bluuebunny/crossref_metadata_2025 huggingface dataset:
Fermi-Surface Studies in Iron and Nickel
Authors: Gold A. V.
Published: January 2006

A review is given of the present state of our experimental understanding of the Fermi surfaces for iron and nickel. Particular emphasis is placed on information derived from the galvanomagnetic coefficients, in both high and low magnetic fields, and on recent detailed studies of the de Haas-van Alphen effect in these metals.
Mössbauer Study of the Electronic and Magnetic Properties of Fe2+ Ions in Some Spinel-Type Compounds
Authors: Hartmann-Boutron F. , Imbert P.
Published: January 2006

We discuss here the results and interpretation of some Mössbauer experiments on FeCr2O4, FeV2O4, and GeFe2O4. A detailed study of the thermal variation of the spectra leads to a determination of both quadrupolar coupling and hyperfine field at the 57Fe nucleus as a function of temperature. Knowing the local symmetry around the Fe2+ ion, which is tetragonal in the first two cases, and trigonal in the last one, it is possible to deduce from the quadrupolar coupling the form of the lowest orbital wavefunction of the Fe2+ ion. In FeCr2O4 and FeV2O4, this may be combined with the optical data obtained by Slack on the very similar compound FeAl2O4, to predict the form and magnitude of the spin Hamiltonian and magnetic anisotropy, as well as that of the hyperfine field tensor (using a reasonable estimate for the core hyperfine field). In GeFe2O4 similar predictions can be made after deducing the distance to the first excited orbital level from the thermal variation of e2qQ. The interest of such calculations in connection with the determination of the magnetic structures and properties of these types of compounds is examined.
Antiferromagnetic Properties of Light Rare Earth Monochalcogenides
Authors: Smolensky G. A. , Adamjan V. E. , Loginov G. M.
Published: January 2006

Magnetic investigation of monochalcogenides MeX where Me = Ce, Pr, or Nd and X = S, Se, or Te at 4°–1300°K was undertaken. Van Vleck's theory was used for describing experimental χ(T) dependences at T>500°K.

It has been observed that monochalcogendies formed by the ions with an odd number of electrons exhibit an antiferromagnetic ordering near ∼10°K in contrast to the monochalcogenides formed by the ions with an even number of 4f electrons (Pr3+, Sm2+) except PrS. An attempt to evaluate the parameters of the exchange interaction using molecular field approximation was made. In order to explain the χ(T) dependences obtained at T < 100°K the approximation which included crystal-field and exchange effects simultaneously is required.
Transferred Hyperfine Interactions and Spin Deviations in Magnetic Salts
Authors: Owen J. , Taylor D. R.
Published: January 2006

Magnetic resonance measurements on transition metal salts show that there is an appreciable hyperfine interaction between the electronic spin of one metal ion and the nuclei of neighboring metal ions. Recently reported measurements of this effect are described, particularly ENDOR studies of the 27Al hyperfine interaction in the structures Fe3+–O2−–Al3+ and Cr3+–O2−–Al3+. Mechanisms which have been proposed for explaining these metal-to-metal hyperfine interactions are also discussed with particular reference to the structures just mentioned and to the work of Huang et al. (1967) on KMnF3 and MnO. The most important process is thought to be the transfer of unpaired spin from d orbitals on the magnetic ion to s orbitals on the neighboring metal ion, usually via covalent and overlap effects with an intervening ligand. One result of such transfers, as emphasised by previous authors, is that the hyperfine interaction for a magnetic ion in a dilute salt is expected to be different from that in a concentrated salt because of the presence of magnetic neighbors. This effect is at least partly responsible for the lack of agreement between theoretical predictions and experimental estimates of zero-point spin deviations in antiferromagnets. Some examples are discussed, including KMnF3, MnO, LaFeO3, and LaCrO3.
Magnetic Effects of Rare-Earth Impurities on Electron Transport in the Noble Metals
Authors: de Vries G. , Bijvoet J.
Published: January 2006

Of the dilute alloys of rare-earth metals in the noble metals, only a few show a small resistance anomaly and a temperature-dependent negative magnetoresistance at liquid-helium temperatures. In a saturating magnetic field the decrease for the Gd alloys is 2%. A calculation in Born approximation shows this to be due to interference between Coulomb and spin-dependent scattering. The absolute value of J is found to be 0.04 eV when the interaction is written as H = − Jσ·Sδ(r−ri).

A similar calculation for two different magnetic impurities contains cross terms in the two coupling constants. For Mn in Ag, J is known to be negative from the resistance minimum (Kondo). It is concluded from the fact that, with 0.20 a.t.% Mn and 0.39 at.% Gd, only a very small magnetoresistance is observed, and that the sign of J is positive. With J = 0.04 eV a small negative Kondo effect can be computed which is of the same order of magnitude as experimentally found.

