bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Axial Ratio Changes on the Elastic Moduli and Grüneisen γ for Lower Symmetry Crystals
Authors: Fisher E. S. , Manghnani M. H.
Published: February 2004

Gerlich has shown that Sheard's model for calculating mode γ's from hydrostatic pressure derivatives of the elastic moduli of hcp Mg and Cd yields Gruneisen γ's at both high and low temperatures that are in good agreement with the γ's derived from thermal-expansion measurements. For hcp Ti and Zr, however, large differences arise, primarily from very small values for dC44/dP. It is proposed that these small values are caused by the changes in c/a ratio with hydrostatic pressure because of a large dependence of C44 on the c/a ratio. The disagreement with thermal-expansion data can be removed by taking into account the difference in d(c/a)/dV between hydrostatic-pressure and thermal-expansion conditions. The effect of Δ(c/a) is not found in tetragonal TiO2, rutile, where γ̄H is in excellent agreement with the thermal expansion γ∞.
Thermal-Expansion Coefficients and Grüneisen Parameters of bcc Li–Mg Alloys
Authors: Lynch R. W. , Edwards L. R.
Published: February 2004

The thermal expansion of eight Li–Mg alloys spanning the bcc solid-solution range (100–31-at.% Li) has been measured from 80° to 370°K using a fused silica dilatometer. The room-temperature linear thermal-expansion coefficients were determined for each alloy from cubic fits of the data between 250° and 370°K. It was found that the linear expansion coefficients of the alloys decreased from a value of 4.6±0.1×10−5 °K−1 for pure Li to 3.9±0.1×10−5 °K−1 for an alloy containing 31-at.% Li. The linear expansion coefficients for Mg-rich alloys are unusually high; the expansion coefficient decreases by only 15% over the solid-solution range, whereas the melting point increases by 190%. The unusual behavior of the thermal-expansion coefficients is in direct contrast with the compressibilities of the alloys which decrease rapidly with increasing Mg content. As a result, the room-temperature Grüneisen parameter increases from a value of about 0.95 for pure Li to 1.75 for the 31-at.% Li alloy.
X-Ray Study of Deformed and Transformed Co–Ni Single Crystals
Authors: Rashid M. S. , Altstetter C. J.
Published: February 2004

Plastic deformation and the fcc⇄hcp martensitic transformation have been studied in a cobalt-30.5% nickel alloy. Small spheres were examined using a single-crystal x-ray diffraction technique with monochromated CuKβ radiation. In both the fcc and hcp structures the probability of intrinsic and growth stacking faults, the strains, and the particle size introduced by plastic deformation and/or transformation were evaluated using Fourier analysis and shifting of intensity profiles. It was found that: (1) In both the hcp and fcc phases, growth faults were present in larger numbers than intrinsic faults; (2) strains in the hcp phase were usually higher than those in the fcc phase, and the hcp→fcc transformation generally reduced the amount of strain; and (3) the particle size decreased with transformation and was affected by transformation on other variants. The faults resulting from single slip were only present on the slip planes whereas the hcp→fcc transformation introduced faults on more than one variant of close-packed plane. There was also some evidence of the formation of extrinsic faults. These data are evaluated in the light of the existing transformation theories.
Mason Dark Space and High-Pressure Arc Re-Ignition
Authors: White John E.
Published: February 2004

A solid object immersed in the plasma of a high-pressure arc is surrounded by a dark sheath. The sheath is at plasma temperature along one boundary and near thermal equilibrium with the solid object at the other boundary. Because of ion diffusion into the sheath, the latter easily transmits low electron current densities. But to pass high current densities, such as those carried by the electrodes, sheath insulation must be broken down. This breakdown or re-ignition process occurs at the electrodes after current zero every half-cycle of an ac arc. In the mercury arcs studied, re-ignition from current zero involves heating of a channel which extends outward more than ¾ mm from the electrode to a temperature of about 4400°K, which requires the input of about 0.64 J/cm3 to the vapor. Addition of iodides to the vapor may inhibit the re-ignition process by either electrode or vapor-phase processes.
Broadening of High-Order SWR Lines in Thin Metal Films
Authors: Bailey Glenn C.
Published: February 2004

Spin-wave resonance (SWR) line half-widths which do not increase with order number have been observed in moderately thick Permalloy films. Data from a number of films are presented which indicate that a uniform thickness across the plane of the film as well as a sharp dropoff in thickness at the film edge is responsible for this behavior. Initially, for example, a rectangular shaped, 2700-Å-thick film exhibited rather small half-widths at 9.4 GHz of 54, —, 24, 26, 26, 30, 36, —, 68 Oe for n=0, 1, ⋯, 8, respectively, where the dashes correspond to those modes whose intensities were unobservable. However, when all of the film was etched away except for a small central circular region of approximately 1 mm diam, the half-widths were 54, —, 23, —, 24, —, 21, —, 23 Oe for n=0, 1, ⋯, 8, respectively. The SWR parameters of another film, 2500-Å thick, were measured before and after etching away all of the film but three, approximately circular, spots with apparently slightly different thicknesses. In this case, the higher-order lines (n≥3), which in the as-deposited film were drastically broadened, were transformed into triplets with smaller half-widths than those of the total film. In addition, the triplets had resonance field splittings which could be described well by Hn(L+ΔL1,2) − Hn(L) = [(2A/M)n2π2/L2] [2ΔL1,2/L], where the thicknesses of the three parts of the film are L, L+ΔL1, and L+ΔL2, and where the other symbols have their usual meanings. Finally, a detailed study of the effect of rf nonuniformity on the resonance parameters was made by positioning a small film at various locations in the cavity. The half-widths and resonance fields were not affected by rf field nonuniformities, although small changes in the line intensities were observed.
Tunneling Currents in Zinc Oxide
Authors: Neville R. C. , Mead C. A.
Published: February 2004

