bluuebunny/crossref_metadata_2025 huggingface dataset:
Tb3+ Fluorescence and Nonradiative Energy Transfer from Gd3+ to Tb3+ in Borate Glass
Authors: Pearson A. David , Peterson G. E. , Northover W. R.
Published: April 2005

The fluorescence behavior of Gd3+ and Tb3+ has been studied with the ions dissolved together in a Calibo-1 glass host. The two ions form a coupled system so that energy absorbed by Gd3+ is transferred to Tb3+ by a nonradiative mechanism and is then emitted as Tb3+ fluorescence.

When Tb3+ is incorporated alone into this glass, concentration quenching effects are observable. These have been found to be due to the shortening of the Tb3+ 5D4 lifetime, which in turn is due to the Tb3+ ions being packed closer together as the concentration of Tb3+ is increased. It is proposed that this gives rise to ``chains'' of Tb3+ ions along which energy can migrate, by a nonradiative transfer mechanism, to sinks in the structure.

The rate of internal conversion from Tb3+ 5D3 to Tb3+ 5D4 has also been studied as a function of concentration. The results have been interpreted as being due to the formation of Tb3+-Tb3+ resonance-coupled pairs, which causes the rate of internal conversion to increase as the concentration of Tb3+ increases.

The effects of changes in temperature and base glass composition on the Tb3+ 5D4 lifetime have also been investigated and are reported.
Single-Crystal Silicon on Spinel
Authors: Manasevit H. M. , Forbes D. H.
Published: April 2005

Evidence is given which shows that silicon epitaxy has been achieved on the commercially available magnesia aluminate spinel by the pyrolysis of silane and reduction of SiCl4 in an atmosphere of hydrogen. Epitaxy as indicated by physical characteristics within the film as viewed optically has been confirmed with x-ray data. The principal limitation to film quality appears to be the substrate quality. The epitaxial mechanism seems to be the same as postulated for the silicon sapphire system, i.e., a substitution of silicon for the metal ion, in this case filling a Mg+2 site and bonding to the oxygen atoms of the spinel. The following orientation relationships were obtained: (111)Si∥(111) spinel; (100)Si∥(100) spinel; and (110)Si∥(110) spinel.
Analysis of the Effect of Fast-Neutron Bombardment on the Current-Voltage Characteristic of a Conductivity-Modulated p-i-n Diode
Authors: Swartz John M. , Thurston Marlin O.
Published: April 2005

Fast-neutron bombardment of silicon diodes changes the excess carrier diffusion length without significantly changing other diode parameters. Such bombardment is thus a useful tool for investigating diode theory. The technique is applied to an expression for the current-voltage characteristic developed for the wide-based p-i-n diode. For high level injection, there are two current density ranges of interest. First, a range where the base voltage is independent of current density and the total junction voltage V varies as exp(qV/2kT) with current. This region corresponds to unity emitter efficiency at each of the junctions. For higher current densities, the emitter efficiency decreases, and the base voltage increases as the square root of the current density. Also, the total junction voltage varies as exp(qV/kT) with current. The theoretical results are then shown to fit the current-voltage characteristics of experimental wide-based silicon p-i-n diodes.
Ionizing Irradiation Effects on the Fracture Surface Energy of Potassium Chloride
Authors: Bhattacharya Tapan K. , Zwicker Earl F.
Published: April 2005

The Co-60 gamma-ray-induced changes in the fracture surface energy φ of KCl at 300° and 115°K, as measured by the Obreimov-Gilman slow cleavage technique, are given by φ=φ0+a1DF12+a2DF23,where φ0 is the fracture surface energy of unirradiated crystal, DF is the F-band optical density per centimeter, and a1 and a2 are constants independent of DF. The square root term represents a plastic-flow contribution which decreases with increasing irradiation and is dominant at room temperature. The two-thirds power term represents an extrinsic, point-defect (EPD) contribution which increases with increasing irradiation and dominates at low temperature. The formation of aggregate centers by room-temperature ``F-light'' bleaching causes an increase in the EPD contribution, which is reversed when the aggregate centers are destroyed by re-irradiation. The external surface energy of Co-60 gamma-ray and 40-kV x-ray irradiated KCl at 300°K, as measured by a pendulum sclerometer, follows a similar relation which is derived under the assumption of a quasistatic friction mechanism. Qualitative observations on spontaneous and forced crack healing in KCl are consistent with the above findings.
Energy Distribution of Energetic Atoms in an Irradiated Medium. II. Single Species Case: Application to Radiation Damage Calculations
Authors: Felder R. M. , Kostin M. D.
Published: April 2005

Collision densities are calculated for a homogeneous time-invariant system of energetic and thermal atoms of a single species. It is assumed that the rapidly moving atoms emanate from a monoenergetic source and undergo only binary elastic collisions with thermal atoms. For a class of interaction potentials whose differential scattering cross sections are independent of the energy of the incident atom, the collision density is found to vary as 1/E near the source energy, and as 1/E2 at lower energies. For hard-sphere scattering, the 1/E2 functionality extends over the entire energy range from zero to the source energy; as the degree of scattering anisotropy increases, the 1/E2 range contracts, and the 1/E variation covers an increasingly broad interval. Analytical expressions are obtained for the collision densities in both regions. Similar conclusions are reached for a less restricted class of interaction potentials, and the results applied to the calculation of the number of displaced atoms produced by a primary energetic atom.
Thermal Resistivity at Interfaces between Metal and Dielectric Films at 1.5° to 4.2°K
Authors: Holt V. E.
Published: April 2005

