bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of Magnets Composed of Elongated Single-Domain Iron Particles
Authors: Yamartino E. J. , Broadley H. R. , Lever R. C.
Published: March 2008

The magnetic and physical stability of permanent magnets compacted from elongated single domain iron particles in metallic and organic matrices under various environmental conditions are reported. Changes resulting from two years exposure to 95% relative cycling humidity and 100°C were measured. The influence of powder compacting temperatures, pressures, powder size, and additives are reported. Compacts with lead matrices exposed to 100°C and 95% relative humidity showed gradual magnetic and dimensional changes from insignificant variations after one month to maximums of 0.5% over a two-year period. These results compared favorably with results obtained for Alnico V magnets subjected to identical conditions. Temperatures of 200° and 250°C produced magnetic changes in the order of 1% after one month with physical degradation occurring after two months at 250°C. Magnetic changes of 1% and weight and volume changes in the order of 2% occurred in organic matrix magnets after one month at 100°C. The magnetic changes resulted from a slow oxidation of the iron particles which caused a small decrease of intrinsic saturation induction and an increase in coercive force.
High Power Effects in Ferrite Slabs at X Band
Authors: Martin Ronald L.
Published: March 2008

Measurements are reported of the attenuation at 9360 mc of full height ferrite slabs in wave guide as a function of ferrite length up to input powers of 120 kw. The ferrites were transversely magnetized to the field for subsidiary resonance. Above the critical power level for the subsidiary resonance the output power was a linear function of the input power with a slope such that the attenuation of that portion of the input power above the critical power was 7.8 db/in. The phase change through the ferrite region was essentially independent of power.
Study of a Microwave Ferrimagnetic Multiple Signal Conversion Process
Authors: Skomal E. N. , Medina M. A.
Published: March 2008

A multiple signal conversion process has been observed in ferrimagnetic materials at microwave frequencies. The second harmonic of the input frequency is generated in a magnetized ferrite and caused to mix with the fundamental frequency in the specimen generating the harmonic. A portion of the upper side band power arising from mixing of the fundamental frequency and its second harmonic is constructively added to the third harmonic occurring from harmonic generation. The total output power at the third harmonic is consequently increased.
Exchange Resonances in Gadolinium Iron Garnet near the Magnetic Compensation Temperature
Authors: Geschwind S. , Walker L. R.
Published: March 2008

The theory of ferrimagnetic resonance in a system of two sublattices is reviewed with emphasis upon the behavior near the compensation point. Experimental studies have been made on the gadolinium-iron garnet system in a temperature region of about 30°C which included the compensation point. The “normal” and “exchange” modes were observed and their field dependence upon temperature above and below compensation was found to be in good agreement with that predicted. From the data near compensation it was possible to derive values for the effective field acting on the gadolinium sublattice at compensation, for the difference in gyromagnetic ratios of the iron and gadolinium sublattices, and for the sum of the anisotropy fields on the latter. Microwave evidence is presented for the existence of antiferromagnetic domains at the compensation temperature.
Ionic Distribution and Ferrimagnetic Resonance in Magnesium Ferrite
Authors: Belson H. S. , Kriessman C. J.
Published: March 2008

Three different ionic distributions have been achieved in the same magnesium ferrite single crystal sphere by appropriate heat treatment. The magnetic moment, anisotropy constants, g value, and magnetic resonance half-width have been measured as a function of temperature from −200°C to +250°C for the different ionic distributions. The treatments resulted in saturation magnetizations of 1.28, 2.23, and 1.41 Bohr magnetons, respectively. At nitrogen temperature |K1| was observed to be higher for higher values of the magnetization in agreement with Folen and Rado. We find for the ferric ion cubic field splitting parameter a, the values −0.0104 cm−1 for the A site and +0.0174 cm−1 for the B site. The resonance half-width depends on the crystalline direction and was narrower in the hard [100] direction for the original ionic distribution. Successive treatments broadened the half-width in the hard direction while the easy direction [111] remained relatively unchanged. After the treatments the narrower half-width was observed in the easy direction. The room temperature g value of about 2.01 was relatively independent of the ionic distribution. A slight dependence of g value on temperature was observed.
Measurement of Ferromagnetic Relaxation by a Modulation Technique
Authors: Masters Joseph I. , Roberts Roy W.
Published: March 2008

A modulation method is introduced as a novel means of studying directly the relaxation process in the case of ferrimagnetic rare earth garnets and ferrites. The method directly measures the relaxation of the spin system of the material which is indentified with the transverse relaxation time by means of the standard equations of motion. A low-power fixed frequency X-band microwave field is amplitude modulated at an rf rate up to 50 Mc while maintaining the sample in ferromagnetic resonance. The resulting precession of the magnetic moment will then contain an rf component which is a function of both the transverse relaxation time and the frequency of the rf modulation. The precession is observed by a single turn pickup loop in which the induced microwave voltage is proportional only to the rotating component of magnetization. The rf signal resulting from demodulation of this voltage then characterizes the response of the precession to the modulation frequency of the driving microwave field. The falloff in this response with increasing modulation frequency is shown to be related to the transverse relaxation time by means of the equations of motion. The predicted form of this falloff is a function proportional to the factor (1+β2τ2)−12 from which the relaxation time τ is obtained. Certain conclusions may be drawn from the excellent agreement of the experimental data with theory.
Observations on Line Width in Ferrimagnetic Resonance
Authors: White Robert L.
Published: March 2008

