bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Magnetic First-Order Transitions
Authors: Rodbell D. S. , Bean C. P.
Published: April 2005

Some transitions between ordered and disordered magnetic states that take place via transitions of first order are tabulated. Among these transitions are some of the order-disorder type. The theoretical basis for such a transition to occur is indicated using a simple physical model that assumes: (1) a strain dependent exchange interaction and (2) a compressible lattice. The necessary condition for first-order behavior is determined, and the theory is compared to the behavior of a real material, MnAs. It is found to be in substantial agreement with the behavior of that compound. The system represented by the simple model employed here possesses ferro-, antiferro-, and paramagnetic states. The equilibrium boundaries between these states are determined in the pressure-temperature plane as an illustration of the possible transitions that may be observed with this model.
Superconducting Materials and High Magnetic Fields
Authors: Kunzler J. E.
Published: April 2005

The recent discovery that Nb3Sn remains superconducting in magnetic fields exceeding 88 kgauss while carrying current densities in excess of 100 000 amp/cm2 has stimulated widespread activity directed toward the construction of superconducting magnets and the understanding of ``hard'' superconductivity. Some of the relevant events that have transpired since the discovery of superconductivity by Onnes in 1911 are reviewed. The critical current versus magnetic field (Ic vs H) characteristics of several materials are discussed and the justification of using such measurements on small samples as a basis for magnet design is presented. Nb-Zr alloys appear useful for magnets capable of fields as large as 80–100 kgauss while Nb3Sn appears to be useful for fields of 200 kgauss. Superconducting magnets of Nb3Sn and of Nb-Zr have been constructed and tested by several laboratories. Fields as large as about 70 kgauss have been generated with Nb3Sn magnets and 60 kgauss with Nb-Zr magnets. Fields exceeding 100 kgauss have been attained by augmenting the field produced by a superconducting Nb3Sn magnet with the field from a conventional Bitter solenoid. Superconducting magnets capable of fields of at least 100 kgauss are almost a certainty and it is quite likely that magnets will eventually be constructed to produce fields of 200 kgauss. Fields of several hundred kgauss are an intriguing possibility.
Properties of Magnetic Films for Memory Systems
Authors: Bradley E. M.
Published: April 2005

The technique of using magnetic thin films in computer memory devices is reviewed, and conclusions drawn as to the properties of the film that are required for successful operation of a memory. A description is then given of a series of experiments which were designed to determine the best compromise in properties. Particular importance is attached to the easy axis dispersion, and it is claimed that the addition of a small quantity of cobalt to the nickel iron alloy reduces this despersion by about a factor 3.
Magneto-Optic Readout for Computer Memories
Authors: Conger R. L. , Tomlinson J. L.
Published: April 2005

Experimental measurements have shown that nondestructive magneto-optic readout from magnetic film computer elements by means of the longitudinal Kerr-effect can operate at rates of at least one million bits per second. If the steady light source of the magneto-optic apparatus is sufficiently bright, a signal-to-noise ratio of four or better can be obtained from the photomultiplier readout tube. Since the reversal time of thin ferromagnetic films is less than a microsecond, writing speed can be as fast as readout. Information readout from a magnetic film can be obtained by scanning with a high-intensity light spot. Spurious variations in surface reflectivity of the films are sufficiently small so that parts of the film magnetized in opposite directions can be clearly determined. Experiments with an electronic strobing magneto-optic method make it possible to observe the details of the magnetization reversal process in very small parts of a film with a time resolution of the order of a nanosecond. Since this strobing process involves sampling and integration, the information bandwidth is too small to be used for digital computer readout. However, this method is useful in studying fine details of the magnetization reversal process. Measurements show that the reversal is repeatable in the different parts of the film.
Switching Properties of Multilayer Thin Film Structures
Authors: Kolk A. , Douglas L. , Schrader G.
Published: April 2005

Structures formed by depositing different ferromagnetic thin metal films in direct contact with each other were found to display a square hysteresis loop without the step discontinuity usually associated with gross heterogeneous magnetic composites. The high-speed switching characteristics of a bilayer structure composed of an electroplated 97 Fe-3 Ni layer in contact with a uniaxially oriented 79 Ni-21 Fe electroplate were intensively investigated. The switching characteristics of the bilayer were compatible with a nucleation and growth mechanism.
Magnetostatic Interactions between Thin Magnetic Films
Authors: Fuller Harrison W. , Sullivan Donald L.
Published: April 2005

This paper discusses some magnetostatic interactions between two thin films that are separated by a small distance between parallel film planes. The external field of a domain wall in one film is calculated using a simple wall model, and the effect of this field on a second adjacent film is determined. The conditions are investigated under which the wall field of the first film together with an external field can cause nucleation of a domain in the second film. The interaction energy between a movable wall in one film and a stationary wall or a linear imperfection in a second adjacent film is calculated using simple models. The equilibrium position of the movable wall as a function of an externally applied field is then determined. Means for electrically modifying the degree of interaction are investigated. Experimental results are presented illustrating the aforementioned interactions. The nucleation of long narrow domains in one film is achieved by the use of a domain wall, a scratch imperfection, or a film edge in a second adjacent film. The influence of a stationary wall in one film on the controlled wall motion of a wall in a second film is demonstrated. A comparison of theory and experiment is made. Mention is made of how the subject interactions might be utilized in new information storage devices.
Demonstration of Magnetic Domain-Wall Storage and Logic
Authors: Ballantyne J. M.
Published: April 2005