The magnetic effects in these alloys are small compared to what is reported in the literature on alloys with trivalent solvents. We have checked in a few cases that the magnetic moment agrees with the free-ion values. The explanation of the apparently small value of J probably must be found in a more careful analysis of the interference terms that may be different for different partial waves.
Orbital Effects on Exchange Interactions
Authors: Elliott R. J. , Thorpe M. F.
Published: January 2006

Many magnetic materials contain ions in which the orbital contribution to the magnetic moment is important. This is normally the case in the rare earths and the actinides, where there is strong spin-orbit coupling and weak crystal fields, and it also occurs in transition metal ions like Fe2+ and Co2+. This orbital contribution leads to asymmetric charge clouds and the corresponding asymmetry of the transfer and overlap integrals means that the exchange interaction between pairs of such ions is not of the Heisenberg form but contains more complicated functions of the angular momentum operators. The microscopic form of the exchange and coulomb interaction between pairs of electrons is considered in the single-electron representation and transformed to the (L, S) and J representations of many-electron atomic states, and finally to a pseudospin representation which spans the lowest-lying atomic states in the presence of crystal fields. The symmetry restrictions on this pseudospin Hamiltonian are considered. Detailed calculations are made of a model of UO2 using Anderson's kinetic exchange mechanism.
Magnetic Interactions in Tb and Tb-10% Ho from Inelastic Neutron Scattering
Authors: Mo/ller H. Bjerrum , Houmann J. C. Gylden , Mackintosh A. R.
Published: January 2006

The magnon dispersion relations and lifetimes have been measured in Tb and a Tb-10% Ho alloy by inelastic neutron scattering, in regions of both ferromagnetic and spiral ordering. In the ferromagnetic phase, the magnon energy is generally finite at zero wavevector and rises quadratically at low q. The magnon energies scale approximately with the magnetization. In the spiral phase the magnon energy rises linearly from zero at low q. The Fourier-transformed exchange parameter J(q) has pronounced peaks in the c direction, which are ascribed to transitions between states close to the Fermi surface. These peaks are less pronounced in the ferromagnetic phase. The primary mechanism limiting the magnon lifetimes appears to be interaction with the conduction electrons. In the alloy, the lifetime for magnons propagating in the c direction in the ferromagnetic phase falls abruptly at about q = 0.35 Å−1, and this may be due to the exchange splitting of the conduction-electron energy bands. The dispersion curve for magnons propagating in the a direction is considerably perturbed around 4 meV, and this is probably due to resonant scattering on the Ho impurities. A strong coupling occurs over the same energy range in the alloy between magnons and transverse phonons propagating in the c direction. This effect is considerably smaller in pure Tb.
Field-Dependent Antiferromagnetic Resonance Modes in CoCl2
Authors: Jacobs I. S. , Roberts S. , Silverstein S. D.
Published: January 2006

Results have been obtained for the magnetic field dependence of the far-infrared transmission of single-crystal antiferromagnetic CoCl2 at 4.2°K. The energy range was ħω > 10 cm−1 and fields up to 26 kOe were applied perpendicular to the hexagonal axis. The two uniform-mode antiferromagnetic resonances, ω1 and ω2, are nondegenerate in zero field with ħω1 = 19.0±0.2 cm−1. The normalized energy-field behavior follows simple curves: for ω1, a circle of radius 32 kOe centered at (0, 0) ; for ω2, a straight line crossing ω1 at 23 kOe and appearing to pass through the (0, 0) point. These results, coupled with high-field magnetization measurements, permit calculation of the isotropic and anisotropic coefficients of exchange (intra- and interlayer) and the g factors.
Details of the Electronic Relaxation in MnxFe3−xO4+γ
Authors: Iida S. , Mizushima K. , Yamada N. , Iizuka T.
Published: January 2006

Magnetic loss angles of MnxFe3−xO4+γ(0≤x<2) were observed at 101∼2 kHz by an automatic recording procedure from 4.2° to 400°K. Disconnection was confirmed between the lower temperature relaxation for x<1 and the higher temperature relaxation for x>0.6. Two peaks were separated for the relaxation below 50°K for x = 0.3, 0.6, and 0.7. Observation of dielectric loss at a microwave frequency have differentiated these electron-transfer relaxations from the single-ion electronic transition for x > 1 at very low temperatures. In general, change in heat treatments introduces a significant change in the relaxations. The results are plotted on the relaxation time τ vs 1/T planes. Five different slow-relaxation mechanisms become apparent, of which three are related to electron transfer on Fe3+ ions, one to electron transfer on Mn2+ and Mn4+ ions and the last one to the reorientational effect of the Jahn-Teller distortion of Mn3+ ions. Observation of the relaxation in magnetostriction at 78°K was performed for the specimens with x∼1, but no effect was observed within an accuracy of 3 × 10−7.
Magnetic Resonances in the Ising Spin Ferro- and Antiferromagnets
Authors: Date Muneyuki , Motokawa Mitsuhiro
Published: January 2006

Two new types of magnetic resonances in ferro- and antiferromagnetic Ising-like spin system are reported. One of them is the spin-cluster resonance first observed in CoCl22H2O. This compound is antiferromagnetic below 17°K with an antiferromagnetic arrangement of ferromagnetic Ising-like linear chains. In such a system, one can expect localized spin-cluster excitations in addition to the usual spin waves. We have observed the resonance with the selection rule Δm = ±1, where m is the number of spins in a short-range-order spin cluster directed opposite to the majority spins in a ferromagnetic chain of CoCl22H2O. In FeCl2, the spin-cluster resonance in a ferromagnetic layer was observed.

