bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetoacoustic Effects in Rare-Earth Iron Garnets
Authors: Franz Judy R. , Luethi Bruno 
Published: January 2005

We have used the techniques of linear magnetoacoustic birefringence and transverse ferroacoustic resonance to measure the real and imaginary parts of the index of refraction of soundwaves in the rare-earth iron garnets. The sound waves act as a probe to study the magnetoelastic coupling and the large rare-earth ion relaxation effects in concentrated samples. We investigated YbIG, DyIG and TbIG in the temperature range from 77° to 300°K. The transverse ferroacoustic resonance geometry, RπM, (R=acoustic shearwave polarization vector, M=magnetization) was used to study the linewidth broadening. In YbIG, even at 77°K, the linewidth is only slightly broader than in YIG and GdIG; in DyIG the broadening is pronounced, especially towards lower temperatures; and in TbIG it is so big that no ultrasonic echoes are observable below the magnetization compensation point. The linear birefringence geometry, R and M at 45°, was used to measure the difference in phase velocity between coupled and uncoupled shearwave components.
We have attempted to calculate linewidths and effective magnetoelastic coupling constants, by applying the so-called ``slow relaxation theory'' to the phonon-coupled spin system. A comparison of this theory with our experimental results will be given.
Effect of Phosphorus on the Magnetization of Nickel
Authors: Albert P. A. , Kovac Z. , Lilienthal H. R. , McGuire T. R. , Nakamura Y. 
Published: January 2005

The effects of phosphorus on the magnetization of nickel have been examined for thin films made by electroless deposition, electrodeposition, and by vacuum evaporation. While P has a very low solubility in bulk nickel, the results indicate that all three processes result in a metastable solid solution of P in Ni, which is transformed into the stable (paramagnetic Ni3P plus Ni) configuration by annealing at 850°K. The concentrations of P in the deposited films were varied and quantitatively established through the use of NaH232PO2 in the deposition process, coupled with radio-analysis techniques.
The magnetic data obtained are in qualitative agreement with z=5 in the expression, μB=n0−cz, where n0 is the number of holes in the 3d band of nickel, c is the concentration of phosphorus, and z its valence. Data on the behavior of magnetic moment and Curie temperature with P content are presented and a tentative explanation put forth for some anomalous behavior of these parameters.
Effect of Aluminum on the Saturation Moments of Fe-Ni Alloys
Authors: Bardos D. I. , Aldred A. T. , Beck P. A. 
Published: January 2005

The saturation magnetizations of Ni-Fe-Al terminal solid solution alloys have been measured by a force method. Field intensities up to 12.5 kOe were applied and the temperature of the specimens varied from room temperature to 8°K. Average atomic magnetic moments were calculated from values of σ∞,0 which were obtained by customary extrapolation procedures.
In the fcc alloy series with constant Ni-to-Fe ratios of 4:1, 3:2, and 2:3, the average-magnetic-moment-per-atom vs Al-content curves were found to have initial slopes of −2.6, −3.1, and −3.8 μB per atom, respectively. The decrease of the saturation moment in the disordered fcc alloys can be satisfactorily accounted for if the average Ni spin moment in any ternary alloy is assumed to be the same as that of the binary Ni-Al alloy with the same Al content, and if the average Fe moment is taken to be the same as in a binary Ni-Fe alloy with the same number of Ni nearest neighbors adjacent to each Fe atom.
Investigation of the First-Order Magnetic Transformation in Mn3Pt
Authors: Krén E. , Kádár G. , Pál L. , Szabó P. 
Published: January 2005

The effect of composition on the first-order transformation from triangular into collinear antiferromagnetic structure (AF-AF transformation) occurring in ordered Mn3Pt has been investigated on ternary Mn3Pt1−xRhx and binary Mn3+yPt1−y alloys using x-ray and neutron-diffraction methods.
On increasing the concentrations x and y an increase in both the Néel and the transition temperatures with a simultaneous decrease in the lattice parameter were observed. The magnetic moment of Mn remained the same irrespective of the concentration and the AF-AF transformation. The results suggest the existence of a critical lattice-parameter value at which the transformation occurs, like that observed for the Mn2−xCrxSb system.
Spin-Density Distribution and Electronic Structure in Fluorides with the Perovskite Structure (ABF3, where A=Na, Rb; B=Mn, Ni, Co)
Authors: Smolenskii G. A. , Petrov M. P. , Pisarev R. V. 
Published: January 2005

