bluuebunny/crossref_metadata_2025 huggingface dataset:
Technologically mediated composition learning: Josh's story
Authors: Bolton Jan
Published: March 2008

An innovative ICT project calledComposehas been implemented in some New Zealand primary schools in an effort to counteract the lack of classroom composition opportunities.Composecombines the use of music software and online learning with attempts to address barriers to primary classroom composition. This article illustrates, through personal narrative, howComposemade successful composition experiences possible for a student in a classroom where no such opportunities had previously existed. The project led to the student acquiring compositional skill and knowledge and a positive music self-concept. Though it is not possible to generalise from a single case study, the findings indicate thatComposecould offer a potentially viable way to increase classroom composition learning opportunities.
Identification of mixing barriers in chemistry‐climate model simulations using Rényi entropy
Authors: Krützmann N. C. , McDonald A. J. , George S. E.
Published: March 2008

This study examines how the Rényi entropy statistical measure (RE; a generalization of Shannon entropy) can be applied to long‐lived tracer data (e.g. methane), to understand mixing in the stratosphere. In order to show that RE can be used for this task we focus on the southern hemisphere stratosphere and the significant impact of the Antarctic polar vortex on the dynamics in this region. Using methane data from simulations of the chemistry‐climate model SOCOL, we find clear patterns, consistent with those identified in previous studies of mixing. RE has the significant benefit that it is data driven and requires considerably less computational effort than other techniques. This initial study suggests that RE has a significant potential as a quantitative measure for analyzing mixing in the atmosphere.
Facilitation of endolithic microbial survival in the hyperarid core of the Atacama Desert by mineral deliquescence
Authors: Davila Alfonso F. , Gómez‐Silva Benito , de los Rios Asunción , Ascaso Carmen , Olivares Hector , McKay Christopher P. , Wierzchos Jacek
Published: March 2008

The hyperarid core of the Atacama Desert is considered the dry limit for life on Earth. Soils in this region have very low abundance of heterotrophic bacteria and are practically barren of photosynthetic microorganisms because of the extreme dry conditions (≤2 mm a−1 rainfall). However, relatively abundant endolithic communities of cyanobacteria (Chroococcidiopsis) occur within halite crusts in paleolake evaporitic deposits. By means of continuous monitoring of the microclimate conditions (temperature, relative humidity, water vapor density, wetness, and photosynthetically active radiation) inside and around the halite crusts, we demonstrate here that water vapor condenses within the pore space of the halite at relative humidity (RH) levels that otherwise hinder the occurrence of liquid water in the surrounding environment. Water condensation occurs at RH >75%, which corresponds to the deliquescence point of halite. We have estimated a total of 57 deliquescence events (i.e., water condensation) within the halite crusts, as opposed to only 1 liquid water event outside. These wet events resulted in a total of 213.8 h of potential photosynthetic activity for the endolithic microorganisms versus only 6 h for organisms outside the halite crusts. Halite crusts may therefore represent the last available niche for photosynthetic activity in extreme arid environments on Earth.
Respiratory and Laryngeal Function During Spontaneous Speaking in Teachers With Voice Disorders
Authors: Lowell Soren Y. , Barkmeier-Kraemer Julie M. , Hoit Jeannette D. , Story Brad H.
Published: March 2008

Purpose

To determine if respiratory and laryngeal function during spontaneous speaking were different for teachers with voice disorders compared with teachers without voice problems.

Method

Eighteen teachers, 9 with and 9 without voice disorders, were included in this study. Respiratory function was measured with magnetometry, and laryngeal function was measured with electroglottography during 3 spontaneous speaking tasks: a simulated teaching task at a typical loudness level, a simulated teaching task at an increased loudness level, and a conversational speaking task. Electroglottography measures were also obtained for 3 structured speaking tasks: a paragraph reading task, a sustained vowel, and a maximum phonation time vowel.

Results

Teachers with voice disorders started and ended their breath groups at significantly smaller lung volumes than teachers without voice problems during teaching-related speaking tasks; however, there were no between-group differences in laryngeal measures. Task-related differences were found on several respiratory measures and on one laryngeal measure.

Conclusions

These findings suggest that teachers with voice disorders used different speech breathing strategies than teachers without voice problems. Implications for clinical management of teachers with voice disorders are discussed.
Vocal Hygiene Education, Voice Production Therapy, and the Role of Patient Adherence: A Treatment Effectiveness Study in Women With Phonotrauma
Authors: Behrman Alison , Rutledge John , Hembree Amanda , Sheridan Sarah
Published: March 2008

Purpose

To assess the effectiveness of vocal hygiene education (VHE) and voice production therapy (VP) in altering patient perception of vocal handicap in adult women with benign, bilateral phonotraumatic vocal fold lesions and the role of adherence in that perception.

Method

Sixty-two women were randomly assigned to 6 weeks of VP (
n
= 31) or VHE (
n
= 31), followed by 4 weeks of self-study. The primary outcome measure was the Voice Handicap Index (VHI) score, assessed at baseline, post-therapy, and post–self-study. Patient adherence was assessed as a cofactor.