Line widths as a function of magnetostatic mode have been measured for Mn-Zn ferrite and YIG spheres. The data are in conflict with the predictions of current scattering type theories of magnetic relaxation. The nature and significance of the conflict is discussed, and qualitative comments on modification of the theory made.
Development of Metallurgical Structures and Magnetic Properties in Iron Silicon Alloys
Authors: Pry R. H.
Published: March 2008

A brief history of the development of silicon iron alloys is given. The processes which lead to the development of strong textures of both the cube and cube-on-edge type are then reviewed and a comparison of some of the magnetic properties of textured silicon iron is presented. It is concluded that major technological and scientific opportunities still lie in the understanding of mechanism of texture development.
Magnetic Properties and Grain Structure of Mn-Zn Ferrites
Authors: Heister W.
Published: March 2008

The relations between sintering temperature, grain size, and magnetic properties of a manganese zinc ferrite of composition MnO:ZnO:Fe2O3 = 28:19:53 are reported. With proper preparation, very low loss materials can be obtained.
Antiferromagnetic Magnon Dispersion Law and Bloch Wall Energies in Ferromagnets and Antiferromagnets
Authors: Orbach R.
Published: March 2008

The exact eigenstates of the exchange Hamiltonian H = 2J  ∑ ι (Sι⋅Sι+1−14) are found for short chains of 4, 6, 8, and 10 atoms of spin 12. A linear dispersion law for magnons in an antiferromagnet is exhibited by the energy spectrum. The periodic boundary conditions are then removed and the ends of the chain held fixed, both parallel or antiparallel. The energy of the 180° Bloch wall is computed and compared with the classical result. It is found that the semiclassical ferromagnetic wall is a good approximation to the exact wall. The energy of the semiclassical antiferromagnetic wall is not a very good approximation to the exact wall energy, but the semiclassical energy appears to have the correct dependence on the wall thickness.
Electromagnetic Support Arrangement with Three-Dimensional Control. II. Experimental
Authors: Fosque Hugh S. , Miller Glenn
Published: March 2008

The first gradient coil configuration described in Part I of this paper has been constructed. In this system the axis of one pair of gradient coils is parallel to the magnetizing field. The details of the mechanical, magnetic, optical, and electronic aspects of this implementation will be presented and discussed.
Shape Anisotropy in a Wide-Range Gaussmeter
Authors: Luborsky F. E. , Mendelsohn L. I.
Published: March 2008

A direct-reading, wide-range, stable gaussmeter is described. It consists of a thin ferromagnetic film mounted on a shaft. This film reacts with a magnetic field to produce a torque whose magnitude is a function of the applied field intensity. The magnetic torque developed is indicated by the angular rotation of the shaft restrained by a spiral spring. Because the magnetic torque is derived from shape anisotropy of the film, the instrument has three most valuable characteristics. First, it cannot be decalibrated by any magnetic field; second, it can cover any useful range from 200 to 20 000 gauss; finally the gaussmeter can be used for alternating as well as static fields.

An analysis of the torque-angle characteristics of this instrument has been made assuming that the magnitude of the film magnetization is uniform and constant and that its direction varies with the field direction and magnitude. Stoner and Wohlfarth's analysis for the ellipsoid which precludes domain boundary formation is used to calculate the anisotropy torque as a function of the applied field. The discrepancies between theory and experiment can be accounted for. Thus, the analysis should prove of interest to those engaged in research on thin films, while the gaussmeter itself has proved a valuable tool for those working with magnetic fields.
Anisotropy and Coercivity in Thin Films
Authors: Kriessman C. J. , Belson Henry S. , Edelman F. H.
Published: March 2008

An arbitrary classification on thin films into three types may be made on the basis of the relative values of the anisotropy field, HK, and the intrinsic coercive force of the material, HI. These three types are (A) HK>H1=0, (B) HK=0; HI≠0, and (C) HI>HK≠0. In case (A) the magnetization will seek the easy direction in the absence of an applied field and the film will have a rectangular hysteresis loop in the easy direction only. Certain films have isotropic magnetic properties in all directions. The magnetization in such films will remain in any direction to which it is moved by a field larger than the coercive force. These films are therefore classified as HK=0 films. The third type of film has rectangular hysteresis loops in all directions but different apparent coercive forces, HF, in different directions.
Properties of Permalloy Films Having a Magnetoelastic Easy Axis Normal to the Film
Authors: Huber Ernest E. , Smith Donald O.
Published: March 2008

Internal isotropic strain in Permalloy films having a negative magnetoelastic constant creates a magnetoelastic easy axis normal to the film. Below a critical thickness tc such films are single domain in the film plane and have a square B-H loop; above this thickness new configurations are established, characterized by a B-H loop of special form and having relaxation properties. Above tc the Bitter pattern is “mottled” and continues so even in the presence of a 10 000 oe field. A domain structure is proposed in qualitative agreement with experiment; mottling is interpreted in terms of centers of microstrain.
Influence of Substrate Processing on the Magnetic Properties and Reproducibility of Evaporated Nickel-Iron Films
Authors: Behrndt K. H. , Maddocks F. S.
Published: March 2008

