bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Cylindrical Magnetic Domains
Authors: Strauss W.
Published: February 2004

Cylindrical magnetic domains in thin platelets of anisotropic single-crystal materials have been detected using the Hall effect in silicon, the pseudo-Hall effect in Permalloy, flux change, and Faraday rotation. The silicon detector, active area ≈400 μ2, active thickness ≈1 μ, input and output resistance ≈1.5 kΩ, and 8-mA rated current, delivered 0.5-mV signals from orthoferrite domains. For 20-mA input current the Permalloy detector, input and output resistance ≈15 Ω, diameter ≈50 μ, and thickness ≈0.03 μ, yielded 0.9-mV signals from 60-μ-diam domains in Sm0.55Tb0.45FeO3 orthoferrite. Domains in Y2.25Tb0.75Ga0.9Fe4.1O12, diameter ≈7 μ, were read with a Permalloy detector approximately 7 μ in diameter. The output was 0.2 mV at 2-mA input current. An output of 1 mV μsec was obtained by detecting the flux change on collapse of a TmFeO3 domain previously expanded 40 times in surface area. A Faraday-rotation detection system consisting of a 5-μW He–Ne laser, sheet polarizers, and an avalanche photodiode has operated at 106 bits/sec with a 20-dB signal-to-noise ratio. Among these detection methods, the Permalloy device appears most promising at this time. It offers the simultaneous advantages of relatively simple fabrication, small active area, small initial cost, and low power consumption. Additional experimental results relating to these detection methods are presented. Their relative merits and limitations are discussed and compared to those of the magnetoresistor and the magnetodiode. The problems associated with the detection of small domains at high speed are also considered.
Magnetic Neutron Scattering from a Nearly Ideal One-Dimensional Antiferromagnet
Authors: Hutchings M. T. , Shirane G. , Birgeneau R. J. , Dingle R. , Holt S. L.
Published: February 2004

We have carried out a detailed investigation of the linear chain antiferromagnet, (CD3)4N MnCl3 using elastic and inelastic neutron scattering techniques. The MnCl3 chains in this compound are found to exhibit purely one-dimensional paramagnetic behavior down to at least 1.1°K, with no evidence for the onset of three-dimensional order. The interactions between Mn2+ ions along the chain are such that a molecular field theory would predict an ordering at 76°K. The quasielastic measurements, which yield ∫dωS(Q,ω)=1/N〈S(−Q,0)S(Q,0)〉 show planes of scattering intensity perpendicular to the chain axis. From the thermal evolution of the planar scattering, the temperature dependence of the correlation length has been obtained and is compared with the theory for the classical Heisenberg linear chain antiferromagnet with which it shows very good agreement. The inelastic measurements show that at 4.4°K for q and ω≠0, S(q, ω) may be described by long-lived spin waves which accurately follow the dispersion relation ℏω=6.1 sin qzc/2 (meV) over the entire one-dimensional Brillouin zone. As the temperature is increased these ``spin waves'' weaken in intensity and broaden asymmetrically, with the scattering increasing on the low-energy side.
Single-Conductor Magnetic-Bubble Propagation Circuits
Authors: Copeland J. A. , Elward J. P. , Johnson W. A. , Ruch J. G.
Published: February 2004

Propagation circuits for circular magnetic domains using only a single electric current conductor are described. A circuit which in addition uses Permalloy dots for domain stability and for determining the direction of propagation has been operated at 475 kHz with a 100-mA amplitude current.
Magnetoresistive Detector for Bubble Domains
Authors: Almasi G. S. , Keefe G. E. , Lin Y. S. , Thompson D. A.
Published: February 2004

This paper describes a simple Permalloy magnetoresistive readout transducer for detecting magnetic bubble domains. The advantages over inductive detection are a large increase in signal and an independence of bubble velocity. The advantages over Hall effect detection are simpler fabrication and higher efficiency. The detector is a strip of thin Permalloy film with two contacts, both of which can be deposited onto the same overlay used for bubble propagation. As an example, a 250 Å×38 μ× 138-μ device (52 Ω) was used with a measuring current of 7 mA to give a 2.3-mV signal when detecting 138-μ diameter bubbles in TmFeO3. The response was constant up to the maximum data rate allowed by the bubble domain, in this case, 106 bits/sec in DyFeO3. The detector itself can switch in less than 10−8 sec. It can be used when conducting strip lines are used for bubble propagation, and also when a rotating field and Permalloy overlay are used. Optimum device placement and shape, as well as ultimate limitations, are discussed in terms of the stray field contours of the bubbles.
Simple Method of Measuring Mobility in Cylindrical Domain Materials
Authors: Seitchik J. A. , Doyle W. D. , Goldberg G. K.
Published: February 2004

A simple method is described for measuring wall mobility in materials which support cylindrical domains. The mobility is determined from the initial velocity with which a domain wall responds to a field step. A sample, which is demagnetized into the stripe domain state, is subjected repetitively to a fast rise-time pulsed field. The displacement of the stripe domain walls is observed optically as the domains adjust to the new equilibrium configuration. In the particular case of viscous damping and negligible wall mass, for a field step H0 which results in an equilibrium displacement x0, the instantaneous displacement is x=x0[1-exp(-ωct)], where ωc is the ratio of the restoring force constant to the damping constant. The mobility μ=x0ωc/H0. The time-dependent displacement can be displayed graphically in a few minutes by a sampling technique. Measurements on TmFeO3 yield results in good agreement with previous data. The mobility for DyFeO3 is found to be 330 cm (sec Oe)−1.
Operational Method for Locating and Mapping Imperfections in Single-Crystal Platelets of Rare-Earth Orthoferrite
Authors: Shumate P. W.
Published: February 2004