Results

Both groups achieved a decrease in VHI scores from baseline to completion of the study, although the improvement was significantly greater for the VP group. The treatment effect size was large for the VP group and small for the VHE group. More participants adhered to VP than to VHE. Only adherent participants achieved significant improvement. Only adherent participants in the VP group improved with self-study. More than two thirds of the VP group achieved final VHI scores within normal limits, compared with approximately one third of those in the VHE group.

Conclusions

VP therapy may be more effective than VHE in addressing patient perception of vocal handicap in adult women with phonotrauma, and self-study may be an important component of therapy. However, adherence is a critical mediator of outcome.
Language Outcomes of 7-Year-Old Children With or Without a History of Late Language Emergence at 24 Months
Authors: Rice Mabel L. , Taylor Catherine L. , Zubrick Stephen R.
Published: March 2008

Purpose

The aim of this study was to investigate the language outcomes of 7-year-old children with and without a history of late language emergence at 24 months.

Method

One hundred twenty-eight children with a history of late language emergence (LLE) at 24 months and 109 children with a history of normal language emergence (NLE) at 24 months participated in direct behavioral assessment of multiple dimensions of language at 7 years. The children were recruited from a prospective cohort study of 1,766 epidemiologically ascertained 24-month-old singleton children.

Results

The group mean for the LLE children was within the typical range on an omnibus measure of general language ability and measures of specific dimensions of language. However, a greater percentage of LLE children, relative to NLE children, performed below normative expectations on a measure of general language ability (20% versus 11%), speech (7% versus 2%), syntax (18% versus 8%), and morphosyntax (9%–23% versus 2%–14%), but not vocabulary or semantics.

Conclusion

The results provide support for growth models of language impairment that predict that late onset of language foretells a protracted growth difference for some LLE children relative to NLE children, particularly for syntax and morphosyntax.
Written and Oral Narratives of Children and Adolescents With Down Syndrome
Authors: Kay-Raining Bird Elizabeth , Cleave Patricia L. , White Denise , Pike Heather , Helmkay April
Published: March 2008

Purpose

This study describes written and spoken narrative skills of school-age individuals with Down syndrome (DS).

Method

Twenty-one students with DS (age 6;6 [years;months]–19;10) and 17 reading-matched, typically developing (TD) controls (age 4;9–10;9) were matched using Word Identification subtest raw scores (Woodcock Reading Mastery Tests—Revised; R. W. Woodcock, 1987; age equivalents: 5;0–9;7 for both groups). Matching on reading resulted in significantly higher mental ages and vocabulary comprehension age-equivalent scores for the controls. Narratives were elicited in 3 modes (oral, handwritten, and word-processed) using single-episode picture sequences. Narratives were analyzed for length, linguistic complexity, narrative structure, spelling, punctuation, and handwriting legibility.

Results

Analyses revealed significant group differences only for measures of narrative length (DS > TD) and handwriting legibility (TD > DS). Oral narratives were longer and more complex than written narratives for both groups. Regression analyses revealed that vocabulary comprehension was the best predictor of narrative skills for the group with DS; age was the best predictor of narrative skills for the TD group.

Conclusions

These school-age students with DS exhibited many oral and written narrative abilities that were comparable with those of real-word-reading-matched controls. Several findings suggest a possible increased constraint of fine-motor skill in the DS group.
Transient Excitation of Nuclei in Ferromagnetic Metals
Authors: Weger M. , Hahn E. L. , Portis A. M.
Published: March 2008

Free precession signals and spin echoes have been observed from Fe57, Co59, and Ni61 nuclei in finely divided multidomain iron,cobalt, and nickel, respectively. Spin-lattice relaxation has been studied in all three metals from temperatures in the liquid helium range to room temperature or above. Although the relaxation is not strictly exponential, the rate of recovery of the magnetization appears to be proportional to the absolute temperature. Spin-spin relaxation has been studied in natural cobalt and in both natural and enriched samples of iron and nickel. The spin-spin coupling is very much stronger in cobalt than in iron or nickel, as expected,because of the very much larger nuclear magnetic moment of Co59. Spin diffusion through the frequency spectrum of cobalt has been investigated at 4.2 and 77°K by the stimulated echo technique. The results are consistent with a theory of one-dimensional diffusion with exchange rate and exchange distance of the order of 1/T2. The spin-echo technique has also been used in all three metals to study the effect of domain wall motion on the nuclear resonance. A dc pulse, which displaces the domain walls by a controllable amount, is placed between the first rf pulse and the echo. This study confirms that the induction signals arise from nuclei in domain walls and further suggests a connection between line broadening and domain wall processes. A weak free-precession signal, arising from domain rotation, has been observed from cobalt in high magnetic fields. The sign of the precession has been determined, confirming that the hyperfine field is directed opposite to the magnetization.
Ferrimagnetic Resonance and Torque Measurements on Ytterbium-Substituted Yttrium Iron Garnet
Authors: Teale R. W. , Pearson R. F. , Hight M. J.
Published: March 2008

