bluuebunny/crossref_metadata_2025 huggingface dataset:
The Atomic Moments and Hyperfine Fields in Fe2Ti and Fe2Zr
Authors: Kocher C. W. , Brown P. J.
Published: April 2005

The magnetic properties of Fe2Ti and Fe2Zr, intermetallic compounds with Laves type structures, were studied using the techniques of neutron diffraction and nuclear resonance fluorescence (Mössbauer effect). Both compounds are ferromagnetic, with magnetic moments of 0.35 and 2.56 Bohr magnetons, respectively, at room temperature, and 0.92 and 3.12 Bohr magnetons, respectively, at liquid helium temperatures. A magnetic form factor for the iron atoms in Fe2Zr was determined. The nuclear resonance fluorescence experiments gave measures of the magnetic fields at the iron nuclei. At room temperature, the field for Fe2Zr was 190±10 kgauss, while that for Fe2Ti was very low, less than 5 kgauss. The relation between the atomic magnetic moments and the magnetic fields at the nuclei is discussed.
Internal Magnetic Fields in Nickel-Rich Nickel-Cobalt Alloys
Authors: Bennett Lawrence H. , Streever Ralph L.
Published: April 2005

The nuclear magnetic resonances of both the Ni61 nuclei and the Co59 nuclei have been observed in a series of ferromagnetic nickel alloy powders containing up to 2.0 atomic percent cobalt. The room temperature value of the magnetic field at the site of the Co59 nucleus in any of these alloys is found to be about 111 koe, much smaller than the 211-koe field at a Co59 site in pure cobalt. This is also considerably smaller in magnitude than the magnetic field at the nickel site in either the alloy or in pure nickel, which, assuming a Ni61 nuclear moment of 0.30 nuclear magnetons, is about 170 koe. The linewidths of both the nickel and cobalt resonances increase with concentration with no detectable shift in frequency. The temperature dependence of the Co59 resonance frequency in a nickel alloy containing 0.59 atomic percent cobalt has been measured, and found to be different fron that of Ni61 in pure nickel and in the alloy.
Inhomogeneous Coherent Magnetization Rotation in Thin Magnetic Films
Authors: Leaver K. D. , Prutton M.
Published: April 2005

Reversal processes in a continuous, thin, uniaxial magnetic film have been studied. The applied field was produced by a narrow strip conductor laid over the film and parallel to its easy axis. A hysteresis loop technique is described for measuring the magnetization distribution under the strip. Gradual changes in the orientation of the magnetization over distances comparable to the strip width are reported. Internal demagnetizing fields are postulated as being significant in causing this distribution.
Support and Extension of the Rotational Model of Thin Film Magnetization
Authors: Schwenker J. E. , Long T. R.
Published: April 2005

This paper describes the magnetic behavior of some thin permalloy films in terms of the rotational model of Stoner and Wohlfarth. Experimental evidence is shown for the existence of a single domain whose orientation is dependent upon the applied field as postulated in the model. Measured orientations agree closely tations agree closely with the predicted ones. Phenomenological explanations for certain observed deviations from the model are given. A modification of the model can be used to account for the deviations and leads to a qualitative understanding of the low-speed region of switching behavior. The films used were flat, evaporated, 81–19 NiFe films about 1000 A thick and films of similar composition about 10 000 A thick, electroplated on a 5-mil-diam wire.
Constriction of Hard Direction Hysteresis Loops in Thin Permalloy Films
Authors: Middelhoek S.
Published: April 2005

According to single domain theory, thin Permalloy films with uniaxial anisotropy should have straight hard direction M-H loops without hysteresis. Practically, however, the M-H loops of almost all films are open, when the ac field is applied exactly in the hard direction and the earth's magnetic field is carefully compensated. Moreover, films thicker than about 800 A often show hard direction hysteresis loops which are constricted at the origin.

As is well known, magnetization reversal in the hard direction is associated with the splitting up of the film into a great number of long domains parallel to the easy axis. Whether the walls separating these domains are of the Bloch or Néel type depends upon the strength of the applied field. It will be shown that the constricted loops can theoretically be constructed when, in addition to the anisotropy energy and the energy of the magnetization in the applied field, the energy of these walls is considered. Bitter observations of the reversal process confirm the theory, showing that the constriction is actually a result of Neél-Bloch-Néel wall transitions.
Bitter Patterns on Single-Crystal Thin Films of Iron and Nickel
Authors: Sato H. , Toth R. S. , Astrue R. W.
Published: April 2005

Basic domain structures of epitaxially grown single crystals of Fe and Ni were investigated by the Bitter pattern technique. Films of these materials were obtained by evaporation onto freshly cleaved MgO single crystals heated to an appropriate temperature in a vacuum of 10−5mm Hg or less. The nature of the resulting films was examined using reflection electron diffraction. The Bitter patterns were obtained with the metal films on the substrate. From the mode of epitaxy, the structure of the domains and the direction of the moments were determined with respect to the orientation of the substrate. The cleavage surface of the substrate is not perfectly flat, but contains rather large steps as well as tear lines, and these defects are clearly observable in the powder patterns. The relations between such imperfections and the domain patterns are discussed. In addition, the patterns show signs of the existence of matching strain between the metal film and the substrate. The effect of the strain becomes more important as the film thickness decreases, as shown by small intricate domains that are formed. The importance of the 90° wall over the 180° wall in the case of thin films with cubic symmetry is emphasized.
Electron Microscope Study of the Roughness of Permalloy Films Using Surface Replication
Authors: Baltz Alfred
Published: April 2005

