bluuebunny/crossref_metadata_2025 huggingface dataset:
High bone turnover but normal bone mineral density in women suffering from schizophrenia
Authors: Bergemann N. , Parzer P. , Mundt C. , Auler B.
Published: March 2008

Background

A potential association between schizophrenia and osteoporosis or osteopenia has recently been reported. Various factors affect bone mineral density (BMD) such as polydipsia, nicotine, alcohol abuse, lack of physical activity, an unbalanced diet, a lack of ultraviolet exposure and/or vitamin D. In addition, decreased BMD in women with schizophrenia has been attributed to drug-induced hyperprolactinaemia and/or secondary hypogonadism. This study was undertaken because empirical evidence from larger patient cohorts is limited and the data are still controversial.

Method

Seventy-two premenopausal, regularly menstruating women suffering from schizophrenia and 71 age- and sex-matched healthy controls were included in the study. Biochemical markers of bone turnover (serum osteocalcin, urinary pyridinium crosslinks), parathyroid hormone and 25-hydroxyvitamin D were measured. BMD at the femoral neck and lumbar spine was determined by dual-energy X-ray absorptiometry in a subgroup of 59 patients. In addition, 17β-oestradiol, prolactin, testosterone, gonadotrophins and dehydroepiandrosterone sulfate were measured.

Results

Compared with healthy controls, both markers of formation and resorption were increased in women with schizophrenia. However, in the subgroup of 59 patients, BMD was within the normal range. In women suffering from schizophrenia, testosterone levels were higher than in controls, and serum oestradiol levels were lower compared with the normal range.

Conclusion

Despite significantly increased bone turnover, we conclude that premenopausal and regularly menstruating women suffering from schizophrenia have normal spine and hip BMD. This may be due to the opposite effects of the various parameters influencing bone metabolism, especially of the gonadal hormones, and due to an intact coupling mechanism.
Curriculum change: an exploration of its impact upon school music in Scotland between 1978 and 2000
Authors: Davies Lloyd
Published: March 2008

The article explores curriculum change in Scottish schools between 1978 and 2000 and its impact on learning and teaching. This period produced far reaching alterations to music curriculum thinking and practice. However, there is presently only limited reference within music education literature to strategies that either support or enhance our understanding of the change process. An attempt is made to address some of these omissions, to identify the conditions that most effectively foster and manage change and so establish a clearer basis for future studies. The wider implications of music curriculum change for classroom practitioners are considered, together with conclusions and implications concerning future curriculum policy in this area.
Creating a musical world in the classroom: application of a Bourdieuan approach towards understanding teacher practice
Authors: Stakelum Mary
Published: March 2008

Whilst a rationale for the content and organisation of knowledge in a standardised curriculum may be clearly articulated at official policy level, factors may come to bear on a teacher operating at a local level which may work against the successful implementation of the curriculum on the ground. Drawing on a Bourdieuan notion of cultural field, ‘habitus’ and cultural capital to examine commonality and difference in teacher practice in an Irish primary school context, the paper reports on a study which highlights the role played by formative experiences in shaping the responses of primary teachers to performance and music literacy.
HAEMODYNAMIC CONTRIBUTIONS TO THE PATHOGENESIS OF PREECLAMPSIA AND ECLAMPSIA
Authors: BERNSTEIN IRA M , CIPOLLA MARILYN J
Published: March 2008

Current hypotheses regarding the origins of preeclampsia have focused on the “Two stage model”. This model suggests that the primary steps in the pathophysiologic sequence of preeclampsia are initiated by abnormal placentation including the classic finding of abnormal trophoblast invasion of maternal decidual spiral arteries. The second stage of the sequence includes the elaboration of a single or multiple substances from these disordered placentas which contribute to the generalized maternal systemic illness, eventually manifesting as endothelial injury, hypertension and proteinuria. Recent studies have focused on the role of pro and anti-angiogenic peptides as potential placentally derived aetiologic agents in this pathophysiologic sequence, although other placental products have been highlighted in recent research. Despite the fact that this modeling of preeclampsia has widespread support significant limitations to this hypothesis can be identified.
Germanium in mid‐ocean ridge flank hydrothermal fluids
Authors: Wheat C. Geoffrey , McManus James
Published: March 2008

We present concentrations of germanium and silicon in sediment pore waters, basaltic formation fluids, and bulk sediment from three ridge flank hydrothermal systems (RFHS). Basaltic formation fluids from warm (>30°C) RFHS have much higher Ge concentrations and Ge:Si molar ratios than overlying sediment pore waters, requiring seawater‐basalt reactions to dominate Ge concentrations in basaltic formation fluids. In contrast to warm RFHS, cool (∼20°C) RFHS have similar Ge concentrations in basal sediment pore waters and underlying basaltic formation fluids, implying that there is little net exchange between these two fluid reservoirs. Despite this low net exchange, Ge:Si molar ratios in basaltic formation fluids are elevated compared to seawater and overlying sediment pore waters, implying that seawater‐basalt reactions must influence Ge and Si cycling. Such seawater‐basalt reactions are likely associated with secondary clay formation because increases in Ge concentration scale with Mg loss from basaltic formation fluids. Processes that control Ge cycling in cold (3–10°C) RFHS are poorly constrained because our data are restricted to sediment pore waters that have been overprinted by diagenetic reactions and possibly sampling artifacts. Although net Ge fluxes from RFHS prevail over a wide temperature range, a refined estimate for the global RFHS Ge flux is currently not possible without data from cold RFHS springs or basaltic formation fluids because cold RFHS transport most of the convective heat and crustal fluid to the oceans.
Estimation of river discharge, propagation speed, and hydraulic geometry from space: Lena River, Siberia
Authors: Smith Laurence C. , Pavelsky Tamlin M.
Published: March 2008