It is pointed out that the comparison of microwave resonance and static torque measurements on single-crystal samples may enable relaxation effects in the former to be identified. Such a comparison is made for a crystal of nominal composition (Yb0.021Y0.979)3Fe5O12 in the temperature range 4.2–250°K. It is shown that for this crystal, as in Yb3Fe5O12, the anisotropy in Hr, the field for resonance, is not due only to magnetocrystalline energy in a range of temperatures below 220°K. It is suggested that the extra reduction in Hr observed,which occurs most strongly in the [111] directions, is associated with the heavily damped motion of the magnetization of the ytterbium ion. Both types of measurement show that between 20 and 4.2°K, the magnetocrystalline energy surface of the ytterbium ion changes very rapidly and develops sharp curvature.
Instability of Magnetostatic Modes in a Microwave Magnetic Field Applied Parallel to the dc Field
Authors: Schlömann E. , Joseph R. I.
Published: March 2008

Previous calculations of the instability threshold have been based on a plane-wave analysis which is strictly applicable only in an infinite medium. This paper describes a more rigorous theory in which the boundary conditions at the surface of the sample are taken into account. The refined theory admits instabilities at frequencies different from half the pump frequency, which are forbidden according to the less rigorous plane-wave analysis. The general theory is applied to the magnetostatic modes of a long, circular cylinder, which is magnetized along its axis. It is concluded that:

1. Pairs of surface modes (with frequencies higher than the highest plane-wave frequency) are not subject to instability.

2. Instability at half the pump frequency can occur only for those cases in which the magnetostatic potential is invariant under rotation around the cylinder axis (m = 0). The instability threshold for these modes is identical to that deduced on the basis of the plane-wave analysis, except that the frequencies now have to satisfy the characteristic equation derived from the boundary conditions.

3. Instabilities at frequencies different from half the pump frequency can occur, but generally have a higher threshold.
Temperature Dependence of the Spin-Wave Spectrum of Yttrium Iron Garnet
Authors: LeCraw R. C. , Walker L. R.
Published: March 2008

The temperature dependence of the exchange constant D in the equation of the spin-wave spectrum has been measured from 4.2°K–500°K in single crystals of very pure yttrium iron garnet. The results are compared,with good agreement up to 325°K, to predictions based on an extension of the random phase approximation to a ferrimagnet.
Elongated Iron-Cobalt: Ferrite, a New, Lightweight, Permanent Magnet Material
Authors: Falk R. B. , Hooper G. D.
Published: March 2008

The preparation of fine particles of elongated iron-cobalt:ferrite is described. Coercive forces ranging from 2400 oe, for particles having 57% Fe, 31% Co, and 12% O, to over 7000 oe, for particles having 47%Fe, 26% Co, and 27% O, have been measured at −196°C. Compacts prepared from particles with the composition 57% Fe, 31% Co, and 12% O had the following magnetic properties when measured at 25°C: Br = 6200 gauss, Hc = 1550 oe, and (BH)max = 4.0×l06 gauss-oe. These compacts have a physical density of 3.7 g/cc, and are stable magnetically at temperatures up to 100°C. Magnets exhibit a reversible decrease in remanence of less than 1% over the temperature range of −196°−+50°C. The observed magnetic properties can be accounted for in terms of a cobalt ferrite shell in exchange contact with its elongated iron-cobalt core.
Structure of Alnico V
Authors: Campbell Robert B. , Julien Carl A.
Published: March 2008

The microstructure and crystal structure characteristics of Alnico V in various conditions of heat treatment have been determined by electron transmission microscopy and by electron and x-ray diffraction. The a0 values of the different cubic phases have been determined from the electron diffraction data by using an MgO smoke film as an internal standard. In the water-quenched condition this material is a single-phase bcc, with a0 = 2.84 A. Transmission electron micrographs of the material in the magnetic field cooled condition show a structure appearing to be comprised of a matrix phase and oriented precipitate particles whose size is dependent on the cooling rate. Corresponding transmission diffraction patterns of such micrographed regions indicate that the matrix and precipitate are both part of the same crystallographic entity having the same crystal symmetry and, within experimental error, the same lattice parameter as the water quenched material. Diffraction patterns of slowly cooled specimens indicate the presence of small quantities of another constituent,bcc, a0 = 2.62 A. In the fully heat-treated (i.e., field cooled plus coercive aged) condition, the same microstructural appearance and lattice parameters, within experimental error, prevail,although magnetic tests show that a marked increase in anisotropy has occurred. Diffraction patterns from regions consisting exclusively of (deliberately induced) “gamma phase” indicate a randomly oriented, fine grained (5–6 grains/μ2) bcc structurea0 = 2.84 A.
Chromium Ion Pair Interactions in the Paramagnetic Resonance Spectrum of Ruby
Authors: Statz H. , Rimai L. , Weber M. J. , deMars G. A. , Koster G. F.
Published: March 2008

The paramagnetic resonance spectrum of Cr3+ pairs in ruby which interact via exchange and dipolar forces have been studied at 15.74 kMc in the temperature range 1.2° to 700°K. Theoretical analysis predicts and experiments confirm that relatively distant neighbors with negligible exchange coupling give rise to resonance lines which cluster around isolated Cr3+ ion lines. Spin pairs coupled through exchange forces large as compared to the Zeeman or crystalline field energies give rise to lines that cluster around magnetic field values different from those for isolated Cr3+ lines. Exact calculations on an IBM 704 computer are used to assign lines in a given cluster to various neighbor pairs. This assignment together with the temperature dependence of the line intensities are used to determine the exchange forces. For nearest neighbors the exchange constant is 390±50 cm−1 while the 3rd through 11th neighbor shells have exchange interactions of order 1 cm−1. Spin-lattice relaxation is discussed for pairs coupled through anisotropic exchange or weak isotropic exchange forces.
Preparation, Growth, and Study of Ultrafine Ferrite Particles
Authors: Schuele W. J. , Deetscreek V. D.
Published: March 2008

