bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulated Dynamic Behavior of Domains in Oriented Electrical Steel Sheets
Authors: Paxton W. S.
Published: January 2005

The dynamic behavior of domains in the alternating magnetic fields used in power applications has been studied in commercial-oriented electrical steel sheets containing 3.25% silicon. Dynamic behavior was simulated by a static method. Domain patterns were first observed on demagnetized samples by the Bitter technique. Flux density in the sample was then increased in known increments, usually 0.5 to 1.0 kg, to an induction of about 19 kG, and patterns were photographed at each step. In more than 1/3 of the 80 samples examined, regions were observed that initially consisted of many domains in the demagnetized condition, but appeared to act in a cooperative fashion at some intermediate value of flux density. The interactions usually extended across grain boundaries separating grains with large differences in orientation and included parts of several grains. These regions, tentatively called ``superdomains,'' maintained their identity to the highest values of flux density produced in the sample. Possible explanations of these regions in terms of domain rotations are discussed.
Structures and Magnetic Properties of Grain-Oriented 3.2% Silicon—Iron
Authors: Littmann M. F.
Published: January 2005

After almost 30 years of use, grain-oriented silicon—iron remains the most important soft ferromagnetic material where high permeability and low core loss are required.

In this paper we show how grain structures which the metallurgist has learned to produce affect permeability at H=10 Oe and core loss at B=15 kG. Deviations from the ideal (110) [001] and (100) [001] are compared. The effect of thickness for both textures is shown over a range of about 1 to 25 mil. Ascertainment of the true effect depends on maintaining other factors constant, such as degree of texture and grain size. The effect of grain size on core loss of Epstein test specimens is shown over a wide range from 0.03- to 20-mm diameter for a relatively constant degree of texture and chemical purity. For very small grain sizes, small grain diameter is detrimental to core loss but the effect is reversed for large grains near 10 mm diameter.

Attainment of superior magnetic properties depends on combination of a high degree of crystal texture together with a grain diameter of about 1 mm. This appears to be the case for both cube-on-edge and cubic textures.
Ferromagnetic Relaxation in Manganese—Iron Spinels
Authors: Blocker T. G. , Heeger A. J.
Published: January 2005

We have extended our previous measurements on the ferrimagnetic manganese—iron spinel system MnxFe3−xO4(x=1) to include the concentrations x=1.25, 0.80, and 0.60. The FMR linewidth and field for resonance were measured over the temperature range 4°–300°K at various X-band frequencies. For each concentration, relaxation mechanisms involving ``lossy ions'' (Mn3+ or Mn4+ and Fe2+) are found to be the dominant source of linewidth. A ``slow relaxation'' mechanism resulting in a linewidth maximum (or shoulder in the x=0.85 and 0.60 cases) near 20°K and an effective field for resonance minimum near 10°K is operable in each concentration studied. The responsible ``lossy ions'' are most likely manganese. For the x<1 concentrations, a ``slow relaxation'' mechanism due to itinerant electrons associated with the Fe2+–Fe3+ conduction yields a linewidth maximum near 70°K. An ``eddy current'' contribution to the linewidth due to the presence of Fe2+ ions is also observed in the x<1 samples. These same phenomena have been observed previously in excess-iron nickel ferrites. Finally in manganese ferrite (x=1), a linewidth peak at higher temperatures (100–300°K) is observed whose position and magnitude is very sensitive to the microwave frequency used. As the driving frequency is swept from 8.7 to 12 GHz, the linewidth maximum shifts from 200 Oe at 250°K to 40 Oe at 160°K. This sensitive frequency (or field) dependence rules out the ``fast relaxation'' mechanism previously proposed to account for this phenomenon and a ``slow relaxation'' mechanism which predicts an increase in the temperature of the linewidth maximum with increasing frequency. Mechanisms involving thermally produced Fe2+ ions are proposed to account for this behavior. A complete account of this work will be submitted as a regular article to this Journal.
Magnetic Properties of Ferrite Single Crystals with the Y Structure
Authors: Verweel J.
Published: January 2005

Single crystals of BaZnFe6O11 (Zn Y) were grown by the flux technique. Chemical analysis showed the presence of some ferrous ions in most batches. A relation between the Curie temperature and the ferrous content could be established. The anisotropy in the specific resistivity was measured (20–260 Ω·cm in the basal plane, 240–1400 Ω·cm in the c direction) and was found to be a structural effect. The magnetostriction in the basal plane was measured to be 1.5×10−6.

The crystal anisotropy field in the basal plane was found to be smaller than 1 Oe at room temperature for all samples and 10–20 Oe at 77°K. Linewidths of thin disks were found to be 14–20 Oe at room temperature and 50–60 Oe at 77°K. The permeability of single-crystal toroids in the basal plane was measured at room temperatures between 0.5 and 500 MHz. Two dispersion mechanisms were found near 10 and 100 MHz, which could be ascribed to wall and spin relaxation, respectively.

