bluuebunny/crossref_metadata_2025 huggingface dataset:
GPS scintillation in the high arctic associated with an auroral arc
Authors: Smith Andrew M. , Mitchell Cathryn N. , Watson Robert J. , Meggs Robert W. , Kintner Paul M. , Kauristie Kirsti , Honary Farideh
Published: March 2008

A rapid signal‐fading event produced by diffractive scintillations was observed around 0123 UT on 8 November 2004 by three closely sited (less than 250 m apart) GPS scintillation receivers in northern Norway. The entire duration of the event was about 10 s and was recorded by all three receivers. Intense, short duration events such as these are not clearly observable in the 1‐min scintillation index (S4) because they do not necessarily last for the entire minute. In spite of their short duration they can cause a receiver to lose lock because of their intensity. The geomagnetic conditions were disturbed at this time with the interplanetary magnetic field southward for a period of several hours. Magnetometers from the IMAGE network in Scandinavia showed evidence of a 2000 nT substorm. The GPS measurements are compared with all‐sky camera (ASC) data to show that the signal fades can be attributed to the GPS ray paths crossing electron density structures associated with the aurora. The ASC images reveal moving auroral structures at the same time as the GPS signals show movement of the ionospheric regions causing fading. The results indicate that at high latitudes low‐elevation GPS signals can suffer sudden fading due to E‐region auroral events. This is the first time that a direct connection has been established between the loss of lock on a GPS receiver and diffractive fading caused by auroral precipitation.
On model selection criteria in multimodel analysis
Authors: Ye Ming , Meyer Philip D. , Neuman Shlomo P.
Published: March 2008

Hydrologic systems are open and complex, rendering them prone to multiple conceptualizations and mathematical descriptions. There has been a growing tendency to postulate several alternative hydrologic models for a site and use model selection criteria to (1) rank these models, (2) eliminate some of them, and/or (3) weigh and average predictions and statistics generated by multiple models. This has led to some debate among hydrogeologists about the merits and demerits of common model selection (also known as model discrimination or information) criteria such as AIC, AICc, BIC, and KIC and some lack of clarity about the proper interpretation and mathematical representation of each criterion. We examine the model selection literature to find that (1) all published rigorous derivations of AIC and AICc require that the (true) model having generated the observational data be in the set of candidate models; (2) though BIC and KIC were originally derived by assuming that such a model is in the set, BIC has been rederived by Cavanaugh and Neath (1999) without the need for such an assumption; and (3) KIC reduces to BIC as the number of observations becomes large relative to the number of adjustable model parameters, implying that it likewise does not require the existence of a true model in the set of alternatives. We explain why KIC is the only criterion accounting validly for the likelihood of prior parameter estimates, elucidate the unique role that the Fisher information matrix plays in KIC, and demonstrate through an example that it imbues KIC with desirable model selection properties not shared by AIC, AICc, or BIC. Our example appears to provide the first comprehensive test of how AIC, AICc, BIC, and KIC weigh and rank alternative models in light of the models' predictive performance under cross validation with real hydrologic data.
Nasal Administration of Osteopontin Peptide Mimetics Confers Neuroprotection in Stroke
Authors: Doyle Kristian P , Yang Tao , Lessov Nikola S , Ciesielski Thomas M , Stevens Susan L , Simon Roger P , King Jeffrey S , Stenzel-Poore Mary P
Published: March 2008

Osteopontin (OPN), a large secreted glycoprotein with an arginine, glycine, aspartate (RGD) motif, can bind and signal through cellular integrin receptors. We have shown previously that OPN enhances neuronal survival in the setting of ischemia. Here, we sought to increase the neuroprotective potency of OPN and improve the method of delivery with the goal of identifying a treatment for stroke in humans. We show that thrombin cleavage of OPN improves its ability to ligate integrin receptors and its neuroprotective capacity in models of ischemia. Thrombin-cleaved OPN is a twofold more effective neuroprotectant than the untreated molecule. We also tested whether OPN could be administered intranasally and found that it is efficiently targeted to the brain via intranasal delivery. Furthermore, intranasal administration of thrombin-treated OPN confers protection against ischemic brain injury. Osteopontin mimetics based on the peptide sequences located either N or C terminal to the thrombin cleavage site were generated and tested in models of ischemia. Treatment with successively shorter N-terminal peptides and a phosphorylated C-terminal peptide provided significant neuroprotection against ischemic injury. These findings show that OPN mimetics offer promise for development into new drugs for the treatment of stroke.
What Can Graph Theory Tell Us About Word Learning and Lexical Retrieval?
Authors: Vitevitch Michael S.
Published: March 2008

Purpose

Graph theory and the new science of networks provide a mathematically rigorous approach to examine the development and organization of complex systems. These tools were applied to the mental lexicon to examine the organization of words in the lexicon and to explore how that structure might influence the acquisition and retrieval of phonological word-forms.

Method

Pajek, a program for large network analysis and visualization (V. Batagelj & A. Mvrar, 1998), was used to examine several characteristics of a network derived from a computerized database of the adult lexicon. Nodes in the network represented words, and a link connected two nodes if the words were phonological neighbors.

Results

The average path length and clustering coefficient suggest that the phonological network exhibits small-world characteristics. The degree distribution was fit better by an exponential rather than a power-law function. Finally, the network exhibited assortative mixing by degree. Some of these structural characteristics were also found in graphs that were formed by 2 simple stochastic processes suggesting that similar processes might influence the development of the lexicon.