The local magnetic fields and spin density on 19F and on A nuclei have been studied by NMR method; in RbCoF3 the measurements being also made on 59Co. The spin density on A nuclei differed from zero only in those crystals where unpaired electrons were on t2g orbitals of paramagnetic ions. The results were analyzed by MO–LCAO.
The optical absorptions of NaNiF3, RbNiF3, NaCoF3, and RbCoF3 were studied from 0.24 to 15 μ. The results were analyzed on the basis of the ligand field theory. The energy of the exchange interaction in the ground and excited states was estimated in some cases from the shift of absorption lines near Néel temperature. The intensity of some lines increased when cooling the crystals. A great increase of intensity of some Mn2+ lines was observed in NaNi0.96Mn0.04F3. The increase took place in those parts of the spectrum where Mn2+ and Ni2+ ions had near-lying electronic states.
Contrast in the Electron Microscope due to Stray Magnetic Fields near Single-Domain Iron Whiskers
Authors: Rodgers J. M. 
Published: January 2005

Single-domain iron whiskers having diameters of 0.5 to 5 μ have been investigated under in-focus Lorentz (Foucault) conditions in normal specimen stages of A.E.I. EM6 and R.C.A. EMU-3 electron microscopes. Contrast is observed in the region of object space surrounding whisker tips which is consistent with that predicted by considering the effect of stray magnetic fields on the electron beam. Such contrast is readily distinguished from that due to electrostatic fields.
A slight modification of the Lorentz technique enables quantitative measurements of the field to be made for certain configurations of the whisker surface. In particular, micrographs of tapered whiskers show the presence of stray fields due to free poles along the prism faces. The measured magnitude of the effect of these fields is in fair agreement with calculated results assuming the magnetization to be uniform and parallel to the whisker axis.
Iron whiskers 300 Å in diameter show no evidence of any magnetic contrast; a suggested detection limit is ∼1000 Å. Reversal of magnetization direction is easily detectable; it is suggested that precise measurements of coercivities of individual whiskers could be made using this technique.
Average Ripple-Angle Magnitude, Wall Pinning, and Susceptibility in Thin Permalloy Films
Authors: Comstock C. S. , Sharp A. C. , Frantsvog D. J. , Pohm A. V. 
Published: January 2005

A modified bias-susceptibility apparatus and other instrumentations were used to examine the average ripple-angle magnitude 〈δφ〉av, the ``strip-domain wall pinning'', and the real and imaginary parts of the incremental susceptibility for several 1000-Å 80−20 Permalloy films with various dispersion angles. The measurements were performed under various field conditions and with various field histories.
The results of the experiments show that, as suggested by Harte et al., the average ripple-angle magnitude 〈δφ〉av depends primarily on a micromagnetic equilibrium between local perturbing torques and the average field aligning the magnetization. The angles typically ranged from 1° to 15°. Similar average ripple-angle magnitudes were obtained when the Stoner-Wohlfarth field threshold was approached with the magnetization at angles of 0°, 45°, and 90° from the rest direction. However, as discussed by Hoffman, second-order effects produced significant differences in the measurements.
Considerable pinning of the walls separating ``strip domains'' occurred. The wall pinning made the measurements sensitive to the magnetic history of a sample and displaced the peaks of the bias permeability loss curves to higher bias field values. Direct measurements indicated that internal demagnetizing fields from pinned walls reduced the real and imaginary parts of the incremental susceptibility in a direction perpendicular to the average magnetization by a factor from 2 to 10.
Spin-Wave Locking of the Uniform Rotational Switching Mode in Magnetic Films
Authors: Harte K. J. 
Published: January 2005