When an Ising-like spin system contains some impurity spins, the impurity spin resonance can be observed under suitable conditions. We have observed the spin resonance of Fe3+ and Mn2+ spins in FeCl2. A more typical example was obtained in Mn-doped CoCl22H2O whose resonance line shows a well-separated fine structure splitting.
Terrace width dependence of cobalt silicide nucleation on Si(111)-(7×7)
Authors: Zilani M. A. K. , Xu H. , Wang X.-S. , Wee A. T. S.
Published: January 2006

We have studied the size, shape transition, and nucleation sites of self-assembled cobalt silicide clusters on Si(111)−7×7 using scanning tunneling microscopy. Step decoration of solid-phase-epitaxy grown clusters (350–1000 °C) is observed on surfaces with narrow terrace widths (25–40 nm). Experiments repeated on surfaces with wide (>70nm) terraces reveal significant differences with respect to shape, size, and growth morphology; a bimodal size distribution is observed due to cluster shape transition from irregular clusters to flat-top islands. The control of silicide island nucleation could have potential applications in electrode formation for molecular electronics and nanodevice fabrication.
Far-Infrared Absorption in CoCl2·2H2O
Authors: Torrance J. B. , Tinkham M.
Published: January 2006

Measurements of the magnetic resonance absorption in CoCl2·2H2O over the frequency range from 18 to 50 cm−1 are briefly reported. Resonance lines are observed in fields up to 55 kOe, covering all three of its magnetic phases. The rather complex spectrum suggests that we observe not only simple, single excitations but also clustered, multiple ones, in which m > 1 spins are flipped. The energy required to create such an m-fold excitation is much less than m times the energy to create a single excitation. This and other major features of the experimental data are accounted for by application of the cluster model of Date and Motokawa, which describes spin clusters in the ferromagnetic chains of CoCl2·2H2O.
Excitation of Nuclear and Electronic Spin Waves in RbMnF3 by Parallel Pumping
Authors: Hinderks Larry W. , Richards Peter M.
Published: January 2006

We report observation of the simultaneous excitation of nuclear and electronic spin waves by parallel pumping, an effect predicted by Ninio and Keffer, in RbMnF3 at a pumping frequency of 8.56 GHz. Wavevectors between near zero and 105 cm−1 are excited by varying H. We operate with H and hrf in a [100] direction and H greater than the value required for flopping. From threshold fields, which are about 1.2 Oe minimum, we calculate, at 4.2°K, ηknηke = 6.1×1010 sec−2 for k→0 and 9.5×1010 sec−2 for k = 1.05×105 cm−1 (n stands for nuclear mode, e for electronic). These figures are smaller by two orders of magnitude than what is obtained from ηke inferred by Cole and Courtney from saturation of the main resonance and the value of ηn taken from the half-width of NMR absorption. To reduce critical-field data to spin-wave linewidths we have applied the methods of Ninio and Keffer to obtain a theoretical expression for hcrit in the case of a flopped antiferromagnet.
Temperature Dependence of the Linewidth of Garnets Containing Fe4+ Ions
Authors: Tchernev Dimiter I.
Published: January 2006

The linewidth of garnets containing Fe4+ ions was measured from 4.2° to 300°K at 10 and 25 kMc/sec for small, well-polished single-crystal spheres in the (110) plane. Within the measuring range the linewidth is proportional to the concentration of Fe4+ ions. For both YIG and LuIG at 25 kMc/sec, the temperature dependence in all three major crystallographic directions exhibits two well-defined peaks. At 10 kMc/sec, all peaks have shifted toward lower temperatures by different amounts, while the linewidth at the peaks has increased by about 20%. In the [100] direction, however, the two peaks seem to overlap and only one peak, with no detectable structure, is observed at 60°K and at 10 kMc/sec. Complementary measurements of the polarity of the Seebeck voltage indicate the presence of holes as majority carriers in our samples. The existence of two peaks in the temperature dependence of the linewidth can be explained by the slow-relaxation theory if one assumes anisotropy of the relaxation time of the Fe4+ ion.
Ferromagnetic Resonance in Si-Doped YIG
Authors: Hartwick T. S. , Smit J.
Published: January 2006

Ferromagnetic resonance at 10 and 30 GHz has been observed in magnetically annealed Si-doped YIG from 4.2°–400°K for all orientations θ. (measured from a [100] direction) in the [110] plane. The results are analyzed quantitatively making use of a doublet orbital ground state for the ferrous ions. The anisotropy in the line width peak at 360°K due to electron hopping has been calculated to be ΔH100/ΔH111 ≈ 3 in agreement with the experiment. Although g varies between 1.96–2.00, the orientation-averaged field for resonance is as much as 2000g below ω/γ in our samples down to 50°K. This is not due to a relaxation mechanism as suggested previously, but is caused by the redistribution of the electrons as the static field is rotated. The temperature dependence of the resonance field leads to | λ | = 90 cm−1. Below 50°K the distribution remains essentially fixed for short periods of time. By quickly measuring at 4.2°K the resonance field as a function of θ for the anneal field in either the [100], [111], or [110] directions, vastly different curves are traced which show peaks in the [110] and θ = 35° directions. These peaks are predicted by the model for the Fe2+ ion. The peak fields are still slightly below the g = 2 value. This can be explained quantitatively by a canting of about 10° of the ferrous ion spins near the energy level crossing giving rise to a localized spin disturbance of the host lattice.
Microwave Resonance and Magnetic Anneal in Magnesium Ferrous Ferrite
Authors: Goswami A. K. , Rosenbloom M. , Teale R. W.
Published: January 2006