Conclusions

The graph theoretic perspective may provide novel insights about the mental lexicon and lead to future studies that help us better understand language development and processing.
A Randomized Trial of Longitudinal Effects of Low-Intensity Responsivity Education/Prelinguistic Milieu Teaching
Authors: Warren Steven F. , Fey Marc E. , Finestack Lizbeth H. , Brady Nancy C. , Bredin-Oja Shelley L. , Fleming Kandace K.
Published: March 2008

Purpose

To evaluate the longitudinal effects of a 6-month course of responsivity education (RE)/prelinguistic milieu teaching (PMT) for young children with developmental delay.

Method

Fifty-one children, age 24–33 months, with fewer than 10 expressive words were randomly assigned to early-treatment/no-treatment groups. All treatment was added as a supplement to services that the children received in the community. Follow-up data were collected 6 and 12 months after the conclusion of the initial 6-month treatment/no-treatment conditions.

Results

No effects of this treatment were detected 6 or 12 months after the conclusion of the initial treatment condition.

Conclusions

M. E. Fey et al. (2006) reported that 6 months of RE/PMT led to a significant treatment effect in the use of intentional communication in 1 of 2 communication sampling contexts. This finding, combined with evidence from other studies, suggests that RE/PMT may be applied clinically at low intensity with the expectation of medium-sized effects on children’s rate of intentional communication acts over the short term. The results of the present study, however, provide no evidence for the anticipated longer term benefits of this intervention. Further investigation of the approach at higher intensity levels and for longer periods of time is warranted.
The Effects of Hearing Aid Compression Parameters on the Short-Term Dynamic Range of Continuous Speech
Authors: Henning Rebecca L. Warner , Bentler Ruth A.
Published: March 2008

Purpose

The purpose of this study was to evaluate and quantitatively model the independent and interactive effects of compression ratio, number of compression channels, and release time on the dynamic range of continuous speech.

Method

A CD of the Rainbow Passage (J. E. Bernthal & N. W. Bankson, 1993) was used. The hearing aid was a programmable, digital, wide dynamic range compression instrument. A fully crossed design and multiple regression analyses were used to evaluate and model the effects of release time (32, 128, and 1024 ms), compression ratio (1:1, 2:1, and 4:1), and number of compression channels (1, 2, and 4 channels) on the short-term octave-band dynamic range of speech.
Dynamic range of speech
was defined as the range between the 1% and 70% exceedance levels within each octave band.

Results

As the compression ratio and number of channels increased, and as the release time decreased, the dynamic range of speech decreased. The effects of channels and release time increased as the compression ratio increased. In all conditions, the amount of effective compression for speech was less than the nominal compression ratio.

Conclusion

A multiple regression model is provided that predicts the effects of various combinations of compression parameters on the dynamic range of speech.
Cognitive Maturation and the Use of Pitch and Rate Information in Making Similarity Judgments of a Single Talker
Authors: Petrini Karin , Tagliapietra Sara
Published: March 2008

Purpose

This study examined age-related differences in speaker similarity judgments, in which acoustic cues known to be important in speaker and speech recognition and identification were varied.

Method

Four groups of listeners of 5- to 6-, 8- to 9-, 10- to 11-, and 25- to 30-year-olds were asked to judge the similarity between an original talker’s speech sample and 9 versions of a second speech sample from the same talker, obtained by manipulating the pitch and speech rate.

Results

Results showed that although pitch was used by all age groups as information to judge the similarity between the single talker speech samples, there was a significant age-related increase in the weight of speech rate attributed to similarity judgments. Furthermore, an age-related effect in accuracy was found, as was an effect of pitch level for the younger group.

Conclusion

The use of relevant acoustic features to discriminate a speaker changes with age, probably arising from a shift in cue weighting strategy as described by the developmental weighting strategy hypothesis (S. Nittrouer, C. Manning, & G. Meyer, 1993). Future studies should clarify whether the present findings can be extended to any pair of acoustic cues and should involve longitudinal methods to precisely detect when the strategy shift occurs.
Ferromagnetic Relaxation at Low Microwave Frequencies
Authors: Green J. J. , Schlömann E.
Published: March 2008

The theory of three-magnon relaxation processes is summarized, and it is shown that such processes are very likely to be important at low microwave frequencies. The instability threshold in an rf magnetic field applied parallel to the dc field has been measured in yttrium iron garnet at room temperature as a function of the dc field at five frequencies between S and X band. The results of these measurements are in qualitative agreement with the theoretical predictions.
Magnetic Properties of Single-Domain Iron and Iron-Cobalt Particles Prepared by Borohydride Reduction
Authors: Oppegard A. L. , Darnell F. J. , Miller H. C.
Published: March 2008

Air-stable, single-domain Fe and Fe-Co particles prepared by the reaction of the metal salts with aqueous borohydride have higher coercivities and axial ratios if prepared in a magnetic field. Oxide and boride impurities are indicated by elemental analyses and lowered saturation magnetizations. Studies of coercivitiesand magnetizations as a function of temperature, remanence ratios, and rotational hysteresis measurements indicate single-domain behavior with coercivity controlled by shape and somewhat by crystalline anisotropy in approximate agreement with the predictions of the Jacobs-Bean “chain of spheres” model.
Paramagnetic Resonance Measurements of Exchange Interactions
Authors: Owen J.
Published: March 2008