Moderate Resolution Imaging Spectroradiometer (MODIS)–derived measurements of Lena River effective width (We) display a high predictive capacity (r2 = 0.81, mean absolute error < 25%) to forecast downstream discharge conditions at Kusur station, some 8 d and ∼700 km later. Satellite‐derived mean flow propagation speed (88 km d−1 or 1.01 m s−1) compares well with that estimated from ground data (84 km d−1 or 0.97 m s−1). Scaling analysis of a ∼300 km heavily braided study reach suggests that at length scales > 60–90 km (∼2–3 time valley width), satellite‐derived We − Q rating curves and hydraulic geometry (b exponents) converge upon stable values (b = 0.48), indicating transferability of the discharge retrieval method between different locations. Put another way, at length scales exceeding ∼60–90 km all subreaches display similar behavior everywhere. At finer reach length scales (e.g., 0.25–1 km), longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space. While at least one gauging station is required for calibration, results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems.
Lexical Representations in Children With SLI: Evidence From a Frequency-Manipulated Gating Task
Authors: Mainela-Arnold Elina , Evans Julia L. , Coady Jeffry A.
Published: March 2008

Purpose

This study investigated lexical representations of children with specific language impairment (SLI) and typically developing, chronological age-matched (CA) peers on a frequency-manipulated gating task. The study tested the hypothesis that children with SLI have holistic phonological representations of words, that is, that children with SLI would exhibit smaller effects of neighborhood density on gating durations than CA peers and that children with SLI would be as efficient as CA peers in accessing high-frequency words but that they would differ from their age-matched peers in accessing low-frequency words.

Method

Thirty-two children (ages 8;5–12;3 [years;months]) participated: 16 children with SLI and 16 typically developing peers matched on age and nonverbal IQ. Children’s word guesses after different gating durations were investigated.

Results

Contrary to predictions, no group differences in effects of distributional regularity were found: Children in both groups required equally longer acoustic chunks to access words that were low in frequency and came from dense neighborhoods. However, children with SLI appeared to vacillate between multiple word candidates at significantly later gates when compared with children in the CA group.

Conclusions

Children with SLI did not exhibit evidence for phonologically holistic lexical representations. Instead, they appeared more vulnerable to competing words.
The Acceptance of Background Noise in Adult Cochlear Implant Users
Authors: Plyler Patrick N. , Bahng Junghwa , von Hapsburg Deborah
Published: March 2008

Purpose

The purpose of this study was to determine (a) if acceptable noise levels (ANLs) are different in cochlear implant (CI) users than in listeners with normal hearing, (b) if ANLs are related to sentence reception thresholds in noise in CI users, and (c) if ANLs and subjective outcome measures are related in CI users.

Method

ANLs and the Hearing in Noise Test (HINT; M. Nilsson, S. Soli, & J. Sullivan, 1994) were examined in 9 adult CI users and 15 adult listeners with normal hearing. In addition, the Abbreviated Profile of Hearing Aid Benefit (APHAB; R. M. Cox & G. C. Alexander, 1995) and a satisfaction questionnaire were administered to CI users only.

Results

Results indicated that (a) ANLs were not significantly different for CI users and listeners with normal hearing, (b) ANLs were not correlated with HINT values for either group, (c) ANL was not significantly correlated with APHAB scores, and (d) ANL was significantly correlated with overall CI benefit on the satisfaction questionnaire.

Conclusions

CI users with large ANLs reported more benefit from implants than those with small ANLs. The results of this preliminary study of ANL in CI users suggest that ANL can be used as a tool for evaluating processing in noise in individual CI users.
Binaural Advantage for Younger and Older Adults With Normal Hearing
Authors: Dubno Judy R. , Ahlstrom Jayne B. , Horwitz Amy R.
Published: March 2008

Purpose

Three experiments measured benefit of spatial separation, benefit of binaural listening, and masking-level differences (MLDs) to assess age-related differences in binaural advantage.

Method

Participants were younger and older adults with normal hearing through 4.0 kHz. Experiment 1 compared spatial benefit with and without head shadow. Sentences were at 0
o
, and speech-shaped noise was at 0
o
, 90
o
, or ±90
o
. Experiment 2 measured binaural benefit with the near ear unplugged compared with plugged for sentences at 0
o
and masker at 90
o
. Experiment 3 measured MLDs under earphones for 0.5-kHz pure tones in Gaussian and low-noise noise, and spondees in speech-shaped noise.

Results

Spatial-separation benefit for speech did not differ significantly for younger and older adults but was smaller than predicted by an audibility-based model for older adults and larger than predicted for younger adults. Binaural listening benefit was observed for younger participants only. Tonal MLDs suggested that listeners benefit from interaural difference cues during noise dips for signals out of phase. Neither tonal nor speech MLDs differed significantly between younger and older participants.