The operations of read-in, shifting, conditional erase, and fan-out in a system of domain-wall storage and logic proposed by Smith have been experimentally demonstrated. The several operations were performed by controlling the current flowing through a configuration of wires placed closely under a 5 to 40 mil wide, 50 to 300 A thick Permalloy strip, and the sequence of events was observed on the top side of the film using the Bitter technique. The basic wiring geometry was a narrow-spaced grid of series-connected parallel wires that made an angle of 50° to 75° with the strip of film, the smaller angles being necessary for the thinner films. Conditional erase was most successful in films below 100 A thick, as in this thickness range walls of the same sense form double walls which require relatively large fields for erasure.
Flux Reversal in Ferrite Cores under the Effect of a Transverse Field
Authors: Li Kam
Published: April 2005

It is known that flux reversal in ferrites involves three switching mechanisms, namely, domain wall motion, nonuniform rotation, and uniform rotation. The experimental results presented in this paper demonstrate that a steady transverse field in conjunction with set and reset pulses is capable of separating these mechanisms into three regions of flux dispersion. Each region is designated by flux components φ1, φ2, and φ3 with corresponding characteristic transverse fields H1, H2, and H3. The output waveform of the longitudinal sense signal during flux reversal is characterized by its first peak, second peak, and the long tail. The 50% value of the second peak occurs at the same characteristic transverse field H2. The transverse field has no appreciable effect on their distribution. The experimental results agree with theoretical predictions in which less flux is switched by domain wall motion at higher drive currents. Furthermore, a proper transverse field has the effect of speeding up the switching time of a ferrite core without sacrificing the amplitude of the output signal due to the fast reversal mechanisms.
Approximate Solution of the Equations of Magnetization Reversal by Coherent Rotation
Authors: Elfant R. F. , Friedlaender F. J.
Published: April 2005

A complete solution of the modified Landau-Lifshitz equation of magnetization reversal by coherent rotation is presented for α2≫Ha/4πMs, where α is the phenomenological damping constant, Ha is the applied field, and Ms is the saturation magnetization. This solution extends previous work in that it is valid for t≥0, whereas, other solutions have not been valid over this entire range. In addition, from this solution the time dependence of the demagnetizing field is found.
A Permanent Magnet Twistor Memory Element of Improved Characteristics
Authors: Alexander E. J. , McAlexander J. C. , Young L. H. , Salhany R. J.
Published: April 2005

A card changeable permanent magnet twistor memory element of improved characteristics has been designed. The desired characteristics were obtained by:

(1) Halving the solenoid width to enhance the drive field.

(2) Replacing the copper return wire in the twistor pair with a reverse wrapped twistor wire.

(3) Installing a Permalloy sheet between the word solenoid and the solenoid board to reduce interaction fields within the memory.

(4) Annealing the twistor wire to lower the coercive force and to increase the squareness ratio of the moly-Permalloy tape.

The chief result of these changes is that the net switching field at the bit is substantially increased and therefore the outputs of the memory are less dependent on the properties of the magnetic materials.

A 210 000 bit card changeable permanent magnet twistor memory utilizing the new element design has been constructed and evaluated.

In comparison to previously reported permanent magnet twistor memories, the new design is characterized by twice the speed, 2.5 times the bit density, 3 times the output voltage level, 2.5 times the signal available for ``1–0'' discrimination, and 4 times the strobe time tolerance.
de Haas van Alphen Effect in Zinc Manganese Alloys
Authors: Hedgcock F. T. , Muir W. B.
Published: April 2005

Observations of the long period de Haas van Alphen effect in pure zinc and in a zinc alloy containing 0.01 at.% manganese have been made to determine whether the Fermi surface of the alloy changes in the temperature region where the zinc manganese alloy exhibits an electrical resistance minimum. On the basis of a nearly free electron interpretation it has been shown that: (i) Within the experimental error the Fermi surface of pure zinc and the 0.01 at.% zinc manganese alloy are identical. (ii) The number of electrons added or subtracted from the conduction band on alloying cannot be greater than 1 electron per impurity atom. (iii) If the resistance minimum is due to a change in the density of states in the conduction band, this change is less than 0.0015%. (iv) If the ionic state of the manganese ions changes in the temperature range of the resistance minimum, then less than half of the ions are involved. In order to obtain a consistent interpretation of the variation of the amplitude of the de Haas van Alphen oscillations in the alloy it was necessary to assume that the collision damping (Dingle) factor varies with magnetic field. A simple extension of the Schmitt scattering model [R. W. Schmitt, Phys. Rev. 103, 83 (1956)] would predict this behavior both for the relaxation time derived from magnetoresistance and the de Haas van Alphen effect.
Crystalline Electric Fields in Spinel-Type Crystals
Authors: Folen V. J.
Published: April 2005