A brief survey is given of some paramagnetic resonance experiments on exchange coupled pairs of paramagneticions in magnetically dilute crystals. The spin Hamiltonian for a pair of coupled spins Si, Si is first discussed. Then the effects observed in the paramagnetic resonance spectrum are outlined. Finally, there is a more detailed discussion of results found for nearest neighbor and next-nearest neighbor pairs of Mn2+ ions in Mn, MgO, followed by a short account of some preliminary results on nearest neighbor pairs of Mn2+ ions in Mn, ZnF2.
Saturation Magnetization and Size of Iron Particles Less than 100 A in Diameter
Authors: Luborsky Fred E. , Lawrence Philip E.
Published: March 2008

Spherical iron particles were prepared by electrodeposition into mercury under conditions which produced average diameters as small as 15 A. The complete magnetization curves were obtained as a function of temperature from 4° to 300°K in fields up to 150 000 oe. Fields of more than 50 000 oe at 76°K were required to determine unambiguously the saturation magnetization; even higher fields were needed at higher temperatures. The saturationmagnetization of larger particle size samples, obtained by aging,remained constant and corresponded to the total iron present. Particle size and size distributions were calculated from the magnetization curves by means of the Langevin function at sufficiently high temperatures so that the samples were completely superparamagnetic. These results were compared to the particle sizes calculated from the temperature dependence of the remanence to saturation ratio. The two methods showed substantial agreement and were consistent with the properties and sizes of larger particles previously determined by direct electron microscope examination. The mean particle diameters thus determined ranged from about 15 A for the freshly deposited samples to about 60 A for the aged samples. Beyond this range the onset of stable magnetic behavior in a large fraction of the particles made the particle size calculation by these methods unsuitable.
Theoretical Magnetization Curves for Particles with Cubic Anisotropy
Authors: Johnson Clare. E. , Brown William Fuller
Published: March 2008

Theoretical hysteresis loops have been calculated for a single-crystal ferromagnetic particle with only cubic magnetocrystalline anisotropy. These calculations have been carried out for various cyrstal orientations with the applied field. The method of computation consists of determining the magnetostatic energy over the unit sphere and then searching for minima. The curves appear similar to those resulting from shape anisotropy (Stoner-Wohlfarth) except that with certain orientations, states of stable magnetization appear which are inaccessible by traversing hysteresis loops. Averaging of the coercive force over all orientations for both positive and negative anisotropy has been carried out in that range of fields where no jumps occur. A complication which causes some uncertainty is the existence, with certain particle orientations, of several stable states at which a jump might terminate. It is impossible to decide from our static energy calculation which path the magnetization follows during reversal.
Anisotropy of YIG Calculated from Crystal Field Parameters Fe3+ in Yttrium Gallium Garnet
Authors: Geschwind S.
Published: March 2008

An expression is given for the anisotropy of YIG in terms of the ground-state crystal field splitting parameters of Fe3+ in YGaG. The low-temperature anisotropy of YIG calculated from these crystal field parameters is 50% higher than the experimentally measured value. Several sources for this discrepancy are discussed.
Torque Measurements on Rare-Earth Doped Yttrium Iron Garnet
Authors: Pearson R. F. , Cooper R. W.
Published: March 2008

This paper describes torque measurements made at 4.2 and 1.5°K on yttrium iron garnet crystals containing small rare-earth ion dopings kindly supplied by Dr. J. F. Dillon, Jr., and Dr. J. W. Nielson of the Bell Telephone Laboratories. Resonance measurements by Dillon (1959) showed that the giant anisotropy peaks observed in yttrium iron garnet at 4.2°K were due to the presence of rare-earth ion impurities and since then his results on samples containing known impurities have been interpreted by Kittel(1960) in terms of energy-level “crossovers” of the rare-earth ionin the combined crystal field and exchange field. In the present work torque measurements have been made on several crystals with different rare-earth ion impurities, but results here are confined to crystals doped with terbium (Tb 0.19%), holmium (Ho 0.19%), and dysprosium (Dy 1.0%). The crystal containing dysprosium was grown by J. L. Page in our laboratories. The torquecurves were measured in a (110) plane [also in a (100) plane for the Tb sample] in a magnetic field of 15 000 oe and the maximum torques were in the range 20–200 dyne cm. For the three crystals,the energy surface deduced from the torque curves is consistent with the resonance field behavior observed by Dillon (1959). The torque curve of the Tb crystal had more pronounced discontinuities than any other samples, and variation in the applied field between 5000 and 15 000 oe altered the magnitude but did not alter the angle at which a particular discontinuity occurred. So far,attempts to correlate the position of the discontinuities in the (110)and (100) planes which showed fewer discontinuities have proved unsuccessful with the above model. At 20°K the torque curve can be analyzed in the standard way giving values of K1 and K2 of+88 000 and −460 000 erg cm−3 respectively. The torque curve for the Ho sample at 4.2°K was steepest at the [110] and [100]directions, in agreement with the position of the resonance peaks reported by Dillon (1959). However, for the Dy crystal, no sharp discontinuities are observed and the torque curve shows a large sin8θ component. On reducing the temperature from 4.2° to 1.5°K,no change in the curve was observed. The curves for Ho and Dy were found to be quite reversible in fields of 15 000 oe.
Low-Temperature Magnetic Properties of Some Rare-Earth Garnet Compounds
Authors: Ball M. , Garton G. , Leask M. J. M. , Ryan D. , Wolf W. P.
Published: March 2008