An examination of the current-voltage characteristics of gold and palladium surface barriers on degenerate zinc oxide has been made. Both chemically prepared and cleaved surfaces were studied. The current conduction mode is shown to be thermionic-field emission at room temperature and to be pure field emission at liquid-nitrogen temperatures. The voltage dependence of the current is in good agreement with theory. The observed current magnitudes in both current modes were approximately one-tenth that calculated by simple theory.
Use of Optical Spectra to Measure Large Electric Fields in a Hot-Ion Plasma
Authors: Scott F. R. , Neidigh R. V. , McNally J. R. , Cooper William S.
Published: February 2004

Intense electric fields found in the beam-plasma interface of Burnout V give rise to satellite spectra of the helium 23P-43D, 3F triplet (4471 Å), and the 21P-41D, 1F singlet (4922 Å) emission lines. Electric-field strengths increasing from near zero on the magnetic axis to about 7 kV cm−1 at 1 cm, and then decreasing to less than 2 kV cm−1 at 2-cm radial distance are found. An Abel inversion giving intensity of the satellite lines as a function of plasma radius together with displacement and intensity of π and σ components in the Zeeman structure of the satellites gives the electric-field strength and implies that the direction of the electric field is perpendicular to the magnetic axis.
Ultrasonic Attenuation in Germanium at Microwave Frequencies
Authors: Kalejs J. P. , Maris H. J.
Published: February 2004

The attenuation of longitudinal ultrasonic waves in single-crystal germanium has been measured at several frequencies between 0.15 and 2.84 GHz in the temperature range 10°–60°K. The measured attenuation was the same for propagation in the 〈100〉,〈110〉, and 〈111〉 crystallographic directions, and varied with temperature as T7 at the highest frequencies and lowest temperatures, and as T3 at the lowest frequencies near 60°K. The frequency dependence was less than linear at the lowest temperatures and between linear and quadratic at 60°K.
Experimental Study of the Elastic-Modulus Effect in the Interaction of Vacancies with Dislocations and Dislocation Ribbons in Pure Silver
Authors: Shieh W. T. , Ricketts B. G.
Published: February 2004

The interaction of point defects with dislocation ribbons was studied experimentally by observation of vacancy clusters in deformed pure silver by means of electron microscopy. The results were in good agreement with theoretical predictions: The energy of the interaction was attractive, increased as the dislocation became more edge-like in character, and decreased as the width of the dislocation ribbon increased.
Influence of Thickness of Thin Fe Films on Magnetization
Authors: Shimony U. , Rabinovitch K. , Biran A.
Published: February 2004

The dependence of Mössbauer-line-area ratio as function of thickness of iron films in the range of 100 to 3000 Å was investigated experimentally, and was related to the magnetic structure of the film. The results were explained by either of two indistinguishable models. In one model all the magnetic dipoles have the same polar angle with respect to the normal to the film. In the second model the magnetic dipoles can be only normal and tangential to the film. In both models no dependence on the azimuthal angle was found. This thickness dependence is discussed on the basis of the film formation.
Variation of Shock Overpressure with Distance in a Shock Tube Driven by an Exploding Gas Mixture
Authors: Dresner Lawrence
Published: February 2004

Results are reported of calculations and measurements of the shock overpressure as a function of distance in an air shock tube driven by an exploding mixture of propane and oxygen.
Temperature and Mode Dependence of Ferromagnetic Thin Film Resonance Linewidths in the Range 4°–300°K
Authors: Shirkey C. T. , Wigen P. E.
Published: February 2004

The perpendicular resonance linewidths of the standing spin-wave modes in permalloy thin films have been measured as a function of the temperature and the mode number in the temperature range 4°–300°K. It is found that the linewidths obey the relation ΔH(T) = ΔH(0) [1—aT3/2], where ΔH(0) is the linewidth at absolute zero. Various two magnon relaxation calculations predict a linewidth that depends on the magnetization as ΔH∼Mq∼M(0) q[1-−qcT3/2] where c is the Bloch constant. The theoretical results for q are strongly model dependent, and published results to date predict q to be either mode independent or increasing slightly with increasing mode number. Experimental values obtained at 9.2 GHz have a value of q that ranges from about 3.3 for the main resonance mode (n=0) and decrease regularly to about 1.6 for the low-field mode as the mode numbers increase. Data at 9.2 and 23.8 GHz indicate there may be a slight frequency dependence to the q values. The data indicate that a two magnon scattering process is the most significant contribution to the linewidth in thin ferromagnetic films. It is suggested that the two magnon scattering process induced by an inhomogeneity in the internal field can produce the observed temperature dependence.
Surface Spin Pinning in Flash-Evaporated Permalloy Films
Authors: Lykken G. I. , Schmitz D. R.
Published: February 2004

A series of Permalloy films in the thickness range 1800 to 4910 Å were deposited by ``flash-evaporation.'' Each set of films consisted of Permalloy only, Permalloy with a thin layer of palladium above, and Permalloy with a thin layer of palladium both above and below. Expressions for the rf surface impedance in both the perpendicular and the parallel configuration for a film with different surface anisotropy energies on each surface were derived and computer solutions for their derivatives were obtained. It was found that the experimental mode intensities and field positions fit the theory extremely well in both configurations. A computer solution for the angular dependence of the resonance field was obtained and it was found that the Pd–Py–Pd films fit this extremely well assuming complete pinning.
Effect of Sulfur on the Magnetic Properties of Molybdenum Permalloy
Authors: Ames S. L.
Published: February 2004