The threshold field for high-speed, uniform rotational switching in magnetic films is experimentally found to be higher than predicted by single-domain theory.1,2 This discrepancy, which leads to the appearance of an intermediate-speed switching process, can be explained by a spin-wave locking model, which is here reviewed and extended. The underlying physical mechanism is the conversion of longitudinal spin-wave modes to transverse modes via the rotation of the uniform mode. A transient state of high magnetostatic energy is thereby created, and if the resultant spin-wave reaction torque becomes greater than the uniform torque, the uniform mode locks.
Two limiting cases are discussed. In the first, the spin-wave relaxation time is assumed to be greater than the uniform-mode switching time.3 It is the initial spin-wave state which acquires a transverse component, and locking can occur at any time up to the minimum in the uniform torque. In the second case, the relaxation time is assumed to be much less than the switching time.4 The initial spin-wave modes remain in equilibrium with respect to the uniform mode and grow in amplitude until they are prevented from reorienting by local instabilities induced by the component of the longitudinal magnetostatic force antiparallel to the magnetization,5 which becomes large near the minimum of the uniform torque. Then. conversion to transverse modes occurs as before, with locking of the uniform mode taking place near the torque minimum.
From calculations based on an initial dispersion-induced ripple state, the ``universal'' relation Tu (0) = 0.122 Kuα is derived for both cases and over a wide range of experimental situtions, where Tu (0) is the threshold starting torque for uniform rotation, Ku is the uniaxial anisotropy energy, and α is the rms hard-axis fallback angle6,7 (in degrees). Experimental results of Telesnin et al.8 appear to verify the above law.
Finally, an experiment is proposed to distinguish between the slow- and fast-relaxation models.
Magnetic Structure of Er2O3 and Yb2O3
Authors: Moon R. M. , Child H. R. , Koehler W. C. , Raubenheimer L. J. 
Published: January 2005

Neutron-diffraction measurements on single crystals and powders of Er2O3 and Yb2O3 have been used to establish the magnetic structures of these materials. Crystallographic structure parameters were determined by single-crystal measurements at 4.2°K and the magnetic intensities were measured at 1.3°K. The Néel temperatures are 3.36°K for Er2O3 and 2.25°K for Yb2O3. A noncollinear antiferromagnetic model is proposed for Er2O3 which gives good agreement with the observed magnetic intensities. In this model the eight rare earth sites with point symmetry C3i have moments along the local 〈111〉 symmetry axis. The remaining 24 Er ions, with point symmetry C2, have moments along the local 〈100〉 symmetry axis. Sites related by the body-center translation have moments in the same direction. This model is identical to that proposed by Bertaut and Chevalier,1 except they conclude that the two sites have equal moments, while we find 6.1±0.1 μB on the C3i sites and 5.4±0.1 μB on the C2 sites. This configuration is consistent with g-factor measurements which indicate highly anisotropic g tensors for both sites with the major axis for each site along the local symmetry axis. The dipole field produced by this array is self-consistent in that the resultant field at each site, due to dipoles at all the other sites, is in the direction of the dipole moment at that site. The dipole-dipole energy for the C3i sites is 4.0°K but is only 0.4°K for the C2 sites, so that superexchange coupling must be invoked to explain the observed transition temperature. A calculation of the expected moment for the C2 sites, based on the ground-state wavefunction given by Gruber, Krupke, and Poindexter,2 gives a value of 2.1 μB, in definite disagreement with the neutron diffraction result.
For Yb2O3 a structure is proposed in which moments of 1.06±0.06 μB at the C3i sites are oriented along 〈111〉 directions but not along the particular 〈111〉 local symmetry axis. The C2 sites have moments of 1.88±0.06 μB, oriented along 〈110〉 directions perpendicular to the local symmetry axis. Sites related by the body-center translation have their moments directed oppositely. This configuration is not consistent with a coupling scheme based on dipole-dipole interactions.
Magnetic Properties of Rare-Earth Compounds
Authors: Busch G. 
Published: January 2005

The magnetic properties of binary rare-earth compounds are reviewed. The influence of crystal field and exchange interaction on the magnetic properties is shown to vary systematically in the group of LnX compounds [Ln=Lanthanide atom, X=N, P, As, Sb]. Crystal-field parameters are calculated.
The europium-chalcogenides are of particular interest. From measurements of the magnetic susceptibility at normal and under high pressure it is concluded that EuSe is antiferromagnetic above 3°K approximately with a Néel temperature of 4.6°K, but it assumes a ferro- or ferrimagnetic structure at lower temperatures.
The optical absorption of EuO, EuS, EuSe, and EuTe was measured as a function of temperature. Energy gaps and their variation with temperature were determined. A giant decrease of the gaps was observed below the Curie and Néel temperatures, respectively. The change of the gaps is shown to be proportional to the magnetization of the specimen. This effect yields a new method to measure the spontaneous magnetization without a magnetic field. A long tail of the spontaneous magnetization above the Curie temperature is found.
Ferromagnetic Resonance Effects under Mode-Segregation Conditions
Authors: Chow K. K. , Buffler C. R. 
Published: January 2005