Low-temperature magnetic susceptibility measurements have been carried out on single crystals of Dy3Al5O12, Dy3Ga5O12, Er3Al5O12, Er3Ga5O12, and diamagnetic Y3Al5O12 and Y3Ga5O12 containing nominally 1% Dy and Er. The dilute samples have also been investigated by paramagnetic resonance (9 kMc at 4.2°K),and with the exception of Dy in Y3Al5O12 for which no resonance was found, the g tensors of the ground state doublets have been determined in each case. A wide range of principal g values was found (1 to 11)and considerable differences between corresponding Al and Ga compounds were observed. These results show that the electronic ground states of the Dy3+ and Er3+ ions are in general very anisotropic in these structures, and that their magnetic properties are very sensitive to small changes of environment. The susceptibility measurements also indicated the presence of low-lying crystal field states, and a weak, but rather complex, interaction between the rare-earth ions. In the case of Dy3Al5O12 the interactions lead to antiferromagnetic ordering at 2.5°K. Difficulties in applying these results to the interpretation of the properties of ferrimagnetic garnets containing Dy and Er are discussed.
Magnetic Properties of the Low-Temperature Form of Magnetite
Authors: Bonstrom D. B. , Morrish A. H. , Watt L. A. K.
Published: March 2008

Some of the magnetic properties of the orthorhombic form of magnetite (Fe3O4) have been studied from 2°K to the transition temperature (∼119°K). Both ferromagnetic resonance measurements on single crystals and coercive force measurements on small particles have been made. The “twinning” of orthorhombic magnetite has been investigated. The crystalline anisotropy constants have been determined;they are of the order of 106 ergs/cm3. The coercive force of single-domain and multidomain particles has been interpreted in terms of the crystalline anisotropy.
Domain Wall Mobility in Single-Crystal Yttrium Iron Garnet
Authors: Hagedorn F. B. , Gyorgy E. M.
Published: March 2008

Reasonable agreement between the damping constant inferred from the resonance linewidth and that obtained from the domain wall mobility has previously been found for ferrites. However, the recent linewidths reported for yttrium iron garnet (YIG) by Spencer, LeCraw, and Clogston are substantially narrower than those for ferrites. On using this narrow linewidth to calculate the YIG wall mobility, one obtains about 106 cm/sec oe. We have measured the YIG wall mobility as a function of temperature and find it to be less than 104 cm/sec oe. This discrepancy can be interpreted in terms of a model for domain wall motion which is based on a type of energy conversion process different from that usually assumed. The customary treatment requires that the domain walldissipate entirely to the lattice all of the magnetostatic energy stored in a given region during the time that the wall passes through this region. For small damping such as exists in YIG, this requirement appears to be unreasonable. The wall motion model proposed here allows the wall to be followed by a wake in which the original magnetostatic energy is temporarily stored as exchange,anisotropy, and demagnetizing energy. The measured wall velocities in single-crystal YIG are in reasonable agreement with quantitative estimates based on this model.
Spiral Walls in Thin Magnetic Films
Authors: Fuller Harrison W. , Rubinstein Harvey , Sullivan Donald L.
Published: March 2008

Dense concentrations of walls were previously observed to appear in very thin magnetic films with the application of an ac demagnetizing field. Other observations showed roughly circular concentric walls around barely discernible imperfections. Particularly clear powder patterns of such walls that were obtained on the thin end of a Permalloy film of tapered thickness are presented. The patterns allow the deduction of the detailed magnetization distribution which takes the form of a pair of antiparallel domains that spiral in toward the central imperfection. A mechanism for the formation of spiral walls is presented, together with confirming experimental evidence. The experiments establish the nature of the central imperfection as a region of abnormally high uniaxial anisotropy where the magnetization is constrained to lie in one direction along the easy axis while the magnetization of the surrounding regions of the film can be rotated with an applied field.
Magnetoresistive Measurements on Domain Rotation and Wall Development in Ni-Fe Alloy Films
Authors: West Forrest G.
Published: March 2008

In low saturating magnetic field, the magnetoresistive effect in a polycrystalline ferromagnet is described by the relation Δρ/Δρ0 = cos2α where Δρ is the resistivity change which occurs when the saturation magnetization Ms is oriented first normal then at an angle α to the electric current i. The maximum change Δρ0 is characteristic of the material. The uniform rotation model of a uniaxially anisotropic film in a transverse magnetic field H⊥ leads to a dependence of Δρ on H⊥ of the form Δρ/Δρ0 = h⊥2 when i is normal to the anisotropy axis (K axis) and of the form Δρ/Δρ0 = 1−h⊥2 when i is parallel to the K axis. In these expressions h⊥ is the ratio of H⊥ to HK, where HK = 2K/Ms, and K is the anisotropy energy constant. The present paper treats the transverse magnetization process in Ni-Fe alloy films on the basis of a simple model in which the K axes in local regions of the film are dispersed in direction about an average 〈K〉 axis. For a single numerical value of the dispersion angle β the transverse magnetoresistive behavior is described by Δρ/Δρ0 = (h⊥+β)2 when i is normal to 〈K〉 and Δρ/Δρ0 = 1−(h⊥+β)2 when i is parallel to 〈K〉. The model also requires that the ratio of transverse remanent magnetization to Ms be sinβ. These predictions are experimentally verified for films which gave values of β from 0.1 to 0.3 (6° to 18°), and show the applicability of the Stoner-Wohlfarth theory to domain rotation.
Determination of the Directions of Magnetization in Polycrystalline Ferrites
Authors: Callaby D. R.
Published: March 2008