The properties of evaporated nickel-iron films, deposited on substrates cleaned with detergent only, were observed to vary widely from one evaporation run to another and even within a run. This erratic variation is believed to be due partially to inhomogeneities in the surface structure of the substrates. Several other substrate cleaning techniques were evaluated for their effectiveness in reducing this variation in film properties. As a result, both wall motion and rotational threshold have been lowered, and the average percentage variations of the magnetic properties have been considerably reduced. Because of the resulting improvement in film reproducibility, it has been possible to verify the predicted dependence of domain wall coercive force on film thickness, even for films which had been deposited in separate evaporations.
Reduction of Saturation Magnetization of γ-Fe2O3 and Fe3O4 by Pile Irradiation
Authors: Henry W. E. , Salkovitz E. I.
Published: March 2008

Through measurements of the magnetization as a function of magnetic field at 4.2°K, the absolute saturation magnetization has been obtained for γ-Fe2O3 and Fe3O4 before and after irradiation in the Brookhaven Pile. The reduction in saturation magnetization amounted to 3% and 15%, respectively for gamma iron oxide (III) and magnetite. A sample motion ballistic method was used at liquid helium temperatures and in magnetic fields up to 60 000 gauss. The reactor, operated at 14 megawatts, for approximately one month, gave total fluxes of 5.4×1018 thermal neutrons per cm2, 8.0×1017 epithermal neutrons, and 1.2×1017  fast neutrons per cm2.
Radiation Effects on the Anisotropy and Magnetostriction of Single Crystals of Several Soft Magnetic Materials Including Ni, Fe, Fe3O4, and Alloys of Ni-Fe, Si-Fe, Al-Fe, Co-Fe, and Mo-Ni-Fe
Authors: Hall R. C. , Byrnes W. S. , Crawford R. G.
Published: March 2008

Single crystals of iron, nickel, nickel-iron, silicon-iron, aluminum-iron, cobalt-iron, cobalt-nickel, molybdenum-nickel-iron, molybdenum-aluminum-iron, and nickel-cobalt-iron alloys and magnetite were tested for anisotropy and magnetostriction before and after irradiation in a nuclear pile. The dosage was 1.7×1018  total neutrons per square centimeter at about 50°C. The anisotropy of iron, nickel, silicon-iron alloys, and low-aluminum iron alloys did not change as a result of the irradiation. Crystals in order-disorder systems including nickel-iron, cobalt-iron, and high-aluminum iron alloys showed variations in anisotropy often corresponding to a decrease in order. The irradiation did change the saturation magnetostriction in the [100] and [111] crystallographic directions in many of the single crystals. Frequently these variations could be attributed to a change in the state of order. However, for some of the alloys, notably the high-aluminum iron crystals, an increase in order would be required to explain the magnetostriction data while a decrease in order would be required for the anisotropy data. Consequently, a mechanism in addition to changes in the degree of order must alter magnetic properties of soft magnetic materials as a result of neutron bombardment.
Magnetic Properties of the Rare Earth Garnets
Authors: Pauthenet R.
Published: March 2008

The magnetic properties, in static fields, of the rare earth garnets are described. The Néel molecular field theory of ferrimagnetism is extended to treat three sublattices of magnetic ions and is shown to account quantitatively for the observed properties. At low temperature, the magnetic moments of those rare earth ions which have nonzero orbital angular momentum, are much less than the moments of the free ions. This is due to the quenching of the moments of the rare earth ions by the crystalline field.
Magnetic-Ion Interaction in Gd3Mn2Ge2GaO12 and Related Garnets
Authors: Gilleo M. A. , Geller S.
Published: March 2008

The existence of appreciable (c)-(a) ferrimagnetic exchange interaction in the garnet structure has been established by the observation of ferrimagnetism in {Gd3}[Mn2](Ge2Ga)O12. [The dodecahedral, or 24(c), ions are enclosed by {}, the octahedral, or 16(a), ions by [] and the tetrahedral, or 24(d), ions by ().] The Néel temperature is about 8°K; the 1/χ vs T curve is linear for T>35°K with an intercept of −8°K at 1/χ = 0 and a Curie constant of 5.6×10−3 μB deg per oersted per formula unit. The magnetic moment at 0°K probably corresponds to 3nB{Gd3+} −2nB[Mn2+] = 11 μB because the moments observed at temperatures between 4.2 and 1.5°K extrapolate to not less than 9.6 μB at 0°K. The moment decreases for the compositions, {MnGd2}[Mn2](Ge3)O12 and {CaGd2}[Mn2](Ge3)O12, in that order. In these three cases the 1/χ vs T curves are concave downward below 20°K, as would be expected in the case of ferrimagnetism.

