bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antiferromagnetic Resonance in Cubic RbMnF3
Authors: Teaney Dale T. , Freiser Marvin J. 
Published: April 2005

Antiferromagnetic resonance has been observed in cubic RbMnF3, and the results are in excellent agreement with a theoretical treatment of the resonance conditions. Because a more detailed publication has recently appeared,1 we present in this abstract a brief background and comments on the observed temperature dependence.
Cubic RbMnF3 is characterized by a strong exchange interaction (TN≃54.5°K)2 and low anisotropy. The anisotropy energy has the form EA = K(α4+β4+γ4), where K is positive. When the sublattice magnetization is close to the preferred {111} direction, the anisotropy may be represented by an effective field of 5.0 Oe at 4.2°K. The exchange field is found to be 710 kOe. The exchange and anisotropy fields may be determined separately because the nuclear anisotropy field, HN, may be calculated and the exchange field obtained from 2H EHN = 2HE× (9.43/T).
We are presently investigating the temperature dependence of the resonance field in the helium range. Within the experimental uncertainty of 2%, we find no change in H EHA from 1.4° to 4.2°K. Work is in progress to extend the temperature range and to increase the experimental accuracy.
Magneto-Optical Readout from a Magnetized Nonspecular Oxide Surface
Authors: Supernowicz E. J. 
Published: April 2005

This paper describes a magneto-optical method for obtaining visual display and electronic readout of magnetic information recorded on a nonspecular oxide surface. A recorded oxide surface is placed in contact with a specular ferromagnetic surface, an external magnetic field is applied normal to the two surfaces in contact; and the recorded information is read out by means of the Kerr effect through the back of the specular surface. The method is a useful tool for studying defects in the writing process independently of the reading process in investigations of magnetic recording on oxide surfaces.
It was observed that when the external field was applied, the magnetic pattern was either sharpened or caused to spread, depending on the polarity of the field.
Study of Permeability Ratios for Use in Nondestructive Readout of Ferrite Memory Devices
Authors: Holzinger Carl S. 
Published: April 2005

A study has been made which determines the ultimate one-to-zero ratio which can be realized in the permeability sensing technique of nondestructive readout of binary information from ferrite memory cores. The study is limited to the calculation and measurement of the ratios of incremental permeabilities of various magnetic states for ferrites in which the permeabilities can be attributed to a rotational process. Calculations are based upon a polycrystalline, randomly oriented grain ferrite with a negative anisotropy constant. Each individual magnetic moment is considered to be constrained to an easy axis only by the anisotropy field. Measurements of possible ratios between the permeabilities for the following three conditions are shown to agree within experimental error to those predicted by the calculations.
I. Completely demagnetized sample.
II. Measuring field parallel to the direction of the remanence existing after the application of a saturating field.
III. Measuring field orthogonal to the direction of the remanence existing after the application of a saturating field.
The experimental verifications were arrived at by measurements performed on a long, thin, extruded ferrite tube. It is concluded that the best one-to-zero ratio can be obtained with materials having as high an initial permeability as possible and which still depend upon the rotational mode of operation. The highest-one to-zero ratio then possible is equal to 3.26. Furthermore, this ratio is obtained by using two orthogonal remanence states with the measuring field applied parallel to the remanence which is to represent the binary zero.
Two-Phase Ferrites for High-Speed Switching
Authors: Baba P. D. , Gyorgy E. M. , Schnettler F. J. 
Published: April 2005