Residual sulfur levels in final annealed 0.014-in.-thick ring samples of moly-permalloy were varied by two methods. In one method vacuum or argon was used for part of the final anneal instead of the usual dry hydrogen. Sulfur levels varied between 5 and 25 ppm but at the same time there was a large variation in residual carbon content. In the second method heats were melted with different sulfur contents resulting in variations in residual sulfur after final hydrogen anneal. Carbon was consistently low. Sulfur impurity has a very potent effect on low induction permeability, much more so than carbon. The μ40 G decreases by about 4000 for each ppm residual sulfur up to 10 ppm. Coercive force is also severely affected, increasing by a factor of four in the range 3–10-ppm sulfur. Properties continue to deteriorate with greater than 10-ppm sulfur but at a reduced rate.
Photoemission of Spin-Polarized Electrons from Ferromagnets
Authors: Busch G. , Campagna M. , Siegmann H. C.
Published: February 2004

The processes that generate and destroy electron spin polarization (ESP) in photoemission from ferromagnetic materials are examined, and an experimental technique is described for observing photoelectron-ESP from thin films in high magnetic fields at liquid-helium temperatures. No significant depolarization occurs in photoemission and the main factor determining ESP is the spin-polarized band structure which can therefore be directly investigated by this technique. When applied to the europium chalcogenides, which are efficient photoemitters and whose first occupied level is completely spin-polarized, we have a new method for the production of intense polarized electron beams.
Magnetic Ordering Effects in the Reflectance of EuO, EuS, EuSe, and EuTe
Authors: Scouler W. J. , Feinleib J. , Dimmock J. O. , Reed T. B. , Pidgeon C. R.
Published: February 2004

In the reflectance spectra of the ferromagnetic semiconductors EuO,1 EuS,2,3 and EuSe2,3 and antiferromagnetic EuTe,4 there are two prominent peaks, E1 and E2, which involve 4f7→4f65d(t2g) and 4f7→4f65d(eg) transitions respectively. Measurements of E1 and E2 in the ferromagnetic compounds as a function of temperature and polarization in a magnetic field show changes with magnetic ordering which indicate exchange splittings of the 5d states of about 0.25 eV. In antiferromagnetic EuTe above 40 kOe applied field, the spectrum becomes characteristic of the ferromagnetic chalcogenides suggesting a transition to parallel spin alignment which saturates at H∼80 kOe. The observed effects also indicate confirmation of the prediction that there are superlattice splittings in the band structure of an antiferromagnetic crystals.
Domain-Wall Processes in SmCo5 Powders
Authors: Zijlstra H.
Published: February 2004

Measurements of minor loops of SmCo5 powders have revealed that wall motion is predominant in the magnetization process. A relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the coercivity of the investigated material is determined by the pinning of domain walls, rather than nucleation. The relation χHc2 = constant has been found in a wide range of coercivities obtained by aging of the material. The aging process is interpreted as a decrease of the density of pinning sites, each site retaining its pinning force. The influence of hydrogen on Hc, which is reported recently, is interpreted likewise. A hysteresis loop measured on a single particle of a few microns size confirms these interpretations and allows for a refined model of pinned-wall coercivity of SmCo5 powders. A full account will be submitted as a regular article to this Journal.
Anisotropic Exchange and the Resonance Linewidth of Europium Iron Garnet
Authors: Foglio Mario E. , Sekerka Robert F.
Published: February 2004

A theory is developed which employs the longitudinal mechanism to explain the linewidth of the ferromagnetic resonance in EuIG. An isotropic exchange interaction between Eu and Fe ions is assumed, and the anisotropy required by this mechanism is attributed to the rhombic crystal field acting on the Eu ions. At T=0, the same value of 1/τ is assumed for the relaxation rate between any of the three J=1 levels of Eu and the ground level J=0. When the resonant frequency satisfies ωτ≪1, the predicted linewidth ΔH is proportional to ω and the maximum of ΔH as a function of T is located very near to the experimental value. By requiring the height of the experimental and theoretical maxima to have equal values, 1/τ=5×1011 sec−1 is obtained at 9.98×109 cps. Linearity of the linewidth with ω is observed by Foner up to ω=4.4×1011 sec−1; but, at this frequency ωτ∼1 and the theory predicts a slower increase of ΔH with ω. One of us (M.E.F.) has extended this theory to include the anisotropic exchange between the Eu and Fe ions. According to Koningstein's assignment of the J=1 levels, this exchange interaction is axially symmetric. With this theory, a typical value of 1/τ=2×1012 sec−1 is derived from the experimental results, and the linear dependence of line width with frequency is predicted at the higher frequency employed by Foner. Some recent indirect measurements of the rhombic crystal field parameters indicate a different assignment of the J=1 levels, and the calculated Eu–Fe exchange interaction is no longer axially symmetric. A preliminary study indicates that agreement with the experimental dependence of ΔH on ω and T is, again, obtained.
Electric Field Gradients in the Spinel Lattice
Authors: Rosenberg M. , Mandache S. , Niculescu-Majewska H. , Filotti G. , Gomolea V.
Published: February 2004