An instrumental technique has been devised for mapping crystalline imperfections which prevent the reliable operation of bubble-domain devices. A special polarizing microscope permits the crystal to be automatically scanned through the field of view in a raster-like manner. Photoelectrically detected distortions induced in a test domain by imperfections are plotted on an x-y output of the scan. This sensitive method easily locates imperfections found with difficulty by other methods and has been used to locate crystals which have later been used successfully in devices.
Liquid Phase Epitaxial Growth of Uniaxial Garnet Films: Circuit Deposition and Bubble Propagation
Authors: Shick L. K. , Nielsen J. W. , Bobeck A. H. , Kurtzig A. J. , Michaelis P. C. , Reekstin J. P.
Published: February 2004

Magnetically uniaxial epitaxial films of Eu2Er1Ga0.7Fe4.3O12 and Er2Eu1Ga0.7Fe4.3O12 5–20-μ thick have been grown free of cracks from PbO·B2O3 solutions on (110) and (111) Gd3Ga5O12 substrates, respectively. Bubble propagating T-Bar and Y-Bar circuits of nickel-cobalt-phosphorus were electrolessly deposited on these films. Operation in excess of one hundred steps has been achieved in T-Bar and Y-Bar bubble domain shift registers. Details of the growth procedure, magnetic properties, and circuit preparation are presented.
Phase Behavior of Models with Competing Interactions
Authors: Bonner J. C. , Nagle J. F.
Published: February 2004

Models with competing nearest-neighbor and very long-range interactions are solved exactly for several one-dimensional cases, including the usual Ising chain (ICCI), the XY model (XYCI), the transverse Ising model (TICCI), and the spherical model (SCCI). For certain ratios of the competing interaction strengths, ICCI and XYCI display triple points and two critical points in a field. In addition TICCI has an apparently enclosed phase in an H-T phase diagram; however, this phase is really paramagnetic as can be seen when an extended phase diagram is used. The extended phase diagrams for ICCI, XYCI, and TICCI display tricritical points and the tricritical exponents have different values from the usual classical values. In contrast to the rich phase behavior of the preceding models, SCCI shows very simple phase behavior, which is directly related to the ground state. Finally, the introduction of a staggered field to ICCI and a simple transformation allows reinterpretation as a metamagnetic model. Using ICCI as a guide the observability of the tricritical exponents is discussed.
Parametric Equation of State Applied to the Magnetization of Nickel Near its Curie Temperature
Authors: Arrott Anthony , Noakes J. E.
Published: February 2004

Data for the surface of magnetization, temperature, and field for single crystal nickel are compared with the parametric equation of state of Schofield, Litster, and Ho [Phys. Rev. Lett. 23, 1098 (1969)]. An excellent fit to the magnetic isotherms is obtained by choosing a reduced temperature for each isotherm, and the variation of the reduced temperature with measured temperature is linear above and below the critical temperature. But whereas the five parameter equation would demand that the slope be the same above and below Tc, the experiments show a 15% change in slope. It is argued that a six parameter equation is needed for the experimental fit and a suitable equation is given.
Frequency Dependence of the EPR Linewidth in MnF2 Near the Critical Point
Authors: Seehra Mohindar S.
Published: February 2004

EPR linewidth measurements at 24.43 GHz have been made near the critical point TN of MnF2. Comparison with similar measurements at 9 and 35 GHz shows that the EPR linewidth near TN depends on the Larmor frequency, its magnitude at a given temperature being smaller at higher frequencies. This is the first observation of this effect recently predicted by Kawasaki. It is suggested that the observed frequency dependence near TN is due to breakdown of the usual exchange narrowing condition.
Electrical Resistivity and Magnetization of Gd–Th and Gd–Mg Alloys
Authors: Mellon D. W. , Legvold S.
Published: February 2004

Electrical resistivity and magnetization measurements have been made over the 4.2–300-K temperature range on single crystal Gd1−xThx and on polycrystalline Gd1−xMgx samples with 0<x<0.15. This work was done because quadrivalent Th increases the number of conduction electrons and hence raises EF, whereas divalent Mg decreases the number of conduction electrons and so lowers EF. Fermi surface changes might then be expected. The most interesting result was obtained with Gd0.88Mg0.12, which showed an increase in resistivity with decreasing temperature below 260 K. The magnetic measurements indicated that all samples ordered ferromagnetically.
Magnetic Properties of the System Au4R(R =Er, Tm, and Yb)
Authors: Sill L. R. , Mass W. J. , Fedro A. J. , Shaffer J. C. , Kimball C. W.
Published: February 2004

Magnetic measurements have been made from 6.1° to 300°K on chemically ordered RAu4(R=Er, Tm, Yb) with the bct MoNi4 structure. No magnetic ordering was found for any of the compounds in this temperature range. The temperature dependence of the reciprocal susceptibility for each specimen satisfied an equation which included both Curie-Weiss and temperature-independent terms. The paramagnetic Curie temperature for each specimen had a negative value and the magnetic moments of the rare earths were those appropriate to the trivalent ion. An RKKY calculation indicates that ErAu4 and TmAu4 should magnetically order at ∼5° and below 2°K, respectively.
Domain Walls in Ferromagnetic Dy and Tb
Authors: Egami T. , Graham C. D.
Published: February 2004