A plot of the inverse switching time vs the applied field yields three regions of different slope for square-loop ferrites. The low-field region has the lowest slope and is commonly attributed to domain wall motion. As the field is increased, a break in the curve occurs and the slope increases. This intermediate-field portion of the curve has been explained by a nonuniform rotational model, and its projection to the field axis is termed the threshold field H0 for nonuniform rotation. In coincident-current memory operation, twice the coercive force is the maximum drive which can be employed for switching from one remanent state to the other. Therefore, it is desirable to minimize the extent of the domain wall region so that the coercive force will approximate H0 as closely as possible. Then 2Hc will correspond to a higher value of the inverse switching time on the nonuniform rotational portion of the curve, and very fast switching can be attained. Prevalent theories describing domain wall motion in the vicinity of nonmagnetic inclusions indicate that domain wall motion can be impeded by the addition of nonmagnetic second phases of proper size and distribution in a magnetic matrix, resulting in an increase in Hc without affecting H0. A similar approach was used by Nesbitt and Gyorgy on gold-doped Permalloy.
To some extent, the desired effect can be obtained by underfiring the ferrite. However, such firing treatments are difficult to control. A method is described whereby the coercive force is increased while employing a noncritical firing treatment. This has been achieved by the inclusion of palladium as a second phase in a magnesium—manganese ferrite. Particles of the order of 1500 Å were dispersed in the ferrite, and toroidal samples were fired at temperatures between 1250° and 1400°C for firing times up to 12½ h. At 1400°C, within the range of 7½ to 12½ h, variations in Hc were very small. Moreover, in samples containing 10% palladium, Hc increased from 0.9 to 2.7 Oe without changing the Hc of 3.5 Oe. In coincident current operation, the 0, 10, and 20% samples switched in 0.70 0.16, and 0.10 μsec, respectively.
Spin-Wave Resonance in Thin Films at Oblique Angles
Authors: Rossing Thomas D. 
Published: April 2005

Spin-wave spectra in thin Permalloy films have been observed as the angle between the applied field and the film is varied from 0 to 90 degrees. The applied field corresponding to the main resonance peak falls very close to its calculated value for all angles. At some critical angle the spin-wave spectrum collapses to a single peak. The observed critical angle is very near the angle at which the resonance frequency becomes independent of small changes in the magnetization, which supports a dynamic-pinning model. The separation between the main peak and the subsidiary peaks reaches a maximum at an angle slightly less than the critical angle and drops sharply as the critical angle is approached. At no angle does the wavelength of the spin waves appear to be a submultiple of the film thickness as would be expected if the surface spins were completely pinned.
As the angle between the applied field and the film increases from 0, the linewidth increases and reaches a maximum near 80°. Beyond this angle the linewidth decreases rapidly, and in many films the linewidth at 90° is less that at 0. Simple theory explains the increase in linewidth with angle, locates the angle of maximum linewidth, but fails to predict the narrowness at 90°.
Magnetic Structure of MnSn2
Authors: Corliss L. M. , Hastings J. M. 
Published: April 2005

An abrupt magnetic transition in MnSn2 was reported by Kouvel and Hartelius1 about one year ago. The salient features of the magnetic behavior are a smooth susceptibility maximum at 86°K and an almost discontinuous decrease in susceptibility at 73°K. At the suggestion of Kouvel, a neutron diffraction study was made to investigate possible changes in magnetic structure accompanying the transition.
MnSn2 has the body-centered tetragonal C16 structure, consisting of alternating layers of Mn and Sn perpendicular to the c axis. Each Mn atom is surrounded by 8 Sn atoms which connect it to its second and third nearest neighbors through angles of approximately 111° and 146°, respectively. Nearest-neighbor Mn atoms have no intervening Sn atoms and are separated by a distance of 2.72 Å in the c direction.
Neutron diffraction patterns show that above the abrupt transition at 73°K, MnSn2 is antiferromagnetic with a Néel temperature in the neighborhood of 330°K, in agreement with recent susceptibility and resistivity measurements of Kouvel2 on the same preparation, as well as with the earlier magnetic measurements of Yasukōchi et al.3 The structure consists of ferromagnetic (110) planes which alternate along the direction perpendicular to the sheets. Individual moments are oriented parallel to the direction of alternation. The superstructure lines, characteristic of the antiferromagnetic state, appear to saturate near nitrogen temperatures and show no anomaly in passing through the susceptibility maximum at 86°K. The value of the Mn moment at 77°K is 2.36 μB.
The abrupt transition at 73°K is marked by the disappearance of the high-temperature antiferromagnetic diffraction pattern and the appearance of a new pattern characteristic of a modulated spin structure. The low-temperature structure is a simple modification of the structure above the transition in which the magnitude of the moment is no longer constant but varies sinusoidally along the direction perpendicular to the ferromagnetically aligned sheets. Thus, the short-range structure and spin direction are essentially the same above and below the transition. The observed modulation has a wavelength of approximately 113 Å or twelve times the face diagonal of the chemical unit cell; the amplitude of the modulated moment is 3.11 μB at 4°K.
Measurement of Film Relaxation Time
Authors: Barrett W. A. 
Published: April 2005