No spontaneous magnetization is observed in {MnY2}[Mn2](Ge3)O12 and {CaY2}[Mn2](Ge3)O12 down to 1.3°K. For these compounds the 1/χ vs T curve is concave upward below 20°K as would be expected for a weak (a)-(a) antiferromagnetic interaction. Only a very weak (c)-(a) interaction is present in the first case as a consequence of one-third occupancy of dodecahedral sites by Mn2+ ions.
On the Nature of Defects in the Magnetic Structure of Wüstite
Authors: Roth W. L.
Published: March 2008

Neutron diffraction patterns from non-stoichiometric FeO specimens obtained at 290°K and 4.2°K show the presence of defects which consist of cation vacancies on octahedral sites and interstitial cations in tetrahedral sites. The average magnetic moment per cation site is much smaller than expected. Magnetization studies show a ferromagnetic remanence is present, and the hysteresis loop is displaced along the H axis. A model is proposed in which clusters of vacancy-interstitial defect complexes form superparamagnetic islands in exchange contact with the antiferromagnetic matrix.
Theoretical Model for Cubic-to-Tetragonal Phase Transformations in Transition Metal Spinels
Authors: Wojtowicz Peter J.
Published: March 2008

According to Dunitz and Orgel, the large tetragonal distortions which occur in a number of transition metal oxides having the spinel structure are presumed to arise as a consequence of a Jahn-Teller type distortion in the immediate environment of certain transition metal ions. All the observed large distortions can be correlated with the results of this crystal field treatment on the basis of the spatial ordering of the local distortions.

In this communication we investigate the detailed properties of the transformations from tetragonal to cubic phases which are observed at elevated temperatures. An approximate model has been constructed which explicitly takes into account the interactions between local Jahn-Teller distortions about neighboring B-site transition metal cations. By the use of the usual method of statistical mechanics it has proved possible to derive the thermodynamic behavior of this model, and hence to contribute to an understanding of the cooperative nature of these transformations. The principal result of importance is the demonstration that the transformations from tetragonal to cubic spinel phases are thermodynamically of the first order. That is, a latent heat, a volume discontinuity, lattice parameter discontinuities, and a lambda anomaly in the heat capacity are to be observed at the transformation temperature. The available evidence seems to support the conclusions drawn from the model.
Effect of Orbital Degeneracy on Magnetoelastic Energy
Authors: Slonczewski J. C.
Published: March 2008

Because of the configurational instability of an orbitally degenerate system, ferrimagnetic crystals containing orbitally degenerate cations should exhibit large magnetostriction. The effect of orbital degeneracy of Co2+ on magnetostriction in cobalt-iron ferrite is calculated by means of perturbation theory. A value of 1.4×103 cm−1 for trigonal crystal field splitting of Co2+ is inferred by comparing calculated results with experimental data.
Exchange Anisotropy in Disordered Ni3Mn
Authors: Kouvel J. S. , Graham C. D.
Published: March 2008

Magnetic hysteresis loop and torque measurements were made on a disordered polycrystalline Ni3Mn specimen which had been cooled to liquid helium temperatures in a magnetic field. The hysteresis loop measured parallel to this field was shifted from its symmetrical position about the origin. The torque curves indicated a single direction (rather than axis) of easy magnetization and revealed a rotational hysteresis which continued to increase up to the highest field of measurement (8000 oe). It is concluded that the coexistence of ferromagnetism and antiferromagnetism at low temperatures in these alloys, as previoulsy reported, gives rise to exchange anisotropy interactions of the type conceived by Meiklejohn and Bean for the ferromagnetic Co-antiferromagnetic CoO system. However, important differences in detail between disordered Ni3Mn and the Co-CoO system are suggested by the experimental results.
Exchange Anisotropy in an Iron-Aluminum Alloy
Authors: Kouvel J. S.
Published: March 2008

Magnetic hysteresis loop and torque measurements were made on a polycrystalline Fe-Al alloy specimen, of 30 atomic percent Al and FeAl-type order, which had been cooled to 1.8°K in a magnetic field. The hysteresis loop measured parallel to this field was found to be asymmetrical with respect to the origin and considerably “squared up” as compared to the loop for zero field applied during cooling. The torque curves had large sinψ and somewhat smaller sin2ψ components; the rotational hysteresis, though decreasing with increasing field, was still appreciable at 8000 oe. The mechanism for these effects is believed to be an exchange anisotropy arising from a coexistence of ferromagnetism and antiferromagnetism in this Fe-Al alloy. However, the experimental results indicate significant deviations from the simple exchange anisotropy model originally proposed for the Co-CoO system.
Anisotropy Constants of Iron and Iron-Silicon Alloys at Room Temperature and Below
Authors: Graham C. D.
Published: March 2008

The magnetocrystalline anisotropy constants of iron and of alloys of 3.1 and 5.1% silicon in iron have been determined at 77, 195, and 300°K from torque measurements on single crystal disks in fields up to at least 15 000 oe.
Measurements of Rotational Magnetic Losses in Ferrites at Very Low Frequencies
Authors: Parker Hermon M. , Bullock B. W. , Dancy W. H.
Published: March 2008

For some time this laboratory has been interested in the rotational magnetic losses in ferrites at low frequencies. Apparatus has been developed and successfully operated in which these losses are measured at frequencies of the order of 0.1 cps in fields up to about 5000 gauss and over a reasonably wide temperature range. It consists of a quartz fiber torsion pendulum (the fiber perpendicular to the field) operating in a vacuum and in a reasonably constant temperature enclosure. The principle involved is that of observing the decay of free oscillations of the system, and determining the torques due to the damped oscillatory system. By a process developed in our laboratory the samples are ground into spheres to accuracies of the order of 0.1% which can be improved it desired.