Electron paramagnetic resonance (EPR) measurements are reported for the Fe3+ ion in long range ``ordered'' and ``disordered'' single crystals of the spinel-type compound lithium aluminate (Li0.5Al2.5O4) which is isomorphous with lithium ferrite (Li0.5Fe2.5O4). In the ``disordered'' aluminate most of the EPR linewidths were found to be very broad, whereas in the ``ordered'' aluminate the linewidths were comparatively narrow. The broadness of the linewidths in the ``disordered'' aluminate prevented quantitative determination of the crystalline electric fields in this state. From comparison of the ``ordered'' and ``disordered'' EPR linewidths, it was deduced that large fluctuations in the crystalline electric fields may exist in other ``disordered'' spinels also. In the ``ordered'' aluminate, the EPR spectrum was measured for the tetrahedral sites (which have trigonal symmetry), and the values |D|=0.104 cm−1, |a−F|=0.0166 cm−1, and gII=2.006±0.002 were obtained. The magnetocrystalline anisotropy of Li0.5Fe2.5O4 was interpreted on the basis of the crystalline electric field parameters measured in the aluminate.
Effect of Substrate Cleanness on Permalloy Thin Films
Authors: Lemke John S.
Published: April 2005

The use of mechanical and chemical cleaning techniques in the production of a clean, random, and smooth microslide glass substrate surface for the vacuum deposition of uniaxial thin Permalloy film elements has been studied. The principal cleaning techniques intensively investigated were: (1) a mild detergent wash followed by a vapor degreasing cycle in isopropyl alcohol; (2) a chalk paste scrub followed by an ultrasonically agitated distilled water rinsing cycle and a forced hot air drying process; and (3) hydrofluoric acid etching followed by a distilled water rinsing cycle and a forced air-drying process. The surface condition of the cleaned microslide glass was assessed with electron micrographs of preshadowed carbon replicas (magnification 88 000×). The micrographs show that the chalk-cleaned glass substrate has the smoothest surface. The variously cleaned substrates were then used for the vacuum deposition of 1700-A 4-mm-diam Permalloy film elements (melt composition 83% nickel, 17% iron). This work was carried out in a 10−6 mm Hg vacuum system. Twenty-five evaporations were made with a total of 54 elements per evaporation. The Permalloy film elements deposited on the differently cleaned glass substrates were then examined by means of a 1000-cycle hysteresis loop apparatus and the following measurements were made: (1) coercive force HC; (2) saturation flux φs; (3) orientation of the anisotropy axis θ; (4) magnetoelastic strain coefficient η; and (5) anisotropy field HK. Dispersion measurements of the easy axis were made on a 1000-cycle crossed field hysteresis loop apparatus. Measured in this manner, the chalk-cleaned glass substrates yielded consistently the lower average value of HC; i.e., 1.4 oe. The average value of HK for the three different cleaning techniques was 2.5 oe. Within the total range of values of coercive force and the anisotropy field, the chalk-cleaned and the acid-etched glass substrates yielded the same values; i.e., HC±0.2 oe, HK±0.3 oe. Measurements of angular dispersion varied from 8° to less than 2° with an average value of less than 3°. The chalk-cleaned substrates yielded the lowest values of angular dispersion.
Induced Magnetic Anisotropy of Evaporated Films Formed in a Magnetic Field
Authors: Takahashi Minoru
Published: April 2005

The origin of the induced magnetic anisotropy in evaporated films of pure iron and nickel-iron alloys formed at normal incidence in a magnetic field was investigated. The temperature dependence of the anisotropy Ku, its relations to film thickness, substrate temperature, and substrate material, and the relaxation phenomena of the anisotropy during isothermal annealings with and without a magnetic field were systematically studied. The temperature dependence of Ku is neither explained by the crystal anisotropy nor by shape anisotropy. The observed relations between Ku and film thickness etc. suggest that the stress induced in the interior of the film, rather than the stress of limited parts of the film, is responsible for the anisotropy if the anisotropy due to the atomic pair orientation is not considered. The interior stress may be caused by the structure defects formed during evaporation. The relaxation phenomena of Ku in the alternate isothermal heat treatments reveals that the anisotropy has originated partly from a directional alignment of such imperfections as vacancies, dislocations, and impurities. It is also suggested that magnetostriction may play an important role in this directional alignment.
Angular Dispersion and its Relationship with Other Magnetic Parameters in Permalloy Films
Authors: Olmen Robert W. , Rubens Sidney M.
Published: April 2005

An experimental investigation has been made of the dispersion of the easy axis in Permalloy films deposited in an orienting field. The dispersion was studied as a function of the following parameters: reversible rotation limit Htr; easy direction coercive force Hc; anisotropy field Hk; and hard direction hysteresis loop squareness ratio (Mr/Ms)d, and coercive force (Hcd). Observations were made with a Kerr magneto-optic apparatus and with a 1000-cycle hysteresigraph. Angular dispersion of the easy axis, measured by the hysteresigraphic method, was found to increase with Hc/Hk. Reversible rotation limit was not found to decrease with increasing angular dispersion as predicted by theory, but rather to decrease more rapidly initially with increasing dispersion and then to increase again at larger dispersion. The initial effect is believed to be due to the influence of local variation of Hk on the reversible rotation measurement. There is some indication that hard direction coercive force increases with increasing dispersion, but there seems to be no simple correlation between dispersion and hard direction hysteretic properties. Reversible rotation limit was found to be roughly proportional to coercive force in most films, except those which exhibit an unusual type of wall motion switching behavior.
Factors Influencing Coercive Force Values in Sputtered Permalloy Films
Authors: Noreika A. J. , Francombe M. H.
Published: April 2005