Measurements of the thermal resistivity at interfaces between metal and dielectric thin films and a bulk substrate are reported. The thin-film structures are representative of a variety of superconducting devices with electrically insulated components. Results were obtained for single and multiple layers from 1.5° to 4.2°K. The magnitude of the observed values are within the range of the Little formulation if only longitudinal phonon contribution is considered. The temperature dependence is approximately T−2.5. The thermal resistivities decreased with increasing heat flux and temperature difference. The resistivity of multiple-layered structures was considerably less than the sum of the resistivities of each layer measured separately. This is consistent with wave propagation through layered media. No appreciable effect of film thickness was noted in the 0.2- to 2-micron range.
Application of an Extension of Linde's Rule to Some Dilute Alloys of Cu, Mg, and Al
Authors: Lucke William H.
Published: April 2005

It is proposed that Linde's rule be extended by including a term linear in the valence difference between solute and solvent. Justification based on the Born approximation and experiment is adduced.
Frost Heave in Soils
Authors: Jackson K. A. , Uhlmann D. R. , Chalmers B.
Published: April 2005

The Jackson-Chalmers model of frost heave is extended with a more detailed treatment of the heat flow and water transport problems in soils. Concepts derived from a study of the interaction between particles and a solid-liquid interface are combined with the previous model and applied to the formation and growth of ice lenses. Quantitative predictions relating heave rate with various soil parameters are found to agree well with available experimental data.
Deformation and Fracture of Bone
Authors: Bonfield W. , Li C. H.
Published: April 2005

The microscopic yield stress (the stress to produce a plastic strain of 2×10−6 in./in.) and the variation of plastic strain with applied stress have been established for bone. A feature of the deformation is the large anelastic contraction which occurs after unloading plastically strained specimens. The fracture characteristics of bone, as determined in impact loading and tensile experiments, are a function of specimen orientation and are also notch sensitive. A study of the temperature dependence of fracture in the range from −190° to 900°C shows that specimens oriented parallel to the length of the bone exhibit a pronounced maximum in strength at 0°C.
X-Ray Diffraction Studies on Tin to 100 Kilobars
Authors: Barnett J. Dean , Bean Vern E. , Hall H. Tracy
Published: April 2005

The high-pressure equilibrium phase diagram of tin is investigated, and the crystal structure of Sn II at 98 kbar and 25°C is shown to be body-centered tetragonal with a=3.70 Å, c=3.37 Å, c/a=0.91, and with two atoms per unit cell. The linear compressibility of white tin is given at 25°C up to the high-pressure transformation at 92 kbar, and the latent heat of the transformation is measured as 225 cal/g-atom.
Properties of InAs Lasers
Authors: Melngailis I. , Rediker R. H.
Published: April 2005

Two different recombination mechanisms can be distinguished in the infrared radiation spectra of InAs. The photoluminescence of n-type InAs corresponds to a direct band-to-band (or weak exciton) transition. The photoluminescence of Zn-doped p-type InAs and the injection luminescence of most Zn-diffused diodes correspond to transitions between conduction-band states (not excluding shallow donors for p-type crystals with a heavy donor compensation) and acceptor states about 17 meV above the valence band. The diode emission, therefore, results from injection of electrons into the p-type side of the junction, although band-to-band radiation has also been obtained in some diodes under certain conditions of current density and magnetic field.

Present InAs diode lasers which emit near 3.1 μ (band-to-acceptor line) have external quantum efficiencies of about 12% and threshold current densities of about 300 A·cm−2 at 11°K, and they can be operated continuously with currents of several amperes. With magnetic fields of several kG applied perpendicular to the diode current the threshold has been further reduced and the efficiency increased to as much as 25%. This enhancement of emission is shown to be associated with a decrease of injected carrier diffusion in the magnetic field which produces a more compact active region. The threshold increases nearly exponentially with temperature up to 150°K, the highest temperature for laser action at present. The angular spread of the coherent radiation beam in the plane perpendicular to the junction plane is about 30°, which corresponds to a coherently emitting region of 6 μ at the junction. Angles as small as 7° were measured in the plane of the junction.

Coherent emission at 3.0 μ corresponding to a band-to-band transition is obtained from n-type (ND=2×1016 cm−3) InAs crystals at 11°K by exciting them with 0.84-μ emission of a GaAs p-n junction laser. The angular spread of the coherent radiation beam in the plane perpendicular to the optically excited plane is 9° which corresponds to a coherently emitting region of 20 μ, over three times larger than the 6 μ for the diode laser.
Complex Longitudinal Magnetoconductivity of n-Type Silicon at 24 Gc/sec
Authors: Armstrong Donald B. , Champlin Keith S.
Published: April 2005

The influence of a dc magnetic field on the microwave conductivity and permittivity of n silicon at 77°K is investigated. The magnetic field is applied coparallel to both the microwave electric field and a [111] axis of crystal symmetry. Because the experimental frequency is comparable to the reciprocal relaxation time, electron inertia produces an appreciable magnetoconductivity component in time quadrature with the electric field. Calculations to second order in B show that this component is nearly maximized by the choice of experimental frequency and temperature. The experimental results are compared with theoretical predictions derived from the frequency-dependent Boltzmann equation by assuming an energy-dependent relaxation time describing both intravalley and intervalley transitions. The average relaxation time of the electrons, deduced from the measured microwave magnetoconductivity, is found to agree well with that obtained by combining the dc mobility with effective mass components determined at 4.2°K by cyclotron resonance.
Static and Dynamic Stress Effects in Cylindrical Ferromagnetic Films
Authors: Weinstein Hillel
Published: April 2005