The shift in the effective gyromagnetic ratio, γe, and the resonance linewidth are discussed for two single-crystal specimens of magnesium ferrous ferrite, which have 1.4% and 5.5% of the iron ferrous. Magnetic anneal is also reported in the helium temperature range. Phenomenological and limited microscopic analysis indicates that three processes contribute to the relaxation effects. Process A gives ΔH rising rapidly with T near room temperature in the sample with higher Fe2+ content; it has a very short relaxation time. An anisotropic ΔH maximum observed at T∼140° K and 7 GHz in the same sample, and also the magnetic anneal and the major part of the shift in γe in both samples are attributed to process B which is interpreted to arise from the migration of electrons between Fe2+ and Fe2+ ions, with the local major axis of symmetry for the energy levels close to crystallographic cube edge directions. Process C is the source of ΔH at low T; it is attributed to single Fe2+ ion relaxation because of its short relaxation time ∼10−11 sec at low T and its proportionality to Fe2+ concentration per unit magnetization. An active Fe2+ excited state at ∼30 cm−1 is suggested. The effects of process B rise much more rapidly than linearly with Fe2+ ion concentration.
Spin-Lattice Heat Transfer in Pulsed Magnetic Fields
Authors: de Vries G. , Verwey E. J. , Roeland L. W. , Miedema A. R.
Published: January 2006

Spin-lattice relaxation in a paramagnetic salt at liquid-helium temperatures has been studied by observing the time dependence of the magnetization in a pulsed magnetic field. The nearly trapezoidal field pulse can be kept constant during 0.3 sec for the largest field of 15 MA/m (200 kOe) and it is possible to determine relaxation times between 10−2 and about 10 sec.

The spin-lattice relaxation in CuCs2(SO4)2·6H2O is found to be governed by the direct process between 1.8° and 4.2°K, the field dependence of the relaxation time being H1.6. Below 1.8°K the relaxation rate suddenly becomes much slower, which is ascribed to an increase of the wavelength for phonon-phonon interaction, such that phonon-heating effects predominate below 1.5°K.
Theoretical Investigations on the Anisotropy of the Spin-Lattice Relaxation in Paramagnetic Crystals
Authors: Ray D. K. , Ray T. , Gupta S. K.
Published: January 2006

Theoretical expressions for the spin-lattice relaxation have been used to study the anisotropies of these parameters in crystals of cubic symmetry. In the case of ions with S = 12, the anisotropy is only present at very low temperature where the single-phonon term is dominant and is shown to be independent of the phonon distribution and determined by the nature of the paramagnetic ion and ligand charge distribution. For the case of ions with S > 12, where also the anisotropy is independent of phonon distribution at low temperature, parameters of the dynamical spin Hamiltonian obtained from static strain measurements for a number of ions in MgO have been used to predict the anisotropies expected. Ions are shown to be more anisotropic if contributions from either Γ3g or Γ5g mode dominate. Anisotropies at high temperature where the two-phonon process is important have been shown to be dependent on the phonon distribution as well, and have been estimated for a number of ions in MgO. The effects of dipolar flip-flop process, the covalency in the charge distribution of magnetic ion and ligands and the modified phonon distribution due to spin-phonon interaction on the anisotropy factors have been discussed. The importance of these studies has been stressed.
On Spin-Spin Relaxation Effects
Authors: Gorter C. J. , Verstelle J. C.
Published: January 2006

Results of different series of observations recently carried out in Leiden on spin-spin relaxation effects in paramagnetic salts of the iron group are reported and discussed. The character of the frequency-zero band and the resonance bands in parallel fields have been studied in different Tutton salts, and is found to be in agreement with the present theory. The behavior of the Kronig-Bouwkamp band in high parallel fields is the same salts is also reasonably well understood; this is not so for Cu(NH4)2Br4·2H2O. The complicated behavior in salts where there is a known tendency to chain formation is also not yet clear.