To explain the switching properties of “square-loop” ferrites,assumptions have had to be made as to the detailed configuration of the magnetization because of the lack of experimental evidence. This paper presents a method, using the Kerr transverse magneto-optic effect, to determine directly the directions of magnetization in individual grains across the surface of a ferrite toroid subject to an alternating magnetic field. A rectangular area of the ferritesurface of size 200×160 μ is illuminated by a tungsten filament source, and the intensity of the reflected beam measured with a germanium photodiode. When the magnetization in the ferrite is reversed with an alternating field of 1100 cps, a modulation of the same frequency appears in the output of the photodiode. The depth of this modulation is approximately 0.01% of the dc output and changes markedly as the light probe is traversed across the ferrite, because of the different directions of the magnetization in the separate grains. By choosing a sample with grains of the same size as the light probe, it is possible to examine the light reflected from an individual grain. By rotating the grain around the light probe and recording the variation in size of the modulation with angle, the disposition of the magnetization in the grain as it reverses with the applied field can be determined. Results obtained with a typical square-loop ferrite composition are presented and discussed.
Theoretical and Experimental Characteristics of a Ferromagnetic Amplifier Using Longitudinal Pumping
Authors: Denton R. T.
Published: March 2008

A ferromagnetic parametric amplifier requiring fractional watts of pump power has been developed and investigated experimentally. The amplifier employs magnetostatic modes as resonances which are parametrically pumped by a longitudinal rf magnetic field. A theoretical discussion of the characteristics of longitudinal parametric pumping on the magnetostatic modes is presented including selection rules for determining which pairs of modes can be pumped and an expression for the threshold pump field required for pumping the modes to oscillation. A relation for the gain-bandwidth product of the amplifier is derived, and it is shown how the coupling to the modes must be adjusted to maximize the gain-bandwidth. A model of the amplifier has been built which utilizes X-band pump power and amplifies at C-band frequencies. The signal circuit is a coaxial line with a loop connected from the center conductor around a sphere of yttrium iron garnet providing coupling to the magnetostatic modes. Results are presented of measurements at two different pump frequencies. In addition, several mechanisms are suggested as possible sources of noise in this amplifier.
Compact uhf Isolator
Authors: Swartz D. Bruce
Published: March 2008

The fundamental characteristics and structure of a strip transmission line isolator which operates to frequencies as low as 200 Mc are reported. This structure does not utilize dielectric material as a mode distorting material to create the necessary conditions for nonreciprocal wave propagation, but instead depends on the asymmetrical placement of the ferromagnetic material on the center conductor. Isolation-to-insertion loss ratios of better than 36 to 0.4 db have been achieved at 725 Mc, while isolation peaks of 35 db to less than 1 db insertion loss have been obtained at frequencies as low as 375 Mc. The over-all length of the device with the above characteristics was 612 in. and recent evidence indicates that this can be substantially reduced.
Synthesis and Properties of Ferromagnetic Chromium Oxide
Authors: Swoboda T. J. , Arthur Paul , Cox N. L. , Ingraham J. N. , Oppegard A. L. , Sadler M. S.
Published: March 2008

Ferromagnetic chromium oxides of high purity have been synthesized by thermal decomposition of chromium trioxide in the presence of water at elevated pressure. These materials consist entirely of a rutile-type crystalline phase with cell constants a0 = 4.41±0.01 A and c0 = 2.91±0.01 A and have compositions that are very close to the exact stoichiometry of the dioxide, CrO2. Saturation specific magnetizations of these oxides are in the range of 98–100 emu/g at room temperature and their Curie temperatures are about 126°C. By using different reaction conditions, it is possible to obtain either microcrystalline particles from 3–10 μ in length and from 1–3 μ in width or single crystals of fractional millimeter size that are suitable for physical studies. In addition, elongated single-domain crystals only 0.5–1.5 μ in length and with length-to-width ratios of 8:1 or higher can also be obtained merely by adding catalytic amounts of Sb2O3 or RuO2 under hydrothermal synthesis conditions.
Effect of Cobalt Oxide in Porous Nickel Ferrites at Very High Frequency
Authors: Remde Harry F.
Published: March 2008

Very high frequency measurements of a series of porous, low-loss ferrites (NiO(1−x)CoOxFe2O2) are described. In many cases, a resonance-type dispersion appears. Comparison of the data with theory indicates that the dispersion results not from domain rotation but from high-frequency wall resonance. Extrapolation of the data for x = 0 to theoretical density gives results which are consistent with single-crystal measurements suggesting that the loss in porous nickel ferrite occurs in small, relatively perfect regions or grains.
Effect of Indium Substitution in Yttrium Iron Garnet. High Permeability Garnets
Authors: Cunningham J. Richard , Anderson Elmer E.
Published: March 2008