Permalloy films evaporated at normal and oblique incidence to a substrate were examined by replication of their surfaces. Electron micrographs revealed chains of particles perpendicular to the incident beam. The degree of alignment and the lengths of the chains depended upon the angle of incidence and the film thickness. A statistical analysis of the micrographs was made. The magnetic data showed a discrepancy between the magnetic thickness and the optical thickness for oblique incidence films.
The Nature of One-Ion Models of the Ferrimagnetic Anisotropy
Authors: Wojtowicz Peter J.
Published: April 2005

Considerable progress has been made toward the understanding of the origin and characteristics of the ferrimagnetic anisotropy through the introduction of the so-called ``one-ion models.'' In this paper the nature of the one-ion model is examined from the point of view of formal statistical mechanics. The purpose is to establish the relationship between the one-ion models and the rigorous theory, to derive a formulation for correction terms, and to determine the conditions under which one-ion theories will be applicable. Under the assumption that the Hamiltonian contains isotropic pair-exchange interactions plus single-ion anisotropy operators alone, the formal theory demonstrates that the anisotropic free energy cannot, in general, be decomposed into a sum of single-ion contributions. It is shown, however, that a one-ion theory based on the correct single-spin density operator will be adequate in certain restricted circumstances. The correction terms to this one-ion theory are found to consist of fluctuations in the expectation values of multiplets of ions and thus represent n-ion contributions. A criterion for the applicability of the one-ion theory has been constructed in terms of the magnitudes of the anisotropy energy and the Curie temperature.
Neutron Diffraction Study of Magnetic Ordering in Thulium
Authors: Koehler W. C. , Cable J. W. , Wollan E. O. , Wilkinson M. K.
Published: April 2005

Neutron diffraction measurements have been made on a single-crystal specimen of metallic thulium at temperatures ranging from 293° to 4.2°K. In the temperature range between 38° and 56°K the magnetic structure of thulium is similar to that observed for the high temperature form of erbium; namely, a simple oscillating z-component type antiferromagnetic structure. Below 38°K additional satellite reflections are observed in the diffraction patterns from which it is inferred that the sinusoidal modulation is modified below this temperature. At 4.2°K the normal lattice reflections show an increase in intensity in zero field which is consistent with a mean magnetic moment per thulium atom of approximately one Bohr magneton directed parallel to the c axis. The low temperature magnetic structure which is proposed for thulium is one in which the moments are parallel to the c axis of the crystal but change their orientations according to the sequence 4, 3, 4, 3 …. The fundamental period of the modulation remains constant over the entire range of temperature at a value corresponding to 3.5 a3 periods.
Neutron Diffraction Studies on Europium Metal
Authors: Olsen C. E. , Nereson N. G. , Arnold G. P.
Published: April 2005

Neutron diffraction investigations have been made on metallic europium which show the metal to be antiferromagnetic with a Néel temperature of 87°±1°K. The observed magnetic reflections can be interpreted in terms of a helical spin structure having a pitch of 3.60 a0 and a helix axis in the (100) direction or an amplitude modulated structure in the (100) direction having a periodicity of 3.60 a0. Between 20° and 87°K, within experimental error, the intensities of the magnetic reflections are proportional to (TN—T)½, where TN is the Néel temperature. The helix pitch is not a function of temperature.
Lattice Theory of Spin Configuration
Authors: Bertaut E. F.
Published: April 2005

In the frame of a given crystallographic symmetry a matrix ζ(k) is constructed, the eigenvectors and eigenvalues of which are directly related to the spin configuration and magnetic exchange energy, respectively. For Bravais lattices the matrix equation reduces to Villain's equation.

When chemical and magnetic unit cells coincide, the eigenvectors of ζ(0) are shown to be identical to the ``basis of irreducible representations'' used by Turov and Dzialoshinski in the construction of an invariant Hamiltonian.

The usefulness of both methods is discussed. The matrix theory is more general in the sense that it remains valid for magnetic cells different from the chemical one. Although the theory presented here starts from conventional crystallographic symmetry, it contains all the configurations possible in the so-called magnetic groups and even those not contained there (helical configurations).

The theory includes isotropic as well as anisotropic (crystalline field, dipolar, pseudodipolar, antisymmetric) coupling in the order 2 approximation.

Various examples of magnetic structures in the fields of perovskites, ilmenites, spinels, garnets, etc., are presented.
Ferromagnetic Resonances in Thin Films
Authors: Chen D. , Morrish A. H.
Published: April 2005

The ferromagnetic resonance spectra of thin films of Permalloy and other materials have been investigated. Frequently more than one maximum in the resonance line is observed. The evidence from various experiments indicates that films with more than one resonance peak are stratified. A simple model in which two layers of film are coupled via the dipole-dipole interaction is considered.
Rotatable Anisotropy in Composite Films
Authors: Lommel J. M. , Graham C. D.
Published: April 2005

The anisotropy in the plane of the film of thin films of Ni evaporated on Mo-covered substrates and of oxidized Ni films has been measured as a function of field and temperature. At intermediate fields, 200–1200 oe, a large rotatable anisotropy is found, about an order of magnitude larger than the usual magnetic annealing anisotropy. At higher fields the rotatable anisotropy disappears and only the magnetic annealing anisotropy remains. The temperature dependence of the rotatable anisotropy indicates a connection with the antiferromagnetic character of NiO.
Ferromagnetic Resonance in Single-Crystal Nickel Films
Authors: Pomerantz M. , Freedman J. F. , Suits J. C.
Published: April 2005

Ferromagnetic resonance measurements have been carried out on single-crystal nickel films obtained by epitaxial evaporation on NaCl under various evaporation conditions. Resonance measurements on thin films by previous investigators have yielded anomalous values of 4πM which have tentatively been attributed to stress in the films. In this paper it is shown that there is a second factor which must be taken in consideration to explain the shift in resonance peak.