De Vrijer's low-field third relaxation has been studied in different salts and is confirmed to be a cross-relaxation phenomenon.
Magnetic-Field Dependence of Spin-Lattice Relaxation by the Resonant Two-Phonon Process in Cerium Magnesium Nitrate
Authors: Hoffman J. T. , Sapp R. C.
Published: January 2006

Measurements of the magnetic dispersion and absorption of cerium magnesium nitrate have been carried out at audio frequencies over the temperature range 1.9° to 3°K in steady magnetic fields from 30 to 2880 Oe, using a self-inductance bridge and a sample-motion technique. Data were fitted with Casimir-duPré functions, from which spin-lattice relaxation times, τ1, could be derived. A least-squares computer fit of the temperature dependence of τ1−1 to the expression D(H)T2+B(H)T9+C(H) exp(−36.25/T) makes possible separate study of the magnetic field dependence of C(H), the coefficient of the resonant two-phonon relaxation process. We find that C(H) falls increasingly below the form derived by Orbach for this term, C(∞) (H2+μ′Hi2/2)/(H2+Hi2/2) in such a way that above 50 Oe T1 is approximately proportional to Hn, with n = 0.89. Possibility of a bottleneck in the resonant two-phonon process is supported by these results.
Mössbauer-Effect Study of Erbium Spin Relaxation in Magnetically Ordered Compounds
Authors: Zinn W. , Wiedemann W.
Published: January 2006

The 166Er hyperfine fields, Er3+ magnetic moments, and electronic spin correlation times in ferromagnetic erbium-aluminum intermetallic structures have been studied between 1.5° and 80°K using the Mössbauer effect of the 80.6 keV gamma rays of 166Er. The spin correlation times deduced from both the rate equation model and the Wegener formula follow approximately a T−1 temperature dependence below TC. Above TC the spin correlation times of about 5 × 10−11 sec decrease by nearly an order of magnitude and are found to be rather sensitive to the distinct assumptions made on the electronic ground-state multiplet and attributed Sz distribution function in the different theoretical approaches.
Formation of a Local Moment: Properties of Iron Dissolved in the ε Copper-Zinc Phace
Authors: Caplin A. D. , Foiles C. L. , Penfold J.
Published: January 2006

Susceptibility measurements show that the magnetic moment on Fe dissolved in the ε Cu-Zn phase drops steeply and almost disappears as the Zn-rich end of the phase is approached. The resistivity and thermopower of these alloys accord qualitatively with the Friedel-Anderson concept of a virtual bound state. No indication can be seen of the formation of a spin-compensated state.
EPR and Magnetic Susceptibility in Solid Solutions of Rare Earths in Noble Metals
Authors: Hirst L. L. , Williams Gwyn , Griffiths D. , Coles B. R.
Published: January 2006

We have measured susceptibilities and searched for EPR in solutions of 1 at.% or less of the elements of the second half of the 4f series in silver of gold, in order to study local moments on the rare earth ions. EPR lines have been found in AgEr, AuEr, and AuYb. The departures from Curie's Law found in the susceptibilities, and the positions (or absences) of EPR lines can be understood and fitted primarily in terms of crystal field effects. In some of the more concentrated alloys impurity-impurity interaction effects are seen. The temperature-dependent part of the EPR linewidth in 0.28 at.% ErAg corresponds to an exchange coupling | Js−f | = 0.15 eV.
Application of a Temperature-Oscillation Method to Thermomagnetic Studies of Magnetic Phenomena at Low Temperatures
Authors: Oder R. R.
Published: January 2006

An oscillating-temperature technique is applied to the study of thermo-magnetic properties of solids at low temperatures; its practical advantages and unusually high sensitivity permit unique studies of temperature- and field-dependent properties of magnetic materials. In this induction technique the temperature of the specimen is modulated while a steady magnetic field is applied. The voltage induced in a pickup coil surrounding the specimen is a direct measure of the temperature derivative of the magnetic moment, ∂μ/∂T. Nonlinear dependence of the susceptibility on the temperature produces harmonics in the induced voltage which may be analyzed to obtain other thermodynamic variables. This technique has been successfully applied to observation of the de Haas-van Alphen effect in Zn and Bi.

At present the system detects ∂μ/∂T ≲ 10−5 emu/gm·°K and this limitation is imposed by a paramagnetic background arising from the cryostat.

Using this magnetometer we have observed a component in the differential-temperature susceptibility of tellurium-doped InSb (η∼1018 electrons/cc) which can be fitted to a Brillouin function with N = (9±3) × 1016 spins/cc, g = 2.2±0.2, and J = 1.2±0.02.
Superconductivity, Low-Temperature Resistivity, and Thermoelectric Power of Dilute Solid Solution of Ce in In and Sn
Authors: Boato G. , Bugo M. , Rizzuto C.
Published: January 2006

An interesting anomalous property of cerium metal is that its valence is not fixed, being able to be in a trivalent (magnetic) or in a tetravalent (nonmagnetic) state. It has been suggested that this, as well as the other anomalous properties of cerium, are due to the fact that the f-electrons are on external orbits, thus being able to interact with the conduction electrons in a similar manner to the d-electrons of the transition metals. If the f-electrons are not tightly bound in cerium metal, the possibility exists that dilute solid solutions of cerium in nontransition metals could induce the similar electron transport anomalies as transition metal impurities.

We have measured the superconducting critical temperature Tc of In-Ce and Sn-Ce solid solutions as a function of the impurity concentration, as well as the resistivity and the thermoelectric power down to 0.3°K. An approximately linear decrease of Tc has been observed in both alloy systems up to the solid solubility limit (150 ppm at.). For In-Ce ΔTc/ρ is −8°K and for Sn-Ce ΔTc/ρ is −20°K, where ρ is the residual resistance ratio R4.2/ (R273−R4.2) which varies linearly with concentration (c) and has the values of ρ/c = 0.31/at.% for the In-Ce system and ρ/c = 0.0471/at.% for the Sn-Ce system.