Measurements are reported that verify the mode-segregation effect of Hines and Chow. This effect occurs when the uniform precessional mode is made to move below the k=0 extrapolated lower limit of the spin-wave manifold by means of an interaction with a dielectric cavity mode, or by means of propagation effects.
The measurements reported show a radical change in both the nonlinear behavior and the linewidth of ferromagnetic resonance as the k&gt;0 spin-wave states are eliminated from the relaxation process.
It is believed that these experiments indicate new avenues of approach for studying basic relaxation mechanisms as well as new areas of practical high-power device operation.
Thin Ferrite Phase-Shifters for Integrated Microwave Devices
Authors: Roome G. T. , Hair H. A. , Gerst C. W. 
Published: January 2005

Theoretical and experimental investigations have been conducted to determine the feasibility of microwave devices which utilize the remanent magnetization characteristics of dimensionally thin magnetic materials. A technique for producing phase-shift (both reciprocal and nonreciprocal) was theoretically developed and proven experimentally.
By investigating the thin sample geometry (ferrite slabs 5 to 20 mils thick), we had the opportunity to use commercially available materials to prove the theory and at the same time extend it to a device configuration which is topologically close to the thin film. Phase-shifting elements composed of a meander line circuit deposited on a thin ferrite slab have been built and tested. By a modification of the meander-line-circuit dimensions and the direction of the ferrite magnetization relative to the circuit, both reciprocal and nonreciprocal devices can be made. A microstrip arrangement of the device was adopted so that the theory could be proved in a structure which closely approximates the ultimate thin-film application.
The Electrodeposition of Thin Magnetic Permalloy Films
Authors: Girard R. 
Published: January 2005

The work of Wolf has shown that electrodeposited magnetic films, above a thickness range of a few hundred Angstroms, could be obtained on flat metallized glass substrates, with properties adequate for computer memories. New problems arise when one tries to prepare very thin films (&lt;300Å) or to deposit on flat or cylindrical metal substrates.
The preparation of very thin films is interesting for studies such as creep, or to insure that thicker films do not present unwanted composition gradients or stresses. The influence of the nature of the plating bath on the amplitude and extension of the composition gradients and on the stresses, and consequently, on the magnetic properties (Hc, HkΔ) are examined.
The deposition on metallic substrates has an obvious interest when using ground planes or wires. In this case the crystalline structure of the substrate has as much importance as its chemical activity, and we will show the usefulness of an intermediate layer of controlled grain size and isotropy.
The results of these studies are related to the aging behaviour of plated films.
Magnetic Ordering in Mn(HCOO)2·2H2O and Related Compounds
Authors: Pierce R. D. , Friedberg S. A. 
Published: January 2005

The heat capacities of the isostructural dihydrated formates of Mn2+, Fe2+, and Ni2+ have been measured between 1.4° and 20°K. Sharp peaks associated with long-range spin ordering are found at 3.72°K for Mn(HCOO)2·2H2O, 3.74°K for Fe(HCOO)2·2H2O, and 14.5°K for Ni(HCOO)2·2H2O. An additional sharp anomaly in Cp is found at 1.72°K for the Mn+2 salt, while Cp of the Ni+2 salt exhibits a Schottky-like maximum at 3°K. Each of these anomalies can be correlated with some feature of the observed magnetic susceptibilities.
A unit cell in these salts contains two each of two inequivalent metal ion sites, types A and B. Formate groups constitute AA and AB bridges and appear to mediate the dominant superexchange couplings. A simplified molecular field treatment of Mn(HCOO)2·2H2O in which JAA = 0.65 k, JAB = −0.10 k, and JBB = 0 provides interpretations of several striking effects. In particular, it shows that below a common transition temperature, B spins order much more slowly than A spins and are nearly ``free'' at 1°K as seen in both magnetic and thermal data. Analysis of the data for the Ni+2 and Fe2+ salts suggests that the effective spins of A and B ions may differ in a given substance.
The Range of Ferromagnetic Exchange Interactions
Authors: Trousdale W. L. , Longworth G. , Kitchens T. A. 
Published: January 2005