Films that were grown at high temperatures (400°C) and in good vacuum (10−10 mm Hg) exhibited an apparent saturation magnetization only 60–70% of the bulk value. This is in accord with the results of ferromagnetic resonance experiments of Kuriyama et al., who attempted to explain their results by the presence of large tensile stresses in the films. However, electron microscope studies of films grown under the above conditions indicated that the films formed discrete, well-separated islands of nickel. The observed particle sizes are such that the demagnetizing factor perpendicular to the film is 60–70% of the value for a continuous planar film. This implies that the shift in the resonance peak was caused not by stresses but by a lowering of the demagnetizing field resulting from the discrete particle growth.

To further substantiate this, continuous films grown at lower temperatures (300°C) and in technical vacuum (10−5 mm Hg) exhibited a magnetization approximately 60% higher than the bulk material values. X-ray diffraction indicated the presence of large compressive stresses in these films. That the increased magnetization was induced by these compressive stresses was convincingly shown by the decrease of the saturation magnetization to bulk value when the stress was relieved by the introduction of water vapor into the cavity. No such change in the external field at resonance was observed for the discontinuous films under a similar exposure to water vapor.
Isotropic Stress Measurements in Permalloy Films
Authors: Weiss G. P. , Smith D. O.
Published: April 2005

Isotropic stress measurements in Permalloy films have been carried out as a function of thickness, rate of deposition, and substrate temperature. The measurements were made by clamping one end of a substrate consisting of a thin strip of glass or mica and observing the deflection of the free end during deposition. Results indicate that the stress is independent of thickness in the range 100–2000 A. However, depending upon the values of the other deposition parameters, one may observe either tensile, compressive, or zero stress.
Magnetization of Localized States in Metals
Authors: Wolff P. A. , Anderson P. W. , Clogston A. M. , Matthias B. T. , Peter M. , Williams H. J.
Published: April 2005

A study has been made of the magnetic properties of dilute solutions of iron in various nonmagnetic 4d series elements and alloys. In some cases the iron atoms possess a localized magnetic moment which manifests itself as an inverse temperature dependence in the susceptibility of the solution. The occurrence of the moment is determined by the valence electron concentration in the solute element (or alloy). As a function of this quantity one finds portions of the 4d series in which localized moments are strictly absent, interspersed by regions—one centered near Mo, the other in the vicinity of Rh and Pd—in which magnetization occurs and at whose edges the moments appear almost discontinuously.

This behavior may be understood in terms of a theoretical model in which the magnetization is ascribed to a virtual level, of the type proposed by Friedel, of the iron atom. Polarization occurs when the virtual level lies near the Fermi level and is sufficiently sharp in energy. A self-consistent Hartree-Fock calculation indicates that under these circumstances the impurity atom develops an exchange potential which splits the level—causing it to have different energies for spin-up and spin-down electrons and thus giving rise to magnetization. The model gives a qualitative description of the experiments and, in particular, is able to account for the fact that the impurity atoms sometimes carry a moment that is a fraction of a Bohr magneton.
Temperature Dependence of YIG Magnetization
Authors: Solt Irvin H.
Published: April 2005

The temperature dependence of the saturation magnetization, 4πM, has been measured for pure, polished YIG spheres in the temperature range from 4–50°K. The technique used involved measuring the magnetic field separation of the 210 and 220 magnetostatic modes as a function of temperature. The mode spacing is equal simply to 4πM/5. This method offers a high degree of precision since the linewidths are less than 1 gauss and the separation of the two modes is the order of 500 gauss. Data were taken for several samples and with the external magnetic field oriented in both the [100] and [111] directions. The experimental results have been fitted to the theoretical expression of Dyson. Only the first-order correction term to Bloch's equation was necessary, the result being M=M0(1−8.19×10−6T32−1.03×10−7T52). A fit to the T32 term alone is definitely excluded.
Substitutions of Divalent Transition Metal Ions in Yttrium Iron Garnet
Authors: Geller S. , Williams H. J. , Sherwood R. C. , Espinosa G. P.
Published: April 2005

Various amounts of the divalent ions of manganese, iron, cobalt, and nickel have been substituted for trivalent iron in yttrium iron garnet. The effect of substitution of Fe2+ or Mn2+ ions in dodecahedral sites has also been studied. Electrical balance was accomplished by the simultaneous substitution of tetravalent silicon or germanium. Under these conditions, it is concluded that the divalent ions prefer octahedral sites.

The great affinity of silicon for the tetrahedral sites in the garnets results in the reduction of trivalent to divalent iron at high temperatures even in air atmosphere when appropriate amounts of finely divided silica are present. In Y3Fex2+Fe5−2x3+SixO12, the maximum attainable value of x (under the conditions of our experiments) appears to be 0.45. In attempting to put Fe2+ ions into dodecahedral sites, greatest success was attained when there was also some in the octahedral sites as in {Y2.9Fe0.12+}[Fe0.32+Fe1.73+](Fe2.63+Si0.4)O12. The 0.1 was the maximum amount that could be put into the dodecahedral sites.