Depending upon the experimental conditions used, the mean composition of a sputtered Permalloy film can change progressively with thickness or can be maintained almost constant. In the first case, the extent to which a homogeneous composition is achieved depends upon the ease with which diffusion and mixing can proceed during film growth. It appears that chemical inhomogeneity, resulting from incomplete mixing, leads to the appearance of an anomalous maximum in the plot of wall coercive force Hc versus thickness within the range 600–1000 A. This maximum is similar to that observed in evaporated films and has previously been identified with the transition from Néel to Bloch-type domain walls. The anisotropy coercive force Hk is found to be relatively insensitive to average film composition and homogeneity, but varies systematically with sputtering power and substrate temperature. A similar variation occurs for Hc in those films which are chemically homogeneous, i.e., in which the mean composition remains substantially constant during growth. The equilibrium temperature attained at the substrate after a few seconds and the resulting values of Hk and Hc can thus be effectively controlled by regulating the electrode potential V and current I.
Magnetoelectric Effects in Antiferromagnetics
Authors: Rado G. T. , Folen V. J.
Published: April 2005

Spin-ordered materials may exhibit a magnetic polarization which is proportional to an applied electric field and an electric polarization which is proportional to an applied magnetic field. In this paper a comprehensive discussion is given of the present knowledge of these magnetoelectric (ME) effects. The specific topics covered include the thermodynamic and magnetic symmetry considerations which are relevant to the ME effects and also to the piezomagnetic and piezomagnetoelectric effects. The major part of the paper is a review of the experimental and theoretical work on ME effects in Cr2O3 carried out by the present authors. This includes measurements of the anisotropy of the ME effects, theory of the temperature dependence and atomic mechanism of the ME effects, observation of the magnetically as well as of the electrically induced ME effect, experiments on magnetic annealing and other structure sensitive aspects of ME effects, and the role of antiferromagnetic domains in the interpretation of the results.
Observation of Antisymmetric Exchange Interaction in Yttrium Orthoferrite
Authors: Treves D. , Alexander S.
Published: April 2005

Sensitive static torque measurements were carried out on single crystals of YFeO3 in order to determine if weak ferromagnetism in this material is caused by single ion magnetocrystalline anisotropy or by anisotropic exchange interaction.

The following symmetry considerations show a priori which cubic and higher terms in the torque can be nonzero. The magnetic energy F is expanded in a series in the applied field H F=Σ σi(0)Hi+12 Σ χijHiHj+Σ CijkHiHjHk+…. Using the fact that F must be invariant under all the symmetry operations of the magnetic point group appropriate to these crystals, one finds that the only cubic coefficients that may be nonzero are Cxxz, Cyyz, Czzz. The expression for the torque T is found using the relation σi = ∂F/∂Hi, where σi are the components of the total magnetization, and T=H×σ.

The ferromagnetic component σ(0), the susceptibility χ, and cubic coefficients Cijk were calculated assuming a two sublattice system for the anisotropic exchange model and also for the single ion magnetocrystalline anisotropy model. The comparison of the measured coefficients to those calculated for the two models indicates that the anisotropic exchange mechanism is predominant in causing weak ferromagnetism in YFeO3.
Magnetic Structure of Manganese Chromite
Authors: Corliss L. M. , Hastings J. M.
Published: April 2005

Numerous attempts have been made to explain the anomalous magnetic properties of chromites and of mixed spinels containing chromium on the basis of the theoretical models of Néel and of Yafet and Kittel. Recent calculations by T. A. Kaplan and co-workers, using a classical Heisenberg model, have shown that over an appreciable range of the ratio of the BB to the AB interaction, the ground state is a ferrimagnetic spiral, i.e., a conical spin configuration in which the transverse components progress in spiral fashion along a fixed direction in the crystal. The object of the present study is to determine the suitability of the various proposed theoretical models in the case of manganese chromite, for which rather complex magnetic behavior has been observed by means of neutron diffraction. From diffraction patterns taken at room temperature, it is readily established that MnCr2O4 is a normal spinel with less than 1% of the Mn2+ ions present on B sites. The Curie temperature, as determined from diffraction data is ∼43°K. Below this temperature the magnetic contributions to the fundamental spinel peaks arising from aligned spins increases as the temperature is lowered and is effectively saturated at about 20°K. At 18°K, additional sharp peaks appear at positions which cannot be indexed either on the original unit cell or on any reasonably enlarged cell. These extra reflections persist with unchanged intensities down to 4.2°K. No change in either the positions or intensities of the fundamental lines is observed in going through the transition. Above 18°K a broad, diffuse peak is present in the region where the principal extra lines develop. This diffuse peak decreases with increasing temperature, but is still observable above the Curie point. Application of a magnetic field along the neutron scattering vector decreases the magnetic contributions to the fundamentals, but increases the intensities of the extra reflections. Analysis of the data shows that while little difficulty is encountered in explaining the observed saturation moments, the Néel model and the Yafet—Kittel model fail to account for major qualitative features of the diffraction results. Agreement is not significantly improved by modifications of the Néel model in which reversed spins (either random or ordered) are introduced, or in which some of the spins remain paramagnetic even at low temperatures. On the other hand, all the qualitative aspects of the diffraction results can be explained in terms of the ferrimagnetic spiral model of Kaplan and co-workers. The theoretical calculations give reasonably good quantitative agreement with the positions and intensities of the extra lines as well as the intensities of the fundamentals, while retaining the expected values for the individual ionic moments and the macroscopic saturation moment. Although some discrepancies still remain, there is every reason to believe that these can be removed by further refinement of the theory and by the extension of experimental measurements to single crystals.
Stress Effects on the Magnetic Properties of Evaporated Single-Crystal Nickel Films
Authors: Freedman J. F.
Published: April 2005