The values of ΔTc/ρ are larger than would be expected on the basis of normal impurity scattering; however, the resistivity and thermoelectric power measurements do not indicate the presence of localized magnetic moments, the former showing no minimum and the latter being positive and small (S ≈ 0.3 mV/°K) for the present temperature range of measurements. We believe that if the assumption is made that a virtual f-level lies near the Fermi energy, the observed magnitude of the suppression of the superconducting critical temperature as well as the small positive thermopowers could be explained on the basis of existing theories.
Spin Relaxation of Localized Magnetic Moments and Conduction Electrons in Metals: Manganese in Silver
Authors: Gossard A. C. , Kometani T. Y. , Wernick J. H.
Published: January 2006

The electron paramagnetic resonance of the localised magnetic moments of manganese atoms dissolved in silver metal has been studied. The manganese EPR linewidth in polished, etched metal slabs broadens linearly with increasing temperature at a rate of 9.7±2.0 G/°K for a 0.26% Mn in Ag sample and at only 3.1±0.3 G/°K for a 1.29% Mn in Ag sample in the temperature range 15°K to 100°K. This behavior can be well-represented by Hasegawa's theory of the spin relaxation of the localized moment spin S by a scalar interaction JS·s with conduction electron spins s. The narrowing with increased Mn concentration is expected when the relaxation is “bottlenecked,” i.e., when spin energy transferred to a conduction electron is more likely to be returned to a local moment than relaxed to the lattice. A further broadening of the Mn resonance line, linear in temperature, is produced when other impurity atoms are added. These broadenings are interpreted as arising from an opening of the bottleneck in the relaxation process by spin-orbit spin-flip scattering of the conduction electrons on the impurity atoms. The deduced spin-flip scattering cross sections are <2.6×10−18 cm2 for Mn, (1.4±0.4)×10−18 cm2 for Zn, (3.2±1.2)×10−18 cm2 for Ga, (2.4±1.7)×10−18 cm2 for Cd, (93±50)×10−18 cm2 for Pt, and (25±10)×10−18 cm2 for Au.
Conduction-Electron Spin Relaxation by Transition-Element Impurities in Copper
Authors: Yafet Y.
Published: January 2006

Gossard et al. have recently measured the conduction-electron spin-flip cross sections σsf of the transition elements Ti, Mn, and Ni in Cu. We give here an interpretation of these measurements based on the Anderson-Friedel theory of localized virtual states. σsf is found to be proportional to the square of the d density of states at the Fermi level and to the square of the spin-orbit coupling which is modified by an orbital enhancement factor. Thus as one moves across the transition series, the variation of σsf should show a qualitative resemblance to that of the residual resistivity ρ, and in particular show a minimum at Mn, in agreement with experiment. The precise variation of σsf is more pronounced and more asymmetric with respect to Mn than that of ρ. Inclusion of the crystal-field splitting affects greatly the calculated value of σsf for Ni and it is concluded that the splitting for Ni must be very small or inverted. Assuming U = 3 eV and J = 0.5 eV, it is found that the values of the virtual level half-width Δ needed to make the calculated σsf agree with experiment are Δ = 1.0 eV for Ti and Δ = 0.3 eV for Ni.
Structure and Energy of a Néel Wall
Authors: Kirchner R. , Döring W.
Published: January 2006

A computer program has been developed for the calculation of the distribution of the magnetization in Bloch and Néel walls. The result of computations for a Néel wall in a 1000 Å Permalloy film is shown. If x is the coordinate normal to the wall and parallel to the film, the component Ix of the magnetization in a large part of the tails of the Néel wall is a linear function of ln x. The distribution Ix = const/x2, which results at large x for a dipole line in the middle of the wall, is valid only for very large x, where Ix is neglegibly small.
A Comparison of the Losses for Domain-Wall Motion and Ferromagnetic Resonance in Thin Ni-Fe Alloy Films
Authors: Patton Carl E. , Humphrey Floyd B.
Published: January 2006

The connection between the losses for domain-wall motion and ferromagnetic resonance in Ni-Fe thin films has been investigated by examining the thickness dependence and temperature dependence of the wall mobility and the linewidth for resonance with the static magnetic field in the plane of the film. The losses at room temperature were compared in terms of Landau-Lifshitz damping parameters for the two processes. The wall-motion damping is approximately equal to 0.014 independent of thickness while the resonance damping increases from 0.005 at 200 Å to 0.010 at 3000 Å. In view of the large differences in damping for wall motion and resonance at 300°K, the relaxation mechanism (s) which contribute to the losses at 300°K in each case must be quite different. The losses as a function of temperature have been compared on the basis of changes in linewidth and mobility between 300°K and 77°K. The linewidth for films is known to exhibit a peak at about 77°K. The wall mobility at 300°K and 77°K has been obtained from Kerr observations (300°K) and flux reversal measurements (300°K and 77°K) for films 150 to 1350 Å thick which exhibited, to varying degrees, the above linewidth peak. A strong correlation between linewidth increase and mobility decrease from 300°K to 77°K was observed. The largest mobility decrease observed was from 1.7×104 to 8×103 cm/sec·Oe for a particular 150-Å film which exhibited a linewidth increase of 15 Oe (from 10 to 25 Oe at 4 Gc/sec). The increase in the losses for wall motion was directly related to the increase in the losses for resonance from 300°K to 77°K. The relaxation processes which contribute to the temperature dependence of the resonance linewidth are important in limiting domain-wall motion in Ni-Fe alloy films.
New Type of Domain Structure of Permalloy “Stripe-Films”
Authors: Krinchik G. S.
Published: January 2006