To investigate the EFG due to the lattice at the octahedral sites of the spinel structure NMR powder patterns of 27Al in MgAl2O4, NiAl2O4, ZnAl2O4, CoAl2O4, and Mössbauer spectra of 57Fe in CoAl1.9Fe0.140 and ZnAl1.9Fe0.1O4 were recorded. The values of (Vzz)lat = (Vzz)exp/(1−γ∞) at the B sites in CoAl2O4 and ZnAl2O4 were found to be 13×1013 esu and 10.1×1013 esu respectively being close to those predicted by a point charge model, taking into account, besides the monopole term, a dipole contribution due to the polarizability of the oxygen ions. Using the value of the quadrupole splitting of the Mössbauer doublet of 57Fe in CoAl1.9Fe0.1O4 and that found for (Vzz)lat in CoAl2O4, a value of (0.20±0.03) b was found for the quadrupole moment of 57Fe.
Ferromagnetic Resonance with the Magnetic Field in a (111) Plane of a Cubic System
Authors: Everett Glen E. , Hughes R. S.
Published: February 2004

The condition for ferromagnetic resonance with the magnetic field directed at an arbitrary angle in a (111) plane of a cubic system has been calculated. The first- and second-order cubic anisotropy contributions have been included and the results calculated to second order. The second-order constant K2 contributes to the angular dependence in first order while both K1 and K2 contribute is second order. The second-order contribution is very important for materials such as EuO which have K1 and K2 of comparable magnitude. We have measured the angular dependence of the ferromagnetic resonance in a (111) plane of EuO at 4.2°K and 25 GHz. The measured amplitude of 4.27 Oe is in good agreement with the calculated value of 4.82 Oe.
Kondo Effect: Does it Exist?
Authors: Heeger A. J.
Published: February 2004

The experimental situation with regard to the well-known anomalies associated with magnetic impurities in simple metals is reviewed in terms of recent work on the Kondo effect and spin fluctuations. Detailed evidence is presented to demonstrate the existence of nonperturbative spin correlations in the conduction electron sea at temperatures less than the Kondo temperature. In particular magnetic susceptibility measurements together with NMR and Mössbauer studies in the system CuFe imply an excess nonlocal contribution to the susceptibility which arises from formation of a quasispin in the electron gas. The experiments imply that the excess polarization resides in a region less than 9 Å from the impurity. Similar results are found for Rh(Fe). Measurements of the 63Cu nuclear spin-lattice relaxation rate in Cu(Cr) provide further confirmation of such spin correlations. For T≪Tk an excess relaxation rate is observed which is more than thirty times that predicted by perturbation theory. It is suggested that the many-electron quasispin can be viewed as arising from an indirect electron-electron interaction (via the impurity spin). Experimental studies of the resistivity and electron spin resonance linewidth in Cu(Mn) doped with trace amounts of Pt support this point of view.
Nuclear Spin Relaxation in Cu(Cr): An Attempt to Suppress the Kondo Effect
Authors: Gladstone G.
Published: February 2004

Nuclear spin relaxation of the 63Cu host nuclei in Cu(Cr) alloy is measured at temperatures below the Kondo temperature of this alloy (TK≃0.5°K). The results indicate that the many-body ground state of this system begins to break up, with both increasing temperature and increasing applied magnetic field, well below TK. The addition of 0.3 at.% Pt to one Cu(Cr) sample causes only a slight reduction of the many-body fluctuations in the ground state.
Magnetic Behavior of Ytterbium Diluted in Silver-Gold Alloys
Authors: Allali V. , Donzé P. , Gainon D. , Sierro J.
Published: February 2004

We report measurements of the magnetic susceptibility and the thermoelectric power of Ag–Au alloys containing Yb as impurity. The results show that the magnetic moment on the Yb atoms disappears in the Ag-rich alloys where spin fluctuations seem to be important. A Kondo effect is observed for Au concentrations from 10 to 30 at.%.
Domain Structures in Magnetically Annealed 3.2% Silicon-Iron
Authors: Houze G. L.
Published: February 2004

Commercial grain-oriented silicon steel (3.2% Si) was magnetically annealed in the[1̄10] direction; the domain structures were examined and magnetic properties determined both before and after the magnetic anneal. The as-magnetically annealed domain structure consisted of narrow strips parallel to[1̄10] but magnetized along the [001]. This was a closure structure for [100] and [010] interior domains and represented a flux path with a resultant[1̄10] directionality. Typical before and after core loss and magnetostriction values measured in the[1̄10] direction were 0.830 wpp vs 0.530 wpp (60 Hz at 10 kG) and +8.85 μin./in. vs +1.46 μin./in. (at 12.75 kG). The property improvements and the domain structure changes illustrate that magnetic annealing created a domain structure which is stabilized by directional ordering. However, the domain structure was bistable, i.e., it could be switched back to [001] antiparallel domains by demagnetizing in the [001] direction, and the process was reversible.
Magnetostatic Energy of Two-Domain Parallelepipeds with Straight and Curved Domain Walls
Authors: Kaczér J.
Published: February 2004

Recent experimental investigations into the domain structure of ferromagnetic single-crystal platelets of high purity and perfection have yielded significant results.1,2 Thus, it was shown1 that over a limited portion of domain-wall excursion no hysteresis losses are incurred and that the magnetization of the platelet over this region is proportional to the applied field. Since the wall energy is shown to be negligible, the problem reduces to magnetostatic and external field energy considerations. We have therefore calculated the magnetostatic energy of a general rectangular parallelepiped as a function of the position and radius of curvature of a 180° domain wall dividing the platelet into two homogeneously magnetized domains. From this the demagnetizing factors, the magnetizing curve and the susceptibility of the platelet were obtained. The demagnetizing factors are compared with those of the general ellipsoid3 and limiting formulas are derived. The calculation shows the importance of the demagnetizing fields for the reversible portion of the magnetizing curve and introduces for the first time the demagnetizing energy of curved domain walls.
Band-Structure Effects in the High-Field Magnetization of Pd and Dilute Pd–Rh and Pd–Ag Alloys
Authors: Andersen O. K.
Published: February 2004