Nickel single-crystal films grown epitaxially on NaCl at elevated temperatures shown anomalously large values for the crystalline anisotropy constant, K1, as well as for K1, the perpendicular anisotropy (i.e., the anisotropy resulting from rotation out of the plane of the film). These values decrease to normal bulk values when the films are floated off the rocksalt.

It has been shown by x-ray diffraction that the as evaporated films exist in a highly strained condition, resulting in a tetragonal distortion of the cubic symmetry. The parameters of the unit cell change from a0=3.524 A for unstrained nickel to a=b=3.500 A in the plane of the film and c=3.546 A normal to the film. It is also shown that the stress causing this strain is elastic in character and is relieved by floating the film off the rocksalt.

A calculation using bulk elasticity data yields a planar compressive stress σ=−1.2×1010 d/cm2. The magnitude and direction of the stress indicates it results from the difference in thermal expansion between the nickel film and the NaCl substrate.

This externally applied stress system influences the magnetic state of the film by contributing to the total energy of the system through a magnetoelastic interaction. Employing the five-constant magnetostrictive equation, it is shown that a planar compressive stress of this magnitude does result in an anomalously high crystalline anisotropy value, as well as an anomalously high value of the anisotropy perpendicular to the plane of the film.
Stratification in Thin Permalloy Films
Authors: Prosen R. J. , Holmen J. O. , Gran B. E. , Cebulla T. J.
Published: April 2005

Permalloy films have been studied to determine composition variations which exist in a direction normal to the substrate surface. These films are formed by a noninterrupted deposition process. They are classified according to the amount of oxygen present on the substrate prior to deposition. If normal care is taken to produce a clean glass substrate, a thin layer of αFe2O3 and NiFe2O4 is produced at the film-substrate interface. Those films produced on a substrate saturated with oxygen have a thick negative magnetostrictive alloy layer adjacent to the substrate. This nickel-rich alloy presumably results from the diffusion of oxygen through the depositing films and the formation of iron oxide and nickel ferrite. In addition to the chemical analysis of the films, evidence to support the idea of stratification is found in the etch experiments, resonance data, saturation magnetization measurements, and cross section analysis.
Unidirectional Hysteresis in Thin Permalloy Films
Authors: Doyle W. D. , Rudisill J. E. , Shtrikman S.
Published: April 2005

A study of torque curves in thin Permalloy films with hc>0.5, where hc=Hc/H̄k is reported. The behavior of a 1400 A, 77% Ni film with hc=0.9 is discussed as a typical example. For applied fields h>0.5, the torque curves are generally complex and the discrepancies with the Stoner-Wohlfarth (S-W) model wide-spread. For h<0.5, if the film is previously saturated, the torque has a period of 2π in agreement with the S-W model. However, when 0.3<h<0.5, it is irreversible and the hysteresis is unidirectional, occurring around the easy direction of the bulk of the film. A model is proposed to explain this effect in which it is assumed that the film contains small regions with negative anisotropy −K2, where K2 is of the order of K1, the anisotropy of the bulk of the film. The torque curves calculated for this model are found to agree qualitatively very well with the experimental results.
Hall Effect Determination of Planar Stress in Ferromagnetic Films
Authors: Coren R. L.
Published: April 2005

Hall effect measurements on a ferromagnetic film can be used to examine the normal anisotropy and the distribution of stresses in the plane of the film. The measured Hall voltage exhibits a smooth transition from low to high field regions rather than the sharp crossover, at technical saturation, which is expected of a single domain. Since the ferromagnetic Hall effect depends upon the component of magnetization perpendicular to the plane one can attribute this difference of behavior to a domain structure describable by a distribution of normal anisotropies. The difference between the single and multi-domain Hall plots depends upon the nature of this distribution and from certain features of the experimentally obtained difference curve one can infer the type and extent of the distribution. If the anisotropy distribution is due to a corresponding range of strains superimposed on the geometric anisotropy of the film one can also estimate the form and extent of the function describing the planar stresses. It is shown that the existence of the anisotropy distribution results in a difference between the field at which the Hall measurements indicate technical saturation and that at which the normal anisotropy distribution is peaked.
Magnetoelastic Behavior of Thin Ferromagnetic Films as a Function of Composition
Authors: Mitchell E. N. , Lykken G. I.
Published: April 2005

A series of films of composition varying from 72% Ni, 28% Fe to 90% Ni, 10% Fe were evaporated at a pressure of the order of 10−5 mm Hg onto a heated glass substrate (250°C) in the presence of a magnetic orienting field in the plane of the film. The composition was controlled by placing a charge of the selected composition on the filament in an amount just sufficient to make the desired 3000 A film when all of the material was evaporated.