Three experimental procedures were undertaken to evaluate the feasibility of a proposed serial, non-volatile, digital memory system, in which the information is statically ``frozen'' in the storage medium. A scanning stress pulse was proposed to locally modulate the anisotropy field in thin, anisotropic, ferromagnetic films and to aid in rotating the magnetization into a direction dictated by an applied magnetic field. A simple experiment was set up for the measurements of the circumferential and axial hysteresis loops of cylindrical, thin ferromagnetic films under calibrated axial stresses. A reduction by a factor of two in the circumferential coercivity of a 73.6% Ni (balance Fe) sample is obtained for a change in stress of 0.5 kG/mm2. The same sample is then bonded to an efficient magnetostrictive transducer. A change in the permanent magnetic flux state is observed when the sample is subjected to a propagating stress pulse in space—time coincidence with an applied magnetic field, as compared to a noncoincidence case. The sensing is accomplished by synchronization with the traveling stress pulse. Nondestructive sensing of the magnetization state via the reverse-magnetostrictive effect is observed.
Microwave Magnetoelastic Effect in Thin Films of Dy, Ho, Gd, and Er
Authors: Maley M. P. , Blackstead H. A. , Donoho P. L.
Published: April 2005

We have observed the generation of microwave acoustic pulses in thin films of four of the rare-earth metals. The pulse—echo technique common to ultrasonic studies in solids was employed. Acoustic generation in Dy, Gd, Ho, and Er has been observed at frequencies between 0.8 and 9.2 GHz at temperatures between 4.2° and 130°K. This effect appears in the antiferromagnetic region only at field values greater than the critical field for ferromagnetic alignment. In Dy, with the magnetic field along the film normal, the echo amplitudes exhibit a monotonic increase with magnetic field up to 20 kOe at 1.0 GHz and 4.2°K. In Gd, however, a resonant peak is seen under the same conditions, similar to that observed in nickel alloys. In Er and Ho acoustic power reaches a plateau at 14 kOe at 1.0 GHz and 4.2°K. The magnetic-field values at which appreciable acoustic generation is observed are generally much lower than would be necessary for ferromagnetic resonance at the frequencies used here.
Adiabatic Magnetization of Nb in the Superconducting State
Authors: Flippen R. B.
Published: April 2005

Studies are reported of the magnetic properties of the type II superconductor Nb upon adiabatic magnetization of the superconducting state. Both polycrystalline and single-crystal bulk samples of varying purity have been used, and the effects of thermal and mechanical treatment have been studied. Typical samples of Nb show large departures from isentropic conditions at all temperatures, although very high-purity material shows a cooling effect of up to 60% of that predicted from entropy data at higher temperatures, e.g., cooling from 5° to 2.5°K is obtained upon adiabatic magnetization. However, at lower temperatures irreversible magnetization effects occur even in the purest samples which lead to sample heating over part of the magnetization curve, the amount of heating increasing with decreasing starting temperature. Less pure samples of Nb show pronounced temperature jumps of up to 3°K at lower temperatures. These are shown to accompany the occurrence of large flux jumps in the material. Annealing of samples under conditions sufficient to remove most of the physical defects produces a further departure from ideal, e.g., reversible magnetization, behavior. These energy dissipative processes are therefore ascribed to properties of flux pinning at chemical-impurity centers in bulk material.
Magnetic Diffusivity in a Type II Superconductor
Authors: Lubell M. S. , Wipf S. L.
Published: April 2005

The magnetic diffusivity D=109ρ/4π has been measured for a cylinder of Nb-25% Zr at T=4.2°K. The cylinder was brought to the shielding portion of the creep curve by a coaxial magnetic field increasing linearly with time. By means of a magnetoresistance probe, we observed the propagation of small coaxial magnetic steps (ΔH=2 to 20 Oe) into the center of a cylinder which remained in a critical state. Fitting the diffusion equation solution for a step function to the measured delay times of the penetrating field, we obtained a value for the resistivity, ρΔ=1.5×10−10 (dH/dt) Ω·cm for dH/dt in the range 2 to 40 Oe/sec. The dependence on both the magnitude of the step and the field was weak. Extrapolation of our data to ΔH=0 yields ρΔ=1×10−10 dH/dt Ω·cm. If on the other hand, the resistivity for the creep state is calculated either by dividing the induced voltage multiplied by geometric factors by the shielding current, or by a steady-state solution of the diffusion equation for a ramp function, one obtains ρcr≈1×10−13 dH/dt Ω·cm. This discrepancy is readily explained by the steepness of the resistive transition curve, i.e., a small disturbance is sufficient to raise the resistivity well above the critical state.
Thermoelectric Power and Electrical Resistance of Chromium-Iron Alloys from 125° to 625°K
Authors: Schröder Klaus , Yessik Michael J. , Baum Neal P.
Published: April 2005

The Seebeck coefficient S of alloys with up to 23 at. % iron has been measured from 125° to 625°K. S of alloys with 10, 15, 19, and 23 at. % Fe was nearly temperature-independent and had values between 6 and 9 μV/°K. Pure chromium and alloys with up to 4 at. % Fe had a nearly temperature-independent S at temperatures above 375°K, with S ranging from 13 to 16 μV/°K. However, S exhibited a pronounced maximum below room temperature. The maximum values and the corresponding temperatures are: pure chromium: 21 μV/°K, 275°K; 1 at. % Fe: 27 μV/°K, 240°K; 2 at. % Fe: 40 μV/°K, 175°K; 4 at. % Fe: 34 μV/°K, 280°K. The resistance anomaly of chromium rich samples with maxima below room temperature was similar to that found by other authors. This anomaly has been attributed to the transition to antiferromagnetism.