Ultrafine ferrite particles were prepared by a chemical precipitation process below 100°C in an aqueous medium. The resulting materials were grown hydrothermally at moderate temperatures for extended periods of time. Samples were removed at various times during the growing process and their magnetic and physical properties determined. Coercive forces varied from zero to about 800 oe at room temperature for some hydrothermally grown cobalt ferrites. At liquid nitrogen temperature coercive forces to 10 000 oe were measured. Crystallite size measurements were made by x-ray line broadening. An apparatus to measure hysteresis loops in pulsed fields was constructed and used for measuring magnetic properties of samples difficult to saturate, i.e., cobalt ferrite samples at −196°C. Good agreement was obtained between pulsed fields and dc measurements where samples could be measured by both systems.
Quantitative Determination of the Interaction Fields in Aggregates of Single-Domain Particles
Authors: Eldridge Donald F.
Published: March 2008

The distribution of interaction fields in a substance composed of single domain particles may be determined from the anhysteretic magnetization characteristic of the bulk material. This characteristic as used here is the remanent induction vs applied field when, during application of the field, an alternating field decreasing slowly from well above the coercive force to zero is applied. It may be seen that when such a process is applied to an isolated single domain particle, the resulting magnetization will always be of the same sense as the applied dc field, even for almost negligible values of applied field. It follows that any group of independent single domain particles will also act in the same way even though there may be a distribution of coercive forces within the group: That is, for any applied dc field, all particles will be magnetized in one direction or the other after the application of the decreasing alternating bias field. This would imply an anhysteretic characteristic rising with infinite slope at the origin. A finite slope does not result if one merely adds a demagnetizing field, since this will only subtract from the applied field and any applied field will still produce saturation. The finite slope of the anhysteretic characteristic may be explained only by including the effects of the interaction fields. The interaction field acting on any particle is the sum of the fields from all the other particles and is determined by the geometrical arrangement of the particles independently of the applied field. Now the total dc field applied to any particle will be the sum of its interaction field and the external dc field. For any value of applied external field, all particles with interaction fields smaller than the applied external field will be magnetized in the same sense as the applied field after the application of the alternating bias field. The total net magnetization of a group of particles will therefore be the cumulative distribution function of the interaction fields and will be independent of the coercive force. The actual distribution of amplitudes of the interaction fields may therefore be readily measured. An expression is derived for the root mean square value of the interaction field at any point in an infinite aggregate of single domain particles. This expression states that the average interaction field may be determined from the volumetric packing factor of the particles and their remanent induction. The calculated interaction fields for an aggregate material is in close agreement with experimentally measured values.
General Superparamagnetic Behavior of an Aligned Assembly of Uniaxially Anisotropic Particles
Authors: West Forrest G.
Published: March 2008

The partition function which describes the thermal equilibrium behavior of an aligned assembly of uniaxially anisotropic particles in a field H applied along the direction of alignment is: Z = 2π  ∫ 0π sinθ exp(−a sin2θ+b cosθ)dθ. In this expression a = KV/kT; and b = μH/kT, where K is the anisotropy energy density;V the particle volume; μ the particle magnetic moment; k the Boltzmann factor; and T the absolute temperature. It is shown that the tabulated function y = exp(−x2)  ∫ 0x exp(l2)dtcan be used to obtain the fractional magnetization m∥ along the direction of alignment for general values of a and b. Numerical results for m∥ have been obtained for a = 0.01, 0.1, 1, 2, 5, 10, 100; and 0.01≤b≥100. Curves of m∥ vs b with a as a parameter are presented. For a<25 the curves are the magnetization curves for superparamagnetism. For a = 1 the maximum deviation from the Langevin function is about 30%. As a → ∝, m∥ approaches tanhb. For a = 10 the latter approximation is fairly good. The dependence on ashows that superposition of magnetization curves when H is normalized to b is allowable only for a≪1 and a≫1. Thus, when a is not known, the use of such superposition as a test for superparamagnetism will not be valid in samples in which there is significant particle alignment.
Fine-Wire Ferrite Limiter
Authors: Stern Ernest
Published: March 2008

The subsidiary resonance observed in ferrite at high microwave magnetic field intensities is suitable for limiting purposes. The limiter threshold power is related to the units of magnetic field intensity produced in the ferrite per unit of power input. The circumferential field about a wire is directly proportional to the current and inversely proportional to the wire diameter. Thus a fine wire embedded in ferrite will produce intense microwave fields at low microwave power levels provided that the wire is properly matched to the microwave structure. The response of a ferrite limiter to a microwave pulse characteristically exhibits a leakage spike and a plateau whose power level is proportional to ΔHK2. Thus, low threshold power levels normally can be achieved with narrow-linewidth materials. This paper analyzes the fine-wire technique for limiter applications and shows that threshold power levels less than a watt can be achieved in ferritewith wide linewidths. Particular structures were designed, built, and evaluated. It was found that a threshold power level less than one watt was achieved, and that the spike duration decreases rapidly with increasing power.
Low-Temperature Pyromagnetic Measurements on Nickel
Authors: Pugh E. W. , Argyle B. E.
Published: March 2008