From Stoner theory we show that the magnetic field-vs-spin magnetization has the form B(σ)=σ/χ(0)+ΔB(σ). The low-field susceptibility χ(0) is exchange-enhanced but, if the effective exchange potential does not depend on magnetization, the deviation from linearity ΔB may be derived solely from the band density of states N(E). The previously reported Pd band-structure calculations, which were in excellent agreement with the de Haas-van Alphen data, have been extended to yield ΔB(σ) for Pd and, using the rigid band model, also for dilute Pd–Rh and Pd–Ag alloys. A van Hove singularity near the Fermi level of the 7% Rh–Pd alloy has a profound effect on ΔB. Our results are consistent with the measurements of Foner and McNiff, but detailed comparison is difficult since ΔB is of the same order as the experimental uncertainty; moreover, the experimental data have previously been analyzed according to a power series expansion of σ(B) that neither separates the effect of band structure from that of exchange enhancement nor applies when van Hove singularities are important. Our formulation suggests a way of analyzing the experimental data.
Knight Shifts in Transition Metals
Authors: Freeman A. J. , Koelling D. D. , Mueller F. M.
Published: February 2004

Analyses of Knight shifts (K) in transition metals commonly assume that the s and d bands are distinguishable at the Fermi energy (i.e., small s-d hybridization). The three major contributions to K are attributed to unpaired s electrons (Ks), unpaired d spins (Kd) and orbital angular momentum (Korb) each arising from counterpart terms in the susceptibility, χ. This partitioning (valid for weak spin-orbit interactions) allows one to relate the s and d contributions to χ to the corresponding densities Ns(EF) and Nd(EF). One further assumes that Ns(E) varies much more slowly than Nd(E) so that the d-spin susceptibility is the only temperature-dependent term. The free-electron description is then used to calculate Ks. We report here investigations of contributions to Knight shifts (and relaxation rates) using ab initio SRAPW band calculations, the combined interpolation scheme and the QUAD scheme. Strong s-d hybridization is found to cause substantial structure in the projected Ns(E) for fcc Ni, Pd and Pt, as was found earlier for Fe. This structure can cause Ks to be temperature dependent [if EF falls at a peak in Ns(E)] and can affect strongly the Van Vleck susceptibility and hence Korb. The structure effect is found to be very weak in the metals mentioned but preliminary results for hcp Sc (and possibly Gd) and bcc Cr and V indicate that larger effects may be expected.
Strain Sensitivity of Mn-Doped Films
Authors: Onyshkevych L. S.
Published: February 2004

Mn-doped films, prepared by vacuum evaporation from melts containing approximately 57% Ni, 38% Fe, plus 5% Mn are found to possess the following properties: uniaxial anisotropy with a mean value of Hk=3.7 Oe; a magnetostriction constant λ with a mean value of 75×10−6; large rotation of the easy axis with applied stress; and magnetization M similar to that of Permalloy. These films are eminently suitable for use in the Sonic Film Memory. They display a figure of merit which is statistically a factor of 6 smaller (better) than that for Ni–Fe and Ni–Fe–Co films. Normal evaporation methods induce oriented strains on the order of 10−5 as a result of nonuniform heating of the substrates to the deposition temperature of 300°C. At this level of strain the highly strain-sensitive Mn films display excessive skew and dispersion. Special, thermally stabilized fabrication facilities have to be used to minimize this problem.
Composition Dependence of the Magnetization-Induced Uniaxial Anisotropy in both Normal and Unconstrained Ni–Fe Thin Films
Authors: Rudee M. L. , Horowitz S. J. , Carson K. R.
Published: February 2004

The magnetization-induced uniaxial anisotropy has been measured for normal and unconstrained vacuum-deposited Permalloy films containing 0% to 40% Fe. It is observed that the unconstrained films possess anisotropies that are quite similar to the limiting values obtainable in magnetic annealing of bulk specimens. The difference between the constrained and unconstrained films is in reasonable agreement with West's version of the magnetostrictive constraint theory, although some disparity exists in films containing Fe in excess of the zero magnetostriction composition. These experiments offer support of the model that the anisotropy in thin films is a combination of the constraint and the directional ordering mechanisms.
Analytical Solution of Field-Induced Magnetic Transitions in Uniaxial Antiferromagnets-Application to Hematite
Authors: Kaczér J.
Published: February 2004

The paper presents an analytical solution of the thermodynamic potential of an antiferromagnet (weak ferromagnet) including a second-order anisotropy term (b/4) sin4θ for the critical orientations of the sublattice magnetizations and the critical fields applied in an arbitrary direction. This was applied to the antiferromagnetic-to-weak-ferromagnetic phase transitions induced in hematite by external fields applied below the Morin point.
Mössbauer Measurements in Europium-Calcium and Europium-Strontium Alloys
Authors: Crecelius G. , Hüfner S.
Published: February 2004

Mössbauer effect measurements have been performed for EuxCa1−x and EuxCa1−x (0≤x≤1) alloys using the 22-keV γ-line in 151Eu. The hyperfine (hf) fields extrapolated to zero europium content are −110 kOe for the EuCa system and −140 kOe for the CuSr system as compared to −150 kOe for the EuBa and EuYb system. On the other hand the charge density at the Eu nucleus decreases only slightly in going from the EuYb to the EuCa system. The explanation of these hf-field measurements as well as g-shift measurements requires a varying d-electron contribution to the conduction band.
Determination of Magnetic Imperfections in Thin Films
Authors: Mills W. A. , Soohoo R. F.
Published: February 2004