In the absence of magnetic anisotropy of the sample, the method can, in principle, distinguish between Coulomb or constant torque losses (customarily assumed for rotational hysteresis loss torque) and loss torques proportional to the angular velocity (viscous). However, for all samples so far measured the anisotropy has been sufficiently large to prevent the disentangling of the Coulomb and viscous losses. (Qualitative indications of the anisotropy are obtained from the measurements and it is interesting that the losses and anisotropy seem to be proportional.) The procedure has been to assume the losses are of the constant torque type and determine them by making the best engineering fit with the decay curves.
Directional Order and Diffusion Aftereffect
Authors: Néel Louis
Published: March 2008

If an anisotropic local atomic configuration is produced in some way or other, the magnetization is stabilized in a direction related to this anisotropy, causing an additional uniaxial magnetic anisotropy. This kind of an anisotropy in the atomic configuration is called a directional ordering. This may be an anisotropic distribution of constituent atoms in substitutional ferromagnetic alloys, of interstitial atoms in a body centered cubic lattice, or of different atoms or ions on the B sites of mixed ferrites, etc. A brief explanation of the phenomena is given in each case. Also because of the coupling between the atomic arrangement and the direction of the magnetization, a relaxation phenomenon may be observed in the magnetization process which depends on the diffusion of atoms. The magnetic aftereffect arising from a small amount of carbon in α-iron is explained in detail.
Millimicrosecond Switching Properties of Ferrite Computer Elements
Authors: Shevel W. Lee
Published: March 2008

An examination of the switching properties of square loop ferrites is presented. Switching times have been studied over the range 5 μsec to 10 mμsec. The switching parameters, threshold field and switching constant, have been studied as a function of temperature and of ceramic processing. The plot of inverse of switching time versus applied fields displays three nearly linear portions for which the slopes vary by a factor of from two to ten. The inverse slope known as the switching constant of the material has therefore three values; this is interpreted as indicating three mechanisms to be responsible for the process of flux reversal, each mechanism being dominant over a certain region of the switching curve. These mechanisms are proposed as being wall motion, incoherent rotation, and coherent rotation. A model allowing a coherent rotation process is proposed. Data are presented for several ferrites which have widely varying properties.
Study of the Residual States of Ferrite Cores in Computer Memory Operation
Authors: Overn W. M. , Korkowski V. J.
Published: March 2008

The two complimentary residual states of magnetic induction used to represent binary information in a ferrite core storage system have been studied. The flux density found at the two states depends on any large fields which may have saturated the core in the past, as well as on the nature of the driving fields employed in the system. The partial-select noise amplitude is a function of the residual magnetic induction and saturation history. By applying this information, “delta” noise can be eliminated. The role of the post-write disturb pulse in preventing errors under certain abnormal operating conditions has been determined.
Inhibited Flux—A New Mode of Operation of the Three-Hole Memory Core
Authors: Baldwin J. A. , Rogers J. L.
Published: March 2008

A new method of operation of the three-hole memory core has been developed. As is the case with the coincident-flux scheme developed by IBM, read and write times may be made very short. However, by using single-line drive rather than coincident current, one need pass but one conductor through each hole. A description is given of a small memory array which uses this method.
Micromagnetics, Domains, and Resonance
Authors: Brown William Fuller
Published: March 2008

Current domain theory is based largely on the wall concept and on the 1935 paper of Landau and Lifshitz. That same paper contained the germ of another theory; in it the basic concept is a spontaneous magnetization whose direction varies continuously with position. This approach, micromagnetics, can in principle yield a complete, self-consistent theory, from which the domain and wall concepts when valid will emerge naturally, without having to be postulated. The present paper summarizes the history, accomplishments, and possibilities of such a theory. The basic partial differential equations of the theory are nonlinear; they have been attacked by four methods. (1) Study of one-dimensional cases formed the basis of traditional domain theory and of other early work. (2) Linearization of the equations proved possible in the study of the approach to saturation. (3) The Ritz method has been used in the study of fine particles and of films. (4) Numerical calculations with electronic computers have been made in some nonlinear cases. The single-domain problem, in certain of its aspects, has been rigorously solved by use of linear equations. The equilibrium equations of micromagnetostatics are closely related to dynamic equations used in the theory of ferromagnetic resonance and of spin waves.
Observations Made on Domain Walls in Thin Films
Authors: Fuller Harrison W. , Rubinstein Harvey
Published: March 2008

Domain walls in thin films of permalloy were previously found, by Huber et al., to frequently exhibit periodically spaced “cross-ties.” These wall structures have been studied in some detail in a variety of alloys and the model advanced by Huber et al., largely substantiated. Of some interest is the great sensitivity of the position of normal spin orientation between cross-ties to externally applied fields. A nonmagnetic overcoating on a thin film, and dark-field illumination with restricted-azimuth are methods which are valuable in such observations using the Bitter technique. Other characteristic wall configurations peculiar to thin ferromagnetic films have been observed and models have been devised for the magnetization distributions. Powder patterns have been observed on an iron film at intermediate stages of the slow switching of the film. The powder is seen to collect along lines perpendicular to the applied field prior to the formation of domains. A model based on magnetization buckling is suggested that establishes a connection between the lines that form before partial switching of the film, and the cross-ties that appear on domain walls after partial switching. Long Neel-wall segments have been observed on thin films by the Bitter technique, and by the use of fields in the plane of the film and at right angles to the wall. It has been found possible to reversibly change the direction of the magnetization in the Neel wall with such fields without introducing wall motion.
Correlation of Energy Losses with Perfection of Crystal Orientation and Domain Structure
Authors: Hu H. , Wiener G.
Published: March 2008