The magnetoelastic behavior of the films was studied by measuring η=ΔHk/(Δl/l), here ΔHk is the change in the anisotropy field upon the application of a stress sufficient to strain the film an amount Δl/l (typically 4×10−5). η was found to decrease linearly with composition to a first approximation with a slope of −26.5×103 oe per percent nickel, with η being zero for a film composed of 81.5% Ni, 18.5% Fe.

The value of η was compared with that of Λm for bulk material where Λm is the change in the magnetization divided by the applied stress in the case where the stress approaches zero and where the bulk material is biased by an applied field sufficient to yield the maximum change in Λ. Using bulk data for the saturation magnetization and Youngs modulus the value of η measured here yields a value for Λm which is too large by an order of magnitude.
NMR in Domains and Walls in Ferromagnetic CrBr3
Authors: Gossard A. C. , Jaccarino V. , Remeika J. P.
Published: April 2005

Nuclear magnetic resonance absorptions have been observed in zero applied field in the insulating ferromagnet CrBr3. Three lines are shown to be a quadrupole split triplet from nuclei in the bulk of the domains. A fourth, with a resonance frequency of 56.58 Mc at 1.34°K and a 250-kc linewidth, is ascribed to nuclei in the domain walls. The nuclear resonance frequencies are proportional to the local magnetization, and thus measure the temperature dependence of the magnetization both in domain walls and in domains. This is the first measurement of the difference between wall and domain magnetizations, and shows that (ΔM/M)wall − (ΔM/M)domain=T/200 in the spin wave region.
Ferromagnetic Resonance in CrBr3
Authors: Dillon J. F.
Published: April 2005

Ferromagnetic resonance has been observed in single crystals of anhydrous chromium tribromide using frequencies of 20 to 27 kMc. At 1.5°K a g value of 2.006 is found along with a uniaxial anisotropy, K=9.4×105 ergs/cm3. Linewidths as narrow as 3.5 oe have been observed at 1.5°K.
Acoustic Losses in Ferromagnetic Insulators
Authors: LeCraw R. C. , Spencer E. G. , Gordon E. I.
Published: April 2005

Studies of acoustic losses in single crystal garnets and ferrites using magnetostrictively driven spherical resonators are described. Resonant modes have been observed in spheres of yttrium iron garnet (YIG) at ∼9 Mc and room temperature with Q′s of ∼107. This is approximately six times greater than any other known material at the same frequency and temperature. These high Q′s have now been observed in both shear and compressional modes. [R. C. LeCraw, E. G. Spencer, and E. I. Gordon, Phys. Rev. Letters 6, 620 (1961). In this reference only a certain compressional mode showed the unusually high Q.] It should be noted that the above Q in YIG may be only a lower bound. Contact losses have been eliminated by levitation and by using higher order modes. However, due to complicating factors such as the relatively large and variable dislocation density (revealed by etching) and surface defects, we are not yet certain whether the measured Q′s are characteristic of perfect YIG. The intrinsic Q could be higher than the above figure and still be consistent with the present results. The dependence of the internal friction Q−1 in pure YIG on frequency and temperature are given. The frequency dependence at 300°K is shown to be Q−1∼f in the megacycle range with possibly a slower dependence on f in the microwave range. Data are given on Q−1 at ∼20 Mc from 300° to 20.3°K. Q−1 is relatively independent of temperature down to ∼50°K. Below 50°K, Q−1 increases rapidly down to 20.3°K, indicating a large absorption maximum below 20.3°K. The origin of this maximum is at present unknown. Data are also presented on Co1.1Fei.9O4 at ∼20 Mc from 300° to 20.3°K. This material has a very large maximum (Q−1∼10−2) at 290°K. Below 50°K, however, it has quite remarkable properties, with Q−1 being lower than YIG. Instead of Q−1 increasing rapidly below 50°K, as in YIG, it decreases rapidly from 50° to 20.3°K, indicating very low losses in the helium range. Investigation of all the above effects is continuing in detail to obtain an understanding of the many questions raised by these results about acoustic losses in ferromagnetic insulators.
Cation-Cation Three-Membered Ring Formation
Authors: Goodenough John B.
Published: April 2005

The stoichiometric compound FeS undergoes an electron-ordering transition at Tα≈140°C on heating, Tα≈100°C on cooling. It is pointed out that the various magnetic, crystallographic, and electric properties associated with this transition are compatible with the formation of three-electron Fe2+–Fe2+ bonds within the basal planes. This rather unexpected effect brings to nine the number of different electron-ordering transitions that can be identified. It is also noted that Mn2Mo3O8 probably represents a closely related type of electron ordering.
Perminvar Characteristics of Nickel-Cadmium Ferrites with Small Additions of Cobalt and Molybdenum
Authors: Lessoff H. , Greifer A. P.
Published: April 2005

During an investigation of low-loss ferrites, it was found that magnetically annealed nickel-cadmium ferrites containing minor additions of cobalt and molybdenum oxide exhibited rectangular hysteresis loops with squareness ratios approaching unity at temperatures up to 400°C. Data showing the effect of formulation and temperature on squareness ratio and coercive force are presented.
Fine-Grained Ferrites. II. Ni1−xZnxFe2O4
Authors: Malinofsky W. W. , Babbitt R. W. , Sands G. C.
Published: April 2005

A series of fine-grained single-phase ferrites was prepared according to the formula Ni1−xZnxFe2O4, where x took the values 0, 0.10, 0.33, 0.50, and 0.67. A previously-described process combining the so-called flame-spraying and hot-pressing techniques was used to obtain grain sizes of approximately 0.1 micron in the densified bodies. μ′ and μ″ were measured to 1000 Mc, with grain size and composition as parameters. Measurements were also made to 3800 Mc on a ferrite annealed through the critical size for multi-domains, confirming previously-reported theory that magnetic poles on the domain walls are the source of the microwave peak at about 2000 Mc. Wall displacement appears to contribute to the static μ0 in large-grained ferrites when x>0.