The domain structure of Permalloy “stripe-films” of thickness 2.5–10 μ was investigated by the magneto-optic method. Three types of measurements were used: (1) measurements of static hysteresis loops from the surface layer of the films, (2) measurements of the ratio IR/IS for the surface layer of the films by means of the dynamic method, and (3) measurement of the magnetization vector orientation in a single surface domain by a device with micron resolution.

The comparison of these results with the static hysteresis loops of the whole film justifies the assumption of a new type of domain structure of the “stripe-films” with closed magnetic flux, the residual magnetization of which is determined essentially by the surface domains. The orientation of the magnetization vector has been determined in the surface and internal domains of the film. The formation of this domain structure is evidently due to the energy dependence of the domain boundaries.
Measure of Self-Consistency in 180° Domain Wall Models
Authors: Aharoni Amikam
Published: January 2006

Two expressions are given for the energy of an interdomain wall, and it is shown that these expressions are identical for wall configurations which represent an energy minimum. In any Ritz method calculation, in which the magnetization distribution inside the wall is approximated by a certain functional form with adjustable parameters, the ratio between these two energy expressions is defined as the self-consistency parameter S. This parameter should, thus, be close to one, if the assumed wall structure is close to some minimum-energy configuration. Although having S ≈ 1 is only necessary, and not sufficient, condition for the structure to be a good approximation to some physical situation, calculating this parameter can serve as a convenient method for eliminating inadequate theories.

The self-consistency parameter S is calculated for the wall models of Middlehoek, Dietze. and Thomas, and Aharoni. It is found that for the Bloch wall, although these theories leave a lot to be desired, they at least yield an S which is of the order of one. Even this is not true for the Néel wall, where S is of the order of ten for Permalloy films, 100 to 200 Å thick.
Wall Streaming: A Gyromagnetically Induced Kind of Wall Motion
Authors: Feldtkeller E. , Stein K. U.
Published: January 2006

A field applied perpendicular to a Bloch wall does not favor one of the adjacent domains. Nevertheless, the gyromagnetic behavior of the wall magnetization, i.e., the precession around the field instead of a rotation towards the field direction, may induce a wall displacement. This has been observed experimentally in Permalloy films with a thickness larger than 0.1 μ when a pulse field has been applied along the hard axis with a pulse risetime smaller than 20 nsec. The effect (called wall streaming) is compared, from a theoretical point of view, with the wall behavior in a pulse field applied parallel to the wall.
Transition Layers between Magnetic Domains
Authors: Wang Franklin F. Y.
Published: January 2006

A new approach is introduced to study the transition layer between magnetic domains in magnetic films. The approach is to approximate the spin configuration in a transition layer by a generalized functional form of a spiral. The equilibrium wall energy and wall thickness can be obtained by the minimization of the total energy. For each prototype of domain wall, the cone angle of the spiral provides an additional variable parameter. External conditions such as imperfections and grain boundaries can cause the spin configuration to assume a different cone angle. A phase diagram of minimum energy 180° Néel wall spin configurations is given.
Structure of a Domain Wall in a Ferromagnet
Authors: Ignatchenko V. A. , Zakharov Yu. V.
Published: January 2006

The structure of the domain wall of a ferromagnetic crystal of finite thickness is determined by perturbation theory and by taking into account the surface anisotropy β′ ≷ 0. When perturbation theory is not suitable, a detailed analysis of the problem is also carried out.
New Interpretation of the Rayleigh Law
Authors: Koller A. , Pfrenger E. , Stierstadt K.
Published: January 2006

In this paper contradictions between the experimental results and the theory of Néel concerning the Rayleigh region are discussed. A model is proposed not based on Barkhausen discontinuities, but on Bloch wall friction. (The friction is equivalent to a constant opposite field. The magnetic field has to overcome the frictional force before wall motion is possible.) With this model the derivation of the Rayleigh law is possible. Furthermore one can explain the contradictions between theory and experiments. Possible mechanisms of Bloch wall friction are discussed.
Anhysteretic Magnetization Processes
Authors: Craik D. J. , McIntyre D. A.
Published: January 2006