A new technique is described for making low-temperature measurements of magnetization changes with temperature by using the pyromagnetic effect. Its sensitivity is one to two orders of magnitude better than previous methods in which the total magnetization is measured at each temperature. The magnetization of a nickel single crystal has been found to decrease monotonically from 4.2°K to 50°K without an anomalous dip near 10°K as has been previously reported.
Paramagnetic Resonance of S8 State Ions in Metals
Authors: Peter Martin
Published: March 2008

A study of the electron paramagnetic resonance spectrum in several intermetallic compounds containing either europium or gadolinium has been made. These ions show very nearly the free ionic g value in their paramagnetic spectra in ionic crystals, indicating that only small admixtures of higher states to the free ionic ground state are caused by the crystalline perturbation. In metals there is, however, a contribution to the ionic g factor which can be attributed to the exchange interaction between the magnetic core and the conduction electrons. We have measured this contribution in GdAl2. The effect was small and could only be identified after careful analysis of the observed line shapes and a correction for the magnetization of the samples. The sign of the exchange interactionis found to be negative, whereas such interactions are always positive in free ions. The interaction also gives rise to an indirect coupling with the other magnetic ions. The resonance lines are therefore exchange narrowed and of the Lorentz type. If other rare earths are substituted for some of the gadolinium, then an additional broadening is observed from which the s-f interaction for all rare earths can be estimated.
Precipitation in Gold-Nickel Single Crystals
Authors: Flanders P. J. , Schoening F. R. L.
Published: March 2008

Magnetic, x-ray, and microscope examinations have been made on single-crystal disks of a Au-Ni alloy containing 24.8 at.% nickel to investigate the precipitation process. The precipitation begins on the surface at discrete areas which grow broader and deeper as annealing progresses. Magnetic data can be interpreted by assuming that the Ni-rich precipitate is elongated in the 〈111〉 directions, electron micrographs indicating the presence of elongation. The Ni-rich phase acquires a small degree of crystalline orientation with increased annealing, whereas the Au-rich phase maintains an appreciable amount of orientation throughout.
Metallurgy and Magnetic Properties of an Fe-Co-V Alloy
Authors: Chen C. W.
Published: March 2008

A comprehensive study of the Fe-49% Co-2% V alloy has revealed many new aspects of the metallography of the alloy and led to a better understanding of its mechanical and magnetic properties. Results of the study necessitate revision of previous reports on the metallography by Greiner and Ellis and Köster and Schmidt. In addition to the well-known phase transformation of γ(fcc) to α(bcc) and the ordering of the αphase, a martensitic transformation has been established. The rapid kinetics of theγ→α transformation can be suppressed by drastic quenching in favor of a diffusionless transformation. Martensite is a metastable bcc structure which decomposes slowly into ordered α at intermediate temperatures. Ordering of the α phase is accompanied by pronounced grain refining. X-ray diffraction studies, elevated temperature measurements of saturation, and metallographic examination have not, however, confirmed the decomposition of the ordered α phase suggested by Greiner and Elli.

The problem of brittleness has been broadly investigated. Cleavage fracture is a major cause of brittleness. Other causes include the gaseous (hydrogen and oxygen) embrittlement at grain boundaries and the cracking at the incoherent interface between the α phase and martensite. Unless specially treated,all bcc constituents, including disordered α, are inherently susceptible to cleavage fracture. The effect of order on the susceptibility to cleavage fracture and the multiple functions of quenchingin the attainment of ductility have been elucidated in terms of current theories of cleavage fracture and lattice imperfections. The main purpose of quenching is to produce a martensitic structure. Only when a ductile matrix has been prepared, can ordering exert an adverse effect on the ductility of the alloy.

Measurements of saturation magnetic moment at elevated temperatures disclose a 2% increase caused by ordering. Room-temperature magnetization curves are compared for different microstructures. The electronic configuration outside the argon core of vanadium atoms is discussed in relation to the composition variation of the average magnetic moment of Fe-Co-V alloys.
Magnetic Film Devices Using Passive Loading
Authors: Daughton J. M. , Smay T. A. , Pohm A. V. , Read A. A.
Published: March 2008

Computer solutions of a pair of differential equations based on the Landau-Lifshitz model indicate that with passive loading, magnetic film devices may be used as storage and logical elements in digital computers. Experimental models of a flipflop consisting of an R-C-L loaded film device show that successive 20-oe,0.1-μsec drive field pulses can switch the magnetization in the film alternately from one rest orientation to the other with repetition rates of the drive on the order of 106 pps. A nondestructive readout memory element consisting of an R-L loaded thin film device is shown which allows films with Hk on the order of 3 oe to be driven in the hard direction by 15-oe, 0.05-μsec field pulses without destroying the stored information,resulting in output voltages of about 25 mv per winding turn. Fabrication by evaporation techniques of a memory employing such elements is discussed.
Magnetic Core Losses Resulting from a Rotating Flux
Authors: Kaplan Asa
Published: March 2008