Conclusion

Binaural processing of sentences revealed some age-related deficits in the use of interaural difference cues, whereas no deficits were observed for more simple detection or recognition tasks.
NMR and the Conduction Electron Polarization in Rare-Earth Metals
Authors: Jaccarino V.
Published: March 2008

The magnitude and sign of the conduction electron polarization in rare earth intermetallic compounds has been determined with the use of NMR techniques. Large, temperature-dependent Knight shifts of the Al27NMR were found in XA12 (X ≡ rare-earth ion). These observations may be explained by assuming that anegative exchange interaction of ∼0.1 ev exists between the localized f electrons of the rare-earth ion and the conduction electrons.
Mössbauer Effect: Applications to Magnetism
Authors: Wertheim G. K.
Published: March 2008

The Mössbauer effect, the resonant absorption of nuclear gamma rays in solids, may be used to obtain the hyperfine structure of Fe57 in magnetic materials. Experiments are performed by observing the absorption by stable Fe57 of the 14.4-kev gamma ray coming from a source which contains radioactiveFe57 produced by the decay of Co57. The experiments are not limited to naturally iron-bearing materials; other substances can be studied, provided only, that small amounts of cobalt can be introduced into lattice sites of interest. The magnetic moments of the ground and first excited states of Fe57 are known and make possible direct determination of the field at the iron nucleus once the hyperfine structure has been measured. The magnetic field at iron nuclei has been determined in the ferromagnetic transition metals (Fe 3.42×105 oe, Co 3.12×105 oe, Ni 2.80×105 oe at 0°K), but no hyperfine structure has been observed down to 4°K in the antiferromagnetic transition metals, Mn and Cr. In the case of yttrium-iron garnet the fields at the iron atoms in the two types of sites have been obtained (tetrahedral 3.9×105 oe,octahedral 4.7×105 oe). The most complete analysis so far has been made in FeF2 where the magnetic field in the antiferromagnetic state (HT = 0 = 3.40×105 oe) and the quadrupole splitting in the paramagnetic state (31.2 Mc/sec) have been obtained. Other materials under investigation are the iron oxides and some ferrites, where, for trivalent iron, fields in the vicinity of 5.0×105 oe have generally been found.
On the Contribution of the Fermi Contact Term to the Magnetic Field at the Nucleus
Authors: Watson R. E. , Freeman A. J.
Published: March 2008

The dominant source of the effective magnetic field at the nuclei in ferromagnets apparently comes from the Fermi contact contribution of the s electrons in the core. This contribution was investigated for transition element atoms and ions by means of a series of spin (or exchange) polarized Hartree-Fock calculations(calculations where one-electron orbitals of differing ms are allowed different radial dependence). Calculations were done for both free-atom and crude crystalline environments. The sensitivity of the 3s electrons to 3d behavior was found to contribute to large differences in calculated effective fields. The differences between core polarizations in metals and ions are discussed with the use of a model for metallic iron (i.e., a 3d8 configuration)which is more consistent with neutron diffraction and energy band results than the free atom 3d6 state (the spin polarized 3d8calculation shows an expanded 3d charge density but an almost unchanged spin density relative to the 3d6 results). The resultant(negative) increase in the effective field is not, however, large enough to overcome the positive contributions of the outer electrons (estimated à, la Marshall) so that although a net negative field is found it is not large enough in magnitude to agree with the Mössbauer measurements. A parallel calculation by Goodings and Heine, based on an artificially expanded 3d chargeand spin densities, is also found to be similarly deficient. Their model is discussed and shown to be incompatible with neutron experiments and energy band calculations.
Nuclear Magnetic Resonance of Fe57 in Unenriched Fe
Authors: Budnick J. I. , Bruner L. J. , Blume R. J. , Boyd E. L.
Published: March 2008

The nuclear magnetic resonance of Fe57 has been observed in iron specimens in the form of powders of various sizes, foils, and whiskers. Our results are consistent with previously reported work of Gossard,Portis, and Sandle on enriched iron, and with the work of Robert and Winter on natural iron. We find that the resonant frequency varies slightly among nominally pure iron specimens taken from different sources,suggesting that it is somewhat sensitive to impurity content. Prestrain of the specimen has a marked effect,the resonance in cold-rolled foil being very broad and weak compared to that observed in annealed foils. Observations of nuclear magnetic resonance in iron whiskers oriented both axially and transversely in the rf coil offer interesting confimation of the domain wall enhancement mechanism put forth by Gossard and Portis. The temperature dependence of the Fe57 resonance has been investigated in the range 77°–785°K.
Nuclear Magnetic Resonance in NiF2 Domain Walls
Authors: Shulman R. G.
Published: March 2008

Two additional nuclear resonances of the F19 nuclei are observed in the antiferromagnetic state of NiF2. These resonances can be observed in zero magnetic field at ν = 26.6 Mc/sec and ν = −51.2 Mc/sec. They are broad, asymmetric, and easily saturated, with an apparent value of T1∼8 sec, at 20.30°K. They correspond to internal fields along [110] and [1̄1̄0] directions respectively for H0 along [110]. These compare quite well with the theoretical values of +18.7 Mc/sec and −54.4 Mc/sec calculated from the measured interaction parameters for a spin alignment along [110] and [1̄1̄0]. These two resonances arise from F19 nuclei in the domain walls.
Classical Theory of the Ground Spin State in Spinels
Authors: Kaplan T. A. , Dwight K. , Lyons D. , Menyuk N.
Published: March 2008