The rotational permeability was found to be about 300, whereas from the anisotropy data at least 1300 would have been expected. This discrepancy could be understood from the investigation of the Bloch-wall pattern of these samples, as will be discussed in some detail.
Preparation of Single-Crystal Ferrite Films
Authors: Gambino R. J.
Published: January 2005

Single-crystal films of spinel ferrites have been deposited epitaxially on MgO substrates from a molten-salt solution by vaporizing the solvent. The ferrite constituents (oxides or carbonates) and anhydrous sodium carbonate are melted on a (100) cleavage surface of a MgO single crystal. The melt wets the MgO so that it spreads over the surface as a uniform, thin, liquid layer. The solution is maintained at 1100°–1250°C for 5–20 h in order to vaporize the solvent, thus depositing the ferrite. Crystals 5–50 μ thick and 1 cm2 area of NiFe2O4, Ni0.5Zn0.5Fe2O4, CoFe2O4, and Li0.5Fe2.5O4 (the latter using Li2CO3 as the molten-salt solvent) have been grown by this method. The ferrite films grow with the same orientation as the substrate.
Magnetic Anisotropy of Some Nickel Zinc Ferrite Crystals
Authors: Van Groenou A. Broese , Schulkes J. A. , Annis D. A.
Published: January 2005

Single crystals of Ni1−pZnpFe2O4 (p=0.20 and 0.65) were prepared from a melt in a PbO:B2O3 flux. The anisotropy constant K1 was deduced from torque measurements in a (100) plane. | K1 | increases linearly with p at low temperatures. Combining the results with data on p=0 and p=0.33 from the literature, one can represent K1 at 4°K as the sum of contributions from tetrahedral Fe3+ (+0.04 cm−1 per ion) and octahedral Fe3+ (−0.07 cm−1) in agreement with data on other iron spinels. The temperature, dependence of K1 for p=0.65 agrees with Wolf's expectations for ferrimagnets with a weak exchange. Above room temperature the torque curves for this sample show a spurious uniaxial term, increasing with temperature. Both K1 and this extra torque are reduced by increasing the external field.
Palladium Hyperfine Field in Ferromagnetic Pd-Fe Alloys
Authors: Budnick J. I. , Lechaton J. , Skalski S.
Published: January 2005

We have measured the 105Pd hyperfine field distribution in a series of Pd-Fe alloys ranging in composition from 0.5 to 25.0 at.% Fe by the NMR spin-echo technique. The features of the observed Pd spectra are strongly concentration dependent, and above 10%, are somewhat heat-treatment dependent, but always display at least two broad maxima. The ratio H̄Pd/μ̄Pd of the average Pd hyperfine field, obtained from our data, to the average Pd moment, as determined from the neutron scattering and magnetization data (assuming a constant value of 3.0 μB for the Fe moment), tends to a constant value of about 525 kOe/μB for Fe concentrations greater than about 4 at.%. As the Fe concentration is reduced below this value, this ratio rises rapidly since μ̄Pd→0, but H̄Pd approaches asymptotically a value of about 72 kOe. The interpretation of our data in terms of the long-range polarization model for the Pd-Fe system is discussed.
Linear Theory of the Vertex Function in Spin Dependent s-d Scattering
Authors: Duke C. B. , Silverstein S. D.
Published: January 2005

Following the field theoretic techniques of Abrikosov,1 we have derived a linear equation for the vertex function associated with the scattering of conduction electrons from magnetic impurities. We consider the model of a general nonlocal interaction consisting of the standard spin-independent impurity potential plus an s-d exchange interaction. In addition to the development of the linear theory, we have made an exact calculation of those terms in the electron proper self-energy which are linear in the density of the impurities to fourth order in the coupling constant for the restricted model of only an s-d exchange interaction.

We show that to logarithmic accuracy (in the sense of Abrikosov1), not only Abrikosov's vertex function, but also that of Suhl2 and the one which satisfies a linear integral equation all give the same result for the proper self-energy. However, the less divergent terms in any order of perturbation theory are not correctly reproduced by any of the vertex functions, which among themselves lead to different contributions to these terms in the self-energy. Thus, the use of the various vertex functions to compute the self-energy must be considered as inequivalent interpolation procedures for obtaining a substitute for the exact perturbation-theory results. We have solved the linear equation for separable s-wave interactions using both the ordinary and s-d terms in the potential. The linear equations do not manifestly exhibit the absence of singularities in the upper half-energy plane, and for weak, long-range separable interactions such singularities occur despite the interference between the spin-flip and non-spin-flip scattering. Although the linear theory is manifestly invariant under rotations, the resulting vertex functions do not satisfy single-channel, energy-shell unitarity2 in channels labeled by the coupled angular momentum of the incident electron plus impurity. The origin of this result is the linear theory's incorporation of correlations in the wavefunction of Fermi gas for which the incident electron couples to both the impurity and a particle-hole excitation to give other states of the same total angular momentum as that of the incident electron plus ``bare'' impurity. The states associated with such correlations assume the role of additional channels for the decay of an initial state with fixed angular momentum.
Upper Limit for the Magnetic Hyperfine Field in Antiferromagnetic Chromium
Authors: Ho James C. , Phillips Norman E.
Published: January 2005

For chromium, the magnetic hyperfine field He at the nuclei is of interest in connection with its antiferromagnetic structure, and for comparison with the values of He for the other 3d metals. The root-mean-square value of He can be determined from the T−2 magnetic hyperfine contribution to the heat capacity, and to determine this quantity, we have measured the heat capacities of two high-purity chromium samples between 0.06° and 1.2°K. The data can be represented by the equation C(mJ/mole deg) =0.00778 T3+1.45 T, in good agreement with the extrapolation from previously reported measurements1 above 1°K. The absence of an observable T−2 term at the lowest temperatures and the precision of the measurements give an upper limit of 13 kOe for the root-mean-square value of He. The resulting upper limit for the ratio of He to the average magnetic moment (∼0.5 μB) is similar to the value of this ratio found for γ-Mn,2 the other antiferromagnetic metal in the 3d group, but conspicuously smaller than that in the 3d-group ferromagnetic metals. This result is in disagreement with the measurements of Stetsenko and Avksent'ev,3 who found a hyperfine heat capacity of 0.086 T−2 mJ/mole deg, corresponding to He = 150 kOe.
Effect of Silicon on the Low-Induction Permeability of 4-Molybdenum Permalloy
Authors: Ames S. L. , Stroble C. P.
Published: January 2005