In addition, the temperature dependence of initial permeability μ0 was studied. The temperature coefficient of μ0 was found to increase with grain size. While the μ0 vs temperature curves were of various shapes generally, still a set of ferrites made up of differing compositions and grain sizes were obtained having linear temperature dependences. Of practical interest are those with slopes of −220 ppm/°C, 0 ppm/°C (NPO), and 220 ppm/°C.

Microwave properties were studied also. Because zero-field (Hdc=0) measurements showed that fine-grains (i.e., below the critical size for multidomains) eliminated the so-called microwave loss peak in the rf dispersion, a decrease in the low-field loss follows. Also, microwave measurements of the main resonance loss susceptibility vs rf power were made at X band using a cavity technique. Although normal critical fields hc were generally found, one sample with x=0.67 and ΔH=655 oe showed an anomalous rise in χ″/χ0″ at high powers, significantly expanding its power-handling capability.
Vanadium Iron Oxides
Authors: Wold A. , Rogers D. , Arnott R. J. , Menyuk N.
Published: April 2005

An investigation in the ternary system FeVO has been made of the chemical, crystallographic, and magnetic properties of the corundum FeVO3, and the spinels FeV2O4 and Fe2VO4· FeVO3 has been reported in the literature as Fe2+V4+O3 and antiferromagnetic at room temperature. However, the study reported in this paper shows that these results are incorrect. Oxidation of the spinel FeV2O4 results in the formation of some FeVO3. Conversely, reduction of FeVO3 ultimately forms FeV2O4+Fe. Therefore both the iron and vanadium are trivalent in the compound Fe3+V3+O3. Furthermore, FeVO3 has a small magnetic moment at room temperature which persists up to approximately 445°K as well as an anomalous rise in the magnetic moment below 150°K. A change in the relative intensity of several lines in the x-ray pattern of the material, which may indicate a shift in the position of the metal atoms was observed down to liquid nitrogen temperatures. However, no change in the symmetry was observed. The magnetic properties of FeV2O4 and Fe2VO4 are also studied. The magnetization curves of both these materials indicate the existence of a magnetic transition at 275°K for Fe2VO4 and 70°K for FeV2O4.
Preparation and Properties of Ferrospinels Containing Ni3+
Authors: Shafer M. W.
Published: April 2005

Nickel-iron spinels with compositions between NiFe2O4 and Ni2FeO4 have been prepared under oxygen pressures up to 2000 psi and at temperatures between 250° and 1000°C. Good agreement was found between the measured lattice parameters of the resulting spinel phases and the values obtained by extrapolating from the previously determined spinel series between Fe3O4 and NiFe2O4. Spinel compositions with lattice parameters as low as 8.3005 A were obtained; this compares with 8.3885 for Fe3O4 and 8.3394 for NiFe2O4. As is the case of the spinel solid-solution series between Fe3O4 and NiFe2O4, the composition of these nickel-rich spinels was found to depend strongly on both the oxygen pressure and the temperature. These relationships have been determined and are briefly discussed. Since it had been shown that there is essentially no measurable deviation from Végard's law between Fe3O4 and Ni2FeO4, lattice parameter measurements were a convenient method of determining the compositions of the spinel phase. The fact that single phase nickel-iron spinels can be prepared with nickel concentrations greater than NiFe2O4 indicates that Ni3+ replaces Fe3+ in the spinel lattice. Of the several possible configurations for a composition such as Ni2FeO4, there is strong evidence from magnetic moment measurements that on octahedrally ligated spinel sites the preferred arrangement is the [Ni2+ Ni3+] ion pair. The corresponding decrease in moment as Ni3+ substitutes for Fe3+ between NiFe2O4 and Ni2FeO4 agrees very well with that predicted by the Néel antiparallel array theory. A lowering of the Curie temperature was also observed in this compositional range.
Textured 6.5% Silicon-Iron Alloy
Authors: Facaros G. , Aspden R. G.
Published: April 2005

Sheet of an iron base alloy containing 6.5% silicon and second phase inclusions was prepared by hot rolling and pack rolling. Two structures were obtained by varying the rate of heating to the final annealing temperature. A slow rate of heating yielded {110} grains in a secondary recrystallization structure, and a fast rate, the primary recrystallization and normal grain growth structure. Only during the slow rate of heating were inclusions effective in suppressing normal grain growth and in promoting growth of {110} secondaries.