Hysteresis and core loss measurements were made on single crystal strips of the (110) [001] orientation, the commercial singly oriented material with a (110) [001] texture, and the doubly oriented material with a fair amount of (100) [001] cube texture. All these specimens were 3% Si-Fe, and has a thickness of 0.012 in. and were measured using an Epstein frame. The energy losses calculated on a domain model were compared with the experimental data. Results indicated that there is little correlation of the observed eddy-current losses with the proposed domain model, and that the energy losses may be strongly dependent on the perfection of crystal orientation.
Saturation Magnetization and Ferromagnetic Interaction in Terbium Metal
Authors: Henry Warren E.
Published: March 2008

The magnetic moment of terbium metal has been directly measured at 295°K, 100°K, 4.2°K, and 1.25°K in applied magnetic fields up to 70 000 gauss. In the liquid helium range, (∂M/∂T)H is zero. Between 35 000 gauss and 70 000, (∂M/∂H)T = (αβ2/ΔE) = 1.04×10−5 Bohr magneton per atom per gauss for 100°K and for the liquid helium range. At 1.25°K and 70 000 gauss, the magnetization is 7.5 Bohr magnetons per atom of terbium. This is perhaps near saturation. At 295°K the magnetization is linear up to about 45 000 gauss and shows a slight beginning saturation at higher fields. At 60 000 gauss the magnetization is 1.53 Bohr magnetons per atom of terbium. From the magnetization curve at 295°K (in the paramagnetic range) and a Brillouin function for the terbium atom in the F67 ground state, a molecular exchange field of 700 000 gauss is calculated. A sample motion ballistic technique is used to measure magnetic moments.
The influence of collective behavior on the magnetic and heating properties of iron oxide nanoparticles
Authors: Dennis C. L. , Jackson A. J. , Borchers J. A. , Ivkov R. , Foreman A. R. , Lau J. W. , Goernitz E. , Gruettner C.
Published: March 2008

Magnetic nanoparticles with a high specific absorption rate (SAR) have been developed and used in mouse models of cancer. The magnetic nanoparticles are comprised of predominantly iron oxide magnetic cores surrounded by a dextran layer for colloidal stability. The average diameter of a single particle (core plus dextran) is 92±14nm as measured by photon correlation spectroscopy. Small angle neutron scattering measurements under several H2O∕D2O contrast conditions and at varying nanoparticle concentrations have revealed three length scales: >10μm, several hundred nanometers, and tens of nanometers. The latter corresponds to the particle diameter; the several hundred nanometers corresponds to a hard sphere interaction radius of the core/shell nanoparticles; >10μm corresponds to the formation of long-range, many-particle structures held together by magnetic interactions and dextran. The long-range collective magnetic behavior appears to play a major role in enhancing the SAR. For samples having nominally equal concentrations and similar saturation magnetizations, the measured SAR is 1075W/(g of Fe) for tightly associated nanoparticles and 150W/(g of Fe) for very loosely associated nanoparticles at an applied field of 86kA∕m (1080Oe) and 150kHz.
Interpreting ultrafast molecular fragmentation dynamics with ab initio electronic structure calculations
Authors: Trallero Carlos , Pearson Brett J. , Weinacht Thomas , Gilliard Kandis , Matsika Spiridoula
Published: March 2008

High-level ab initio electronic structure calculations are used to interpret the fragmentation dynamics of CHBr2COCF3, following excitation with an intense ultrafast laser pulse. The potential energy surfaces of the ground and excited cationic states along the dissociative C–CF3 bond have been calculated using multireference second order perturbation theory methods. The calculations confirm the existence of a charge transfer resonance during the evolution of a dissociative wave packet on the ground state potential energy surface of the molecular cation and yield a detailed picture of the dissociation dynamics observed in earlier work. Comparisons of the ionic spectrum for two similar molecules support a general picture in which molecules are influenced by dynamic resonances in the cation during dissociation.
Comparing the density of states of binary Lennard-Jones glasses in bulk and film
Authors: Ghosh Jayeeta , Faller Roland
Published: March 2008

We used Wang–Landau density of states Monte Carlo to study a binary Lennard-Jones glass-forming mixture in bulk and films between noninteracting walls. Thermodynamic properties are calculated using two different ensembles and film data are compared with the bulk. Bulk properties are in good agreement with previous simulations. We confirm the formation of a glass using various properties, e.g., energy, heat capacity, and pressure with temperature. We find a change in slope in the energy per particle and pressure as a function of temperature. We do not find any defined crystal structure. A higher glass transition temperature is found for the film.
Quantum dynamics of inelastic excitations and charge transfer processes in the H++NO collisions
Authors: Amaran Saieswari , Kumar Sanjay
Published: March 2008