Although, it appears that the Co2+ ion is the easiest to substitute into yttrium iron garnet, it is perhaps the most difficult to understand, and only a few of the results on experiments with this ion are included.

In all substitutions of divalent magnetic ions not involving the dodecahedral sites, the 0°K moments are smaller than those calculated on the basis of the simplest interaction model. Several possible explanations are explored; a plausible one is the random canting of some tetrahedral ion moments resulting from weaker interaction with the octahedral divalent ions. The possibility that some of the divalent ions enter tetrahedral sites is not entirely excluded especially in the case of the Co2+ ion.

The divalent magnetic ions do not behave like the trivalent magnetic lanthanide ions when substituted in the dodecahedral sites. They appear not to contribute to the net spontaneous moment appreciably.
Low Temperature Anisotropy of Manganese-Iron Ferrites
Authors: Palmer Wilfred
Published: April 2005

The anisotropy of the composition system MnxFe3−xO4, 0.40≤x≤1.80, has been measured between 4.2° and 77°K by the torque method, supplementing previous measurements on this system by Penoyer and Shafer between 77° and 313°K. The anisotropy curves for 0.4≤x≤1.25 show a minimum below 110°K and appear to be the summation of a number of components of different sign and different temperature dependence—negative components which decrease in magnitude relatively slowly with increasing temperature and positive components which decrease more rapidly. Over most of the composition range studied K1 is negative at 4.2°K, but at x=0.80 the magnitude of the positive, low temperature contribution is sufficient to change the sign of K1 from negative to positive at 34°K. In the region x≤1.0, this contribution can be attributed to the presence of Fe2+ ions, but such an explanation is not applicable to the positive contributions observed in compositions for which x≥1.25 and in which there is no Fe2+. For 1.25≤x≤1.80, negative values of K1 at 4.2°K of unexpectedly large magnitude (<−3.7×105ergs/cm3) are observed. Unlike values at 77°K in this composition region, these values of K1 are of too large a magnitude to be attributed to the splitting of the 3d levels of Fe3+ ions in a cubic crystalline field.
Rare-Earth Ruthenates
Authors: Aléonard R. , Bertaut E. F. , Montmory M. C. , Pauthenet R.
Published: April 2005

In the pyrochlore compounds Ru2M2O7 (where M=Pr, Nd, Gd, Tb, Dy, Ho, and Y), RuIV contributes to the Curie constant 1 instead of the value 3 which would be expected for a d4 state with g=2 and j=2.
Recent Developments in Soft Magnetic Alloys
Authors: Adams Edmond
Published: April 2005

The present status of soft magnetic alloys used in power generation, communication, and special devices applications will be reviewed with emphasis on future prospects for their improvement. Although the study of microscopic structure of magnetic materials has led to important advances, present and future improvements require an understanding of the fundamental processes of magnetization and a study of submicroscopic and atomic influences.

The bulk of present day magnetic materials is based on alloys of iron with silicon, aluminum, nickel, and cobalt in varying proportions. Their quality has been constantly upgraded by better control of purity and composition through improvements in melting, processing, and annealing practices. Some examples of how each of these factors affects the ultimate magnetic properties of soft magnetic alloys will be given. Brief summaries will also be presented on the magnetic properties of current soft magnetic materials and how they relate to modern devices. Some interesting properties of magnetic alloys based on iron, silicon and/or aluminum will be reported. The development of a hardenable, corrosion and abrasion resistant nonmagnetic alloy based on a ductile intermetallic compound TiNi will also be disclosed.
Magnetic Properties of Tape-Wound Cores of High-Purity 3% Silicon-Iron with the (110)[001] Texture
Authors: Walter J. L.
Published: April 2005

Tapes, 1 mil thick, with sharp (110)[001] textures have been prepared from high-purity 3% silicon-iron. Surface energy driving forces were utilized to obtain the texture in the impurity-free silicon-iron.

Magnetic properties of wound cores were measured at 60, 400, and 1000 cps. Exceptionally high values of peak induction, residual induction, and squareness, compared to ordinary silicon-iron, were obtained. Losses and excitation were comparable to 1-mil Deltamax properties.

In a half-wave magnetic amplifier, the silicon-iron cores produced as much as 22% higher current output and 40% higher gain than did equivalent Deltamax cores.
Cooling Rate Effect on Initial Permeability of 4–79 Molybdenum Permalloy
Authors: Lykens Armand A.
Published: April 2005