The spin structure and energy of ferromagnetic domain walls in Dy and Tb have been calculated, using an iterative method which takes into account exchange interactions, magnetocrystalline anisotropy, and magnetoelastic anisotropy. The domain walls are found to be very thin (less than 20 atom layers) and to have relatively high energy (∼10 erg/cm2), as compared to the ferromagnetic transition metals. An intrinsic coercive force for wall motion is predicted for these very thin walls; it is analogous to the Peierls-Nabarro force on a dislocation, and is estimated to be of the order of 1 kOe for Dy and 30 Oe for Tb at absolute zero.
Magnetic Properties of Europium: Pressure and Impurity Effects
Authors: Menyuk N. , Dwight K. , Kafalas J. A.
Published: February 2004

A study has been made of the magnetic properties of europium in the vicinity of the transition temperature Tt as functions of hydrostatic pressure. A marked drop in the moment, consistent with a first-order transition, is observed at atmospheric pressure, but the sharpness of this transition decreases at higher pressures. The variation of Tt with pressure is nonlinear above 4 kbar, with ΔTt/ΔP=0.45°±0.03°K/kbar in the limit P→0. This value corresponds, via the Clausius-Clapeyron relation, to twice the volume change previously estimated on the basis of direct thermal-expansion measurements. In addition, it is found that dθ/dP<0, where θ is the paramagnetic Curie temperature. Below Tt, the magnetic susceptibility of europium is known to rise anomalously. Although our sample was nominally ``high-purity'' europium, the presence of a ferromagnetic component is observed at 4.2°K. In addition, the temperature variation of the susceptibility is shown to be consistent with a presence of a small amount of some ferromagnetic europium salt with Tc∼16.5°K in the bulk of the sample.
Single-Crystal Neutron Diffraction Study of hcp Alloys of Th with Ho and Er
Authors: Child H. R. , Koehler W. C.
Published: February 2004

A study of single crystals in the Ho–Th and Er–Th systems has now been carried out to determine the effect of dilution by Th on the magnetic structures of these rare earths. A 95 at.% Er–Th alloy shows three regions of magnetic order similar to pure Er, but the basal plane component of the conical structure is greatly reduced in magnitude while the c-axis component remains the same as pure Er. Alloys containing 90 and 85 at.% Er, however, have only a ferromagnetic structure in which a magnetic moment of 8 μB/Er atom is aligned along the c axis, and no evidence is observed for any modulation of the magnetic moments at any temperature. Alloys of 95 and 90 at.% Ho show a spiral magnetic structure which transforms as the temperature is lowered into a structure having a large ferromagnetic moment in the basal plane in contrast to the low-temperature structure of pure Ho, which has only a small ferromagnetic component along the c axis. In addition, these alloys have very small satellite reflections at 4.2°K, indicating that some modulation of the magnetic moments is still present. An 84-at.% Ho–Th alloy shows no such satellites below its spiral to ferromagnetic transition at low temperatures, but the basal plane ferromagnetic component is only about 90% of the expected moment for the Ho+3 ion.
Short-Range Order Effects on 59Co NMR Spectra in Equiatomic FeCo
Authors: Strauss G. H. , Forester D. W.
Published: February 2004

Spin-echo spectra of 59Co at 4.2°K have been obtained for ten samples of FeCo. The samples had various degrees of short-range order induced by quenching from temperatures Tq of 500°C to 850°C or by mechanical disordering. With increasing Tq, the spectra display a progression: from a sharp peak at 286 MHz with weak satellite structure; through a broad asymmetric shape strongest near the same frequency; to a symmetric shape 90 MHz in extent, centered at 255 MHz. (In contrast, the 57Fe frequency increases with Tq.) The most rapid change occurs in a small temperature range below the onset of long-range order. The various shapes have been reproduced, by invoking different degrees of short-range order in the CsCl structure, in a computer model which assumes that the Co hyperfine field is increased locally each time Fe replaces Co within the first two shells of neighbors. The variation of short-range order with Tq is in reasonably good agreement with the theoretical results of Cowley.
Mössbauer Study in α-Phase Solid Solutions of an FeGe System
Authors: Brossard L. , Fatseas G. A. , Dormann J. L. , Lecocq P.
Published: February 2004

The internal magnetic fields, isomer shifts, and quadrupole interactions on 57Fe nuclei of iron germanium-quenched alloys in the solid-solution range (from c=0 to 18-at.% Ge) were investigated by Mössbauer resonance experiments at room temperature. The added solute Ge atoms give rise to individual satellites sites, whose shapes were correctly analyzed by a computer program, assuming a two-shell model of random distribution of Ge atoms. The lower concentration Ge alloys (c<12%) give the following results. The first and second Ge neighbors reduce the internal field linearly by definite amounts which depend on their distance from the iron atom and are concentration independent. The mean value H̄ of the internal field presents a linear concentration dependence, the isomer shift increases slightly with c and the quadrupole interactions are very small. In the region of higher concentrations some different features are observed. The field H00 without impurity neighbors is concentration dependent, rising to values higher than that of pure iron and reflecting the effects of more distant shells. At about 12% Ge a deviation from the linear decrease of H̄ is observed due to the presence of a new site. X-ray analysis and intensity arguments have led us to propose the appearance of an order, of Fe3Si type, as the most probable explanation of this site.
Chlorine NMR in Antiferromagnetic CsNiCl3
Authors: Clark R. H. , Moulton W. G.
Published: February 2004