Magnetic film memories and other devices depend upon the relaxation from a state of hard direction magnetization to an easy direction state in the presence of a small easy direction ``tipping'' field HL. The relaxation times of five Permalloy films of thicknesses 0.1, 0.25, 0.4, 0.5, and 1.0 μ have been measured with an apparatus of switching field turn-off time &lt;0.5 nsec and a detection risetime of 0.85 nsec. The relaxation time is defined as the time for a 10–90% easy direction flux change. It is found that the relaxation time varies roughly inversely with easy direction field and is to some extent independent of the initial hard direction field (8 Oe for the following remarks).
The tangent slope Sw to the 1/τs vs HL curve at a field HL=1 Oe fits the relation Sw=1+10d2 Oe nsec, where d is the film thickness in μ, within experimental error (∼20%). The Sw predicted from the Landau-Lifshitz equation for the rotational model with λ=108 cps is 1 Oe nsec. The rotational model also predicts that τs approaches 2 nsec for HL→0. The limiting τs for the real films varied from about 7 nsec for the 0.4-μ film to about 40 nsec for the 0.25-μ film with no thickness correlation. In addition, the 0.1-, 0.25-, and 0.5-μ films exhibited a distinct slow-switching component for |HL| &lt;Hdisp (Hdisp is the field HL necessary for a 90% relaxation in one direction). Observation of the final state of the 0.1- and 0.25-μ films by the Bitter technique revealed a fine-scale domain structure for |HL| &lt;Hdisp and a single domain state for |HL| ≳Hdisp.
The two thicker films were electrodeposited on a BeCu substrate, while the three thinner films were evaporated on a glass substrate. Since all five fit the same Sw vs d relation, it would appear that substrate-induced damping is not large.
Influence of Grain Size on Square-Loop Properties of Lithium Ferrites
Authors: Schwabe E. A. , Campbell D. A. 
Published: April 2005

Pure lithium ferrite can be obtained as a very good square-loop material if certain precautionary steps are taken in material preparation, firing, and cooling. Due to its simple composition and high Curie temperature, this material is of practical as well as of theoretical interest.
In a series of memory cores prepared under various conditions, grain size was found to be the determining factor for switching time and threshold field. The series covered a range of 2 to 30 microns in average grain size. Below 2 microns good squareness was not obtained even in samples with uniform grain size. Cores with 2.3-μ average grain size proved to have as little as 120-nsec switching times under coincident current test conditions. Results indicate that there is little magnetic interaction between radially adjacent grains. Therefore, the best guarantee to obtain a square hysteresis loop requires a relatively narrow distribution of grain sizes. Cores fired under conditions which resulted in a wide distribution of grain sizes exhibited poor squareness. The change of threshold field with temperature of lithium ferrite is only 0.15% per °C compared with 1.5% per °C in some extreme cases of commonly used MgO–MnO ferrites with high ZnO content. The procedures used for obtaining grains of uniform size are discussed. Adjusting the powder particle size to a certain fraction of the grain size desired in the finished core was found to be the best physical method of controlling grain growth without introducing complications through use of oxide additions acting as fluxes or grain growth inhibitors. Powder particle size was measured by use of x-ray diffraction line broadening techniques. As a very practical relative measure of the powder particle size in the submicron range, the intrinsic coercive force can be used.
Single-Crystal Ferroxdure, BaFe12−2x3+Irx4+Znx 2+O19, with Strong Planar Anisotropy
Authors: Tauber Arthur , Kohn J. A. , Savage R. O. 
Published: April 2005