It has been shown that the peak of the phonon drag term S (phon) in pure chromium occurs at 25°K. The observed peaks in our experiments above 125°K should be due to the electron-diffusion term S (diff). It can be deduced from S of alloys with 10 to 23 at. % Fe, that s-d scattering has only a small effect on the S (diff) and it is concluded that the structure change of the conduction band at the transition to antiferromagnetism is responsible for the maxima in S. The indicated energy dependence of the Fermi surface is in qualitative agreement with band models deduced from Hall-effect measurements in the same alloys.
Antiferromagnetism in Chromium Alloys
Authors: Mackintosh A. R.
Published: April 2005

The antiferromagnetism of Cr and its alloys has recently been extensively studied by neutron-diffraction1–3 and transport-property measurements.2,4 The concentration dependence of the moment, the Néel temperature, and the periodicity of the magnetic ordering can be correlated with the theoretical band structures and the anomalies in the transport properties just below TN.

Magnetic ordering in Cr is a consequence of the localized nature of the d-functions, which give rise to a large intra-atomic Coulomb interaction; and the narrow d bands which favor the formation of a magnetic state.5,6 The magnetic form factor7 is in qualitative agreement with the relative occupancy of the d bands of different symmetry.8 Decreasing the electron concentration by the addition of V causes a decrease in magnetic moment and TN and also decreases the Q vector of the magnetization. It has been shown6,9 that in some cases, the magnetic periodicity of such a structure is determined by the extension of a prominent piece of the Fermi surface and it appears that, in this case, the distance between the octahedral faces of the electron jack at Γ and the hole surface at H determines Q.10 This hypothesis is in approximate agreement with the calculated Fermi surface dimensions,11 and the change in periodicity and moment with alloying can also be qualitatively understood. The transport properties provide evidence that the magnetic ordering destroys a significant proportion of the Fermi surface. Increasing the electron concentration by adding Mn causes the moment and TN to increase and, in addition, tends to make the magnetic periodicity commensurate with the lattice. This allows a maximum interaction between the magnetization wave and the d electrons. The addition of Mo or W causes a gradual decrease in the moment and TN, probably due to the less localized nature of the d functions in these metals.

In pure Cr there is a transition from a transverse to a longitudinal spin density wave on cooling through 121°K, due to the extra entropy associated with the former spin configuration. This transition is rapidly eliminated by the addition of impurities, for reasons which are not at present understood.
Self-Consistent Energy Band Calculations for Chromium. I. Charge and Spin Densities
Authors: Switendick A. C.
Published: April 2005

Electronic energy bands corresponding to the 3d and 4s states of nonmagnetic, bcc chromium were calculated using the augmented-plane-wave method. A charge density corresponding to the occupied states plus the atomic core was used to construct a new crystal potential. This procedure was repeated until the charge density was self-consistent. The self-consistent charge density is compared with the atomic density and with the initially assumed crystal density. A direct application of Slater's superlattice model of an antiferromagnetic band structure was made for chromium assuming spin-up localization on the cube corners and spin-down localization in the body-centered position. The same procedure for self-consistency is yielding a large net spin per site of greater than three Bohr magnetons of d-like character and less than 0.05 magnetons of the same sign for the conduction electrons. The spin densities for this situation are given along with a discussion of the approximations leading to this physically incorrect result.
Impurity Scattering of the Conduction Electrons in Dysprosium Alloys
Authors: Chen C. W.
Published: April 2005

The electrical resistivities of the intra-rare-earth alloys of dysprosium have been determined at 4.2°K, 77°K, and 296°K for a continued study of the impurity scattering of the conduction electrons. The resistivity data reveal that substitution of La, Ce, Pr, Nd, and Sm in Dy leads to considerable increases of the residual resistivity of Dy at low temperatures, but the increases disappear at 296°K. The impurity-induced resistivities Δρ0 are predominantly due to the exchange scattering of the electrons via the Ruderman-Kittel type exchange interaction between the 4f and conduction electrons. The exchange scattering is shown to depend only on the difference between the atomic spins of the solvent and solute ions, with the spin-orbit coupling playing an insignificant role. Since these features have also been observed in the Gd alloys, they are considered to be characteristic of the impurity scattering of the electrons in all rare-earth alloys. In the Dy alloys, however, the contribution to Δρ0 of the electrostatic scattering is much larger than that found in the Gd alloys. Also, at 77°K, the resistivities of the Dy alloys containing such solutes as Ce, Pr, and Nd show complex behavior, due probably to the formation of an antiferromagnetic spin structure.
Magnetoresistance in Iron Single Crystals
Authors: Coleman R. V. , Isin A.
Published: April 2005