Using 350-g arc-melted button heats, measurements have been made of the effects of residual silicon on the initial permeability (μ40B) of 4-Moly Permalloy. Cooling rates in the atomic ordering range (1200°–600°F) were varied between 70° and 4750°F/h. Silicon has a considerable effect on cooling rate response, its effect being similar to molybdenum in that it slows down the cooling rate (CRopt) required to develop the best permeability. Since minor variations in nickel and molybdenum content also affect CRopt, it cannot be stated unequivocally that silicon is good or bad for properties. It is demonstrated that if the cooling rate is too fast for a given base composition, silicon is detrimental, while the reverse is true if the cooling rate is too slow for the base composition. However, in the latter case, the benefit of silicon is dependent upon maintaining a dry hydrogen atmosphere during the final anneal; with a −30°F dew-point hydrogen, the improvement is lost due to oxidation of the silicon. Some further effects of dew-point variations during the final anneal on magnetic properties are described in relation to residual silicon and aluminum.
Effect of Compositional Variation on the Permeability of Molybdenum Permalloy
Authors: Cohen Philip
Published: January 2005

Elemental pure powders can be used to produce magnetic alloys by blending and sintering. This approach was used to precisely define composition in a study of the effect of small composition changes on the permeability of Moly-Permalloys in the range of 4–6 wt % Mo, 78–82 wt % Ni, balance Fe. The alloys were sintered, hot and cold rolled to strip, and processed to rings in as identical a fashion as possible. The results show a uniform and consistent response to molybdenum content, nickel content, and cooling rate. Sharp peaks of permeability were not found. The results indicate that high permeability can be obtained for a wide range of compositions and cooling rate.
Anhysteretic Magnetization of Ni–Fe Tape Cores
Authors: Friedlaender F. J. , McMillen J. D.
Published: January 2005

Results of an experimental investigation of the anhysteretic magnetization of ``square-loop'' Ni–Fe tape cores are presented. Anhysteretic remanence and magnetization curves are identical below saturation remanence and can be reproduced with an accuracy of about ±10%. The initial slope of the anhysteretic magnetization does not depend on core geometry for a wide range of sizes, and takes on values from 3.6 to 29 H/m for different 50% Ni–Fe and square Permalloy cores. It is shown, by comparing hysteresis loops taken from an initial anhysteretic state, with minor loops taken conventionally, that the anhysteretic state seems to correspond to a state of about equal average flux at each cross section of the tape. On the other hand, saturation in opposite directions for the inner and outer wraps of the tape seems to occur when partial flux reversal is obtained by slowly increasing an applied dc field.
Elastic Flux-Switching Properties of a Thin Ferrite Core
Authors: Nitzan David , Hesterman Victor W.
Published: January 2005

A thin ferrite core (o.d./i.d.=1.06; Fc=0.9 At; φr=3.45 Mx) of nominal composition [Mg0.32Zn0.10Mn0.58]2+[Mn0.52Fe1.48]3+O4was mounted coaxially in a 50-Ω transmission line. Rectangular current pulses (0.4-nsec 10%−90% risetime Tr, and amplitude I varying in five steps from 0.9 to 40 A) were generated by a mercury-relay pulser and fed into the line. The pulses switched the core elastically from remanence (φ=φr) further into saturation (``shuttle'' switching). For each I value, the elastic φ̇(t), φ̇ε(t), was photographed on a sampling oscilloscope, and was found to include two components: an initial spike, φ̇εr(t), and a decaying tail, φ̇εw(t). [When a 1200-Oe transverse field was superimposed, φ̇εw(t) disappeared.] Each component was computed by solving a second-order differential equation of the form: φε+δφ̇ε+ηφ¨ε=εF, where δ, η, and ε are coefficients, and F is the applied mmf. Accounting for air flux, a very good fit was obtained in the entire I range by using the values δr=0.28 nsec and ηr=0.08 nsec2 for φ̇εr (underdamped with 490 Mc/sec oscillation), and δw=4 nsec and ηw=2 nsec2 for φ̇εw (overdamped). Correlation of φ̇εr(t) with Gilbert equation yields α≈0.57 and K1≈[minus]3.6·104 ergs/cm3. For either component, φε+δφ̇ε≈εF if Tr≫η/δ, e.g., if Tr≳5 nsec. It was found that δr and δw increase with Tr. For Tr=65 nsec, δr≈δw≈6 nsec; hence, φ̇εr≈εrḞ and φ̇εw≈εwḞ if Tr≳60 nsec.
Contrast Enhancement of the Transverse Kerr Effect
Authors: Hunt Robert P.
Published: January 2005

It is shown theoretically that the transverse Kerr effect can be enhanced in a similar manner to the longitudinal Kerr effect by applying a suitable dielectric to the surface of the magnetic medium. The parameters of the dielectric (thickness and refractive index) for optimum contrast must be adjusted to meet the usual antireflection conditions. These conclusions are substantiated by measurements on dielectrically enhanced thin evaporated molypermalloy films. The contrast, measured by the relative change in reflectivity, Δr/r, is enhanced by a factor of about 15. The same sample demonstrates a 20-fold enhancement in the longitudinal Kerr rotation (going from 6 min to 2 deg).
Raypath Trajectories in Magnetic Delay Lines
Authors: Addison R. C. , Auld B. A. , Collins J. H.
Published: January 2005

Behavior of the magnetoelastic waves in a magnetoelastic variable delay line has been simulated using geometrical acoustics. Assuming a magnetic field which approximates the internal field of a rod immersed in a uniform field, differential equations for the magnetoelastic rays have been obtained and solved numerically.