By means of a selective ferromagnetic resonance technique, we have succeeded in determining the spatial distribution of the magnetic properties of thin magnetic films. In contrast to other types of diagnostic techniques, the method determines the relevant local magnetic parameters of the sample directly. This is accomplished by sequentially exposing small areas of the film to an rf magnetic field via an aperture in one of the walls of a microwave cavity. To obtain maximum resolution at a given apparatus sensitivity, the aperture wall is substituted by a vacuum-deposited copper film on a dielectric substrate. To data, magnetic quantities such as anisotropy, exchange constant, linewidth, gyromagnetic ratio, magnetization, etc. of regions as small as 5 μ in diameter have been selectively examined. Since spatial variation of these quantities is due to imperfections in the material, results of our measurement exhibit the direct influence of these imperfections on the local magnetic properties of the film. For example, we have found that the effective magnetization decreases and linewidth increases substantially near a nonmagnetic imperfection, and also the existence of regions where the magnetic easy axis rotates gradually over π/2 rad, etc. Typical data on Permalloy films are presented along with a discussion of the theoretical and experimental aspects of the method.
Surface-Roughness-Induced Demagnetizing Fields in Thin Films and Their Influence Upon the Approach to Saturation
Authors: Schlömann Ernst , Joseph Richard I.
Published: February 2004

The magnetic field generated by the magnetization has been calculated for films with rough surfaces. At large magnetic fieldstrengths the film is uniformly magnetized. Simple formulas for the demagnetizing factors are given, which are applicable provided that the inclination of the local film surface relative to the mean surface is not too large. A rough estimate of the demagnetizing factor for a direction in the plane of the film is given by π〈p2〉/λd. Here 〈p2〉 is the mean-square (linear) deviation of the actual film surface from the mean surface, λ the predominant wavelength of the surface roughness, and d the film thickness. A relatively small surface roughness, if distributed anisotropically, is sufficient to induce a significant uniaxial magnetic anisotropy. If the magnetic fieldstrength is only moderately high, the surface roughness gives rise to misalignment of the magnetization vector near the surface relative to the mean magnetization vector. The effect of this misalignment upon the average magnetization has been calculated by a method that takes account of the dipole-dipole interaction. The hard-axis magnetization curves calculated for films with anisotropic surface roughness are compared with those expected for films having uniaxial (bulk) anisotropy. Depending upon the degree of anisotropy of the surface roughness the two types of curves can be either very similar or quite different.
Variation of Stripe-Domain Spacing with Applied Field
Authors: Lo D. S. , Norman D. I. , Torok E. J.
Published: February 2004

Theory has predicted that because of the exchange and demagnetizing energies, the stripe-domain spacing is a function of the amplitude of the (periodic) component of the magnetization normal to the film plane. Experimentally the stripe width was reported not to vary when the normal component of the magnetization was changed by applying a field parallel to the stripes. This disagreement, which was attributed to the coercive force of the stripes, has prevented a close comparison between theory and experiment. It has been found that the application of an oscillating field above some critical value in the plane of the film and normal to the stripes overcomes the coercivity associated with the stripes and allows the domain spacing to relax to that of a lower energy state. A change of spacing up to 50% has been observed in some Ni–Fe films. Experimental curves of the stripe width as a function of amplitude of the normal component of magnetization in the stripes are in rough agreement with the theoretical curve of Saito et al., except that his model and other one-dimensional models do not predict the change in stripe spacing to be as large as that observed. The dependence of the change in stripe spacing on the amplitude of the oscillating field and film parameters is discussed.
Magnetic Excitations in a Cr–Mn Alloy by Inelastic Neutron Scattering
Authors: Sinha S. K. , Liu S. H. , Wakabayashi N. , Muhlestein L. D.
Published: February 2004

The inelastic magnetic scattering from a Cr0.98Mn0.02 alloy single crystal has been studied both below and above the Néel temperature. In the spin-wave regime at 300 K, we have obtained a value of 1.29×107 cm/sec for the spin-wave velocity by using the diffraction method and suitably extracting the resolution function. At a temperature of 1.16 TN, we have observed quite strong inelastic magnetic scattering and fitted the results quite well by calculating the imaginary part of χ(Q) for paramagnetic chromium. A triple-axis spectrometer was used to study the magnetic excitations in a crystal of Cr0.99Mn0.01 below, above and close to the Néel temperature of 514 K. At low temperatures, peaks at the magnetic superlattice points were seen consistent with the above spin-wave velocities. These appear to go smoothly into the slightly broader paramagnon peaks as the temperature was raised through TN without any sudden change of intensity. The absence of Stoner excitations near TN suggests that either the neutron cross section for these is very low or else that the sample is gapless near TN due to phonon broadening of the electronic states. Full details are published elsewhere.1
Spin Disorder Scattering in Iron-Base Alloys
Authors: Schwerer F. C. , Cuddy L. J.
Published: February 2004

Resistivities of dilute alloys of iron with Cr, Mn, Co, Ni, Ge, Si, W, and Ru were measured from 4° to 1180°K. The solute resistivity was strongly temperature dependent, generally showing a large increase to a maximum near 400°K, a sharp drop to the Curie temperature, and then remaining relatively constant at a value much lower than that measured at 4°K. Apart from a factor of 2 these features are well described by a simple spin disorder model.
Antiferromagnetism and Electrical Resistivity of Chromium Alloys Containing Ruthenium and Osmium
Authors: Arajs Sigurds , De Young Tice F. , Anderson Elmer E.
Published: February 2004