Most work in the past for determining magnetic core losses has been based on the assumption of an alternating flux. However,in parts of many machines such as generators, the flux rotates rather than alternates. Because of this, it would be advantageous when calculating the losses in a machine if data on losses due to a rotating flux were available. At the 1957 Conference on Magnetism,a paper was delivered in which the magnetic core loss comparator(also known as the magnetic probe) was described. Since that time, a procedure has been devised by means of which the magnetic core losses caused by a rotating flux can be determined using this instrument. One obtains a rotating flux by inserting the legs of a cross-shaped lamination into two sets of magnetizing coils, each set at right angles to the other. If the phases of the magnetizing currents going into each set of coils are adjusted so that the resulting fluxes are 90° out of phase (electrically) with one another, a rotating flux results in the lamination. Core loss readings are made every 30° (geometrically) about a point near the center of the lamination using the magnetic probe. The actual loss of the material can then be determined by adding the losses in any two mutually perpendicular directions. Core loss measurements were made under varying flux conditions ranging from a pure alternating flux (flux in only one direction) to a pure rotating flux (flux in two mutually perpendicular directions of equal magnitude). Intermediate to these two extremes, measurements were made with the flux densities in the two directions of unequal magnitude. This latter condition is a close approximation to that found in an actual generator. Utilizing the above technique, the magnetic core losses caused by a rotating and an alternating flux were determined for an oriented and a nonoriented silicon iron.With both materials, the rotating losses were substantially higher than the alternating losses with the relative increase being greater for the oriented iron. However, the oriented iron was still the lower loss material under all flux conditions.
High-Temperature Stability of Magnetic Materials
Authors: Pavlik Norman
Published: March 2008

Magnetic materials able to perform in environmental extremes are a prerequisite to many military applications such as space vehicles, ballistic missiles, and other advanced systems. Industry,in cooperation with various government agencies, is in constant search for better magnetic materials to meet these requirements. Of the environments to be considered for these applications, temperature has the most deleterious effect on magnetic materials. Most high Curie temperature magnetic materials will show a significant irreversible change in magnetic properties as a result of exposure to 500°C and return to room temperature. This paper will present a possible explanation to the cause of some of these changes especially in the high Curie temperature alloys. Our investigations showed that cobalt-iron alloys containing from 27 to 43% cobalt can be stable magnetically up to at least 600°C. The 49% cobalt alloy can be stable up to at least 500°C. However,this temperature stability is dependent upon several important considerations. One of these is the geometry of the test system. For example, a tape-wound toroidal core tested at elevated temperatures in air becomes severely oxidized—this oxidation or the strains induced by it adversely affect the magnetic properties. However, when the same core is tested in a neutral atmosphere,the strains due to oxidation are minimized and the magnetic properties remain stable. Data will be presented comparing tests on toroids with and without neutral atmospheres, both oriented and nonoriented alloys containing 27%, 35%, 43%, and 49%cobalt. Finally all results will be compared with square punchings relating the differences in high-temperature stability of the magnetic properties due to geometric configurations.
Growth of Yttrium Iron Garnet Single Crystals by the Floating Zone Technique
Authors: Abernethy L. L. , Ramsey T. H. , Ross John W.
Published: March 2008

A MoSi2 susceptor was used to melt and move an iron-rich zone through polycrystalline YIG bars. Crystals 0.25 in. diam or larger, with dielectric constant about 10 and dissipation 0.002, were obtained using the highest stable-zone temperature, a zoning rate of 0.1 in./hr, and an O2 pressure of 100 psig. Silicon contamination, crystalline imperfections, or nonequilibrium phases broadened linewidth, but highly polished test spheres yielded ΔΠ values of 1–2 oe.
Reinterpretation of the Reaction Kinetics of Nickel Ferrite
Authors: Turneull R. C.
Published: March 2008

The kinetics of formation of nickel ferrite from the oxide components has been studied using saturation magnetization to follow the course of the reaction. The data has been interpreted in terms of an empirical expression developed by Tammann. This expression, which gives quite satisfactory agreement with the data, is C = A logt+B, where C is the percent of reaction product, t is the time, and A and B are constants. The sharp breaks that occur in the percent reaction vs log time curves indicate that three separate and distinct mechanisms occur. These are interpreted as (1) an initial surface diffusion of significance at temeratures in the 600° to 800°C range, (2) bulk diffusion in the temperature range from 700° to 950°C, and(3) crystallization into a relatively defect-free crystal lattice above temperatures of 950°C. Activation energies for the surface diffusion and bulk diffusion are 30 and 18 kcal, respectively. Both the low activation energy for the bulk diffusion in comparison to the surface diffusion, and the high initial reaction rate at higher temperatures, suggest that the reaction proceeds through iron diffusing into an active metastable NiO phase.
Cation Distributions in Magnesium-Nickel Ferrites
Authors: Kriessman C. J. , Harrison S. E.
Published: March 2008