Magnetoresistance in single crystals of iron has been studied in fields up to 50 kOe at temperatures from 1°–300°K. Iron whiskers 40–700 μ in diameter grown by the hydrogen reduction fo FeCl2 and having residual resistance ratios ρ300°K/p4.2°K from 200 to 2000 have been used for the experiments. In low fields the magnetoresistance shows a behavior related to the development of a net magnetization through domain growth and spin rotation. At low temperatures the predominant low-field behavior consists of a large negative magnetoresistance which develops for both transverse and longitudinal field orientations. This effect is present at 77°K and increases by an order of magnitude at 4.2°K. Strong hysteresis effects are also observed at 4.2°K. Correlation of the low-field magnetoresistance with the domain structure is discussed for both 〈100〉 and 〈111〉 axial whiskers. At high fields and low temperatures the magnetoresistance is in general agreement with theory and indicates that open orbits may exist for certain field directions. At high temperatures the high-field behavior shows a negative slope in agreement with previous experiment and theory while at low fields structure associated with domain development is observed.
Magnetic-Moment Distribution in Nickel Metal
Authors: Mook H. A. , Shull C. G.
Published: April 2005

The magnetic form factor for nickel metal has been determined for the first 27 Bragg reflections. Magnetic-moment density maps have been obtained in three dimensions by Fourier inversion of the form factor. It is found that the moment density is quite asymmetric about the lattice sites and is negative in the region between lattice sites. The measured form factor agrees very well with a free-atom form factor for Ni++ provided a uniform negative contribution is included in the moment density. From the comparison of the free-atom and measured form factors we have found that 81%±1% of the 3d electrons occupy t2g orbitals compared to the 60% required for spherical symmetry. The size of the negative contribution needed for agreement between the measured and free-ion form factors agrees very well with that given by the moment density maps, and the analysis of the data is consistent with the following model for the magnetization of nickel: 3d spin+0.656 μβ, 3d orbit+0.055 μβ, negative constant −0.105 μβ.
Some Neutron-Diffraction Investigations at the Nuclear Center of Grenoble
Authors: Bertaut E. F. , Bassi G. , Buisson G. , Burlet P. , Chappert J. , Delapalme A. , Mareschal J. , Roult G. , Aleonard R. , Pauthenet R. , Rebouillat J. P.
Published: April 2005

In orthorhombic CrRO3 (R=rare earth and Y), Cr spins are ordered in a G mode between TN 282°K for R=La, to 112°K for R=Lu. The rare-earth ordering is coupled to the Cr-spin ordering, with the exception of terbium. In the magnetoelectric compound Fe1.15Ga0.85O3, four sites are available for cations, one of these mainly occupied by Ga. Neutron-diffraction and magnetic-susceptibility measurements give evidence of a ferrimagnetic ordering. Tetragonal FeS shows no evidence for magnetic ordering by neutron diffraction and Mössbauer effect down to 1.7°K. The CrS-MnS solid solution has NaCl type. First kind of facecentered magnetic ordering is observed.
Magnetic Properties of NaO2 and KO2
Authors: Sparks Joseph T. , Komoto T.
Published: April 2005

The powder magnetic susceptibility of NaO2 and KO2 has been determined as a function of temperature from 63°K to around room temperature. The data for NaO2 show anomalies at 190° and 225°K which are in good agreement with the location of λ-anomalies reported in the specific heat and structure changes shown by x rays. A Curie-Weiss relation χ=C/(T−θ) is obeyed above 225°K with θ=−46°K, and C gives a value for the average effective moment of 1.77μB. The low susceptibility below 190°K and its temperature dependence suggest that the marcasite phase is antiferromagnetic. KO2 shows no evidence of magnetic ordering down to 63°K. The reciprocal susceptibility curve is made up of two linear regions with the change in slope at 150°K. The effective moments are 1.20 and 1.03μB with θ=−53° and −3°K for the high- and low-temperature regions, respectively. Neutron-diffraction results show a crystallographic distortion occurring at about 25°K.
Antiferromagnetism in Potassium Superoxide KO2
Authors: Smith H. G. , Nicklow R. M. , Raubenheimer L. J. , Wilkinson M. K.
Published: April 2005

Neutron-diffraction measurements made on polycrystalline samples of KO2 at several temperatures from 295° to 1.4°K have shown the existence of an antiferromagnetic transition in this compound at 7°K. These measurements have also revealed a crystal structure change slightly above the Néel temperature at about 12°K. Since the packing in the crystal structure involves close contacts between neighboring oxygen molecules, there is probably a correlation between the packing arrangements of these molecules with the onset of magnetic order, and the antiferromagnetic structure could be the result of direct exchange. Only two magnetic reflections definitely can be observed and a unique antiferromagnetic structure cannot be determined. However, the reflections suggest a structure in which there are ferromagnetic sheets of moments parallel to the (00l) planes and the moments on molecules in adjacent planes are antiparallel. The magnetic form factor determined from an analysis of the paramagnetic neutron scattering is in satisfactory agreement with that obtained from theoretical calculations based on the O2 molecule.
Scattering of Polarized Neutrons by Spin Waves in YIG
Authors: Ferguson G. A. , Sáenz A. W. , Podgor S.
Published: April 2005

The neutron diffraction technique has been employed to study the inelastic scattering of polarized 1.08-Å neutrons by magnetic spin waves in yttrium iron garnet (YIG) at room temperature. Measurements were made for the case when the YIG scatterer was oriented near the position for (220) Bragg reflection. Quantitative confirmation has been obtained for the theoretical predictions of the dependence of this scattering on the incident neutron polarization. Two new methods are described for determining the parameter D appearing in the expression Dk2 for the energies of long-wavelength acoustic magnons in usual ferromagnets and ferrimagnets. These methods require only measurements of the peak intensities of the diffuse magnetic reflections. The values D=0.25(+0.04, −0.03) eV·Å2 and D=0.26±0.02 eV·Å2 have been obtained for YIG by these procedures.
Observation of the Dispersion Relation for Spin Waves in Hexagonal Cobalt
Authors: Alperin H. A. , Steinsvoll O. , Shirane G. , Nathans R.
Published: April 2005