Electrical resistivity ρ has been studied as a function of temperature T of chromium alloys containing 0.9, 2.1, 3.0, and 4.8 at.% Ru and 0.3, 0.6, 1.1, and 2.0 at.% Os. The onset of antiferromagnetism causes large anomalies in the ρ vs T curve. The Néel temperatures TN of both alloy systems increase rapidly with increasing solute concentrations up to 2 at.%, remain approximately constant, and then decrease with larger solute contents. The initial increase in TN with increasing solute concentration can be understood by Fedders and Martin's theory assuming that additions of Ru and Os to Cr cause an increase in the electron jack and a decrease in the hole octahedron which enlarge the interaction area of the two Fermi surfaces. The incommensurable antiferromagnetic structure in both alloy systems exists up to about 0.5 at.%. For higher concentrations the antiferromagnetic phase, bordering the paramagnetic region, is commensurable with the lattice. The large increases in the electrical resistivity of the commensurable antiferromagnetic alloys is interpreted as resulting from the superlattice boundaries. For incommensurable phase alloys the resistivity anomaly is due to mutual annihilation of hole and electron Fermi structures.
Magnetoresistance of Nickel Alloys and Electron Scattering Dependent on Spin Orientation
Authors: Fert A. , Campbell I. A. , Ribault M.
Published: February 2004

We discuss the transverse magnetoresistance of nickel at low temperature and its dependence on residual impurity. It appears from our results on some nickel dilute alloys that the difference between the relaxation times of spin ↑ and spin ↓ conduction electrons is a dominant mechanism for the magnetoresistance.
Effects of Pd and Pt Impurities on the Magnetic Susceptibility of Ni3Ga
Authors: Wohlleben D. , Luo H. L. , Sales B.
Published: February 2004

The static magnetic susceptibility of Ni3Ga is strongly decreased by dilute Pd and Pt impurities. A linear relationship is found between that temperature and that impurity concentration which produce the same change of the susceptibility. The effective spin-flip energy of the impurities is derived and found to agree with their spectroscopic spin-orbit energy if differences of the effective local exchange enhancement between host and impurity are assumed to be negligible.
High-Field Properties of Ni–Cu Alloys Near the Critical Concentration
Authors: Foner S. , McNiff E. J.
Published: February 2004

High-field magnetic moment measurements have been completed in NixCu1−x alloys1 near the critical concentration2 (x≃0.44). Fields of 150 kG or higher and temperatures from 4.2 to 1.5 K were employed. The general features of the data are: (1) the differential susceptibility at high field, χHF, decreases with increasing field and with decreasing temperatures; (2) χHF increases with increasing x up to x=0.42 and is relatively constant from x=0.44 to 0.48; (3) linear extrapolation to H=0 yields a moment σ(0) which is linear with x for x≥0.44 corresponding to about 0.6 μB/added Ni atom; (4) for x<0.44, σ(0) decreases less rapidly down to x=0.32 (the lowest value of x investigated so far). These results are compared with recent low field measurements of Kouvel and Comly3 and Robbins et al.4 The general features of χHF and σ(0) are compared with uniform and nonuniform (or clustering) models3,4 for occurrence of ferromagnetism in Ni–Cu alloys.
Two-Magnon Scattering of Neutrons by MnF2
Authors: Holden T. M. , Svensson E. C. , Buyers W. J. L. , Cowley R. A. , Stevenson R. W. H.
Published: February 2004

The inelastic scattering of neutrons by two-magnon processes has been studied in MnF2 at 4.2°K. The two-magnon scattering was seen most clearly at the reciprocal lattice point (2π/a, 0, 0) where it took the form of a shoulder on the high-frequency side of the one-magnon peak with a well-defined cut-off in energy. Similar results were obtained at other wavevectors around this point but sharp peaks due to magnetovibrational scattering were then superposed on the broad two-magnon scattering distribution. The line shape, the cut-off in energy, and the intensity calculated from the cross-section formulas are consistent with experiment.
Spectroscopic Determination of Crystal-Field Levels of Pr3+ in the Paramagnetic Metallic Compound PrBi
Authors: Birgeneau R. J. , Bucher E. , Passell L. , Price D. L. , Turberfield K. C.
Published: February 2004

The Pr3+ 4f2 3H4 manifold is split by an octahedral crystal field into four levels Γ1, Γ3, Γ4, and Γ5. Transitions between these levels in PrBi have been measured using neutron time-of-flight spectrometry. Peaks in the observed spectra corresponding to crystal-field transitions are identified both by their temperature dependence and by comparison with corresponding data from (nonmagnetic) LaBi. Well resolved crystal-field transitions are observed at 11.7 and 5.8±0.6 meV at 90°K. Additional scattering observed at room temperature is consistent with unresolved transitions at 7.6 and 4.1 meV. As it is known from magnetic measurements that the Γ1 singlet lies lowest, these four transitions may be identified as Γ5 to Γ4, Γ4 to Γ1, Γ5 to Γ3 and Γ3 to Γ4 respectively, thus accounting for all transitions allowed by magnetic-dipole selection rules. These data give the parameters A40 〈r4〉=6.89±0.30 meV and A60 〈r6〉=0.24±0.10 meV.
Properties of SmB6 Doped with Eu and Gd
Authors: Geballe T. H. , Menth A. , Buehler E. , Hull G. W.
Published: February 2004