The dependence of the nonthermal part of the internal energy (u1) of mixed magnesium-nickel ferrites, MgyNi1−yFe2O4 on the cation distribution has been studied. The cation distribution,which is charactered by the parameters η (the fraction of Mgions on tetrahedral sites) and ξ (the fraction of Ni ions on tetrahedral sites), is determined from measurements of the saturation magnetization of samples quenched from temperatures between 1400° and 400°C. As in the case of magnesium-manganese ferrites it is found that u1 = u0+R(θ0−12θ1η2). The parameters θ0 and θ1 are related to the energies necessary to transport Mg ions from octahedral (B) to tetrahedral (A) sites. The Madelung energy portion of θ0 predicts a linear dependence of θ0on y and this is observed experimentally. It is also demonstrated that θ0 is increased considerably by the substitution of Ni ions for Mn ions in the spinel lattice as dictated by the Madelung energy. The dependence of θ1 on y can also be qualitatively explained. It is shown that the magnetic moment data considered as a function of composition can give useful information about the degree of inversion in the spinel lattice despite the two degrees of inversional freedom (ξ and η). The variation of the maximum attainable value of η with composition depends on ξ and the magnetic moment of the Ni ion. Values of ξ and the Ni ionic magnetic moment compatible with the observed data are discussed.
Impulse Selection for Core Logic
Authors: Tancrell Roger H.
Published: March 2008

Impulse selection is a scheme for operating ferrite cores which have low values of coercive force. Two different threshold properties of a core are utilized. One threshold is the dc coercive force, which can be changed electrically. The other threshold results from the inertial magnetic effects within the core which are predominant when pulses of very narrow widths are applied. The switching behavior of ferrite cores is discussed when two threshold currents, a low amplitude current and an impulse of current, are combined. The application of this property to core logic is considered.
Spin-Flopping in MnF2 by High Magnetic Fields
Authors: Jacobs I. S.
Published: March 2008

Observations of spin-flopping, or decoupling between the direction of antiferromagnetism and the easy axis of the crystal, are presented for MnF2 in single crystal and powder form at low temperatures. Magnetization measurements in pulsed fields to 140 koe are employed to explore the critical interaction energy in this antiferromagnet, as an alternative tool to microwave resonance. The orientation dependence predicted by Néel in 1936 is confirmed. The critical field for spin-flopping given by the combination of anisotropy and exchange, (2HEHA)12 is found to be 93±2 koe in excellent agreement with resonance results of S. Foner[(a) Phys. Rev. 107, 683 (1957); (b) J. phys. radium 20, 336 (1959)], and F. M. Johnson and A. H. Nethercot [Phys. Rev. 104, 847 (1956); 114, 705 (1959)].
Infrared Antiferromagnetic Resonance in MnO
Authors: Keffer F. , Sievers A. J. , Tinkham M.
Published: March 2008

Antiferromagnetic resonance has been observed in powdered MnO at 364 μ at 1.5°K. The resonance frequency as a function of temperature falls roughly as the square root of the Brillouin function of spin 52. Fields of the order of 104 oe have no observable effect on the line at 1.5°K. All of these results give quantitative confirmation of a model in which the sublattice magnetizations are constrained to a (111) plane by magnetic dipolar interactions and are held to a preferred direction within the plane by a much weaker anisotropy.
Epitaxial Growth and Magnetic Properties of Single-Crystal Films of Iron, Nickel, and Permalloy
Authors: Chikazumi Soshin
Published: March 2008

A number of single-crystal films of iron, nickel, and Permalloy were made epitaxially by evaporation onto(001) cleavage surfaces of NcCl and MgO. Magnetic anisotropies for the rotation of magnetization within the plane as well as out of the plane of the film were measured. Values of the observed fourth-order anisotropyK1 were anomalously large for Ni on NaCl and Ni on MgO, but it was normal for Fe on MgO. The effects of magnetic annealing were also investigated for single-crystal films of Permalloy and nickel.
Structural and Magnetic Properties of Mn-Co-C Alloys
Authors: Holtzman A. H. , Conrad G. P.
Published: March 2008

Mn X Co (80− X ) C 20 alloys were studied for magnetic properties, crystal structure, and metallographic appearance. A superlattice having the stoichiometric composition Mn2Co2C was found to be markedly magnetic. The structure of this alloy is pseudo-f.c.c. with the C atom in the central 121212 position, the Mn atoms in the 000 and 12120 sites, and the Co atoms in the 01212 and 12012 sites. A magnetic structure was deduced from a consideration of the effect of atomic separation on magnetic vector alignment and an indication that electrons transfer from the central C atom to its nearest neighbors, the face atoms.
Relaxational Behavior of Fine Magnetic Particles
Authors: Brown William Fuller
Published: March 2008

Weil and others have used the temperature variation of remanence and a formula of Néel's to determine volume-distribution curves for a powder of single-domain particles. The basic principle is that the time constant for spontaneous reversal of the magnetization, through thermal agitation, is effectively infinite for particle volume v>vc and zero for v<vc, where vc varies with absolute temperature T. Néel's derivation is open to criticism, in that the gyromagnetic properties of the particles are taken into account only up to a certain point in the argument and are thereafter ignored. A new formula has been derived by adaptation of a method of Kramers to angular coordinates and to a gyroscopic equation of motion. Like Néel's theory, this gives for the mean rate of transition between orientations a formula of the form v = c exp(−W/kT); W is the same in both theories, but in the new theory c = (γ′/2)(vJsHc3/2πkT)12. Here Hc = critical field for static  reversal, Js = spontaneous magnetization, γ′ = (2ηJs)[(ηJs)2+1/γ2]−1, γ = (magnetic moment)/(angular  momentum), η = coefficient in the damping torque −ηM×(dM/dt) in Gilbert's equation of motion. The new values of v/T vs time constant do not differ seriously from Néel's.
Microwave Resonance in Hexagonal Ferrimagnetic Single Crystals
Authors: Belson Henry S. , Kriessman C. J.
Published: March 2008