Ir4+, substituted in ferroxdure (BaFe12O19), has been observed to couple ferrimagnetically. Replacement of Fe3+ by Ir4+Zn2+, according to the formula BaFe12−2x3+Irx4+Znx 2+O19, reduces the intrinsic axial anisotropy. The room temperature anisotropy becomes planar at x=0.3–0.4 and increases to 22 000 Oe at x=0.6. Magnetization and Curie temperature are decreased by the substitution of Ir4+Zn2+; ferrimagnetic resonance linewidth is increased. The nonaxial anisotropy is believed to derive from spin-orbital coupling of Ir4+.
Single crystals up to ¼ in. across were grown from a Bi2O3 flux in platinum crucibles. Specimens are hexagonal tabular, black, lustrous, and well-developed. Single-crystal x-ray diffraction patterns showed that a0 increases with increasing Ir4+Zn2+ substitution while c0 remains unchanged.
Rare-Earth Ion Relaxation in Ferrimagnetic Resonance
Authors: Clarke B. H. , Pearson R. F. , Teale R. W. , Tweedale K. 
Published: April 2005

The linewidths in ferrimagnetic resonance ΔH and the frequency dependence of the anisotropy field for iron garnets containing rare-earth ions are explained on the basis of a model for relaxation which was used by Clogston for nickel ferrous ferrite. It is assumed that the population of the rare-earth ion energy levels relaxes towards equilibrium with a finite relaxation time τ. Consequently for ωτ≳1, where ω is the measurement frequency, significant departures from equilibrium occur and give rise to the effects noted above.
If the static torque, linewidth, and the resonant field can be measured in a temperature range where only the lowest two rare-earth ion energy levels are appreciably populated, τ can be deduced for the magnetization along [100] and [110].
The consequences of the model are described; they differ quite extensively from those of the fast relaxing ion model. A quantitative comparison with the theory for iron garnets containing ytterbium supported the theory and yielded values for τ. In the case of erbium, however, the static torque was found to be strongly field dependent and hence only a qualitative comparison is possible. It is nevertheless concluded that the effects observed support the model. At 55°K τ for the ground doublet is about 10−11 sec.
Eddy-Current Losses Calculated From a Domain Model and Observed Densities of Mobile Walls
Authors: Wycklendt Daniel A. 
Published: April 2005

Recent measurements involving the superposition of small audio-frequency field increments on silicon iron sinusoidally magnetized at low frequencies indicate that the number of mobile domain walls varied during the cycle. This experimental technique has been considerably refined to provide a better measure of the number of active domain walls. Based on a simple domain model, a calculation of the number of active walls can be made from the experimental data.
The principal objective of this study is an explanation of the anomalies in the loss-frequency curve of grain-oriented silicon iron magnetized to high flux densities at low frequency. The data obtained from the superposed incremental magnetization experiment can be directly applied to a calculation of the eddy-current losses with a simple domain model. Since no better information is available, it is necessary to take the speeds of the walls to be equal to complete the calculation. With this assumption and the audio-frequency data, the losses are then calculated point-by-point over a cycle of magnetization. Comparing the calculations to loss measurements, 60 percent of the anomalous eddy-current loss and some of the downward curvature of the measured loss-frequency curve are accounted for in the 0–30 cps range. Considering the assumptions made, this result gives plausibility to the domain model and the interpretation of the audio frequency magnetization data.
Eddy-Current Effects with Rapidly Varied High Magnetic Fields
Authors: Elder Tait , Barte William 
Published: April 2005

Eddy-current broadening of magnetic hysteresis loops in iron and Alumel wires has been studied with oscillatory fields of varying amplitude (100–14 000 Oe) which change as rapidly as 7×105 Oe/sec in the irreversible part of the loop. Under conditions where eddy currents dominate, coercive forces which are 50 times the static coercive force of a few oersteds can be observed. Experimental data obtained at 77°K and at 300°K with both materials agree qualitatively with a theoretical expression derived by Brown under the simplifying assumption that the outer skin reverses in magnetization before the inner core magnetization changes. The coercive force in this expression increases as the square root of the product of conductivity, cross sectional area, saturation magnetization, and rate of change of field.
When the irreversible part of the loop is traversed at some fixed rapid rate, the observed coercive force increases with increasing amplitude or duration of the immediately preceding magnetic field. This effect on coercive force of the previous aligning field amplitude and duration is attributed to flux-reversal delays similar to those denoted as magnetic viscosity by Mitkevitch. Such delays have also been interpreted in terms of domain wall nucleation time by Becker.
Thin Soft Magnetic Tapes in Small High-Frequency Fields
Authors: Boll R. 
Published: April 2005