The rays are found to oscillate rapidly about the rod axis when they are predominantly spin waves. As they change into predominantly acoustic waves, the rays stop oscillating and propagate at a nearly constant angle with the rod axis. The final angles of the rays are quite dependent on the shape and magnitude of the magnetic field. Because of this, the final angles of the rays in the acoustic region of a delay line will vary as the delay is changed by adjusting the magnetic field. When these rays are not parallel to the rod axis, they will not retrace their paths upon reflection at the end of the rod. This phenomenon may explain oscillatory variations of insertion loss with delay which have been observed in delay line experiments. The validity of this interpretation is explored using results of the computer simulation.
Suppression of Spin-Wave Instabilities by Field Modulation
Authors: Hartwig C. P.
Published: January 2005

Spin-wave instabilities associated with ferromagnetic resonance have been suppressed in experiments on parallel pumping as well as ``second-order'' saturation of the main resonance. A method is described in which a modulating field (∼1 Mc/sec) is applied along the dc bias field. Theoretical suppression curves have been derived and are compared with experiments on spheres of YIG at X band. An experiment is described in which the cone angle of the uniform precession is opened beyond the usual instability threshold without the generation of sidebands.

The extent of suppression is determined by the modulation index δ, which is proportional to the ratio of modulating field strength to modulating frequency. In the parallel-pumping experiment, threshold power is expected to increase 7 dB per decade increase in δ for δ>0.92. Experimentally the threshold has been raised in excess of 10 dB. A mathematical model has been developed to explain deterioration of the suppression when the modulating frequency is comparable to or less than the relaxation frequency of the spin waves. Stabilization of the main resonance requires application of both transverse and longitudinal modulation. Where a ``second-order process'' is involved, only half as much suppression is possible as in the case of parallel pumping for equal δ.
Variation of Sound Velocity with Magnetic Field in Mn-Doped YIG
Authors: Gyorgy E. M. , Krause J. T. , LeCraw R. C. , Testardi L. R. , Van Uitert L. G.
Published: January 2005

The variation of the sound velocity with magnetic field in Mn-doped YIG has been studied in both rods and spheres. The samples were single crystals containing 2.3 wt % Mn. With the rods, which were approximately 0.3×0.3×2.0 cm, the sound velocity was measured directly while with the spheres (about 0.3 cm in diameter) the resonant frequency was measured. For a rod with the sound propagation in the 〈111〉 direction, the change in ultrasonic shear velocity for a field change from 200 G (required for saturation) to 2 kG was 13% at 87°K, 13% at 106°K; 9.5% at 140°K, 8% at 213°K, and 3.4% at 290°K. For rods with the sound propagation in the 〈100〉 direction, the change in velocity with magnetic field at any temperature was greatly reduced compared to that observed for the 〈111〉 direction. Furthermore, the velocity of longitudinal waves did not show any appreciable field dependence. With spheres magnetized along 〈111〉, the resonant frequency of the lowest shear mode changed by 30% at 77°K for a field change from 0.8 kG (sufficient to saturate the sample) to 6.0 kG. Some of the experimental observations can be interpreted on the basis of the simple theory of magnetostrictively coupled phonon and spin waves. However, this picture fails in some important aspects, indicating that the interaction of the acoustic waves with the magnetization in Mn-doped YIG is more complex.
Phase-Shift Characteristics of Magnetostatic Spin Waves
Authors: Webb D. C. , Moore R. A.
Published: January 2005

The phase-shift properties of magnetostatic modes propagating through single-crystal yttrium iron garnet rods are developed. The dispersive equation for these modes propagating in an infinitely long cylinder is combined with the expression for the inhomogeneous field in the rod. The total integrated phase shift is calculated by using a second-order expansion of the field about the center, since the majority of phase shift occurs in that portion of the rod. The phase shift was found to diverge logarithmically as the magnetic field approaches a characteristic value at which the group velocity of the center of the sample becomes zero. Experimental verification of the analytical results was conducted by measuring the magnetic-field increment to produce a 2π phase shift as a function of magnetic bias. Excellent correlation is achieved for both the slope of the field increment vs the bias curve and the position of the phase pole. Using the same constants in the expression for group velocity, adequate correlation is achieved with published time-delay data. It is, therefore, concluded that the model employed does provide an accurate description of the phase-shift process for many applications.
Propagation and Variable Delay on a Periodic Circuit of YIG Spheres
Authors: Egan William F. , Shaw H. J. , Chodorow Marvin
Published: January 2005

