generate a matrix of cells. Each cell has basically a major-minor structure. With exchange switch pairs and geometry tolerant junction elements, the bubbles can be transferred between major loops of the adjacent cells in the same row or column. The control functions of those cells in the same row are also interconnected to the edge of the wafer, and thus can share the same driver electronics. These cells are integrated magnetically and electrically. They can share one or a few I/O ports and effectively form a large capacity chip. Since all the cells are identical, the final chip size can be any combination of the cells. A yield model study is performed to show the relationship between chip size and yield.
Bubble propagation pattern analysis
Authors: Matsutera H. , Hidaka Y.
Published: February 2003

Asymmetric and symmetric chevron patterns are analyzed using a continuum model which modified P. K. George’s original model by assuming a uniform magnetization within each block and taking periodic structure for simulating practical propagation patterns. The potential well contours are illustrated over drive field phase of 360°. The potential well dependence on drive field phase angles for small bubble sizes at several points traversing the pattern gap clarifies the gap-tolerance differences between asymmetric and symmetric chevron patterns.
Cross-tie shift register
Authors: Lo D. S. , Benrud V. M. , Cosimini G. J. , Johnson L. H. , Nelson G. G. , Paul M. C. , Torok E. J.
Published: February 2003

The principle, design, fabrication and operating conditions of a shift register memory device using cross-tie wall structure in polycrystalline magnetic films will be described. This device is nonvolatile, silicon compatible and can be fabricated in a three mask level process. Each data track of this device consists of a stripline conductor, a 25 μm wide magnetic film data strip and single level data generator/propagator/detector circuitry. This is the first such device to incorporate a functioning generator, propagate circuit, and detector on a single level, thus greatly simplifying fabrication and increasing reliability and yield. A spatially varying magnetic field produced by the periodic wide/narrow propagate bias stripline is used in conjunction with the magnetic field produced by a uniform stripline to achieve propagation. Propagation is accomplished by generating cross-tie/Bloch line pairs and subsequently annihilating trailing pairs. Cross-tie shift registers have been fabricated on both glass and silicon substrates and have been tested.