The secondary recrystallization texture was of the {110} 〈001〉 type. The normal grain growth texture had a similar degree of alignment of 〈100〉 directions with the rolling direction and a nearly random distribution of planes of the 〈100〉 zones parallel to the rolling plane. Similar dc and ac magnetic characteristics were observed for these two structures since they had the same degree of alignment of 〈100〉 directions (easy directions of magnetization) with the rolling direction.
A Method of Magnetic Annealing of Vanadium Permendur-Type Alloys
Authors: Burket R. E. , Stewart D. M.
Published: April 2005

A method of magnetic annealing of 2 V Permendur (2% V, 49% Co, 49% Fe) stamped rings and laminations in zero externally applied magnetic field is discussed. It is shown that an internal magnetic field biasing technique yields highly improved magnetic properties.

This method involves magnetizing the samples when they are still in a hard condition, i.e., as stamped or low temperature (500° to 600°C) annealed, and then subsequently annealing them at the normal time and temperature employed for the development of optimum magnetic properties (800–900°C). No external magnetic field is applied during any of the anneals.

This technique utilizes the internal magnetic field which remains after magnetizing the samples at room temperature. It is shown that a marked improvement may be obtained in 1-DU type laminations although the samples are unstacked after the initial magnetization (before annealing). Apparently, although the samples are partially self-demagnetized, there is still a sufficiently high internal field remaining to produce a self-magnetic annealing effect during the anneal. It is also shown that the cooling rate employed in this anneal is important—just as it is in conventional magnetic annealing.

Normal dc and 60 cycle magnetic properties are presented for 0.014-in. ring and 1-DU samples from a number of heats. The data indicate that the effect is manifested by a two to threefold increase in the dc μmax and a 35 to 50% increase in the rectangularity of the dc hysteresis loop (Br/Bm). It does not necessarily cause a decrease in the dc coercive force or the 60-cycle watt loss.
Neutron Magnetic Scattering from Rare-Earth Ions
Authors: Blume M. , Freeman A. J. , Watson R. E.
Published: April 2005

The theory of neutron scattering by paramagnetic rare-earth ions has been given by Trammell and more recently by Odiot and Saint-James. Unlike the case for the iron series transition metals, for which the orbital angular momentum of the 3d electrons is almost completely quenched, the magnetic scattering of neutrons from the rare earths (except for gadolinium and europium) arises from both the spin and orbital contributions to the magnetization. Using recently determined Hartree-Fock wave functions for some of the trivalent rare-earth ions we have determined the functions 〈jn〉 and 〈gn〉 (for n=0, 2, 4, and 6) which are necessary for the theoretical evaluation of the spin and orbital contributions respectively to the magnetic form factor. A comparison of these theoretical results with the experiments of Koehler and Wollan for Nd3+ and Er3+ and of Koehler, Wollan and Wilkinson for Ho3+ is presented. Differences are found between theory and experiment and some possible reasons for this are discussed.

A paper on these matters is being submitted to the Physical Review.
Far Infrared Spectra of Magnetic Materials
Authors: Tinkham M.
Published: April 2005

The far infrared spectral region (∼10−100 cm−1) corresponds to kT for T=15−150°K or βH for H=105−106 oe. Materials with characteristic temperatures or fields of these orders of magnitude may have interesting far infrared spectra. We have studied far infrared resonance spectra in antiferromagnetic and in ferromagnetic rare-earth iron garnets.

Antiferromagnets have a resonance frequency which depends on the exchange and anisotropy fields, HE and HA. If HE is found from χ⊥, HA can be found from ω0, and compared with theory. We have done this with FeF2, MnO, and NiO, which have resonances for T≈0 at frequencies of 52.7 cm−1, 27.5 cm−1, and 36.6 cm−1, respectively. As the temperature is raised, these frequencies fall, reaching zero at TN. When a magnetic field is applied along the easy axis of FeF2, there is a first-order Zeeman splitting, from which a g value of 2.25 was determined. In MnO and NiO, however, there is an easy (111) plane. In this case the resonant mode is nondegenerate and hence the Zeeman effect is second-order and unobservably small.

The exchange coupling between the rare earth and iron ions in garnets is typically of order 20 cm−1 (30°K), while the iron ions are coupled strongly together, corresponding to their Curie temperature of about 550°K. Because anisotropy breaks down selection rules, transitions in which a single rare-earth ion spin flips in the exchange field of the iron may be observed at far infrared frequencies. We also observe Kaplan-Kittel exchange resonances, in which the entire sublattice of rare-earth ions precess together and induce a corresponding precession of the iron sublattice. Since the frequency of such a resonance depends on the rare earth sublattice magnetization, it is quite temperature dependent, in contrast to the single ion absorptions. To obtain quantitative agreement with experiment, the Kaplan-Kittel theory must be generalized to take account of anisotropy energy. In YbIG at 2°K, with the magnetization along the [111] easy direction, we find single ion resonances at 23.4 and 26.4 cm−1 and an exchange resonance at 14.1 cm−1. The latter rises in frequency as the temperature is raised, whereas the former frequencies are nearly constant up to 60°K, where the intensity becomes too low for observation. The corresponding frequencies at low temperatures in ErIG are 18.2, 21.6, and 10.0 cm−1, whereas in SmIG the exchange resonance occurs at 33.5 cm−1 and decreases with increasing temperature. The small temperature dependence of the single ion exchange splittings suggests a rare earth-rare earth coupling (perhaps via spin waves in the iron sublattice) of magnitude ∼4% of the iron-rare earth coupling.