A microwave-propagating structure has been investigated which is composed of a periodic, linear array of coupled YIG spheres operating in the uniform precession mode. Theoretical and experimental data on the propagation characteristics are presented. Both forward and backward types of waves exist. The system has characteristics of an electronically controllable filter and delay line whose properties are controlled by varying the applied dc magnetic field. Delay times in the nanosecond to microsecond range, with control of group velocities over a range of 5 to 1 or more, at signal attenuations on the order of 0.03 dB/nsec of total delay, appear possible.
Neutron—Diffraction Study of Cr and Cr Alloys
Authors: Werner S. A. , Arrott A. , Kendrick H.
Published: January 2005

The principle quantities which parameterize the antiferromagnetism of Cr are studied by neutron diffraction as a function of temperature, pressure, magnetic field, and concentration of solute atoms. In order to account for the observed intensities of the magnetic reflections, their dependence on magnetic field and temperature, the torque measurements of Montalvo and Marcus, and the creation of a ``single-Q'' state in field-cooling, a model is proposed based on the presumed existence of thermally active polarization domains within a ``single-Q'' region of the crystal. The variation of the polarization axis from place to place and with time lowers the free energy by an increase in entropy. The pressure dependence of the first-order phase change at 38.5°C is given as dTN/dP=−5.4 deg/kbar. The temperature dependence of the length of the wave vector below TN is given as (1/Q) (dQ/dT)=6.3×10−5 deg−1. Alloys with 0.5 and 0.78 wt% Fe and with 0.9 wt% Co show a decrease in TN of ∼20°K per at.% of solute. The amplitudes of the magnetization waves increase and the wave vector Q approaches commensurateness with the lattice periodicity with increasing solute concentration in contrast to results for other solutes. Some unusual effects were observed for 2.3 wt% Fe samples.
Magnetic Form Factor of Ni in the Paramagnetic State
Authors: Caglioti G. , Cooper M. J. , Minkiewicz V. J. , Pickart S. J.
Published: January 2005

A polarized beam measurement of the magnetic form factor of Ni in the paramagnetic region (T∼1.6 Tc) has been performed to detect any possible differences in the spin density distribution from that of the ferromagnetic state. Because of the smallness of the effects, the measurement, carried out in an applied field of 13 kOe at 1030°K, was limited to the first five Bragg reflections. After correction for extinction and depolarization, the magnetic amplitudes (other than at the origin) are found to scale reasonably accurately with the room-temperature values, so that we may conclude there is no gross difference in the localized part of the spin density. The value at the origin, derived from the susceptibility, does not scale similarly with the ferromagnetic moment, and this difference is tentatively ascribed to changes in the conduction electron distribution.
Nuclear Spin Relaxation in Antiferromagnets
Authors: Pincus P.
Published: January 2005

The early theoretical studies by Moriya on the role of spin-wave processes in relaxing the nuclear magnetization in antiferromagnetic insulators have been extended to include three magnon processes. This process is the lowest order T1 mechanism which is allowed by both energy and angular momentum conservation in systems where the hyperfine interaction is isotropic. In collaboration with Beeman, Jaccarino, Kaplan, and Loudon, a detailed experimental and theoretical investigation of the 19F relaxation in MnF2 has been carried out and the dominant Raman mechanism has been identified. Narath and Fromhold have measured the 53Cr spin-lattice relaxation rate in metamagnetic CrCl3 and have clearly identified the three magnon processes. These experiments appear to constitute the first unambiguous observations of intrinsic magnon-induced nuclear relaxation in magnetic insulators.
A Mössbauer-Effect Study of Antiferromagnetic FeCl2·4H2O
Authors: Johnson C. E. , Ridout M. S.
Published: January 2005

Measurements of the Mössbauer effect of 57Fe in single-crystal and polycrystalline absorbers of ferrous chloride tetrahydrate, FeCl2·4 H2O, have been made from the Néel temperature (TN∼1.1°K) down to 0.4°K. The hyperfine field at the iron nuclei was 260±5 kG and the Fe2+ spins were shown to align at a small angle to the symmetry axis of the electric-field gradient tensor and to make an angle of about 30° with the b axis, in confirmation of the conclusions drawn from susceptibility and quadrupole splitting data. The decrease in the effective magnetic field at the nuclei with increasing temperature was small. Near TN the linewidth became very broad owing to the slowing down of the electron-spin fluctuations.
Antiferromagnetic Resonance in Cubic TlMnF3
Authors: Eastman D. E. , Shafer M. W.
Published: January 2005

Antiferromagnetic resonance has been observed in single crystals of a new cubic antiferromagnet with the Perovskite structure, TlMnF3. The crystals were grown from a melt in a sealed platinumlined molybdenum container under a slightly positive TlF pressure. AFMR at 25 GHz was used to determine TlMnF3 to be an undistorted cubic antiferromagnet at 4.2°K with 〈111〉 easy axes. At 4.2°K the exchange field was determined as HE = 630 kOe, the cubic anisotropy field as HA = −4K1/3Ms = 6.8 Oe and the linewidth as 80 Oe. The linewidth is mainly due to inhomogeneous strain broadening. From measurements of AFMR field vs axial stress, the Néel temperature has been determined as TN = 76±1°K and the magnetostriction constant as λ100 = −4b1/[3(c11−c12)] = −3.2×10−6 at 4.2°K. The spin-lattice stress coefficient for Mn2+ is C11 = 4.7×10−13 cm/dyn per ion after correcting for the magnetic dipolar contribution. The paramagnetic Curie temperature has been determined from high temperature susceptibility measurements as θ = −138°K.
Uniform Mode Resonance and Spin-Wave Instability in RbMnF3
Authors: Cole P. H. , Courtney W. E.
Published: January 2005