State-resolved differential cross section, integral cross section, average vibrational energy transfer, and the relative transition probability are computed for the H++NO system using our newly obtained ab initio potential energy surfaces (PES) at the multireference configuration interaction level of accuracy employing the correlation consistent polarized valence triple zeta basis set. The quantum dynamics is treated within the vibrational close-coupling rotational infinite-order sudden approximation using the coupled ground state and first excited state ab initio quasidiabatic PES. The computed collision attributes for the inelastic vibrational excitation are compared with the state-to-state scattering data available at Ec.m.=9.5eV and Ec.m.=29.03eV and are found to be in overall good agreement with those of the experiments. The results for the vibrational charge transfer processes at these collision energies are also presented.
Generalized Bloch analysis and propagators on Riemannian manifolds with a discrete symmetry
Authors: Kocábová P. , Šťovíček P.
Published: March 2008

We consider an invariant quantum Hamiltonian H=−ΔLB+V in the L2 space based on a Riemannian manifold M̃ with a countable discrete symmetry group Γ. Typically, M̃ is the universal covering space of a multiply connected Riemannian manifold M and Γ is the fundamental group of M. On the one hand, following the basic step of the Bloch analysis, one decomposes the L2 space over M̃ into a direct integral of Hilbert spaces formed by equivariant functions on M̃. The Hamiltonian H decomposes correspondingly, with each component HΛ being defined by a quasiperiodic boundary condition. The quasiperiodic boundary conditions are in turn determined by irreducible unitary representations Λ of Γ. On the other hand, fixing a quasiperiodic boundary condition (i.e., a unitary representation Λ of Γ) one can express the corresponding propagator in terms of the propagator associated with the Hamiltonian H. We discuss these procedures in detail and show that in a sense they are mutually inverse.
Magnetic coupling of pinned, asymmetric CoPt∕Ru∕CoFe trilayers
Authors: Yu Chengtao , Javorek Bryan , Pechan Michael J. , Maat S.
Published: March 2008

Magnetic exchange coupling in pinned, asymmetric CoPt18(50)∕Ru(x)∕CoFe16(38) trilayers with 0⩽x⩽25Å has been investigated with magnetometry and ferromagnetic resonance. We found the parameters associated with coupling (remanence, coerctivity, and resonance position) to be oscillatory as a function of Ru thickness with extrema at x=7Å [antiparallel (AP)], 14Å [parallel(P)], and 20Å (AP), consistent with observations for Ru spacer material in unpinned, more symmetric systems. Utilizing analysis methods unique to pinned systems with resonance arising from the soft layer only, we were able to extract coupling strengths of 0.55, −0.29, and 0.27erg∕cm2 at Ru thicknesses of 7, 14, and 20Å, respectively. Noteworthy in the analysis method is the ability to extract P coupling strength of both signs from magnetization data. The resonance linewidth correlates with coupling, where minimum relaxation rates occur at low coupling strengths. Variable temperature magnetization loops revealed that the exchange coupling monotonically increases with decreasing temperatures.
Tailoring magnetic anisotropy at the ferromagnetic/ferroelectric interface
Authors: Duan Chun-Gang , Velev Julian P. , Sabirianov R. F. , Mei W. N. , Jaswal S. S. , Tsymbal E. Y.
Published: March 2008

It is predicted that magnetic anisotropy of a thin magnetic film may be affected by the polarization of a ferroelectric material. Using a Fe∕BaTiO3 bilayer as a representative model and performing first-principles calculations, we demonstrate that a reversal of the electric polarization of BaTiO3 produces a sizable change in magnetic anisotropy energy of Fe films. Tailoring the magnetic anisotropy of a nanomagnet by an adjacent ferroelectric material may yield entirely new device concepts, such as electric-field controlled magnetic data storage.
Origin of conductive surface layer in annealed ZnO
Authors: Look D. C. , Claflin B. , Smith H. E.
Published: March 2008

The highly conductive surface layers found in nearly all as-grown or annealed bulk ZnO wafers are studied by temperature-dependent Hall-effect and secondary-ion mass spectroscopy (SIMS) measurements. In this work, we have used annealing in N2 at 900°C, and forming gas (5% H2 in N2) at 600°C, to cause a large enough surface conduction that SIMS measurements can be reliably employed. The increased near-surface donor density, as determined from two-layer Hall-effect modeling, is consistent with an increased near-surface concentration of Al, Ga, and In atoms, resulting from diffusion. There is no evidence for participation of any donors involving H.
Acoustic wave transmission through a bull’s eye structure
Authors: Mei Jun , Hou Bo , Ke Manzhu , Peng Shasha , Jia Han , Liu Zhengyou , Shi Jing , Wen Weijia , Sheng Ping
Published: March 2008

We study experimentally and theoretically acoustic transmission through a bull’s eye structure, consisting of a central hole with concentric grooves imprinted on both sides of a thin brass plate. At wavelength slightly larger than the groove periodicity, a transmission peak was observed for normally incident acoustic wave, with excellent collimation (only ±2° divergence) at far field. This phenomenon is a manifestation of the two-dimensional circular version of structure-factor induced resonant transmission. Theoretical predictions based on this mechanism are in good agreement with the experiments.
Unpicking Environmental Policy Integration with Tales from Waste Management
Authors: Watson Matthew , Bulkeley Harriet , Hudson Ray
Published: March 2008