An investigation of the ground state of the classical Heisenberg exchange energy in spinels has led to several new results. By means of a recent generalization of the method of Luttinger and Tisza, we have rigorously obtained the ground state in part of the exchange parameter space defined by nearest neighbor AB and BB interactions for tetragonally distorted spinels. The regions in this space where the Néel and Yafet-Kittel configurations minimize the energy are much smaller than predicted by the Yafet-Kittel six-sublattice theory. Outside of these regions, there exists a domain where the ground state is an antiferromagnetic spiral similar to those recently introduced in the literature. In still other regions, the ground stateis a new type of spiral which is ferrimagnetic. An investigation of a parameter region including cubic spinels shows that such a ferrimagnetic spiral yields an appreciably lower energy than that given by the Yafet-Kittel model and is locally stable up to a specified ratio of BB to AB interactions. The generalized Luttinger-Tisza method shows it to be the best possible ferrimagnetic spiral up to and beyond the point of instability, but fails to prove it to be the ground state. An examination of small deviations at the point of instability indicates the existence of spin configurations much more complex than the magnetic spirals proposed here.
Ferromagnetic Resonance in Piezoelectric Ga2−xFexO3
Authors: Dymanus A. , Kaminow I. P.
Published: March 2008

Microwave resonance measurements at 55 kMc and lower frequencies on Ga2−xFexO3 single crystals which are both ferromagnetic and piezoelectric have been made from room temperature to the Curie point. The crystals exhibit a large orthorhombic anisotropy with easy, intermediate, and hard directions along the orthorhombic c, a, and b axes respectively (c<a<b), Linewidths are approximately 1 koe and anisotropy fields approximately 17 koe at room temperature. The origin and representation of the anisotropy is discussed.
Ferromagnetic Resonance due to Magnetic Fields Generated by Displacement Currents in Ferrites
Authors: Bady Isidore , McCall Gilbert
Published: March 2008

The displacement current due to the interaction of the relatively high dielectric constant of a ferrite with the electric field in a waveguide generates a magnetic field which may be comparable to the transverse magnetic field in the unperturbed waveguide. Hence, a thin ferrite rod located at an E field maximum(H field minimum) may experience a strong ferromagnetic resonance absorption even though the rf magnetic field at the rod, due to the unperturbed waveguide modes, is negligible. A formula is given for the ratio of energy absorbed when the rod is at an E field max as against being at an H field max. A formula is also given for the biasing field required for resonance when the rod is at an E field max. Test results agree well with theory.
Anisotropy of the Spin-Wave Spectrum
Authors: Muller M. W. , Buffler C. R.
Published: March 2008

The frequency of a spin wave depends on its propagation vector and on the effective internal field in which it propagates. In an isotropic medium this implies that all the spin waves of a given wavelength lying on a θk cone about the effective field are degenerate. In anisotropic media this degeneracy is removed in those directions in which the minimum of the energy surface is not axially symmetric. This effect can be observed by measuring the contribution to the ferromagnetic resonance linewidth from scattering into moderate-kspin waves as a function of frequency and orientation in single crystal samples. Theoretical predictions and experimental results are given for a sphere of yttrium iron garnet.
Ferrimagnetic Resonance in a Single-Crystal Disk of Yttrium Iron Garnet
Authors: Smith Archibald W. , Watanabe Akira
Published: March 2008

The use of a disk instead of a sphere for the investigation of the uniform mode is discussed briefly. The discussion and the experiments are restricted to a disk with the dc field perpendicular to the plane, and to a single-crystal sample of YIG. Resonance measurements have been carried out on a disk 0.157 cm in diam and 0.0085 cm in thickness. The linewidth and saturation curve were determined in a shorted coaxial line by detecting changes in VSWR with a slotted line and probe. The frequency was 1980 Mc. The linewidthwas (0.78±0.05) oe, and the line shape appeared to be Lorentzian. The critical rf field for saturation was found to be (5.2±0.3)×10−3 oe by extrapolation of the 1/hrf portion of the saturation curve. The resultant linewidth of the unstable z-directed spin wave 0.08 oe. This is 20 times smaller than the value reported for a sphere at 6200 Mc.
Ferromagnetic Resonance Linewidth in Cobalt-Substituted Ferrites
Authors: Haas C. Warren , Callen Herbert B.
Published: March 2008

The resonance linewidth contribution of small concentrations of cobalt ions substituted in ferrites is investigated by computing the magnon scattering due to the variation from ion to ion of the spin-orbit interaction. The effect of the spin-orbit coupling is particularly large in the cobalt ion because it has a degenerate orbital ground state when situated in a trigonally symmetric crystalline field. The resultant linewidth is found to be of the order of 20–30 oe for each percent of cobalt introduced into a normal (noninversed) ferrite or into magnetite. For other ferrites, the effect of the cobalt ions is diminished because the nonequivalence of all octahedral-site ions destroys the trigonal symmetry of the local crystalline field and lifts the orbital groundstate degeneracy. This diminution is calculated as a function of the degree of inversion.
High-Power Characteristics of Low-Magnetization Garnets
Authors: Saunders J. H. , Green J. J.
Published: March 2008