Initial studies on the effect of small substitutions of indium for iron in polycrystalline yttrium iron garnet showed a substantial increase in the initial permeability over that of YIG. Since previous substitution of other ions has produced either little change or a decrease in the permeability, we have studied the effect of indium substitution on the garnet structure in more detail. Due to the size increase of In3+ radii over that of Fe3+,the substitution of In3+ into the garnet structure is limited to the larger of the available Fe3+ sites. The general formula can be written Y3(Fe2−xInx)Fe3O12 where x may take on values up to 2.0. X-ray determination of the lattice parameters for this series shows a linear dependence on x with an apparent change in slope for x>0.6. For x<0.65 there is no “detectable” trace of a second phase and the lattice constants vary from 12.376±0.005 A (x = 0) to 12.445±0.005 A (x = 0.6). For x = 0.65 a small perovskitephase is present, which becomes more apparent with larger x. Since the lattice constant of the garnet phase in the two-phased samples does increase with x, it appears that x will enter the garnet structure for x>0.65. However, repeated firings at various temperatures have so far failed to remove the perovskite phase. The relative initial complex permeability μ* was measured over a frequency range from 103 to 2×109 cps on high density toroids. Increases in μ0′, the low-frequency value of μ′, over that of YIG were found for all of the single-phased garnets in the series. A plot of μ0′ as a function of x shows an essentially linear increase from μ0′ = 112 for x = 0 (YIG) to μ0′ = 518 for x = 0.6. Measurements of μ0′ as a function of temperature up to the Curie point for this series are also presented. Magnetic moment measurements were made from −196°C to the Curie temperature for this series. As in the case of other substitutions for Fe3+, the substitution of In3+ resulted in a decided decrease in the Curie temperature from 278±2°C for YIG to Tc = 148±2°C for x = 0.6. The room temperature moment is only slightly higher than that of YIG (6.8μB). On the basis of comparison of their thermal magnetic properties, it could be expected that Sc3+ substitution in small amounts would also produce a rise in μ0′. The increase in μ0′ is attributed to the lowering of the Curie temperature while the magnetic moment is held nearly constant or slightly increased.
Ferrite System for Application at Lower Microwave Frequencies
Authors: Jefferson Clinton F. , West Russell G.
Published: March 2008

The ferrimagnetic system (LiFe)1−0.5a−0.5xZnxFe2a−yTi1−aAlyO4 is found to form a single-phase solid solution for the investigated values 0≤a≤l, 0≤x≤0.1, and 0≤y≤0.l5. For approximately 0.2≤a≤0.4,the system exhibits relatively high Curie temperatures and properties compatible with the requirements of ferrites for utilization in nonresonant devices at the lower microwave frequencies.
Neutron Diffraction Study of Metallic Erbium
Authors: Cable J. W. , Wollan E. O. , Koehler W. C. , Wilkinson M. K.
Published: March 2008

Neutron diffraction measurements were made on erbium single crystals in the temperature range 298°–4.2°K. The material is antiferromagnetic below 80°K and ferromagnetic below 20°K. In the antiferromagnetic region, the magnetic scattering consists of satellite reflections corresponding to a modulation of the magnetic scattering amplitude along the c axis. The spacing and intensity distribution of these satellites show two distinct subregions of antiferromagnetism. In the upper region, between 80° and 52°K, the data suggest a sinusoidal modulation of the magnitude of the c-axis component of magnetic moment with a period of 3.5 c0. Between 52° and 20°K the wavelength of the modulation varies continuously from 3.5° c0to 4.0 c0. In addition, there is a squaring up of the modulation and a simultaneous ordering of the component of the moment normal to the c axis. Below 20°K the material is basically ferromagnetic with a moment of 7.2 μB directed parallel to the c axis.
Antiferromagnetism of α-Mn and Its Alloys
Authors: Arrott Anthony , Coles B. R.
Published: March 2008

Low-temperature magnetic isotherms of α-Mn and its alloys with Fe, N, and H have been examined. Hysteresis loops and effects of cooling in an applied field are reported. Similar properties are found for single crystals of Cu-Mn. It is pointed out that the spin density wave mechanism of antiferromagnetism,proposed by Overhauser, provides explanations for these phenomena. Neutron diffraction data are reinterpreted and provide further evidence for spin density waves in α-Mn and its alloys.
Remarks on the Magnetic Properties of Au-Mn System
Authors: Sato Hiroshi
Published: March 2008

The nature of the interaction between Mn atoms which is responsible for the helical magnetic structure and the metamagnetic behavior of Au2Mn is examined by analyzing the magnetic behavior of Au-Mn system in general. From the comparison of the magnetic structure of Au2Mn and that of Au4Mn, the magnetic dipole interaction is suggested as one of the possible main weak interactions which connects the successive layers of Mn atoms of Au2Mn.
Magnetic Susceptibility of FeCl2·4H2O at Low Temperatures
Authors: Pierce R. D. , Friedberg S. A.
Published: March 2008

The magnetic susceptibility of powdered FeCl2·4H2O has been measured between 1.3° and 4.2°K and from 14° to 21°K by an ac mutual-inductance method. A maximum, apparently associated with an anti-ferromagnetic-paramagnetic transition, is found near 1.6°K. In the hydrogen region, a Curie-Weiss law is obeyed, the Curie constant yielding a splitting factor g = 2.19 for the Fe++ ion if its effective spin is assumed to be S = 2.
Anisotropy in Nickel-Iron Films
Authors: Smith D. O.
Published: March 2008