This paper shows the combined effects of Ni and Mo on the optimum cooling rate of 4–79 molybdenum Permalloy and provides an empirical equation for calculating this rate (CRopt) for highest 60 cycle initial permeability at B=40 gauss (u0). Cold-rolled strip was obtained from heats of the Carpenter Steel Company's HyMu 80 with Ni between 79.29 to 80.63% and Mo between 4.08 to 4.44%. Before cooling rate studies were run, duplicate ring lamination samples from each heat were thoroughly purified by annealing in hydrogen at 2050°F to remove carbon and other nonmetallics. This was done to obtain the true effects of Ni and Mo on the u0 —cooling rate relationship. Magnetic measurements were made after each four hours at temperature until the u0 of each heat stabilized. An average cooling rate of 150°F/hr through the critical ordering temperature range was employed. As annealing time increased, u0 gradually increased and then stabilized for each heat at various values between 30 500 and 43 250. The stabilized samples, when repeatedly heated to 2050°F in hydrogen and cooled at different rates between 60° and 810°F/hr, displayed values of CRopt between 100° to 600°F/hr. As the CRopt decreased, the peak of the u0—cooling rate curve became more abrupt. The following regression equation was calculated: CRopt (°F/hr) = −26201.2+365.0 (%Ni) −633.3 (%Mo). The standard deviation of the difference between the observed and the predicted values was calculated to be 45°F/hr. The Mo has nearly twice the influence as Ni on the CRopt but in an opposing direction.
Magnetocrystalline Anisotropy of Rare-Earth Iron Garnets
Authors: Pearson R. F.
Published: April 2005

This paper will review recent anisotropy data, deduced from static and resonance measurements, on the rare-earth iron garnets of formula 5Fe2O3 3M2O3, where M is Y, Gd, Yb, Er, Sm, Tb, Dy, and Ho, respectively. Both the high temperature behavior (up to 300°K) which can be expressed in terms of the anisotropy constants K1 and K2 and the anomalous anisotropy properties which occur at liquid helium temperatures are discussed. The results are interpreted in terms of the single ion model which considers the anisotropy resulting from the effect of the combined crystal and exchange fields of the garnet on the energy levels of the individual magnetic ions, and the extent to which this model can describe the anisotropy of rare-earth iron garnets will be briefly discussed.
Ferromagnetic Resonance in Terbium-Doped Yttrium Iron Garnet
Authors: Walker L. R.
Published: April 2005

Calculations have been made on a specific model of a terbium-doped yttrium iron garnet system to determine its behavior in ferrimagnetic resonance. Good qualitative agreement has been found with the experiments of Dillon. Quantitative agreement is probably as good as can be expected in view of the fact that the crystal field has to be determined empirically in the course of the calculations.
The Contribution of Rare-Earth Ions to the Anisotropy of Iron Garnets
Authors: Calhoun B. A. , Freiser M. J. , Penoyer R. F.
Published: April 2005

The low-temperature properties, in iron garnets, of rare-earth ions with an odd number of electrons can be described by a simple model. This model represents the energy levels of the rare-earth ion by an isolated doublet which is subjected to an anisotropic exchange interaction. The complex shapes of the torque curves, predicted by the model and observed at low temperature, are represented by Fourier expansions. A small torque contribution proportional to the applied magnetic field is predicted, and evidence of its existence is observed in (YbY) and (YbGd) iron garnets. A comparison of the behavior of Yb and Dy in YIG and GdIG indicates a moderate influence of the host lattice on Yb and a drastic influence on Dy. The anisotropy anomaly observed for Yb in YIG [at 32° from [001] in the (110) plane] is not present when Yb is substituted into GdIG.
Properties of Reset Cores in Radar Pulse Transformers
Authors: Lee Reuben
Published: April 2005

This paper outlines permeability and loss measurements on large uncut toroidal cores of Hipersil and Supermendur alloys. With forced cooling, large increments of core induction can be utilized; with a reset core, pulse permeability is much higher than it is in cut cores, and alters pulse transformer design radically. At inductions up to 24 kgauss, pulse permeability of fully oriented Hipersil and Supermendur alloys were about 6000, compared to approximately 1500 for cut cores at lower flux densities. It appears practicable from these tests to operate Hipersil alloy with excursions of induction up to 30 kgauss and Supermendur alloy up to 40 kgauss, and to reduce pulse transformer weight by 80%.
A Miniaturized Ferrimagnetic High Power Coaxial Duplexer-Limiter
Authors: Clark J. , Brown J.
Published: April 2005

The device to be described in this presentation is a miniaturized high power coaxial component performing within a single package the functions of circulation, power limiting, and preselection. Attention is principally directed to the limiting and preselection functions which are accomplished through the use of a crossed-strip gyromagnetic coupler which differs from those previously reported in that the second-order nonlinear process rather than the first-order process is the basis for its operation. This limiter has been tested independently at power levels as high as 8 kw and found to exhibit a flat leakage output less than 200 mw and a spike leakage energy of about 0.5 erg. The limiter is mechanically tunable over a frequency range greater than 10% in C band. At a fixed setting the 3 db bandwidth is about 20 Mc. The recovery time of the limiter is determined by the kickback of energy from the garnet spin system. Experimental values of this quantity will be presented. The duplexer-limiter package operates at peak powers up to 40 kw into a 2:1 antenna mismatch. Input VSWR at the transmitter port is less than 1.35. Insertion loss from the transmitter port to the antenna port is less than 0.7 db. Low power insertion loss from antenna port through the limiter to the receiver port is 1.0 db.
Nonlinear Effects in Ferrite-Filled Reduced-Size Waveguide
Authors: Hickernell F. S. , Auten B. H. , Sakiotis N. G.
Published: April 2005