Large signal ferromagnetic resonance measurements have been performed on low-magnetization polycrystalline garnets in which aluminum or gallium has been partially substituted for iron. Measurements have been made at 1.3, 5.5, and 9.3 kMc. For some samples the temperature was varied between 77°K and the Curie temperature. The results are in qualitative agreement with recent theories of ferromagnetic relaxation.
Resonant Frequency Shift in Ellipsoidal Samples
Authors: Matcovich T. , Belson Henry S. , Goldberg N.
Published: March 2008

A polished, ellipsoidal, single crystal, yttrium iron garnet sample with rotation axis along a [100] direction and ΔH = 1.0 oe was prepared. X-band measurements of the microwave resonant frequency were made as a function of rf power. The resonant frequency was found to shift at the rate of 41 Mc/w. The shift of the resonant frequency was related to the number of k = 0 magnons (n0) and the number of k ≠ 0 magnons (nk)by means of spin-wave theory. From this relation and the experimental data the value of nk/n0 was determined to be 2.7.
Some Investigations on Iron-Cobalt Permanent Magnet Alloys of the Vicalloy II Type
Authors: Baran W. , Breuer W. , Fahlenbrach H. , Janssen K.
Published: March 2008

A permanent magnet alloy composed of 52% Co, 8% V, 4% Cr,balance Fe was subjected to severe cold forming by drawing or rolling to produce a reduction in cross-sectional area of over 90%,and to subsequent heat treatments at temperatures varying between 20 and 700°C, after which the following properties were measured: magnetic saturation as a function of temperature in the range from −200 to +700°C; coercive force as a function of temperature in the range from −200 to +400°C; remanence;torque in the magnetic field, anisotropy energy, and longitudinal magnetostriction as a function of temperature in the range from+20 to +400°C. Vickers hardness, ultimate tensile strength,Young's modulus, and coefficient of expansion were also determined in some cases and electron micrographs of the structure taken. The permanent magnet alloy tested consists of a fine twophase structure, the body-centered cubic α phase alone being ferromagnetic above room temperature, while the second phase becomes ferromagnetic only at temperatures below room temperature. Magnetizing and demagnetizing of this alloy, too, is brought about chiefly by domain rotation. Basically, permanent magnetcharacteristics are not produced by crystal anisotropy or anisotropy of directional order but by a uniaxial anisotropy which may be either a shape or a strain anisotropy. The measured magnetic properties can be more easily explained by an anisotropy of internal stresses which in one model concept is produced by the process of α-γ transformation because of the clearcut textures of both components. There are also indications that the mutual transformation of the two structure components is coincident with noticeable shifts in chemical composition or order, particularly in the γ phase.
Anisotropic Curie Temperature
Authors: Callen Earl R.
Published: March 2008

In an anisotropic ferromagnet the Curie temperature is a function of the direction of the magnetization. The Curie temperature is high in easy directions, and can drop quite low in harder directions for large ratio of anisotropy to exchange energy. Magnetization curves as a function of temperature also depend upon the orientation. In sufficiently hard directions, the magnetization drops from a large value precipitously to zero at the Curie temperature.
Subsidiary Resonance in YIG
Authors: Hartwick T. S. , Peressini E. R. , Weiss M. T.
Published: March 2008

The real and imaginary components of susceptibility at subsidiary resonance have been measured for a polished YIG sphere at 9253 Mc. These measurements were made as a function of dc magnetic field and power level for hrf, both parallel and perpendicular to the applied magnetic field, with a cw and a pulsed pumping source. The initial increase in χ′′ with power level for a cw source is found to be much more gradual than theory would predict for the perpendicular case. Furthermore, intense relaxation oscillations are observed at high power levels for both parallel and perpendicular pumping. The real part of the susceptibility,χ′, shows a small increase for the parallel pumped case; for the perpendicular pumped case χ′ first decreases and then increases with respect to its low power value as Hdc traverses the subsidiary resonance.
Behavior of Ferro- or Ferrimagnetic Very Fine Particles
Authors: Lin C. J.
Published: March 2008

Very fine particles refer here to single-domain particles of such a size that the thermal effect on their magnetization directions is significant. If thermodynamic equilibrium is maintained during a magnetic measurement, these particles may display a quasi-paramagnetic behavior which is usually referred to as superparamagnetism. Observation of this behavior may depend on the apparatus used unless relaxation times are much shorter than the instrumental time constant. If it is assumed that equilibrium is achieved,the expressions for the initial susceptibility characterizing this behavior can be derived for the standard crystalline symmetries. While the result for random particles is well known, only the aligned crystalline cases need be examined. The experiments have been limited to the measurements of a number of random ferrite samples.
Fine-Grained Ferrites. I. Nickel Ferrite
Authors: Malinofsky W. W. , Babbitt R. W.
Published: March 2008