The magnetic and optical anisotropies of evaporated iron-nickel films deposited at an angle to the substrate normal are found to be sensitive to the rate of deposition and the orientation of the magnetization M during deposition. It is postulated that crystallite elongation toward the vapor beam or in the direction of M occurs. Study of spatial inhomogeneities in the normal-incidence M-induced anisotropy field Hk is an aid in understanding the origin of this anisotropy and the switching behavior of films. Small-angle dispersion of Hk is attributed to local deviation from isotropy of the isotropic tension present in films; measurements support this model. Magnitude dispersion is estimated from rotational hysteresis experiments. Large-angle dispersion of a special type has been identified wherein certain regions of a film have an easy axis perpendicular to the field present during deposition, i.e., Hk is negative in these regions. For alloy compositions within a few percent of 83% Ni and 17% Fe, the normalized wall coercive force hw = Hw/Hk has significance beyond the defining concepts. Thus, hw is a measure of resonance linewidth and an internal field inferred from resonance data; for hw>1, a unique “locking”phenomenon occurs. Bitter-pattern studies of quasi-static switching show that negative-Hk regions are present and that hw is in some sense a measure of these regions. A tentative model forM-induced anisotropy which qualitatively explains both positive and negative Hk is proposed which invokes directed pairs of iron atoms and strain anisotropy arising from elongated crystallites. In nonlocking films, quasi-static switching by coherent rotation is broken up by labyrinth domains consisting of alternating regions of switched and unswitched M. Propagation of these domains is postulated to be caused by dispersion in the magnitude and orientation of Hk. If a pulsed reversing field exceeds the switching threshold of all regions of the film, a transition from labyrinth switching to coherent switching should occur, as has been observed experimentally.
Magnetic Anisotropies of Nickel Films Evaporated and Measured at 10−8 mm Hg and Below
Authors: Graham C. D. , Lommel J. M.
Published: March 2008

The magnetic anisotropies in evaporated polycrystalline nickel films have been measured with a torque magnetometer over a range of fields from 10 to 2000 oe. The films are deposited in a vacuum better than 10−8 mm Hg, and the measurements are carried out in the vacuum system at pressures below 10−9 mm. The magnitude of the induced uniaxial anisotropy has been measured as a function of temperature up to the Curie point of nickel (360°C), and the kinetics of the magnetic annealing process have been measured from room temperature to 200°C. The anisotropy Ku decreases roughly linearly with temperature above room temperature, reaching zero near the Curie temperature. If f is the fraction of the annealing process completed at a given temperature, we find that 1−f = exp(−t/τ)13, and 1/τ = 1/τ0 exp(−9000/RT).
Anisotropy Rotation in Thin Permalloy Films at Room Temperature
Authors: Matcovich T. , Korostoff E. , Schmeckenbecher A.
Published: March 2008

It has been observed that the magnetic anisotropy direction of certain thin Permalloy films prepared by the thermal decomposition of nickel and iron carbonyls can be rotated through 90 deg at room temperature by fields less than 10 oe. The experimental conditions under which these films were prepared suggest that this phenomenon is due to the presence of carbon. The relaxation time for the rotation of the anisotropy axis was calculated from the time dependence of the induction and found to be 10 msec. A simple model has been developed which relates the anisotropy rotation to specific domain wall configurations and to the establishment of a “directional order” among interstitial carbon atoms.
Some Properties of Uniaxial Permalloy Films Prepared by Cathodic Sputtering
Authors: Francombe M. H. , Noreika A. J.
Published: March 2008

A preliminary study has been made of the magnetic and structural properties of Permalloy films prepared by cathodic sputtering. Films of the nonmagnetostrictive Ni:Fe::81:19 composition were deposited by sputtering in argon both from solid Permalloy cathodes and from copper cathodes which had previously been electroplated with Permalloy. Using a gas pressure of 100 μ, with the electrode potential 3500 v and a discharge current 150 ma, a deposition rate of about 15 A/sec is obtained. When deposited in an applied field of 20 oe, the films display uniaxial anisotropy with Hc ≈ 2.5 oe and Hk/Hc ≈ 1.5. An evaluation of the uniformity of film thickness, reproducibility of coercive force, and alignment of the magnetic easy axis indicates that films prepared by this method would be suitable for use in planar memory matrices.
Magnetic Thin Films Prepared by Sputtering
Authors: Kay Eric
Published: March 2008

Experimental study of magnetic thin films prepared by sputtering in a glow discharge environment showed that crystal structure and chemical purity, as well as particle size and surface morphology, can be controlled. Different physical properties, including B-H characteristics, can be reproducibily obtained by the location of the collecting substrate with respect to the characteristic zones of the glow discharge; e.g.,Crookes dark space, negative glow, positive column, etc. This is the result of variations in deposition rate and energy distribution of the material arriving at the substrate, as well as variations in intensity of electron bombardment and the consequent temperature of the substrate. Typical results on nickel and iron filmsare reported. In contrast to several reports in the literature, ferromagnetic fcc nickel films were deposited directly by sputtering. Completely unoriented, polycrystalline bcc Fe films were prepared in which Br/Bs∼1, Hc∼250 oe, and Br∼20 000oe; i.e., the magnetic characteristics were quite different from those obtained by high vacuum evaporation.
Effect of Magnetic Annealing on the Properties of (110) [001] Oriented 3 14% Silicon-Iron Strip
Authors: Fiedler H. C. , Pry R. H.
Published: March 2008