The acoustic branch of the spin-wave spectrum of hexagonal cobalt has been measured for values of the magnon wave vector q up to qc/2π=0.2 by observing the inelastic scattering of polarized neutrons by the diffraction method. The results indicate a decided departure from the dispersion law expected for a Heisenberg ferromagnet. In particular, if the energy is expressed as a sum of q2 and q4 terms, then the q4 term should only contribute 3% to the energy, whereas a contribution of 35% is observed. The coefficient of the q2 term yields an exchange stiffness parameter D=490±20 meV·Å2.
Magnetic Structure of MnP
Authors: Forsyth J. B. , Pickart S. J. , Brown P. J.
Published: April 2005

In magnetic measurements on a single crystal of MnP, Huber and Ridgley1 found a ferromagnetic Curie point at 291.5° and a transition at 50°K, below which the crystal was metamagnetic, i.e., it exhibited an antiferromagnetic-ferromagnetic transition which was a function of the applied field and temperature. We have carried out a neutron diffraction investigation at 4.2°K on this same crystal. Magnetic scattering was observed in pairs of satellite reflections displaced by ±δ from each nuclear peak in the [010] and [100] zones, with δ=0.112c*; in most cases the intensities of the two satellites of a single reflection differed markedly. Their existence and displacements along c* show that the spin structure is modulated in this direction, and the existence of only a pair of satellites to each reflection shows that the modulation is closely sinusoidal; however, the inequality of the pairs indicates that the structure cannot be a simple spiral. MnP has an orthorhombic B31 type structure, space group Pnma with 4 Mn in 4(c) (x, ¼, z). Detailed consideration of the satellite intensities shows that the spins all lie in the ab plane and are coupled ferromagnetically across the centers of symmetry of space group Pnma. The spiral is propagated by rotations of the spins by approximately 20° for each operation of the screw diad parallel to c. The field dependence of the satellites has also been studied: no change in spiral wavelength with field was detected. A complete account of this work will be published elsewhere.
Microwave Characteristics of Fine-Grain High-Power Garnets and Spinels
Authors: Blankenship A. C. , Huntt R. L.
Published: April 2005

One approach in materials engineering to increase the nonlinear power absorption threshold of ferrimagnetic materials is that of reducing the grain size. A program is described wherein this has been successfully carried out. The use of hot pressing techniques provides dense small-grain materials suitable for device construction and evaluation. The method has proven equally successful for both garnet and spinels. An order of magnitude increase in threshold is readily achievable with no increase in low-power insertion loss. Measurement of linewidth (ΔH), gyromagnetic ratio (γ), dielectric constant (ε′), loss tangent (tan δ), saturation magnetization (4πMs), coercive force (Hc), spin-wave linewidth (ΔHk), and high-power threshold values are given. The predominant effect of reduced grain size is to increase the spin-wave linewidth (ΔHk), which explains the measured increase in threshold. Case histories of application of fine-grain materials in production devices are given as well as laboratory studies of both device performance and ΔHk measurements.
An Extremely High Power X-Band Three-Port Circulator
Authors: Wantuch E. , Lepore D.
Published: April 2005

The modifications of typical ferrite materials by either hot-pressing or the addition of fast relaxing impurities are compared in a three-port circulator.

A standard MgMn ferrite with empirical formula Mn0.08Mg1.25Fe1.67O4± was tested in the three-port circulator model. It showed an onset of nonlinear behavior at 20 kW. By hot-pressing, the peak power level was extended to 200 kW with 0.1 dB rise in insertion loss, and to 500 kW with 0.25 dB increase in insertion loss.

A gadolinium-substituted garnet with empirical formula 3(Y0.6Gd0.4)·5(Fe)O12 was tested in the same geometry. It exhibited a threshold power level of 10 kW. A 4% substitution of dysprosium greatly extended the peak power handling capability of the three-port circulator. No increase in insertion loss over low-power readings was noted up to 500 kW peak.
Magnetic and Microwave Properties of Calcium Vanadium-Substituted Garnets
Authors: Hodges L. R. , Rodrigue G. P. , Harrison G. R. , Sanders A. D.
Published: April 2005

Polycrystalline ferrimagnetic pentavalent vanadium garnet compositions conforming to the general formula {Y3−2xCa2x} [Fe2] (Fe3−xVx) O12 for x equal 0 to 1.5 were investigated and evaluated along with the ``yttrium-rare-earth-free'' garnets of the system {Bi3−2yCa2y} [Fe2] (Fe3−yVy) O12 for y equal 0.75 to 1.5. Single crystals of the latter system have been investigated for 1.01.0 to 1.5, linewidth values are 100 to 200 Oe. In the BiCaVIG compounds, the linewidths are higher (500 Oe) for values of y<1.0 and approximately 200 Oe for 1.0<y≦1.5. Dielectric constants (X band) for these compounds varied from 29 to 13 for y=0.75 to y=1.5, respectively. Compositions in both systems were prepared possessing dielectric loss tangents (X band) as low as 0.0001. The temperature characteristics of these vanadium garnets are compared to the more widely used yttrium aluminum and yttrium gadolinium iron garnets. Single-crystal samples (y=1.33, 4πMs=500 G) were prepared possessing measured linewidths at C band of 1.0 Oe.
L-Band Properties of Single-Crystal 600-G Calcium Vanadium Bismuth Iron Garnet
Authors: Lehman Kenneth A.
Published: April 2005