Experimental investigations on the characteristic length over which two magnetic atoms interact in a nonmagnetic metal have been carried out. Two methods are used: (a) measurement of the transition temperature as a function of the magnetic atom concentration in zero field, and (b) study of the magnetization distribution in alloys in the region just below the transition temperature as determined from the magnetic hyperfine field distribution.
These experiments have been done using palladium as the nonmagnetic and iron as the magnetic atoms. In the FePd alloys it is found that the transition temperature and the nature of the magnetic transition depend strongly on the method of sample preparation and in particular on the annealing of the samples. Samples quenched from the melt to room temperature show a diffuse transition and a relatively slow rise in magnetization with decreasing temperature. Those which have been annealed show a relatively sharp transition and a narrower magnetization distribution below the transition temperature, indicating that the process of annealing produces a more homogeneous distribution of the iron atoms. Interpretation of this phenomenon and its relation to the range parameter are discussed.
Assuming that the magnetic interaction between two iron atoms is due to the overlap of the matrix polarization, the range obtained in this investigation from a simple statistical model is in excellent accord with neutron diffraction measurements.
Stress and Dilatation Fields of the 〈111〉 Dislocation in Cubic Crystals
Authors: Chou Y. T. , Mitchell T. E. 
Published: January 2005

Exact expressions of the stress components and dilatation of a straight dislocation, lying in a 〈111〉 direction in a cubic crystal, have been obtained analytically. The transitions in the contours of stress and dilatation fields are found to be controlled by an elastic anisotropy parameter R. For bcc crystals, the transition of σ23 contours of a screw dislocation takes place atR=(32)1/2 and that of σ13 contours at R=3 (for W, Ta, V, Cr, Mo, Nb, and Fe,R&lt;(32)1/2; for Na, K, Li, (32)1/2&lt;R&lt;3). The results of the stress analysis are useful in treating the dissociation of screw dislocations in the bcc lattice.
The dilatation contours of a [111] dislocation of the mixed type with Burgers vector a/2[111̄] are illustrated. The differences in shape of the contours for the anisotropic and isotropic cases are greater for the pure edge dislocation than for the mixed-type dislocation.
Optical Lever Observation of Hypervelocity Impact Shock Waves
Authors: Gregson Victor G. 
Published: January 2005

An optical lever system was used to observe the impact shock wave arrival and free-surface motion at the rear surface of a 2.54-cm-thick 2024-T4 aluminum target plate. The projectile was a 0.636-cm-diam. steel ball and struck the target at a velocity of 5.28±0.11 mm/μsec. The shock-wave data, in the range 30–1 kbar, extend data by Fowles to lower pressures. The measured elastic shock velocity of 6.23±3% agrees with ultrasonic values and with elastic shock values by other investigators.
Elastic shock amplitudes do not maintain a constant value as in one-dimensional experiments, but decay at a rate faster than predicted for spherical elastic waves.
Nucleation of Polymer Droplets
Authors: Koutsky J. A. , Walton A. G. , Baer Eric 
Published: January 2005

The nucleation of droplets of polyethylene, polyethylene oxide, polyoxymethylene, nylon 6, poly (3,3-bis-chloromethyloxacyclobutane), isotactic polypropylene, and isotactic polystyrene, suspended in silicone oil, has been investigated. Under conditions of slow cooling (0.1°C/min), two different phenomena were observed; occasional droplet solidification at low degrees of subcooling, the number of droplets solidified and the temperature at which nucleation occurred being a function of the thermal melt history; and a sudden catastrophic, history-independent, nucleation phenomenon at large subcooling. The latter event may be identified as a critical phenomenon occurring at a subcooling ΔTc which is only slightly dependent upon the rate of cooling.
For polyethylene and isotactic polypropylene, the ΔTc's correspond closely with values obtained by other authors using different suspending media and have been identified with homogeneous nucleation. Homogeneous nucleation may also be explored by the method of kinetic-rate measurements, with the advantage that rate constants can be evaluated directly rather than by theoretical derivation. Interfacial energies calculated from nucleation theory using the first (slow-cooling) method, have been compared in this work with those obtained from the second (isothermal) method. Such comparison shows that the isothermal method gives values of the same order as, but somewhat lower than, the slow-cooling method.
For the other polymers, most of which are glass-forming, it is not entirely clear that the catastrophic event corresponds with homogeneous nucleation. Whereas critical supercooling and solidification rates resemble those for homogeneous nucleation, there is evidence that the interfacial energies recovered are too low and the circumstances surrounding the catastrophic event suggest that the suspending medium may be catalyzing nucleation.