Nuclear magnetic resonance studies have been performed on single crystals of the hexagonal antiferromagnet CsNiCl3 (TN=4.5 K).1 The 35Cl transitions occur at 15.16 and 10.43 MHz in zero external field at 1.3 K. The corresponding 37Cl transitions are at 12.30 and 8.60 MHz. The NQR transitions in the paramagnetic state (8.0 K) occur at 8.60 and 6.74 MHz for 35Cl and 37Cl. A computer fit to these transitions, using values of e2qQ and η from data taken above TN, shows that the internal magnetic field at all Cl sites is 22.5 kg. The fields lie in the plane of the three Cl atoms arranged in an equilateral triangle between the collinear Ni atoms and points toward and away from the center of the triangle in alternate planes. This configuration of internal fields was confirmed by rotation experiments about two axes in external fields of 500, 1000, and 1500 g. Dipole sum calculations and symmetry considerations show that these results are consistent with the collinear spin configuration and are not consistent with the noncollinear spin structures previously proposed by others. The temperature dependence of the magnetization has been obtained from the frequency shifts in zero field from 1.3 K to 3.4 K.
NMR Studies of Fe2P and Fe3P
Authors: Koster E. , Turrell B. G.
Published: February 2004

A variable-frequency pulsed spectrometer was used to search for zero-field NMR lines in the two ferromagnetic compounds Fe2P and Fe3P. In Fe2P we observed spin echoes at 17.0, 20.5, 77.5, and 86.6 MHz. We deduce for the iron atoms hyperfine fields of 123 kOe (Fe II site) and 148 kOe (Fe I site). The phosphorus hyperfine fields are 45.0 kOe (P II site) and 50.2 kOe (P I site). The frequency shift under applied magnetic field indicates the phosphorus hyperfine fields are positive. The temperature dependence of the 31P NMR frequency was studied. In Fe3P a rather complicated NMR spectrum was observed. Tentatively we deduce hyperfine fields of 190, 260, and 300 kOe for the three iron sites and a phosphorus hyperfine field of 52.2 kOe. The calculated hyperfine fields for both compounds are in good agreement with previous Mössbauer data.
Low-Temperature Phase Transition in PrCl3
Authors: Hessler Jan P. , Carlson E. H.
Published: February 2004

Previous measurements of the specific heat, susceptibility, and Cl-NMR in PrCl3 have assumed that the Pr spins undergo short-range linear order giving a broad peak in the specific heat centered at 0.85 K. The splitting of the NQR line and the sharp peak in the specific heat at 0.42 K have been interpreted as the onset of long-range antiferromagnetic order. We have carried out Cl-NMR studies in the ordered state in applied magnetic fields. Our measurements show that the ordered phase is nonmagnetic. They indicate a crystallographic phase transition in which the chlorines become inequivalent. To a first approximation the space group in the ordered phase is P6̄ or P3. We have also measured the susceptibility in the temperature range 4.2–1.2 K. There is an anomalously large temperature-independent susceptibility perpendicular to C3. Parallel to C3 the susceptibility does not follow any of the predictions based on the measured g-values.
Samarium-Cobalt (SmCo5) Magnetic Palpebral Prostheses
Authors: Grob D. , Stein P.
Published: February 2004

Ptosis (eyelid drooping) may result from refractory myasthenia gravis, ocular muscular dystrophy, third-nerve palsy, or congenital causes. Severe ptosis obstructs vision and requires correction. An externally applied magnetic palpebral prosthesis has been developed for relief of ptosis consisting of permanent magnets attached below the eyebrow and a strip of ferrous magnetic material that, when adhered at the eyelashes, is attracted toward the magnet, elevating the eyelid. The immobile portion consists of several high-energy-product SmCo5 magnets embedded in polyurethane to form a fitted arc. The 1×2×2-mm magnets in the prosthesis weigh less than 0.2 g. Adjacent magnets have alternate N-S polarity in the 1-mm direction and are spaced to produce appropriate field gradients. The mobile portion is a thin 0.4-g 2.5-cm-long magnetically soft strip to which false eyelashes may be attached for cosmetic purposes. Lid closure is achieved by blinking or winking. In an alternate use of the prosthesis, the SmCo5 magnets are placed on the inferior eyelid to improve eye closure in patients with orbicularis oculi weakness resulting from facial nerve palsy or muscle disease.
Magnetically Controlled Prostheses for Management of Urinary Incontinence and Bladder Dysfunction
Authors: Grob D. , Stein P.
Published: February 2004

A magnetically controlled prosthesis for control of urinary incontinence has been developed, consisting of a metal spring, oriented when implanted to gently compress the urethra. The spring, in the normally closed condition, prevents urethral flow. When desired, a magnet is placed against the perineum externally and the movable half of the ``U'' spring is attracted away from the urethra, permitting micturition. The prosthesis has so far been used only in dogs. In patients unable to void voluntarily, the prosthesis will be used in conjunction with magnetically induced bladder emptying, previously reported in J. Appl. Phys. 40, 1042 (1969). This has been carried out in dogs by suturing a polyurethane-coated ferrous disk to the posterior wall or dome of the bladder, which may then be emptied by applying an external magnetic field so as to attract the implanted metal toward the abdominal wall, thereby compressing the bladder. This compression yields a rapid rise in intravesical pressure and a 100% increase in bladder emptying rate, upon opening of the urethra. The prostheses are intended to eliminate the widespread use of indwelling catheters in patients with urinary incontinence or bladder dysfunction, including the aged and patients with spinal cord injury or disease.
Automatic Coagulation Profile System
Authors: Adler Stanford L. , Tse Ann , Widmark R. M.
Published: February 2004