A process has been developed for preparing dense nickel ferrite bodies composed of grains small enough to remain single domain. The magnetic and crystallographic properties of these bodies have been determined. This was accomplished by combining two techniques, flame-spraying and hot-pressing, and investigating the effect of varying the parameters in each of these. Powder as fine as 0.02 micron was prepared of single phase nickel ferrite, which was subsequently densified by hot-pressing while maintaining the crystallite size as small as 0.06 micron (below the critical size for multidomains). The effect on the dispersion of the complex permeability as the ferrite is annealed through the critical size is shown. Properties measured included μ′and μ′′ (to 3800 Mc), Bmax, Brem, and Hc, as well as microwave properties. Of practical interest were an improvement in the temperature coefficient of initial permeability over conventionally prepared ferrite, and good linearity in the main resonance loss at high power levels at X-band. X-ray diffraction determinations of crystalline phases and crystallite sizes are given, along with measurements of apparent density. Theoretical considerations indicate domain rotation to be the mechanism responsible for the resonances observed at high frequencies.
Domains and Extreme-Value Statistics
Authors: Brown William Fuller
Published: March 2008

Consider a ferromagnetic crystal at small fields. In a domain of type i (i = 1, 2,…,n), the spontaneous magnetization lies along the ith direction of easy magnetization; the free-energy density associated with externally controlled fields is Ei, and that associated with random internal forces is εi, Postulate: at each point, ε1, ε2, …, εn are independent random variables, with a common distribution function F(x);, and the actual orientation is that of smallest Ei+εi. Let pj be the probability that a randomly chosen point is in a domain of type j. Then pj = ∫−∞∞{Πi≠j[1−F(x−Ei)]}F′(x−Ej)dx. When E1 = E2 = … = 0,the integrand is 1/n times the probability density Ψn′(x)of the smallest value among the n εi's. Under certain conditions,the distribution function Ψn(x) of the smallest value reduces asymptotically, for large n, to 1−exp[−eαn(x−un)], where F(un) = 1/n and αn = nF′(un). Under the same conditions, pi reduces asymptotically to e−αnEj/Σie−αnEi. This Boltzmann-type formula,variously “derived,” was used in an old “statistical” domain theory recently revived. Its limited success is understandable when it is interpreted as an asymptotic approximation, since n is usually only 2, 6, or 8. Use of the rigorous formula, with a reasonable form for F(x), might give better results.
Possibilities of All-Magnetic Logic
Authors: Gianola U. F.
Published: March 2008

A sequential logic circuit must have a capacity for memory, unidirectionality, and gain. The problem of obtaining these features in magnetic components is considered, and a number of approaches are described. The organization of a circuit using multiapertured cores is discussed, and a method for introducing added combinational logic in a compatible manner is described. The status of these techniques is summarized.
Domain Structures in Iron Whiskers as Observed by the Kerr Method
Authors: Fowler C. A. , Fryer E. M. , Treves D.
Published: March 2008

An improved magneto-optic Kerr instrument was used for observation of magnetic domains in iron whiskers undergoing a magnetization cycle with applied peak fields of 6000 oe, parallel to the axis of the whisker. It was found that a domain structure persisted near the tip of the whiskers even under the maximum applied field. The domain configuration at fields above 2000 oe is simple, consisting of domains magnetized perpendicular to the axis of the whisker and in the same sense around all of its lateral faces. The width of these domains decreases as the field is increased.
Antiferromagnetic Materials for Millimeter and Submillimeter Devices
Authors: Heller G. S. , Stickler J. J. , Thaxter J. B.
Published: March 2008

Owing to their high internal fields, antiferromagnetic materials have natural resonant frequencies in the millimeter and submillimeter wavelength region of the electromagnetic spectrum. Since these normal modes are circularly polarized and can be tuned by an applied magnetic field, devices similar to the usual ferrite devicesare possible at these high frequencies with the application of relatively low fields. The dynamics of a simple antiferromagnetic system are briefly reviewed and the important quantities which characterize antiferromagnetic devices are discussed. The figures of merit for antiferromagnetic resonance isolators and phase shift devices are derived. Experimental data on resonant frequency and linewidth, as well as a typical nonreciprocal resonance absorption trace showing a reverse to forward loss of 10 to 1 in chromic oxide at 140 kMc and at 77°K are presented.
Traveling-Wave Frequency Doubling in Ferrites
Authors: Auld B. A. , Shaw H. J. , Winslow D. K.
Published: March 2008

A perturbation analysis has been made of frequency doubling in a ferrite-loaded rectangular waveguide. These calculations give quantitative predictions for second-harmonic power output as a function of various parameters. The values and ranges chosen for these various parameters are the same as used in experiments which were performed to check the theory. Good correlation has been obtained between experimental results and second-order perturbation theory.
Perturbation Techniques for Miniaturized Coaxial Y-Junction Circulators
Authors: Clark John
Published: March 2008

Using theoretical synthesis procedures as a guide, systematic means were developed for constructing miniaturized coaxial Y-junction circulators at frequencies in C and X band. Subsequent investigation revealed that these techniques are useful at all frequencies down to the uhf region. Maximum realization of theoretical possibilities calls for techniques of symmetrically altering the junction that yield broad-range adjustment of the junction scattering matrix eigenvalues. Such techniques, involving dielectric loading and systematic deformation of the junction, are described. The device to be described, including permanent magnets, measures 1.5 in. in diameter, 0.75 in. in height, and weighs less than 4 oz. Using the techniques to be presented, the device can easily be made to operate as a circulator at all frequencies from approximately 4 kMc to 10 kMc. Adjusted for use over the 5.4–5.9 kMc range, the circulator exhibits isolation greater than 20 db, insertion loss less than 0.5 db, and VSWR less than 1.3. These characteristics are maintained over a temperature range from −55°C to 110°C. At 5.65 kMc the circulator was operated satisfactorily at peak powers above 25 kw and average powers in excess of 25 w. No special cooling techniques were employed.
Induced Magnetic Anisotropy Created by Magnetic or Stress Annealing of Iron-Aluminum Alloys
Authors: Birkenbell H. J. , Cahn R. W.
Published: March 2008