Low-power resonance linewidth and high-power second-order spin wave instability measurements have been performed at 4.2°K on the cubic antiferromagnet RbMnF3. With increasing power level the uniform mode susceptibility shows a small initial rise, followed by a hyperbolic decline from a critical rf field of 0.32 Oe. The very large low-power resonance linewidth of 140 Oe, much greater than the width of the spin-wave band, can be understood by assuming a variation of anisotropy over the sample in the manner suggested by Eastman. The instability thresholds for spin waves excited in the regions of large amplitude precession in nonuniform samples is derived by a iterative solution of the coupled equations of motion. To the first order, the departure from the uniform sample threshold depends upon the range of correlation r0 of the anisotropy fluctuation. When r0≫10−5 m, simple formulas for the susceptibility and critical field can be used. The theory has been fitted to the observed decline of susceptibility curve with the value ΔHk = 7.6 Oe. This result may be compared with the value ΔHk = 3×10−2 Oe which is obtained from a uniform sample theory, and assuming the relaxation rate of the uniform mode to be given by the resonance linewidth.
Antiferromagnetic Resonance in NaMnF3
Authors: Shane J. R. , Lyons D. H. , Kestigian M.
Published: January 2005

The angular dependence of the AFMR in oriented single crystals of NaMnF3 has been investigated at 70 GHz and 4.2°K. In addition to the usual AFMR which is found at all applied field orientations, spin-flop resonance modes which are double valued in applied field are observed over a narrow angular interval centered about the [100] axis of the orthorhombic unit cell. A two-sublattice model has been used to derive the equilibrium positions of the sublattice moments and the angular dependence of the field for resonance. The model contains anisotropy fields consistent with the orthorhombic crystal structure and canting fields resulting from both single-ion anisotropy, and antisymmetric-exchange interactions, which produce a weak ferromagnetic moment parallel to the c axis. The effects of both types of canting mechanisms are described, and the constants used in the model have been determined from the resonance data. It was found that resonance absorptions in several crystals displayed structure which depended upon the sizes and shapes of the samples. In particular, nonspherical samples of the order of 1 mm or larger contained many lines with complex angular dependences. The splittings in smaller, spherical-shaped samples are interpreted as resulting from magnetostatic modes.
Spin-Wave Impurity Effects in Iron-Manganese Ferrites
Authors: Houston T. W. , Heeger A. J.
Published: January 2005

Studies of the temperature dependence of the 55Mn nuclear magnetic resonance in the system MnxFe3−xO4 for 0.1≤x≤1 are presented. From the experimentally determined temperature dependence of the local magnetization, we obtain evidence for the importance of spin-wave impurity effects in the region of dilute Mn impurities in Fe3O4. A comparison of the data from Mn1Fe2.9O4 with Boyd's 57Fe NMR data for A sites in Fe3O4 shows that the magnetization at the impurity manganese sites is falling off more rapidly with temperature than the host Fe3O4 magnetization. This is consistent with an increased probability of finding a spin deviation at manganese sites as expected for JMn-Fe<JFeFe. The deviation of the impurity magnetigation from that of the host is well explained by the theory of Hone, Callen, and Walker, using a ratio of Ji/Jh=0.7 as obtained from experiments on the pure materials at either end of the series.
Ferromagnetic Properties of Single-Crystal Nickel Platelets and Submicron Whiskers
Authors: DeBlois R. W.
Published: January 2005

Nearly perfect nickel, nickel alloy, and iron single-crystal platelets of thin-film thickness are excellent specimens for basic ferromagnetic domain, domain-wall,1,2 and resonance3 studies. Submicron nickel whiskers that grow with the platelets are also ideal for nucleation studies.4 Individual whiskers as thin as 600 Å (2 pg) are readily observed (by Rayleigh scattering), tested, and handled. Physical buckling of the whiskers into forms of the elastica5 allows measurements of both end and infinite-rod nucleation fields. Observed fields versus whisker diameter and versus field angle follow curling theory.6 Thickness comparisons by electron microscopy and by bending yield an effective Young's modulus near 10×1111 dyn/cm2, about half the handbook value. A motion-picture film showing the physical bending and the magnetic nucleation of whiskers suspended in a thin layer of oil and viewed through a microscope by dark-field illumination was presented at the conference.

The platelets show with classic simplicity many details of domain and domain-wall structure and behavior, making them especially suitable for educational purposes, for testing theories, and for supplementing thin-film studies. Recent platelet observations include double 90° and 180° Bloch walls; a double wall apparently composed of 180° walls of mixed Néel-Bloch character; 180° Bloch walls that may press against a platelet edge without parting; 45° walls formed by magnetostrictive anisotropy; a field-induced stripe pattern in [100] Ni-Co platelets with +K1; and the transitional domain structure in a Ni-Co platelet with a linear variation in composition from +K1 to −K1.
Evidence for Domain-Wall Compressibility in Permalloy Wire
Authors: Schulz-DuBois E. O.
Published: January 2005