Through an exploration of UK municipal waste policy, this paper examines debates on environmental policy integration (EPI) and governance. We argue that this policy arena has been characterised by modes of vertical integration, which have failed to promote the horizontal integration required to move beyond the limits of anachronistic institutional structures and have failed to achieve the paradigm shift needed to make meaningful progress towards sustainability. Through this analysis we develop three critical arguments. First, that the analysis of EPI requires attention to embedded paradigms, structures, and dynamics at all levels of governance, emphasising the importance of incorporating subnational levels of governing to EPI analyses. Second, that both analysis of and arguments for EPI need to engage more fully with broader dynamics of governing and to recognise the coexistence of contradictory processes of integration. Finally, we sound a note of caution in relation to calls for EPI. In the messy, dynamic, and multilevel reality in which EPI has to be implemented, such calls must recognise both sustainability and policy integration as iterative processes rather than as predetermined blueprints.
Governing Agri-Environmental Schemes: Lessons to Be Learned from the New Institutional-Economics Approach
Authors: Smits Marie-José , Driessen Peter , Glasbergen Pieter
Published: March 2008

The authors analyze agri-environmental schemes (AES) from the perspective of new institutional economics (NIE). The field of NIE studies the effect of institutions on the decisions of economic actors. Policy is intended to shape institutions and thus influence behavior. NIE is therefore particularly suitable for the analysis of policy programs such as AES. Their aim is to explain some of the management problems that have arisen in AES and to contribute to finding solutions by using insights from NIE. To this end a specific Dutch AES is used as a case study, in which a number of administrative problems are analyzed. These problems prove to be similar to those that have been identified in other European AES, and are related to the ecological efficacy of this particular type of policy program, its economic efficiency, its administrative sustainability, and the level of sociopolitical support it enjoys. The explanation for the problems identified is based on NIE; this approach is also used to identify solutions. The solutions derived from this theory are then compared with the solutions that have been applied in reality. The authors conclude with a discussion of what these lessons imply for AES in general.
Analysing the Impact of Objective 1 Funding in Europe: A Review
Authors: Gripaios Peter , Bishop Paul , Hart Trevor , McVittie Eric
Published: March 2008

This paper examines the impact of Objective 1 funding in Europe in reducing country and regional disparities in gross value added per capita by presenting a critical review of both empirical studies and end-of-term programme reports. In practice, it is very difficult to establish impact effects because it is hard to establish the counterfactual. This difficulty arises as a consequence of different theoretical predictions as to what would happen in the absence of intervention, overlapping funding streams, and the regional impact of other policies such as European integration. There are also evaluation problems caused by data inadequacies and noise. Even so, the balance of evidence suggests that Objective 1 funding has had remarkably little demonstrable impact and there is, therefore, a strong case for reform.
Public-Private Partnership: On the Edge of Project and Process Management. Insights from Dutch Practice: The Sijtwende Spatial Development Project
Authors: Edelenbos Jurian , Teisman Geert R
Published: March 2008

The aim of this paper is to describe and analyze the management strategies of cooperation in public-private partnerships (PPPs) in spatial planning. We describe a specific case study: the Dutch location development project ‘Sijtwende’. We deal with the main question of what this case teaches us about the management of complex processes of cooperation between public and private partners. We will describe the difficulties in the cooperation. Furthermore, we will look for important breakthroughs in the process of collaborative development of the area. In this paper we combine theoretical thoughts on PPP models, and management and empirical insights from out in-depth case study, in order to find balances in using project and process management strategies for managing complex spatial planning processes.
Frequency stabilization using fuzzy logic based controller for multi-area power system
Authors: Mathur H.D. , Manjunath H.V.
Published: March 2008

In this paper, a fuzzy logic controller is proposed for load frequency control problem of electrical power system. The fuzzy controller is constructed as a set of control rules and the control signal is directly deduced from the knowledge base and the fuzzy inference. The study has been designed for a two area interconnected power system. A comparison among a conventional proportional integral (PI) controller, some other fuzzy gain scheduling controllers and the proposed fuzzy controller is presented and it has been shown that proposed controller can generate the best dynamic response following a step load change. Robustness of proposed controller is achieved by analyzing the system response with varying system parameters.
Cadmium uptake and distribution in tomato plants (Lycopersicon esculentum Mill)
Authors: Cherian S. , Ramachandran V. , Sudhakaran S. , Nair H.
Published: March 2008

The growth responses and accumulation of heavy metal cadmium (Cd) was studied in tomato plants. Tomato seedlings were raised in sand-culture and watered with nutrient solution containing cadmium (in the form of CdCl2) at doses ranging from 0 to 7.12 mM. At low concentrations, there was no marked growth reduction in terms of fresh and dry mass. However, the highest concentration (7.12 mM) of cadmium depressed growth in terms of fresh and dry mass and caused reduction in chlorophyll content. Sodium Dodecyl Sulfate Page Gel Electrophoresis (SDS-PAGE) of proteins showed the expression of low molecular weight proteins (~18, ~30 kDa) in Cd-treated plants when compared to control. Among the different plant parts examined for Cd accumulation, the root tissue showed maximum accumulation. The uptake, distribution and possible implications of cadmium tolerance in tomato plants are discussed.