Nonlinear effects were investigated at 9375 Mc in ferrite-filled reduced-size rectangular waveguide with transversely applied magnetic fields. The cross-sectional area of standard X-band waveguide was reduced to as low as one-tenth its original value, maintaining approximately the same aspect ratio. Factors investigated were insertion loss, threshold power level, spike characteristics, dynamic range of limiting, and breakdown power level. These are discussed with relation to waveguide size, frequency, ferrite loading geometry, ferrite material parameters, and temperature. Thresholds as low as 3 w peak were observed using standard polycrystalline ferrite materials. It was possible to realize useable limiter configurations whose low power losses were less than 1 db. The application of these effects in the design of a compact X-band limiter are mentioned, as well as the advantages and limitations of devices utilizing these effects.
New Type of Flux-Gate Magnetometer
Authors: Geyger William A.
Published: April 2005

The use of an ordinary toroidal core without air-gap as a flux-gate magnetometer has been overlooked. A magnetometer using such a core as the field-sensitive element with semicircularly wound and differentially connected second-harmonic detector windings has been developed. The semicircle portions of a nickel-iron-alloy ring core act here like two separate cores (corresponding to the two parallel nickel-iron-alloy strips or scrolls of conventional forms of flux-gate elements), as far as second-harmonic flux components are concerned. By using tape-wound or laminated (washer-type) Supermalloy cores having i.d.-o.d. ratios in the range from 0.85 to 0.98, a sensitivity of 1000 μamp/oe or 1 v/oe can be achieved. Such ``ring-core flux-gate elements'' make it possible to: (1) use ultrathin, ⅛-mil tape and correspondingly high excitation frequencies, 10–40 kc/sec, (2) make ``point measurements'' by reducing the core diameter to 0.5 in., or less, (3) minimize the magnetizing-current requirements, (4) obtain linear characteristics, (5) eliminate memory effects, (6) facilitate matching of the magnetic characteristics of the two active parts of the flux-gate element which belong here to the same core, (7) detect very small changes in the earth's magnetic field, and (8) apply multiple detector windings on a common core. The power requirements of a portable magnetometer, operated from a 6-v battery, have been reduced to 50 mw by combining the ring-core flux-gate element with a switching-transistor magnetic-coupled multivibrator in such a way that the oscillation frequency is solely determined by the parameters of the ring core and its excitation windings.
Ferromagnetic Resonance Magnon Distribution in Yttrium Iron Garnet
Authors: Matcovich T. J. , Belson H. S. , Goldberg N. , Haas C. W.
Published: April 2005

The presence of excited magnons results in a shift of the ferromagnetic resonance frequency. Calculations of this frequency shift have been made by retaining terms in the Hamiltonian up to fourth order in the spin wave variables. The shift can be expressed in terms of the number of excited k=0 magnons and k≠0 magnons. Determination of this shift can then be used to study the magnon distribution during resonance. This frequency shift has been measured in four single-crystal yttrium iron garnet spheres at 9 Gc. The shifts are observed to be directly proportional to the rf power absorbed by the sample, positive when the dc magnetic field is in [100] direction, and negative when the dc magnetic field is in the [111] direction. These results require a distribution of k≠0 magnons dominated by magnons with 48°<Θk<60°. If it is assumed that the k≠0 magnons are degenerate with the k=0 magnons, the total number of k≠0 magnons is approximately equal to the number of k=0 magnons, and magnons in the region centered about k=1−2×105 cm−1 dominate. This result is in agreement with a prediction of the surface pit scattering model; namely, the relaxation of the k=0 magnons results in the production of k≠0 magnons with wavelength approximately equal to the pit size. The results are in disagreement with any model requiring a uniform distribution of degenerate modes.
Pulsed Critical Field Measurements in Magnetic Systems
Authors: Foner Simon , Hou Shou-Ling
Published: April 2005

Pulsed field magnetic moment measurements in several magnetic systems are briefly summarized. Particularly high sensitivity is attained for systems which exhibit a nonlinear variation of magnetization versus applied field, e.g., ``spin-flop.'' Changes of magnetization as small as 0.1 gauss could be observed with applied fields of over 100 kgauss under favorable circumstances. Critical fields for Cr2O3 and (Cr2O3)0.9·(Al2O3)0.1 from 4.2°K to about 0.95 TN and the corresponding calculated values of (2λK)½ are presented, where λ is the exchange constant and K is the anisotropy energy. The values of (2λK)½ agree with earlier antiferromagnetic resonance measurements in similar crystals. Results of measurements in antiferromagnetic MnF2, CoF2, and FeTiO3, and in metamagnetic FeCl2 and CoCl2 are briefly discussed. Application of the method to paramagnets is also indicated.
Impurity Ion Effects in the Ferrimagnetic Resonance of Ordered Lithium Ferrite
Authors: Schnitzler A. D. , Folen V. J. , Rado G. T.
Published: April 2005

Experimental results are reported on the ferrimagnetic resonance linewidth, g factor, and magnetocrystalline anisotropy field of ionically ordered lithium ferrite monocrystals containing impurity ions. The measurements were made at frequencies ranging from 16.0 to 30.9 kMc and at temperatures ranging from 4.2° to 300°K. It is shown that: (a) the temperature dependence of the g factor is proportional to 1/T at ``high'' temperatures (50∘K≲T≤300∘K) but less pronounced at ``low'' temperatures (T≲50∘K); (b) the linewidth vs temperature curves exhibit a maximum in the transition region (T ≈ 50°K) for all crystallographic directions which are not in the vicinity of [110]; (c) at 300°K the linewidth in the [111] direction increases linearly with increasing frequency; (d) all these experimental results can be interpreted on the basis of the theory of rapidly relaxing impurity ions proposed by Kittel and co-workers. In regard to the anisotropy field, it is shown experimentally that at 4.2°K anomalous peaks exist in the [110] and [112] directions of the (110) plane, and that the amplitude of the former is twice that of the latter. An analysis based on Kittel's theory of anomalous anisotropy fields is supplemented by specific assumptions to explain both of these observations as well as the other details of the angular dependence of the anisotropy field.
The Formation of Monocrystalline Alnico Magnets by Secondary Recrystalization Methods
Authors: Steinort E. , Cronk E. R. , Garvin S. J. , Tiderman H.
Published: April 2005