The microwave properties of calcium vanadium bismuth (CVB) garnet spheres with a 4πMs of 600 G, grown from a melt, were evaluated for use in an L-band filter. The material tested had linewidths ranging from 0.7 to 1.0 Oe at 1.5 Gc at room temperature when oriented with the [111] axis normal to the dc field and at a point of minimum thermal drift (a point where the resonant frequency, in Mc/sec, is 2.8 H, in oersteds, and is temperature-independent). The upper limit of coincidence limiting was 1.15 Gc/sec. The onset of limiting at this frequency for CVB is quite rapid when compared with 600-G GaYIG. It is particularly interesting to note that the microwave properties measured at the minimal thermal drift axis and the other major axes behave essentially the same as YIG, assuming pure YIG were available at 600 G. Data on the materials used in filters are discussed as well as the potential of CVB at a lower band. The material is superior to 600-G GaYIG because it has a more consistent composition. It also helps to reduce multiball tracking problems by eliminating the large concentration gradient usually observed in GaYIG materials.
Infrared and Visible Laser Modulation using Faraday Rotation in YIG
Authors: Zitter R. N. , Spencer E. G.
Published: April 2005

Faraday rotation in YIG has been employed to modulate 3.39-μ radiation in a helium-neon laser. YIG has sufficient transparency at this wavelength to permit placement within the optical cavity. Modulation at 13 Mc/sec corresponds to the round-trip time 2L/c of photons in the cavity, and with the lasing condition, mode locking is observed with a spiked output beam similar to effects previously reported for lasers at 6328 Å. By the use of prisms and separate mirrors, lasing can occur simultaneously at 3.39 μ and 6328 Å, where modulation effects in the 3.39-μ beam are transferred to the visible 6328-Å beam. A variety of effects in the visible beam are observed, depending on the state (lasing or superradiant) of the 3.39-μ beam; in particular, ``spiking'' or its opposite may be induced in the visible beam.
Recent Developments in High-Energy Alnico Alloys
Authors: Cronk Edward R.
Published: April 2005

A brief review of the ``state of the art'' with emphasis on developments of the past several years is given. It is shown that with but two major exceptions, all significant advancements in energy product enhancement have been achieved by special foundry techniques to promote crystal anisotropy, and not by alloy composition variations. The exceptions are found in the advent of the family of high-coercive-force alloys using increased amounts of cobalt and titanium known today as Alnico 8, and in secondary recrystallizing techniques on special forms of Alnico 5 to produce a single large crystal from a polycrystalline aggregate. The latter technique was described in an earlier paper at this conference [E. Steinort et al., J. Appl. Phys. Suppl. 33, 1310 (1962)]. Work on producing crystalline anisotropy in a modified form of Alnico 8 has produced energy products as high as 10.5 MG·Oe and magnets are commercially available as Alnico 9 with energy products averaging 9.0 MG·Oe. Further work is described which shows that it is possible to apply the techniques of secondary recrystallization to a columnar aggregate of Alnico 9 and achieve further energy product enhancement to 12.5 MG·Oe for a large single crystal.
Evaluation of Long-Term Magnet Stability
Authors: Zingery W. L. , Whalley W. B. , Romberg E. B. , Wheeler F. W.
Published: April 2005

Precision long-term measurements have been made of the change of permanent magnet fields of several magnet configurations and several magnet materials. The application of permanent magnets to small, low-power, precision instruments demands, for some applications, long-term stability of the inhomogeneous magnet field of a few parts per million over many months. Magnet configurations studied include multipole designs. Materials measured include the Alnicos, Ticonal XX, and PtCo. Precision instrument systems for long-term measurements are briefly described. Eleven instruments of six different designs were used in the study. The best instrument could resolve a change in the inhomogeneous field of less than 1 ppm while the magnet remains in the measuring instrument and could resolve a change of a few ppm long term. The natural magnetization adjustment is accelerated by artificial stabilization processes but the type of processing and the order of events greatly influence the resulting stability. Asymmetric demagnetization results in instability. Data are presented which show stability of a few ppm per year.
On the Alnico Problem
Authors: Shtrikman S. , Treves D.
Published: April 2005

Alnico alloys were ground and separated by sedimentation. Mössbauer and fluorescence analysis techniques were used to study the separated phases. The main result is that alloys heat treated for optimum permanent magnet properties contain a paramagnetic phase, probably bcc, rich in nickel and copper, while quenched Alnico V does not contain such a phase.
Evidence by Lorentz Microscopy for Magnetically Active Stacking Faults
Authors: Zijlstra H. , Haanstra H. B.
Published: April 2005

In the ordered MnAl crystal containing magnetic atoms which are coupled ferromagnetically, stacking faults are postulated through which an antiferromagnetic coupling exists between the atoms on either side of the fault. These account for the anomalous magnetic behavior1 of fine MnAl powder. Such faults give rise to a domain structure the walls of which are strongly pinned to these crystallographic defects. A direct evidence for the occurrence of these stacking faults is obtained by using Lorentz electron microscopy, whereby shadow patterns of opaque MnAl particles show a characteristic distortion of their contours when the microscope is used out of focus. The distortion is interpreted in terms of stray fields due to the domain structure. Experiments were carried out in a Philips EM 200 electron microscope.