A fully automatic system is described which simultaneously performs prothrombin time and activated partial thromboplastin time for coagulation defect screening and anticoagulant therapy control, using a new end point detection technique that provides greater sensitivity and a sharp, clearly defined end point. A sample of plasma is metered onto a section of film bearing a predeposited spot of magnetic iron oxide that is resuspended in the plasma. This mixture is opaque to the electro-optical system until the end point occurs, then abruptly becomes transparent.
Electrical Resistivities of Co(C) and Ni(C) Solid Solutions
Authors: Swartz J. C.
Published: February 2004

From resistivity measurements, both during carburization and after quenching, resistivities of interstitial carbon in Co and Ni were determined. The data are corrected for effects on the host resistivity from the change in Curie temperature with alloying. Representative values for the solute resistivity in μΩ cm/at. % C are: 4.4 at 4.2 K, 5.2 at 300 K, and 0.9 at 1400 K for Co(C); and 3.3 at 4.2 K and 200 K, 1.7 at 650 K, and 2.6 at 1270 K for Ni(C). The large decrease in solute resistivities between 300 K and the Curie temperature is attributed to spin-disorder scattering from the reduced moments of the solvent atom neighbors of interstitial carbon. Quantitative analysis, using simple expressions of Schwerer and Cuddy for solute induced spin-disorder scattering, indicate greater moment perturbations in cobalt than in either of the other two solvents. Subsidiary experiments determine that carbon solutes in cobalt reduce the Curie temperature by (31±2)°C/at. % C.
Ferromagnetism in Heusler-Type Alloys Based on Platinum-Group or Palladium-Group Metals
Authors: Hames F. A. , Crangle J.
Published: February 2004

New single-phase alloys have been prepared having the compositions T2MnX and TMnX, where T represents the platinum-group or palladium-group metal, and X is an element of groups III, IV, or V. Their crystal structures are ordered forms of the bcc structure. Some are apparently ferromagnetic with Curie temperatures of several hundred degrees Kelvin and magnetic moments between 3 and 4 Bohr magnetons per formula unit.
Direct Measurement of the Positive Conduction Electron Polarization (CEP) Due to 3-, 4-, and 6-nn Fe Atoms
Authors: Stearns Mary Beth
Published: February 2004

The internal field shifts due to the first six neighbor shells in ordered Fe–Si alloys have been well resolved in pulsed NMR experiments. This well establishes the shape of the CEP curve for Fe metal. A consistent picture of the origin of the hyperfine field (hff) in Fe is suggested. The hff observed at the Si atoms agrees excellently with that obtained by summing over the CEP due to neighboring Fe atoms.
Temperature Dependence of the Magnetization of Iron
Authors: Aldred A. T. , Froehle P. H.
Published: February 2004

The temperature and field dependence of the magnetization σH,T of high-purity (99.999%) iron has been measured at a series of temperatures between 5° and 295°K and at incremented applied fields from 6 to 14 kOe. A force technique was used and the field gradients were calibrated separately at 5°K. The data were least-square fitted initially to the spin-wave equation σH,T=σ0,0 − A (T/D)3/2×F(3/2), where A is a constant, D is the spin-wave stiffness coefficient, and F(3/2) is the Bose-Einstein integral function. This analysis gave σ0,0=221.81±0.09 emu/g and D=259.7±17.6 meV Å2 with an over-all standard deviation of 0.18 emu/g which was considerably larger than the experimental precision of 0.08 emu/g (0.04%). After modifying the spin-wave equation to include a temperature dependence of D of the form D=D0−D1T2, an excellent fit to the data was obtained with the following results; σ0,0=221.66±0.03 emu/g, D0=318.7±7.4 meV Å2, D1=(7.4±0.8)×10−4 meV Å2 °K−2, with a standard deviation of 0.06 emu/g.
Properties of Polymer-Coated, Submicron Magnetic Alloy Particles
Authors: Robbins M. , Swisher J. H. , Sherwood R. C.
Published: February 2004

Submicron particles of Fe–Co and Fe–Co–Ni alloys were prepared and stabilized with respect to air oxidation by surface polymerization. The addition of Co to Fe served to increase the saturation magnetic moment of polymer-coated Fe particles up to 50%. The coercivity also increased. Addition of small amounts of Ni to Fe–Co alloys decreased the coercivity. Aging tests were made to test the protection afforded by the surface polymer. The submicron alloy particles were found to be stable when heated at 97°C in air.
Nonmagnetic Identification of Magnetic Flaws in Oxide Coatings
Authors: Holmstrom F. E. , Engel J. M.
Published: February 2004

In testing storage media, such as oxide coatings used on magnetic recording disks, it is customary to record data with a magnetic writing head and then search for missing bits with a magnetic reading head. Alternatively, recorded data may be erased and afterward the erased area is checked for bits that still remain. The presence of either type of flaw serves as a basis for determining the quality of the coating. Physical analysis of flaws, which have been previously detected by magnetic means, is difficult and usually destructive. In this paper, a nondestructive testing technique is described. This technique, in which a scanning electron beam is used, offers analytic advantages such as determining location, dimensions, and shapes of flaws. Physical correlation is achieved between specimens studied via this technique and flaws detected with a magnetic tester.
Zinc Depletion in Zn–Mg–Mn Ferrite Memory Cores
Authors: Norman D. I. , Hewitt F. G.
Published: February 2004