A brief review of the progress of the ``Alnico Art'' is given, tracing early attempts at increasing energy yield by changes in composition to present day techniques of promoting polycrystalline growth parallel to the magnetic axis. Energy product values have steadily risen to the present commercially available level of 7.5 (MGO). Since research has apparently reached a temporary impasse in further improvement in polycrystalline Alnico magnets, except by an uneconomic fabrication from a much larger initial casting or expensive foundry mold techniques an, attempt to take advantage of the 12.0 mega gauss-oe energy product available from single crystals of Alnico is an obvious solution. Two known methods of producing single crystals sufficiently large to be of practical value are described, and the obvious economic and production problems discussed. New work on a third method is described in which normal foundry techniques are used, but the formation of a single monocrystal of the entire magnet is promoted by secondary recrystallization. It is shown that if a sufficiently large grain edge strain can be induced in a polycrystalline aggregate, resulting in secondary recrystallization, formation of a single large crystal is possible. It is also shown that if a sufficiently large internal stress can be introduced by both mechanical and thermal means, the required grain-edge shift can be accomplished. The additions of normally prohibitive amounts of either carbon, nitrogen, manganese, or other ``gamma-phase'' promoting elements will serve to provide the necessary mechanical strain, and methods of controlling their effect on the magnetic results are shown. The thermal stresses are accomplished by a simple maintainance of 60–80°C gradient across the magnet poles. This process has yielded single crystals approaching ¼ lb in size whose energy product is 11.0 megagauss-oe. The practical nature of this process is discussed, and possible mass production techniques outlined.
Study of Particle Arrangements and Magnetic Domains on the Surface of Permanent Magnets
Authors: Kronenberg K. J.
Published: April 2005

Some types of permanent magnets are compacts of very small particles. Their properties depend largely on mutual magnetic influence between particles or groups of them. To determine these, more should be known about packing arrangements, orientation, separating layers, and the homogeneity of the compact. A method is described which makes surface details visible and simultaneously reveals magnetic phenomena of such compacts. The size of the compacted particles mostly requires the resolving power of an electron microscope. Special replicating techniques combine shadow-graphing and colloid application even on rough and porous surfaces.

Examples are presented of such surface studies on barium ferrite and iron-cobalt particle magnets. Surfaces of barium ferrite magnets with crystal sizes of 0.2–1 μ show indications of magnetic domains smaller than observed before, sometimes with less than 0.1 μ-width. On compacts of small elongated iron-cobalt particles, structures have become visible which indicate particle groupings varying with the methods of compacting. Colloid outlines surface pole arrangements in correlation to particle groups.
Exchange Anisotropy—A Review
Authors: Meiklejohn W. H.
Published: April 2005

Exchange anisotropy describes a magnetic interaction across the interface between two magnetic materials. A shifted hysteresis loop, sinθ torque curve, and rotational hysteresis in magnetic fields greater than 2K / Ms may result from this interaction if one of the materials is antiferromagnetic. This interaction has been found to exist between ferro-antiferromagnetic materials, ferri-antiferromagnetic materials, and ferri-ferromagnetic materials. The work of various people is discussed in terms of the expected behavior in these exchange coupled systems. Some interesting results of the exchange interaction are reviewed. These include improved properties of fine particle magnets, a memory effect in a mixed ferrimagnetic spinel, a rotatable anisotropy in thin films, and an explanation for the reverse magnetization of a deposit in the earth's crust. The interfacial conditions necessary to obtain the interaction between the two magnetic systems are discussed, and it is shown that they are met in several cases. Models are presented which yield rotational hysteresis in magnetic fields greater than 2K / Ms as has been found in all of the exchange coupled systems.
Structural and Magnetic Properties of Copper-Substituted Manganese-Aluminum Alloys
Authors: Sugihara Makoto , Tsuboya Ichiro
Published: April 2005

Magnetic properties of ternary Cu(0–12.5 at. %) — Mn(55–42.5 at. %) — Al(45%) alloys have been studied in relation to the change of the tetragonal structure from the binary Mn–Al alloy to the ternary alloys. The substitution of Mn by Cu stabilizes the ferromagnetic tetragonal phase of the Mn–Al alloys. An increase of the Cu content brings about a decrease of the Curie temperature, the intrinsic coercive force, and the ratio of remanence to saturation induction. Correspondingly, the introduction of Cu into Mn–Al alloys first reduces the axial ratio c/a of the tetragonal phase from 1.30 in the 55 at. % Mn–Al alloy to 1.20 at 10 at. % Cu, and then converts the tetragonal structure into body-centered cubic at more than 10 at. % Cu. In the latter case, the ternary alloys are ferromagnetic disregarding aging conditions.
Anomalous Magnetic Moments and Transformations in the Ordered Alloy FeRh
Authors: Kouvel J. S. , Hartelius C. C.
Published: April 2005