This paper describes dynamic magnetization experiments in hard-drawn niobium silver Permalloy wire of the type used in domain wall shift registers. In particular, it reports evidence for the compression under the influence of an applied bucking field of the transition region separating two domains of antiparallel longitudinal magnetization. In the absence of external field, the transition region is characterized by a domain wall roughly in the shape of a paraboloid of revolution with a minimum length of about 1 cm for wire of 0.005-cm diameter. Within the transition region a longitudinal derivative of flux exists which may be conveniently referred to as magnetic pseudo charge. For a transition, the total charge is conserved and the length of the transition is inversely proportional to charge per unit length. The charge contained in about 0.1-cm length of wire was measured by a pickup coil consisting of two adjacent coils with opposite sense of winding, connected in series, and subsequent electronic integration. The charge under this coil was increased and decreased by applying a 60-Hz longitudinal field to the wire with a reversal of direction under the pickup coil. These dynamic experiments with or without an additional homogeneous field result in hysteresis loops of particularly simple and predictable shape. The identifiable individual processes within the cycle are nucleation, wall compression and expansion, and wall motion. A compression of the longitudinal dimension of the domain wall by a factor 4 is inferred from that increase in charge when the compressing field is ±17 Oe. The curved portions of the loop follow, with good accuracy, a square-law dependence. Such a shape is expected from dimensional arguments applied to the magnetostatic situation which predict the proportionality Q ∝ (HB±HW)½, where Q is the charge under the pickup coil, HB is the applied bucking field, HW is the wall motion threshold, and the choice of signs implies some hysteresis connected with the motion of parts of the wall. Loops taken without the additional homogeneous field indicate the absence of a distinct nucleation phenomenon. A process akin to pair creation is proposed which converts a wall of positive charge, for example, into a sequence of positive, negative, positive charged walls and where the outer two walls then move away by conventional wall motion.

A more complete account of this work is intended for publication elsewhere.
A Recording High-Field Oscillating-Specimen Magnetometer
Authors: Strnat K. , Bartimay L.
Published: January 2005

An instrument for measuring magnetic moments in the range of 10−4 to 102 emu on small samples (1–100 mg) up to 50 kOe and at temperatures between ∼8° and 425°K is described. The specimen oscillates between the centers of two pickup coils 21 mm apart. It is driven by a synchronous motor and eccentric at 2–20 cps. The output of the coils is measured with an integrating digital voltmeter having 1 sec normal integration time. Quasicontinuous recording of the moment as a function of temperature and field strength is possible through the use of a digital-to-analog converter and X-Y recorder. The sample is magnetized in a superconducting solenoid. Moment measurement is relative to a nickel standard. Present performance figures and possibilities for improving the detection limit to below 1.2×10−5 emu are discussed.
Nucleation and Growth of Reverse Domains
Authors: Childress J. D.
Published: January 2005

The nucleation and growth of ``spike'' domains of reverse magnetization at grain boundaries are analyzed in detail to show how these domain may account for hysteresis-loop rectangularity in polycrystalline soft magnetic materials. In a development based on the usual idealizations and approximations, the minimum-energy-condition equations are solved numerically for material values representative of the Mg–Mn ferrites. Results are presented to show (1) the variation of the size and shape of reverse domains with applied field, and (2) the critical fields for nucleation (nucleation field) and for unlimited growth (threshold field) of such domains as a function of grain-to-grain misalignment of magnetization vectors. The coercive force (equal to minimum threshold field) is shown to be Hc=4.9 σw/MsD and a condition for hysteresis-loop rectangularity to be 〈ω*2〉≪12.9 σw/D, both in fair approximation. Here σw is the domain-wall energy density, Ms is the saturation magnetization, D is the grain size, 〈ω*2〉 is the average of ω*2, where ω*=n·(M1−M2) is the pole density at the grain boundary. These results are in satisfactory agreement with earlier qualitative ideas.
The Spectrum of the Magnetic Aftereffect in Neutron-Irradiated Ni Single Crystals
Authors: Seeger A. , Walz F. , Kronmüller H.
Published: January 2005

The magnetic aftereffect of Ni single crystals following an irradiation of 1019 neutrons/cm2 was investigated in the temperature interval between 90° and 400°K. In addition to small peaks, major relaxation peaks were observed at −125°C, −98°C, −79°C, and −28°C. Above 0°C some broad peaks are observed. An analysis of the disaccommodation shows that the relaxation peaks are due to single relaxation processes, the relaxation times of which depend on temperature through an Arrhenius equation. The relaxation peaks are attributed to the reorientation of point-defect clusters. A detailed analysis shows that the relaxation peak at −28°C is due to the reorientation of divacancies (orthorhombic symmetry). The relaxation above 0°C is the result of a diffusion of the divacancies within the domain walls. The low-temperature peaks are tentatively ascribed to the reorientation of trivacancies (trigonal symmetry) and other point-defect clusters, some of them possibly involving impurities.
The Contribution of Dislocations to the Magnetocrystalline Energy and Their Effect on Rotational Hysteresis Processes
Authors: Kronmüller H.
Published: January 2005

Internal stresses of dislocations interact in ferromagnetic crystals with the spontaneous magnetization through the magnetoelastic coupling energy. The magnetic free energy (MFE) of a straight dislocation line is calculated by means of Brown's micromagnetic equations. This energy corresponds to a magnetostrictive contribution to the magnetocrystalline energy which is superimposed on that of the ideal crystal. In a material with isotropic magnetostriction the MFE of a straight edge dislocation line possesses orthorhombic symmetry.