Three varieties of ferrite cores containing zinc were examined with an electron microprobe and electron diffraction. A depleted zone in zinc near the surface was observed in all three types. A zinc-depleted ``skin'' has been postulated to give rise to decreased permeability and threshold response delay in some ferrite memory cores.
Operational Characteristics of 103-Bit Garnet Y-Bar Shift Register
Authors: Danylchuk I.
Published: February 2004

The availability of uniaxial magnetic garnets has permitted fabrication of relatively high-density (≈0.4×10+6 bits per square inch) propagating cylindrical domain devices. A shift register of 103-bit capacity has been built and tested. In the construction of the shift register a Y-bar propagate circuit element and Gd2.34Tb0.66Fe5O12 garnet crystal have been used. Based on functional tests, performed at quasistatic speeds, sufficient operating margins relating to propagation along straight lines and around corners, as well as margins relating to bubble generation, have been obtained and are presented.
Thin-Film Surface Bias on Magnetic Bubble Materials
Authors: Liu T. W. , Bobeck A. H. , Nesbitt E. A. , Sherwood R. C. , Bacon D. D.
Published: February 2004

A method of reducing the external magnetic bias field to maintain stable cylindrical domains (magnetic bubbles) in uniaxial orthoferrites or garnets is presented. A thin film of a permanent magnetic material is sputtered onto a platelet inducing an exchange coupling interaction across the interface. This interaction manifests itself as an effective bias field which reduces the external applied field required to stabilize bubbles. So far the largest effective bias obtained has been about 25 Oe, using Co3.2Cu1.3Fe0.5Ce0.25Sm0.75 sputtered onto a 15-μ-thick platelet of Sm0.55Tb0.45FeO3. Dynamic properties do not seem to be appreciably altered for low-speed operation in a T-bar rotating field device.
Fabrication of ``Bubble''-Propagating Circuits by Electroless Deposition of Nickel-Cobalt-Phosphorous
Authors: Reekstin J. P.
Published: February 2004

Propagating cylindrical magnetic domains, or ``bubbles,'' in garnet platelets is accomplished by placing a periodic thin-film magnetic circuit, such as T bars, in contact with the platelet and applying an in-plane rotating field to alternately magnetize different segments of the circuit element. A process has been developed for fabricating high-density bubble-propagation circuits utilizing electroless deposition of an Ni–Co–P alloy. Circuits have been deposited both on glass substrates and directly on garnet platelets cemented to glass substrates. The highest density, 2.8×106 bits/in.2, has been achieved in a 0.6-mil period 1000-bit Y-bar shift register. Linewidths of 2 μ are currently attainable and appear limited by the resolution of available photolithographic techniques. The process results in rapid turn-around time, the materials are inexpensive, and no sophisticated equipment is necessary for the plating process.
Oligatomic Film Memories
Authors: Benrud V. M. , Forslund G. L. , Hanson M. M. , Horst R. L. , Kaske A. D. , Kolling J. A. , Lo D. S. , Nordstrom M. J. , Oredson H. N. , Simon W. J. , Tolman C. H. , Torok E. J.
Published: February 2004

For years the desideratum of flat-film fabricators has been a simply constructed high-density random-access NDRO bit organized memory with word and digit current levels low enough for high-density integrated electronics. This paper describes a new direction in flat-film memories that achieves that goal and a projected cost/bit an order-of-magnitude less than that of integrated circuit wire or core memories. Permalloy films only 100-Å thick, continuous in at least one direction to avoid registration problems, are deposited on glass or metal substrates; overlays having densities up to 40 000 bits/in.2 requiring word and digit currents as low as 25-mA peak are attached. The low-signal problem is solved by using rf alternating current in the word-line overlay and a sense amplifier tuned to double the word-current frequency. Switching is by magnetization creep, which allows bit organization and sharing of sense amplifiers similar to that of plated wire. Functional performance, uniformity, and reproducibility of four types of array geometries (10 000–30 000 bits/in.2) are described. Electron micrographs of domains in a 100-Å NiFe mirror being written, disturbed, and erased with 2-mil word and digit lines are shown. Also described are: a word driver and selection system which provides a constant word current of 35-mA rms at 35 MHz applicable to an array of 4096 word lines, and a sense gating system capable of sensing a 20-μ volt-induced sense signal at a frequency of 70 MHz with a 5:1 ``1'' to ``0'' ratio before discrimination; the sense amplifier has a 12-MHz bandwidth which allows 50-nsec changes in sense signal to be followed, but rejects word and digit noise. The access and cycle times of a prototype module under construction are 2 μsec.
Time-Dependent Spin Correlations in Heisenberg Linear Chains
Authors: McLean F. B. , Blume M.
Published: February 2004

We have used the self-consistent theory of Blume and Hubbard1 to calculate the Fourier transform S(q, ω) of the time-dependent spin pair correlation function for the Heisenberg linear chain at finite temperatures. The spins are treated as classical unit vectors2 and the time-independent correlation functions for the linear chain with nearest-neighbor interactions are used as initial conditions for the approximate integrodifferential equations. Numerical solution of these equations yields S(q, ω) for both ferromagnetic and antiferromagnetic interactions. At low temperatures in the paramagnetic regime, ``spin-wave'' type peaks are found in the scattering function. The shape and position of these peaks as a function of temperature agrees qualitatively with the experimental results of Birgeneau et al.
Spin Correlations in the Paramagnetic Phase
Authors: Hubbard J.
Published: February 2004