Magnetization and electrical resistivity measurements on an iron-rhodium alloy of approximate composition FeRh, having CsCl-type structure, confirm recent x-ray and neutron diffraction evidence for a first-order antiferromagnetic-ferromagnetic transition at about 350°K. From 350°K down to 77°K, an essentially constant, field-independent susceptibility of about 1×10−4 emu/g is observed. Above 350°K, the alloy behaves like a normal ferromagnet with a Curie point of 675°K and a saturation magnetization (extrapolated to 0°K) of 130 emu/g. This σ0 value is equivalent to an average atomic moment of 1.85 μB, or to 3.85 μB per iron atom if the rhodium moment is assumed to be zero. Alternatively, if the iron moment is taken to be 2.2 μB, the rhodium moment has to be about 1.5 μB. Qualitative results are given for the effect of high magnetic fields and pressures on the first-order transition temperature of this alloy.
Magnetic Susceptibility and Internal Friction of Tetragonal Manganese-Copper Alloys Containing 70 Percent Manganese
Authors: Schwaneke A. E. , Jensen J. W.
Published: April 2005

Relation of structure to magnetic susceptibility and internal friction is described for a 70% manganese-30% copper alloy. The aged alloy exhibits a reversible fct to fcc transition at temperatures from 20° to 140°C, depending on the amount of aging. Magnetic susceptibility apparently obeys the Curie-Weiss law but a change is observed in the temperature-susceptibility curve at the structure transition temperature. The low-stress internal friction of this alloy shows a resonance peak at the temperature of the structure change.

Aging experiments with the 70 and 80% manganese alloys give evidence that quenching of alloys containing more than 80% manganese from solid-solution temperatures does not prevent changes typical of alloys aged to initiate precipitation of alpha manganese. Thus the fct⇄fcc transformation that others have associated with the disappearance of antiferromagnetic ordering also is associated with an early stage of the alpha-manganese precipitation.
Magnetic Susceptibilities and Exchange Effects in Four Organic Free Radicals
Authors: Burgess J. H. , Rhodes R. S. , Mandel M. , Edelstein A. S.
Published: April 2005

Studies of EPR intensity and linewidth in four free radicals at temperatures between 300° and 1.5°K have shown the presence of antiferromagnetic exchange coupling. In two cases a low-temperature paramagnetism occurs following a Curie-Weiss law with positive Weiss constant. A model involving isolated spins in a magnetically dilute system is proposed to explain these results.
Nickel Aluminum Gallium Ferrites for Use at High Signal Levels
Authors: Nielsen J. W. , Zneimer J. E.
Published: April 2005

A new nickel ferrite has been developed which contains simultaneously aluminum and gallium. Compositions have been prepared according to the formula NiAlyGaxFe2−(x+y)O4. The total substitutions of gallium and aluminum have been varied from 0 to 1.2. Several ratios of aluminum to gallium have been made. The unique feature of this system is that since the gallium substitutes in the tetrahedral sites and aluminum in the octrahedral sites, the compensation point normally associated with nickel aluminum spinels can be shifted to much higher nonmagnetic ion substitutions. There exists a composition for which there is no compensation point. Measurements of saturation magnetization, Curie temperature, linewidth, and geff factor have been made. A C-band circulator-switch using one of these materials has been constructed and successfully tested at 75-kw peak power with a 0.001 duty cycle. This device was also successfully tested at a power level of 475 w cw in an ambient temperature of 85°C.
Magnetic Properties of Yttrium-Gadolinium-Aluminum-Iron Garnets
Authors: Maguire E. A. , Green J. J.
Published: April 2005

The magnetic and microwave properties of polycrystalline garnets of the Gd3−xYxFe5−yAly O12 type were investigated. Compositions of low magnetization (∼600 gauss) and narrow linewidth (∼125 oe) were found which are suitable for operation in devices where temperature compensation is required.
Spin Wave Excitation in Planar Ferrites
Authors: Bady Isidore , Schlömann Ernst
Published: April 2005

The large magnetic anisotropy field that is encountered in many planar ferrites markedly affects the rf magnetic field at which spin wave instability sets in. When the rf magnetic field is applied perpendicular to the dc field, spin wave instability can occur through the first- or second-order process. At ferromagnetic resonance, the first-order process dominates if the frequency is smaller than a characteristic frequency ωc. This characteristic frequency has been calculated for ellipsoidal samples. For most sample shapes, the anisotropy field tends to increase ωc, thus favoring the occurrence of the first-order process. In addition, the anisotropy tends to decrease the critical field at which the spin wave instability sets in. Assuming the spin wave relaxation rates to be equal in the two situations compared, we find that the second-order threshold is reduced (approximately) in the ratio of (8πM / Ha)½ for relatively high frequencies; and in the ratio of (ω/γHa)½ for relatively low frequencies. In parallel pumping, the threshold field is reduced in the ratio of 4πM / (4πM+Ha) at low biasing fields.
Frequency Doubling in Anisotropic Ferrites
Authors: Douthett D. D. , Kaufman I. , Risley A. S.
Published: April 2005

Simultaneous measurements have been made of the absorption at 8.5 kMc and of the second harmonic magnetization generated in single crystal Zn2Y. The high planar anisotropy of this ferrite enhances its frequency doubling behavior. The results agree well with the predictions of the equation of motion for the magnetization with anisotropy and losses included.