By using the normal objective lens, the pattern can be studied with or without a strong applied field. Fields up to 9000 Oe could be applied. Domain structures were observed that showed a remarkable indifference for these fields. This rigidity is explained by assuming that the walls are pinned to stacking faults.

Domain structures with a high pole density on the walls were also observed. These structures are unfavorable owing to large magnetostatic energy. Their occurrence is also explained by the presence of stacking faults.

A full account of the method and the results will be submitted as a regular article to this Journal.
Intercrystalline Fracture in Alnico 5
Authors: Curran R. E. , Mendelsohn L. I.
Published: April 2005

In the production grinding of Alnico 5, small grains break loose from the body of a magnet leaving a void. This pickout problem can be avoided by controlling the cooling rate to about 250°C/min from the molten condition. Magnetic and physical strength measurements as well as metallographic studies explain the need for cooling-rate control to achieve the best compromise between remanence and physical strength.
A Current Review of Lodex Permanent Magnet Technology
Authors: Falk R. B.
Published: April 2005

The history of elongated, single-domain permanent magnets, commencing with the theoretical considerations of Stoner and Wohlfarth and others to the reduction to practice by Paine, Mendelsohn, and Luborsky, and final development of product (Lodex) manufacturing capabilities, is briefly reviewed.

The present Lodex permanent magnet is prepared by a relatively complex electrochemical and amalgam metallurgical process. A wide variety of magnetic properties may be obtained by altering the ratio of elongated particles to matrix material during processing. Isotropic and anisotropic permanent magnets having complex shapes and extremely close tolerances are formed directly by a variety of powder metal and extrusion processes. Such magnets consist of antimony-coated particles of iron-cobalt embedded in a metallic lead matrix.

The use of Lodex magnets in automotive, meter, communication, and control applications is discussed in detail. Current laboratory development work on oxide-coated iron-cobalt particles, coercive force improvements on existing particles, and physical property improvements of the present magnet structure is reviewed.
Recent Ferrite Magnet Developments
Authors: Cochardt A.
Published: April 2005

Currently used ferrite magnets (also called ceramic magnets) are modifications of the magnetoplumbites MO·6 Fe2O3 where M stands for Ba or Sr—with additions of other compounds, off-stoichiometric ratios, flexible binders, etc. The first commercial magnetoplumbite magnets were of the barium ferrite type, but the newer ones are modified strontium ferrites which are about 30% higher in coercive force at the same level of remanence and 4% lower in weight than the barium ferrites. They are also easier to manufacture. The results of hysteresis loop measurements on some 20 000 anisotropic different ferrite magnets are summarized. The highest values, which are all obtained on modified strontium ferrites, range from (BH)max = 4.8 MGOe at IHc = 2.4 kOe to (BH)max = 0.8 MGOe at IHc = 11 kOe depending on process and chemical composition. The permanent magnets with the highest presently known energy/cost ratios are obtained by subdividing a green body of sulfate-modified strontium ferrite using a ``cookie-cutting'' technique and by quick-firing the magnets so that they contain nonequilibrium structures.
Critical Point of the Cubic Antiferromagnet RbMnF3
Authors: Teaney D. T. , Moruzzi V. L. , Argyle B. E.
Published: April 2005

We have studied the critical region of RbMnF3 (TN=83°K) using specific heat, x-ray, and strain-gauge measurements. Because RbMnF3 so closely resembles an ideal Heisenberg antiferromagnet, experimental results may be especially relevant to theoretical predictions. The specific heat is found to diverge logarithmically over three decades for T<TN, but only over two decades for T<TN. No distortion from cubic symmetry is detectable in the range 20° to 300°K. Finally a remarkably small thermal expansion anomaly is found in a narrow region near TN.
Effect of Hydrostatic Pressure on the Metamagnetic Transitions in FeCl2·2H2O, CoCl2·2H2O, FeCl2, and FeBr2
Authors: Narath Albert , Schirber J. E.
Published: April 2005

The pressure derivatives of the two interchain exchange constants in FeCl2·2H2O and CoCl2·2H2O, and of the interlayer exchange constant in FeCl2 and FeBr2 have been obtained from measurements of the respective metamagnetic transition fields in the temperature range 1°–4°K. Hydrostatic pressure to 4 kbar were generated by isobaric freezing of 4He. The antiferromagnetic exchange constants in these compounds exhibit large positive pressure derivatives which range from 2% to 9% per kbar. The magnitudes of the average interlayer exchange energies in the hexagonal layer compounds FeCl2 and FeBr2 appear to be strongly influenced by crystal imperfections such as stacking faults. In FeCl2 a polymorphic transformation (presumably between CdCl2 and CdI2 structure types) is observed near 2 kbar, which is accompanied by a 12% increase in the transition field.
Analysis of Absorption Edges in Uniaxial Antiferromagnetic Powders
Authors: De Meo E. A. , Heller G. S.
Published: April 2005

The shape of the absorption edge in a uniaxial antiferromagnetic powder has been obtained theoretically and compared with existing experimental data for the case of MnTiO3. The absorption edge is computed from the susceptibility tensor for a single crystal with an arbitrarily oriented applied magnetic field by averaging appropriately over the individual crystallites. Agreement between resulting calculations and the experimental data shows that it is possible to predict the effective internal magnetic field, the effective g value, and the single-crystal antiferromagnetic resonance linewidth using experimental absorption-edge data from powdered materials. For the MnTiO3 sample used, the best fit was obtained for an effective internal field of 55 kOe and a linewidth of approximately 500 Oe.