A method for calculating approximately the time-dependent spin-correlation functions in the paramagnetic phase of a Heisenberg ferromagnet is sketched. The predicted inelastic neutron scattering line shapes and widths at high temperatures and in the critical region (where dynamic scaling is predicted) are described.
Photoemission Studies of f States and Valence Bands in Several Rare-Earth and Uranium Compounds
Authors: Eastman D. E. , Kuznietz Moshe
Published: February 2004

Photoemission spectroscopy measurements of f states and valence band energies are reported for EuS, GdS, and US using photon energies for 5 to 41 eV. The energy dependence of photoemission spectra permits the ``l'' character of various levels to be identified. Characteristic energy-dependent emission strengths of ``p'', ``d'', and ``f'' states are observed. In a typical case, the emission strength of the 4f7 level in EuS increases about 100-fold relative to the ∼2.9-eV-wide valence ``p'' band (which lies just below the 4f7 level) as ℏω increases from 10 to 41 eV. Metallic GdS shows a ``d''-like conduction band at the Fermi level EF, a 4.5-eV-wide ``p''-band centered at ∼5 eV below EF, and a 4f7 level at 9 eV below EF. Uranium monosulphide shows a narrow ``f-d'' conduction band at EF and a 4.7-eV-wide ``p''-band centered at 4.7 eV below EF.
Spin-Wave Interactions in Layered Structures
Authors: Silberglitt Richard
Published: February 2004

We consider a layered Heisenberg ferromagnet with two unequal exchange constants, J⊥ between nearest-neighbor spins in the same layer and Jz between nearest-neighbor spins in adjacent layers. The spin-wave renormalization is obtained to lowest order in the density but to all orders in the magnon-magnon interaction. In the case Jz≪J⊥ it is shown that spin waves propagating in the z direction renormalize much more strongly and those propagating in the ⊥ direction much more weakly than their counterparts in an isotropic (Jz = J⊥) system. This effect is produced by the monotonically increasing nature of the spin-wave interaction with increasing wave vector and the fact that the ordering temperature is small compared to the k⊥ (but large compared to the kz) zone boundary spin-wave energy. Thus at relatively low temperatures there are many more large kz and many less large k⊥ magnons than would be present in a system with Jz = J⊥ and the same ordering temperature. These ideas have been applied to CrBr3 and to the two-dimensional antiferromagnet K2NiF4 and are in agreement with experimental observations. They also lead to an understanding of certain similarities between the two systems.
Spin-Orbit Interaction and Landau Levels in Ferromagnets
Authors: Fivaz R. C.
Published: February 2004

From the so-called spontaneous Hall effect of ferromagnets, it is known that the spin-orbit interaction modifies the impurity scattering by linking the magnetization to the spatial wavefunctions of the electrons. The effects of the modified scattering on the Landau level distribution are evaluated within the effective Hamiltonian approximation. This distribution is obtained from time-correlation functions of the energy estimated by a Green function technique. The spin-orbit interaction is thus found to introduce specific electron-hole correlations in the second Born approximation which alter the energy spectrum in two ways. Firstly the average energy of the levels close to the Fermi energy is lowered and the density of states at that energy is decreased; secondly the levels are broadened into non-Lorentzian lines. As these alterations depend on the direction of the magnetization, they affect directly the galvanomagnetic effects; in addition, the de Haas-van Alphen oscillations may be substantially damped by comparison with ordinary metals, and split into doublets.
Magnetic Aftereffect in Oxidized Ni–Fe Films
Authors: Charap S. H. , Fulcomer E.
Published: February 2004

Displaced hysteresis loops, loop contraction, and increased coercivity are measured in oxidized 76–24 Ni–Fe film at low temperatures at frequencies of 0.05, 20, and 100 Hz using the Kerr effect. Switching in constant applied field by slow wall motion is also observed. A calculation of the observed temperature and frequency dependence of coercivity and loop displacement, based upon the magnetic aftereffect of fine antiferromagnetic oxide particles which are exchange coupled to the ferromagnetic film and have a distribution of anisotropy and coupling energies, is described.
Origins of Nondestructive Readout of Plated Wires
Authors: Luborsky F. E. , Skoda R. E. , Barber W. D.
Published: February 2004

The nondestructive readout (NDRO) capability of 3650-Å-thick Permalloy electroplated onto a variety of substrates has been evaluated using an on-line Belson test. The NDRO quality is evaluated using, not only the wall motion coercive force, but also the write threshold, the read only limit, Hk and the signal output. Various combinations of physical roughness and grain size of copper and gold substrates are compared. On smooth very fine grained Au substrates low dispersion and low coercive force films are produced which are not suitable for NDRO; with increasing grain size and roughness the NDRO quality improves. A substantial further improvement in NDRO quality is obtained by producing a new kind of substrate surface; namely, a surface composed of Au islands on rough Cu. The same small quantity of Au deposited on a smooth, finer grain Cu, although better than Permalloy deposited on the smooth very fine grain Au, is not as good as Permalloy directly on rough Cu. The presence of Au islands is confirmed from scanning electron micrographs and electrochemical measurements. Their effect on the magnetic properties is believed to be due to the additional roughness and to the fluctuation in Permalloy composition they produce. The composition fluctuations and stress in the Permalloy provide high anisotropy regions needed to prevent local saturation and therefore provide the restoring force, through coupling with the remainder of the film, to return the magnetization to its original direction.
Role of Thin Intermediate Layers between Polycrystalline Copper and Magnetic Films
Authors: Crowther T. , Frongillo M.
Published: February 2004