SmB6 behaves as a nonmagnetic semiconductor at low temperatures. Gd- and Eu doped samples have been prepared. The paramagnetic behavior of the doped materials shows that Eu remains divalent and consequently it does not alter the low-temperature electrical properties appreciably. Gd, on the other hand, increases the electrical conductivity and the paramagnetic behavior corresponds to the trivalent Gd ion. The paramagnetic susceptibility flattens out below 0.1°K indicating a magnetic ordering of the Eu samples in contrast to the pure SmB6.
Specific Heat of Nearly Ferromagnetic Borides (Co–Ni)2B and (Fe–Co)B
Authors: Kuentzler R.
Published: February 2004

Low-temperature specific heats were measured in the systems of borides Co2B–Ni2B and FeB–CoB, especially near cF, the critical composition for ferromagnetism. In the critical concentration range the linear term γT is largely increased and the specific heat curves reveal anomalies at low temperature. Except for this cF range, the γ values, in conformity with the magnetic moments, describe the filling up of a d band in a rigid band model.
Magnetic and Optical Properties of the High- and Low-Pressure Forms of CsCoF3
Authors: Longo J. M. , Kafalas J. A. , O'Connor J. R. , Goodenough J. B.
Published: February 2004

CsCoF3 has hcp (h) and ccp (c) CsF3 layers alternating hhchhchhc at atmospheric pressure (9L structure of BaRuO3) but a cchcch sequence (6L structure of RbNiF3) if quenched from 700°C at pressures greater than 20 kbar. The octahedral-site Co2+ ions are between the layers and give the 9L structure a pink color, the 6L structure a lavender hue. The 9L phase obeys a Curie-Weiss law above 70°K with Cm=3.7 emu°K/mole and Θp=−62°K. It has TN=8°K with evidence for a spin-flop transition at Hc≈11 kOe and an anisotropy constant K≈5×104 ergs/cm3 at 4.2°K. The 6L phase has Cm=3.3 emu°K/mole, Θp=−65°K and is ferrimagnetic below TC=50°K. The magnetization is not saturated at 17.2 kOe and 4.2°K, where μ̄=0.8 μB/Co2+ is smaller than the 1.23 μB/Co2+ anticipated at saturation for RbNiF3-type ordering. Optical data show a larger trigonal-field splitting for the 6L structure. For both phases, Dq≈760 cm−1, spin-orbit interaction parameter ζ≈500 cm−1, and long wavelength cutoff≈13 μm.
Magnetic and Optical Properties of Single-Crystal CsFeF3
Authors: McGuire T. R. , Moruzzi V. L. , Shafer M. W.
Published: February 2004

CsFeF3 appears to be a Néel type ferrimagnet whose magnetization forms cones of revolution having a 25-deg angle with the hexagonal c axis. The moment along the cone angle increases in an anomalous manner in fields up to 25 kG. In addition, the anisotropy energy at 4.2°K is extremely large with K1≈−7.8×106 ergs/cm3 and K2≈2.2×107 ergs/cm3. At room temperature the optical absorption coefficient is about 1 cm−1 for wavelengths 6000–8000 Å. In a field of 20 kG at 84°K the Faraday rotation is 100 deg/cm for a wavelength of 6000 Å.
Interdiffusion in Lead Selenide
Authors: Brodersen R. W. , Walpole J. N. , Calawa A. R.
Published: February 2004

A theoretical model has been developed to explain the movement of a p-n junction in PbSe by the interdiffusion process. This model, which is a modification of an interdiffusion theory due to Brebrick, has one value for the diffusion coefficient in p-type material and another value in n-type material. Solutions to the diffusion equation for this model are obtained and compared to experimental interdiffusion data for PbSe at 400°C obtained by the p-n junction method. The significance of the results to device fabrication and annealing is discussed.
End-Region Analysis for Stress and Optical Pathlength Change in Composite Laser Rods
Authors: Cuff David W. , Leon Gonzalo S. , Lynch Francis DeS.
Published: February 2004

A general solution is presented for the end-region stress in a composite cylindrical rod where differential thermal expansion or contraction occurs between the core and cladding. Results describe local conditions set up in the ends of clad laser rods during manufacture and permit an analytical assessment of the optical path distortion which can arise in this geometry from residual strain. The formulations are obtained by superposition of the infinite rod solution and a solution to the boundary value problem posed by an axial force distribution, of equal but opposite magnitude to the infinite rod stress, applied to the surface of a stress-free cylinder. Expressing the applied tractions as a Fourier-Dini expansion at the axial boundary and the radial stress as a Fourier expansion at the radial boundary leads to a double infinite series form for the principal stresses. Implementation of Fejer's theorem was helpful in smoothing the numerical results; however, summing as many as 100 series terms with the computer was necessary to gain satisfactory convergence. Principal stress-strain distributions are presented for a typical glass rod with a core-cladding diameter ratio of 0.7 to 1 and contraction ratio below the transformation temperature of 0.95 to 1. Results show the end-region domian extends less than 1 rod diameter. Optical pathlength variation across the core aperture for radial and tangential beam polarizations was computed to be 0.58 and 0.51 μ, respectively.
Electron-Optical Investigation of the Origin of Asymmetries in Air-Cored Solenoids
Authors: Amboss K. , Jennings J. C. E.
Published: February 2004

The field asymmetries introduced in winding air-cored solenoids are investigated theoretically by treating the solenoid as a suitably deformed single turn. Regarding the solenoid as an electron lens, aberrations are calculated for the various field integrals. Using a novel method of measuring aberrations, these are compared with results obtained from carefully wound test lenses.