The theoretical results may be compared with those of an investigation of magnetization processes of plastically deformed Ni single crystals by Köster. Analysis of measurements of the magnetostriction and of the increase of magnetization as a function of the applied field has shown that in deformed Ni crystals the MFE of the dislocations may become comparable to the magnetocrystalline energy constant K1 of the ideal crystal.
Anomalous Behavior of the Negative Magnetoresistivity in Au-Fe Alloys
Authors: Rohrer H.
Published: January 2005

The magnetoresistivity of dilute Au-Fe alloys containing 0.1 at.% to 1 at.%Fe has been measured in the temperature range 2° to 77°K and in magnetic fields up to 200 kOe. Although the residual resistivity ρ is proportional to the Fe concentration, the negative magnetoresistivity Δρm/ρ, due to the freezing out of the contribution of the exchange scattering, drops rapidly with increasing Fe concentration. We find Δρm/ρ = − (A + Bc)−1, where c is the Fe concentration in at. % and A and B are parameters which depend on temperature and magnetic field. At low temperatures A and B are positive and of comparable magnitude; B is decreasing with both increasing field and increasing temperature. Above 22°K, B is small and negative.

At low temperatures, two anomalies of the magnetoresistivity are observed: First, in the highest fields applied no saturation of Δρm is obtained and second, below a certain temperature T0, Δρm is no longer a function of μH/kT only, as theoretically expected [except for very slowly varying terms of the form ln (EF/μH)]. These anomalies become more pronounced with increasing impurity concentration. T0 increases from 10°K for 0.1 at.%Fe to about 50°K for 1.01 at.%Fe. By extrapolating Δρm/ρ to zero Fe concentration these anomalies remain. Therefore, they seem to be intrinsic and are merely enhanced by correlation effects between the impurities.

Further, from the temperature dependence of the zero-field resistivity and the high field resistivity, the s-d interaction parameter, J, was obtained to be 0.064 eV < J < 0.1 eV. This value of J is considerably smaller than previously reported for similar alloy systems like Cu-Mn, Y-Ce and others. It is shown that the reason for such high values of J is an incorrect application of Kondo's expression for the exchange resistivity.
High-Temperature Magnetostriction in Alloys
Authors: Belson Henry S.
Published: January 2005

Conventional theory predicts that the magnetostriction coefficients h1 and h2 fall monotonically to zero with increasing temperature. Callen and Callen have proposed a theory to account for the presence of an anomalous peak in h1 for iron just below the Curie temperature, based on the fact that an ellipticity in the magnon spectrum permits a lowering of the free energy by crystal distortion. An anisotropic magnon-phonon interaction near the Brillouin-zone boundary is largest when thermal magnon renormalization has lowered the magnon spectrum to degeneracy with the phonon spectrum, at which a peak in h1 occurs. Thus, iron whose Curie temperature is substantially greater than the Debye temperature shows this effect. To test this theory further we have measured h1 in a cubic single crystal of 56.96 wt% Ni-42.82 wt% Co with Curie and Debye temperatures approximately those of iron, using a capacitative method. We find a monotonic decrease in h1 from 1.49 × 10−4 at 80°K to close to zero at 1000°K, and no hint of a peak. We have also checked a prediction of the theory that the peak in iron should be shifted to lower temperatures by alloying with a light element and unshifted by alloying with a heavier element by measuring h1 for alloys of Fe +1.25 wt%Al and Fe +3.43 wt% Sn. We observe no shift in the peak from the pure-iron position. Measurements on cubic 90.1 wt% Co-9.83 wt% Fe, which has a Curie temperature substantially above its Debye temperature, show h1 is negative at 300°K and has a large positive peak at 950°K.
Lorentz Microscopy in Polycrystalline Ni–Fe Films 2000-Å Thick
Authors: Lo D. S. , Olson A. L. , Olson C. D. , Oredson H. N. , Simon W. J. , Torok E. J.
Published: January 2005

The use of Lorentz microscopy has been reported on polycrystalline films 1450 Å and thinner. In this paper the use of Lorentz microscopy on polycrystalline films in the thickness range between 1200 and 2000 Å is presented, and some of the more unexpected results discussed. The intermediate wall cross-ties observed in a 1450-Å film as reported earlier were not found in a low-dispersion Ni–Fe film 2000±50 Å thick (the thickness measurements were made carefully with torque magnetometer, Tolansky apparatus, and loop checker with calibrated standard), but when the film was annealed in vacua so that the crystallites became enlarged and Hc and α90 increased, the intermediate wall cross-ties were observed. The conclusion is that the biaxial inhomogenities caused the 180° Bloch wall to become a 170° wall in some segments and a 190° wall in others. Then, according to intermediate wall theory, these non-180° walls must have a Néel component which alternates along the length of the wall, thereby causing the cross-ties. Stripe domains were also observed in samples from other evaporations, but when fields were applied in the microscope to observe the switching processes, the stripes were erased and could not be brought back.
Anisotropy Constant of 50:50 Ni–Co Alloy Films
Authors: Carter Walter S.
Published: January 2005

Measurements have been made on a series of films, about 1000-Å thick, prepared from Ni–Co ingots having a Ni content of 50% by weight. The depositions were made on glass microscope slides in the temperature range 20°C to 400°C. The measurements were made with a Kerr effect loop-plotter on an area of 2 mm sq. The results show a correlation between HK (Kobelev's method) and αq which is not directly dependent on the substrate temperature. By extrapolation, HK(αq = 0) = 33 Oe. This value is 40% higher than that calculated assuming that the anisotropy is due to the magnetoelastic constraint energy mechanism. However, because of the assumptions used, the calculated value is considered to be close enough to propose that this mechanism is dominant in determining the anisotropy. The relation between HK and αq is interpreted as due to both parameters being dependent on the intercrystallite coupling.