Polycrystalline samples of five iron-aluminum solid solutions were subjected to various heat treatments(1) in a strong magnetic field, or (2) under tensile stress. For treatment (1) the samples were in the form of cylinders, while in case (2) they were machined into this form after stress treatment. Torque-azimuth plots were obtained from each sample by means of a torque magnetometer; further heat treatments were then applied, followed again by torque measurements, to permit correction for the intrinsic anisotropy resulting from unavoidable preferred orientation of grains. The maximum value of anisotropy, whether field or stress induced, arises at 21–22 at. % aluminum. Induced anisotropy energies of up to 17000 ergs/cm3 were recorded. A variety of heat treatments were used to explore the inhibiting effect of spontaneous long- or short-range order on the development of induced anisotropy. This inhibiting effect is pronounced, and in stoichiometric Fe3Al it is possible to prevent almost completely the creation of induced anisotropy. Such inhibition is to be expected if the induced anisotropy is caused by directional order. A close correspondence is observed between the composition dependence of induced anisotropy and that of the Zener internal friction.
Preparation and Properties of Low-Loss Ferrites
Authors: Grelfer Aaron P. , Nakada Yoshinao , Lessofe Howard
Published: March 2008

Nickel-zinc ferrites containing 1–3 mole % cobalt ferrite and small additions of molybdenum oxide or vanadium oxide have been prepared with μ0Q products ranging from 50 000 at 1.0 Mc to 4500 at 60 Mc. The effect of stoichiometry, ferrous iron content, firing temperature, and firing time on the initial permeability μ0 and the magnetic quality factor Q is discussed. It is believed that a necessary condition for good high-frequency response is the domination of the resonance phenomena by a spin-rotation mechanism in preference to a domain-wall process. The nickel ferrite-zinc ferrite system appears to be unique in this respect. In properly constituted nickel-zinc ferrites, low-loss characteristics are achieved by combining a relatively high density with a low magnetocrystalline anisotropy and a very small grain size. The properties in general are intimately related to the Perminvar characteristics these compositions possess, and are interpreted in terms of the Néel-Taniguchi theory.
Neutron Diffraction Investigation of Magnetic Ordering in Dysprosium
Authors: Wilkinson M. K. , Koehler W. C. , Wollan E. O. , Cable J. W.
Published: March 2008

Neutron diffraction measurements on a single crystal of dysprosium show that the magnetic structure in the antiferromagnetic region between 179° and 87°K closely resembles a helical-type arrangement of the atomic moments. In this arrangement the moments within a hexagonal layer are aligned parallel and point in a direction perpendicular to the c axis of the crystal. The moment direction in adjacent layers is rotated by a specific angle which is dependent on the temperature of the sample. A slight modification of this structure exists below about 140°K, and a transition to ferromagnetism occurs at 87°K.
Anisotropy in Permalloy Films Evaporated at Grazing Incidence
Authors: Cohen M. S.
Published: March 2008

The magnetic and optical anisotropies observed in oblique-incidence Permalloy films show anomalous behavior for incidence angles greater than 60° (grazing incidence). In particular, the easy axis and the direction of greatest optical absorption are parallel to the vapor beam for incidence angles greater than about 70°, while they are perpendicular to this direction for smaller angles. The anomalies for grazing-incidence films are caused by a shape anisotropy differing from that previously found in lower angle oblique-incidence films. This new shape anisotropy is attributed to the elongation in the beam direction of the particles composing the crystallite chains which are found in all oblique-incidence films; such shape anisotropy has been directly observed by electron microscopy.
Rotatable Anisotropy in Thin Permalloy Films
Authors: Prosen R. J. , Holmen J. O. , Gran B. E.
Published: March 2008

Films which possess rotatable anisotropy have been observed. In these films, the easy direction of magnetization can be selected by the application of a sufficiently large magnetic field. The temperature dependence of hysteresis and resistivity have been studied. Films have also been examined by electron diffraction combined with partial etch techniques. It is concluded that a nickel oxide layer on the surface of the film is essential for the existence of rotatable anisotropy. Some mechanisms that may be responsible for this phenomenon are discussed.
Free Oscillations of the Magnetization in Permalloy Films
Authors: Wolf Peter
Published: March 2008

Free oscillations of the magnetization are excited in magnetic uniaxial Permalloy films by a small dc step pulse field with less than 0.35 nsec risetime. This field is applied perpendicularly to the magnetization and in the plane of the film. The resulting damped oscillations of the magnetization are detected by a sampling oscilloscope and investigated between 500 Mc and 1200 Mc. The eigenfrequency is determined by a dc field parallel to the magnetization and by the orientation of the easy axis. The eigenfrequencies agree reasonably with the ferromagnetic resonance frequencies of the same films. The damping constants λ evaluated from the decay time of the free oscillations and from the linewidth of ferromagnetic resonance also agree fairly well and are in the range from 100 Mc to 300 Mc. The experimental results are analyzed by means of the Landau-Lifshitz equation.
Influence of Various Heat Exposures on Alnico V. Magnets
Authors: Tenzer Rudolf K.
Published: March 2008