The complex permeability of iron-nickel and Permalloy alloys in tape thicknesses down to 2 μ has been measured at frequencies up to 1000 Mc. Toroidal cores with different heat treatments and in the cold-rolled state were used.
Curves of complex permeability (Cole-Cole diagrams) differ more and more from the classical eddy-current curve with decreasing thickness. It is concluded that spin relaxations and resonances are effective as known from ferrites. The effects are clearer in alloys with low rather than high initial permeability; and are strongly marked in thin cold-rolled tapes and magnetic films.
Curves of complex permeability are analyzed by means of the equations for domain-wall motions and domain rotations, and the significant parameters are discussed.
These measurements brought new knowledge about the limiting frequency and the loss factor of thin tapes. The limiting frequency tends clearly towards an upper limiting value with decreasing thickness. This is in contrast to the classical eddy-current theory. The upper limiting frequency is identical with the ``gyromagnetic'' limiting frequency as calculated by Snoek, which is accordingly not valid for ferrites only, but for metals as well. The frequency-dependent part of the loss factor tgδ has a lower limiting value. This loss minimum and the upper limiting frequency are really reached at annealed tapes of some microns, and with dust cores of fine powders.
Further improvements are possible by using special anisotropies. An example is the magnetic films which have a direction of hard magnetization and a plane of easy magnetization. Cold-rolled and half-hard thin tapes with Isoperm-like hysteresis loops show effects in similar direction.
The results show that a tape thickness of 3–6 μ is normally sufficient to applicate metals in the Mc range. Further decreasing of the tape thickness seems successful only if reduced to the order of 1000 Å and also using the strong shape anisotropy used with the magnetic films.
Magnetic Properties of Some Divalent Europium Compounds
Authors: McGuire T. R. , Argyle B. E. , Shafer M. W. , Smart J. S. 
Published: April 2005

The compounds of divalent europium form an attractive series for magnetic investigations because the magnetic ions are in S states and the crystal structures are generally simple. Moreover, true ferromagnetism, which is quite unusual in compounds, has been observed in EuO by Matthias, Bozorth, and Van Vleck.
We have prepared samples of EuS, EuSe, EuTe, EuCO3, EuTiO3, EuZrO3, EuSO4, and EuCl2, and studied their magnetic properties in the temperature range 4–300°K. The sulfide, selenide, and telluride all have the same NaCl crystal structure as EuO; we find that the first two also become ferromagnetic at low temperature, while EuTe is paramagnetic, or possibly antiferromagnetic, at 4.2°K. The Curie temperatures for EuS and EuSe are about 18° and 7°K, respectively. The saturation moments of EuS and EuSe extrapolated to 0°K correspond to 6.8 and 6.7 μB per Eu++ ion, respectively, in good agreement with the expected value of 7 μB. None of the other compounds were ferromagnetic at liquid helium temperatures, and all exhibited θ values very near to 0°K. A tentative interpretation of the exchange interactions in the rocksalt compounds is made using a molecular field treatment.
New Technique for Identifying Particles Observed by a Scintillation Counter
Authors: Gersch W. 
Published: April 2005

A new technique is offered to determine the quantity of radioactive particles observed by a scintillation or proportional counter when the distribution of the source particles vs particle energy is immersed in the distribution of the background particles.
The particle identification problem is interpreted from the point of view of a parameter estimation problem in mathematical statistics in the following way: Assume there are M events, where an event is the occurrence of a scintillation counter pulse. M is a known number, N of these events are associated with the desired source particles and the scintillation counter output is source plus background. The remaining (M-N) events consist of background alone. The background statistics are assumed known and the source pulse amplitude distribution is assumed known to within K distribution parameters. One number, the amplitude of the counter response, is observed for each of the M events. The problem is to estimate N.
There are (K+1) unknown parameters: the number N and the K unknown parameters of the source pulse distribution. The problem is solved by what is essentially a method of moments technique. The estimation procedure has desirable statistical properties for large N and M in that the estimate of N is asymptotically unbiased and that the relative variance of the estimate of N asymptotically goes to zero.
Implementation of this technique supplants the conventional multichannel pulse-height analyzer with digital recording of the individual pulse count amplitudes and subsequent data processing by a modest size digital computer.