The resonance conditions for a hexagonal single crystal with hard direction normal to the basal plane, and magnetocrystalline anisotropy with hexagonal symmetry in the basal plane, are presented. The anisotropy energy surface may be described by E=K0+K1α32+K2α34+K3α36+K4(α16−15α14α22+15α12α24−α26). From the resonance conditions and data on a single crystal of Ba2Co2Fe12O22 we find K1 = 1.38×105 ergs/cm3, K2+3/2K3=1.42×106 ergs/cm3, and K4=1.10×104. These constants with the loss parameter determined from measurements of the ferromagnetic resonance line width accurately predict the initial permeability spin resonance in a partially oriented polycrystalline sample.
Coupling of the Magnetostatic Modes
Authors: Fletcher Paul C. , Solt I. H.
Published: March 2008

Interaction has been observed between magnetostatic modes due to propagation effects and surface irregularities. The interaction may be characterized by a resonant field shift and intensity exchange similar to the response behavior of two tuned coupled circuits. The mechanisms causing the interaction are discussed.
Surface-Independent Spin-Wave Relaxation in Ferromagnetic Resonance of Yttrium Iron Garnet
Authors: LeCraw R. C. , Spencer E. G.
Published: March 2008

In contrast to the ferromagnetic resonance tine width ΔH, which depends strongly upon surface polish, the “line width” ΔHk of a z-directed spin wave is shown to be surface independent. This permits observation of a relaxation process which appears to be determined primarily by collisions between thermally excited spin waves rather than by a volume or surface distribution of magnetic inhomogeneities. In yttrium iron garnet ΔHk is observed to be 0.10 oe at room temperature and to increase monotonically with increasing temperature. The 0.10 oe corresponds to a relaxation time of 1.14 μsec. It is believed this is the narrowest line width yet indicated for a ferromagnetic material.
Direct Observation of Spin Wave Resonance
Authors: Seavey M. H. , Tannenwald P. E.
Published: March 2008

Resonance due to standing spin waves has been observed in thin films of Permalloy. The results are interpreted in terms of the Kittel spin pinning boundary condition and an ω vs k dispersion relation for good conductors. The method leads to a determination of the exchange constant subject to film thickness uncertainty but to a precise determination of the temperature variation of the exchange constant.
Anisotropy in Permalloy Films
Authors: Smith Donald O.
Published: March 2008

Evaporated films of Permalloy are found to be uniaxially anisotropic under all the conditions of preparation studied so far, including deposition in dc, zero, and rotating-circular magnetic fields. Three principal effects have been identified as contributing to this anisotropy, namely; (1) the formation of directed Fe pairs in the Ni matrix, (2) an effect due to the angle-of-incidence between the substrate and the depositing beam, and (3) anisotropic stress in combination with the isotropic magnetostriction. The evidence for directed pairs comes from the compositional dependence of the anisotropy; the angle-of-incidence effect is demonstrated by depositing onto tilted substrates; anisotropic stress effects are shown by detaching the film from the substrate. The simultaneous presence and interaction of the above effects is thought to be the reason for the variability in the anisotropy which is encountered in Permalloy films.
Barkhausen Effect in Nickel-Iron Films
Authors: Ford N. C. , Pugh E. W.
Published: March 2008

A statistical study of Barkhausen discontinuities in nickel-iron films has been made by observing independent hysteresis loops obtained from different areas of each film. The magnetization changes were detected by photomultiplier sensing of the light output from a standard Kerr magneto-optical apparatus. Observations could thus be restricted to any desired region of the film by suitably varying the light spot size and location. The sequence of Barkhausen discontinuities in a given reversal is generally random and cannot be predicted by the sequence in a previous reversal. The statistical distribution of discontinuity sizes obtained from many reversals is shown to be well described by a simple model of wall moton in which the probability of a wall stopping in an interval of distance dx is proportional to dx. The applicability of this model to bulk materials is discussed.
Neutron Diffraction Investigation of a Possible Ferro-Antiferromagnetic Transition in Mn0.2Cr0.8Sb
Authors: Pickart S. J. , Nathans R.
Published: March 2008

Neutron powder patterns of the hexagonal compound Mn0.2Cr0.8Sb, in which magnetization measurements indicate an antiferromagnetic-ferromagnetic phase change, show that within the antiferromagnetic region the spin structure is similar to that of CrSb. Below the ferromagnetic Curie point weak superstructure lines appear, with the relative intensities of the remainder of the neutron pattern changing only slightly. Additional measurements on the compound MnSb indicate that the spin structure is ferromagnetic with the moments directed along the hexagonal c axis. The results are discussed in relation to the types of exchange interactions present in these materials.