Alnico V magnets were exposed to temperatures between 350 and 550°C for as long as 1000 hours. Remanence was determined at room temperature intermittently during the exposures. The changes in remanence appeared to be caused by metallurgical as well as magnetic processes. The two effects were separated and it was found that the Alnico V material responds to temperatures as low as 350°C.
Shape Distribution of Magnetite Powders
Authors: Johnson Clark E. , Brown William Fuller
Published: March 2008

The shape distribution curves of single-domain magnetite powders calculated from magnetic data do not agree with those observed in the electron microscope. The Stoner-Wohlfarth theory, from which the magnetic unaveraging process was derived, ignores magnetocrystalline anisotropy. This may be one of the contributory causes to the lack of agreement. To establish this, the shape curves were measured magnetically on both acicular and equant magnetite powders at various temperatures. The magnetocrystalline anisotropy of magnetite is temperature dependent, changing from about −1 × 105 ergs/cc at room temperature to +1 × 105  ergs/cc at −165°C.

The magnetically calculated shape curves show some change with temperature; this indicates a contribution from the magnetocrystalline anisotropy.
Limitations of Elementary Mode Considerations in Ferrite Loaded Wave Guide
Authors: Fletcher R. C. , Seidel H.
Published: March 2008

A consideration of the fundamental TE modes in a wave guide containing a low-loss ferrite slab leads to a mode with a group velocity corresponding to power transfer in a single direction only. A completely reactive isolator, however, is prohibited by general energy conservation principles. We have analyzed a rectangular wave guide with a ferrite slab against one wall. We have found that there are higher order propagating modes wherever the unidirectional TE mode is cut off. Furthermore, it can be experimentally demonstrated that these modes can be excited from a simple boundary with no variations along the magnetic field. A possible mechanism for this excitation will be described. It is suggested that these modes may carry the power when the unidirectional TE mode is cut off. An experimental situation in which the proposed reactive isolator is tried will be described. Where the reactive isolator should be cut off and perfectly reflecting, it is highly absorptive. This can be explained by the lossiness of the higher order gyromagnetic modes.
Low-Loss Gyromagnetic Coupling through Single Crystal Garnets
Authors: DeGrasse R. W.
Published: March 2008

This paper describes methods of synthesizing filters and gyrators using strong coupling of a small volume of ferrimagnetic material to an electromagnetic circuit. The small volume of material is treated as a lumped element resonator and it is shown that energy can be coupled through this resonator with low loss. The device uses the material for low-loss transmission of microwave energy.

The practical realization of devices using this principle depends upon strong coupling of the material to the circuit and the use of “low-loss” materials such as single crystal garnets.

The synthesis leads to the design of physically small electronically tunable filters, compact circulators and isolators. Such techniques may also be useful for the realization of low-frequency lumped element devices. Calculations and preliminary tests indicate that devices of this type will lead to the practical realization of solid state TR cells.
Harmonic Resonances in Small Ferrimagnetic Ellipsoids
Authors: Morgenthaler Frederic R.
Published: March 2008

This paper considers the response of the magnetization of a small ferrimagnetic ellipsoid to spatially uniform rf magnetic fields of one or more frequencies. Only a few pertient cases can be considered in this short paper. The analysis is applicable to other excitations and a more complete report will be published elsewhere. Some of the work presented here duplicates that of Pippin [Proc. Inst. Radio Engrs. 44, 1054 (1956)], Jepsen, and others, but the approach to the problem is quite different and allows one to extend previous results, as well as to derive new ones.

The effects of symmetry planes and anisotropy will be considered as well as the permeability tensor for the general ellipsoid when modulation terms of the magnetization are neglected.
Ferromagnetic Resonance near the Upper Limit of the Spin Wave Manifold
Authors: Buffler C. R.
Published: March 2008

Measurements of line widths of polycrystalline garnets as a function of frequency and temperature are reported. The variation of these parameters allows the uniform precessional mode to move above the k = 0 upper limit of the spin wave manifold so that this mode is no longer degenerate with the low k value spin wave states. When this occurs the line width undergoes a radical change, since these low k states can no longer take place in the relaxation process. When the uniform precession is thus “outside” the manifold, the behavior of the line width should be attributed to the theory of Clogston, Suhl, Walker, and Anderson. When the uniform precession is “inside”the manifold, the behavior is best described by the theory of Schlömann.

It is believed that the measurements reported indicate convincingly the utility of the spin wave analysis of ferromagnetic relaxation.
Ferromagnetic Resonance in Polycrystalline Ferrites with Hexagonal Crystal Structure
Authors: Schlömann Ernst , Jones R. V.
Published: March 2008

A theory is developed for the shape of the ferromagnetic resonance line of polycrystalline ferrites with hexagonal crystal structure. The theory is applicable if the anisotropy field is much larger then the saturation magnetization. It predicts the occurrence of several absorption peaks whose locations and intensities depend on the magnitudes of the various anisotropy constants. For intermediate values of the anisotropy constants two absorption peaks should occur on the low-field side of ω/γ if K1<0; one peak should occur on each side of ω/γ if K1>0. Experimental results on various hexagonal compounds are in good qualitative agreement with the theory.