It is well known that magnetic films deposited on evaporated copper on a glass substrate have wall coercive forces Hc much larger than those directly deposited on glass. This is due in part to the surface roughness of the large copper crystallites. This work demonstrates that there is a significant additional contribution to Hc due to stress in a material in which λ100≠λ111 even though λs=0. Electron-microscopy crystallite-size measurements suggest this stress arises from epitaxial growth. This stress can be relieved by stripping the films from the glass and selectively etching away the copper. For example, a 600-Å nonmagnetostrictive film evaporated from a 50 Co 47 Ni 3 Fe melt on a freshly evaporated 1-μ evaporated copper film on a 200°C glass substrate had a Hc of 72 Oe. After this film was stripped and the copper was etched away, Hc was reduced to 35 Oe. For a companion film deposited directly on glass Hc = 13 Oe. Several materials evaporated as thin (∼100 Å) intermediate layers which successfully inhibit epitaxial growth and stress include Cr, Mn, Ti, and Pt.
Ripple Field Resonance in Cylindrical Films
Authors: Kehler T. P. , Coren R. L.
Published: February 2004

Measurements of the transverse differential susceptibility χ were made on cylindrical NiFe films over the range 10–400 MHz. The field dependence of the real and imaginary susceptibility components were determined; both display regions of positive and negative values. These curves were analyzed using a dynamic equation of motion with Gilbert damping. It is found that the effective ripple field model alone can not explain the observed variations but that one must include coupling to higher-order spin modes. With appropriate assumptions this analysis leads to a quadratic frequency dependence of the effective field at the zero of χ(imaginary).
Magnetic Field Detection Using Coherent Magnetization Rotation in a Thin Magnetic Film
Authors: Abadeer W. W. , Ellis D. M.
Published: February 2004

A magnetometer utilizing coherent magnetization rotation in a thin magnetic film has been constructed. Easy-axis fields at 4.2 and 6.5 MHz are used to drive the film. The drive fields are restricted to much less than Hk. The theory of operation shows that the sense voltage at 10.7 MHz detected along the film hard axis varies linearly with hard-axis static field in a small range around zero applied field. A closed-loop system utilizing linear synchronous detection of the sense voltage and calibrated magnetic feedback is used to extend the dynamic range of the magnetometer.
Photomagnetic Effect in Ferric Borate
Authors: Lacklison D. E. , Chadwick J. , Page J. L.
Published: February 2004

We have observed that the susceptibility of ferric borate may be changed by exposure to radiation in the wavelength range 0.4–1.1 μ. At 77°K, the photoinduced change does not thermally decay away, and can be erased by magnetically saturating the material. The sensitivity to radiation depends on wavelength in a similar way to that of the optical absorption. These features differ significantly from those found in the other two known photomagnetic materials, silicon-doped YIG, and gallium-doped cadmium chromium selenide. At higher temperatures disaccommodation occurs, and the photoinduced change relaxes back immediately when the radiation is removed. The temperature dependence of the relaxation time can be associated with an activation energy of 0.27 eV. The changes in susceptibility with intensity of illumination and time fit a differential equation, which is consistent with a one-center model. The experimental results can be explained in terms of a simple domain-wall effect.
Intrinsic and Field-Induced Anisotropy of Si-Doped YIG from 4.2 to 300 K
Authors: Churchill R. J. , Flanders P. J. , Graham C. D.
Published: February 2004

The effect of Si additions on the crystal anisotropy and on the field-induced anisotropy in yttrium iron garnet crystals has been measured from 4.2 to 300 K, using a rotating-sample magnetometer (RSM). Use of the RSM makes it possible to separate the effects of induced anisotropy from those of the crystal anisotropy, which has not been possible in previous torque and resonance measurements. The experiments reported here were all done with the sample shielded from light, so that photoinduced effects have been deliberately avoided. Silicon in amounts up to about one atom per formula unit Y3Fe5O12 has almost no effect on the anisotropy of YIG at temperatures above about 150 K; at lower temperatures there is a large positive contribution to K1. Over most of the composition range studied, K1 (negative for pure YIG) becomes positive at low temperatures. The change in K1 is approximately linear with Si content, and hence presumably with Fe2+ content. The induced anisotropy, which is also measured in the RSM experiment, becomes significant at the same temperature (150 K) where departures from the anisotropy of pure YIG are observed. This induced anisotropy is remarkable in that it shows a very wide range of relaxation times (10−3–10−1 sec in our work, and 1–100 sec in previous work) which vary relatively slowly with temperature.
Correlation Effects in Dilute Magnetic Alloys
Authors: Murata K. K. , Wilkins J. W.
Published: February 2004

For the Kondo Hamiltonian a self-consistent theory which incorporates correlations between the local spin and the electrons is found to predict behavior substantially different from the Bloomfield-Hamann (BH) theory for the electron lifetime at the Fermi surface. The inverse lifetime 1/2τ≈(c/πρ)π2S(S+1){1−[2|γ−2|/γe](T/TK)2};  γ=|J|(ρ/N),has initial power law [(T/TK)2] behavior as opposed to the logarithmic (ln−2T/TK) behavior of the BH theory. Also the scale over which an 80% variation in the resistivity occurs is decreased considerably to about one decade of temperature. The correlations are introduced via a certain class of self-energy and vertex diagrams, which are chosen as in the Nozieres, Gavoret, and Roulet calculation for the x-ray problem and summed to logarithmic accuracy. A new divergence in the spin-flip amplitude [(−TK/ω)2S(S+1)] is regulated by a freezing out of the local spin due to the correlations, giving rise to a power law behavior in the lifetime.