Polycrystalline 3 14% silicon-iron strip with (110) [001] texture was heat-treated in a magnetic field. Both ac and dc properties were investigated before and after magnetic annealing with the field parallel to the 〈100〉, 〈110〉, and 〈111〉 directions. Distinct improvement in properties was obtained, particularly in the 〈110〉 and 〈111〉 directions. This improvement is the result of the realignment of domain boundaries to 〈100〉 directions that more nearly coincide with the direction of the applied field. The anisotropy energy that arises from the magnetic annealing is about 900 ergs/cm3, which is but a small fraction of the magnetocrystalline anisotropy energy of this material.
Recent Developments in the Field of Elongated Single-Domain Iron and Iron-Cobalt Permanent Magnets
Authors: Falk R. B. , Hooper G. D. , Studders R. J.
Published: March 2008

The experimental physical and magnetic properties of elongated single-domain permanent magnets have been previously reported and are briefly reviewed with respect to their means of preparation. A successful process is described for making ESD magnets available commercially at a limited initial rate. The material produced is described and contains elongated single-domain particles of iron or iron-cobalt embedded in a metallic matrix to protect them from environmental attack. Maximum magnetic energies of 2.2 megagauss-oersteds for iron and 3.6 megagauss-oersteds for iron-cobalt are available.
Properties of Multidomain Particles
Authors: Amar Henri
Published: March 2008

The theoretical interpretation of the size-dependence of the coercive force Hc(x) of one ferromagnetic powders and thin films is still an unsolved problem. Kittel and Néel's treatments are discussed, and some recent work of the author along similar lines is presented. An alternative heuristic approach is suggested, leading to an expression Hc = const × (x2+b2)−1 and is compared to some of the recent experimental data.
Y Circulator
Authors: Chait Herman N. , Curry Thornton R.
Published: March 2008

It is well known that the field distribution in a rectangular wave guide containing a magnetized ferrite can be asymmetrical even though the physical configuration is symmetrical. By properly choosing the ferrite, its shape, and location, it is possible to concentrate the energy on one side of the wave guide. Reversing the field or changing the direction of propagation will cause the energy to concentrate on the other side of the wave guide. This phenomenon has been utilized to construct a new type of circulator. A ferrite post has been placed at the junction of three wave guides intersecting at 120 degrees. The dc field is applied transverse to the broad side of the wave guide. Circulator action can be obtained by using a ferrite rod of the correct size and applying a dc field of the proper magnitude. Similar results have been obtained by using single and double slab configurations as well as with wedges.

A wave-guide switch can be obtained by reversing the direction of the applied field. Results to date indicate that it is possible to build this Y-type circulator with a loss less than 0.5 db and isolations and reflections of greater than 20 db over a 300-megacyle band at X band. A four-port junction operating on this same principle is also under investigation.
The Reggia-Spencer Microwave Phase Shifter
Authors: Weiss Jerald A.
Published: March 2008

The essential properties of the wave-guide phase shifter reported by Reggia and Spencer are explained by means of a composite phenomenological model which incorporates the two dominating effects: the elliptic wave-guide symmetry and a dielectric wave-guide effect. The model provides an advantageous starting point for more precise calculations, as well as a qualitative guide to further device development. It also sheds further light on Faraday rotation and its associated interference effect under conditions of elliptic symmetry.
Ferromagnetic Resonance g Factor to Order (kR)2
Authors: Mercereau J. E.
Published: March 2008

The static approximation, ∇×H=0, for the normal modes of a nonconducting ferromagnetic sphere can be improved in an iterative fashion by calculating the displacement current generated by the motion of the “static” fields and using this current as the source of vorticity in the next higher approximation to the actual field. This procedure has been carried out to (kR0)2 for the “uniform” mode of ferromagnetic resonance.
Experimental Determination of the Hyperfine Coupling in Ferromagnetic Metals and Alloys
Authors: Kurti Nicholas
Published: March 2008

Methods for the experimental determination of hyperfine coupling in ferromagnetics based on specific heat measurements and on the observation of anisotropic γ emission are described. The results for cobalt, cobalt-nickel, and cobalt-iron alloys are presented and discussed in the light of recent ideas about the electronic structures of these ferromagnetic metals and alloys. The hyperfine coupling in metallic terbium is found to be nearly the same as for Tb3+ in terbium ethyl sulfate, a small difference being tentatively attributed to a difference in the 4f orbit radii in the two cases.
Will Photoelectrons from Magnetic Metals be Polarized?
Authors: Dayhoff E. S.
Published: March 2008

Photoelectrons obtained from magnetic metals are expected to show a magnetic polarization or spin alignment under favorable conditions. Arguments are given for expecting the degree of alignment to be much greater than that characterizing the average d-shell electron in the metal when the light has a wavelength near the threshold. Furthermore the orientation of the photoelectrons may be either with or against the magnetization of the metal depending upon details of its band structure. A discussion is given of depolarization by scattering in the metal which appears to be insignificant. It is concluded that a high degree of polarization (perhaps greater than 50%) is possible with favorable metals.