Theoretical magnetization curves in which the processes consist of reversible 180° domain wall motion controlled by magnetostatic effects, are derived for (1) isolated uniaxial crystals with plane 180° walls (2) arrays of crystals corresponding to a perfectly orientated polycrystal with the gain boundaries represented as magnetic gaps and (3) arrays in which the crystals have a certain misorientation about the common easy axis. The curves are compared with the results of earlier calculations on crystals with special shapes.
Basic Equations of Micromagnetism
Authors: Hoffmann Horst
Published: January 2006

All calculations of the free energy of ferromagnetic crystals require the knowledge of the local magnetic field H(r) at the point r. A theory of the local field has been developed, concerning nonlinear changes of M which may be caused by many distortions of the sample. Within a certain volume, lying symmetrically around r, the direction m(r) of the magnetization is given by a Taylor's expansion up to the second derivatives ∂2mi(r)/∂xi∂xk at the point r. The part of the stray field, which is due to the magnetization divergences in this region, is the most important one. It is a sort of coupling field, which is not included in the case of one isolated distortion, which has been solved by Brown. The local field, derived in this way, has been used for the calculation of the free energy. The variational principle leads to a system of differential equations for the determination of M(r). These basic equations may be used in all cases of micromagnetic calculations in the many distortion case. In this theory the influence of the intrinsic stray field is of quite another kind than in Brown's approximation. The coupling length of the stray field can be of macroscopic dimensions. It depends not only on the magnetization but also on the applied field and on the kinds of lattice disturbances. In general, the stray field cannot be neglected even in high applied fields.
A Modification of the Kittel Open Structure
Authors: Szymczak R.
Published: January 2006

We have examined a wavy structure model characterized by the domain width D, wave amplitude α, wavelength γ, wave-vanishing depth l, and crystal thickness L. The critical thickness of the crystal plate at which the Kittel open structure changes to a wavy structure, and the corresponding values of Dcr and γcr, can be calculated by minimizing the total energy of the model. The dependence of D, α, and γ on the crystal thickness has been established. A simple mathematical transformation makes it possible to use calculations made for a particular ferromagnet in order to predict the domain structure of one having different magnetic parameters. Examination of the Bitter patterns on barium ferrite and magnetoplumbite single crystals has confirmed the theoretical predictions of the changes of width and domain shape with increasing crystal thickness.

Qualitative and quantitative studies of the influence on the wavy structure of an external magnetic field perpendicular to the easy axis provide additional confirmation of the theoretical conclusions.
On the Interaction Energy of Interstitial Atoms and Solute Atom Pairs with the Magnetization
Authors: Ferro A. , Montalenti G. , Soardo G. P.
Published: January 2006

A method has been devised to determine the magnitude and sign of the interaction energy with the magnetization of interstitial atoms and solute atom pairs in iron. By applying a uniaxial stress to the specimen, a known amount of interstitials or solute atom pairs can be distributed over a given class of sites, and the magnetic anisotropy energy induced in this way is compared with the one obtained by conventional annealing under magnetic field in the absence of stress. The induced anisotropy energies are measured either from the magnetization curve or by means of a magnetic-torque magnetometer. The data obtained for C in α-iron show that the magnetic interaction energy is positive, i.e., the tetragonally distorted cells occupied by the interstitials tend to have their tetragonal axis aligned at right angle with the magnetization, thus confirming a previous result of De Vries et al. obtained from magnetostriction aftereffect. Some preliminary results are also given for aluminum solute atom pairs in a Fe-Al alloy.
Magnetization Processes and Reversal in Ferrimagnetic Oxides with High-Anisotropy Field
Authors: Rosenberg M. , Tănăsoiu C. , Florescu V.
Published: January 2006

The magnetization process of SrO·4Fe2O3·2A12O3 single crystals with 2–4 domains was investigated. The total area of the Bloch walls diminished during their displacement and the saturation was reached at 75 Oe. The magnetization reversal occurred by nucleation and growth of a reverse domain and the nucleation field shifted towards higher negative values for increased values of the magnetizing field. For nucleation fields higher than 75 Oe the reversal of the magnetization occurred abruptly and the hysteresis loop became ideally rectangular.
Analysis of the Processes of Magnetic Reversal in Hard Magnetic Ferrites
Authors: Heinecke U. , Müller H. G.
Published: January 2006

The remanence method of Wohlfarth used for the analysis of the interaction in hard magnetic materials is extended to the investigation of complete measurements of the inner loops. It is possible to demonstrate on anisotropic strontium ferrite samples with different values of the intrinsic coercivity that the degree of the reversibility of the corresponding magnetization changes may be established by determining the loop area of partial cycles. Simultaneously in this way the change of the influence of interaction and proportion of magnetic reversal respectively by Bloch-wall movement dependent on coercivity is ascertained quantitatively. The differing shape of the virgin curves may be easily interpreted by the results of these investigations.
Exact quantum dynamics of N(D2)+H2→NH+H reaction: Cross-sections, rate constants, and dependence on reactant rotation
Authors: Lin Shi Ying , Guo Hua
Published: January 2006

Using an exact Chebyshev wave packet method, initial state-specified (vi=0, ji=0,2) integral cross-sections and rate constants are obtained for the title reaction on the latest ab initio potential energy surface. Reaction probabilities up to J=29 are dependent on the reactant rotation and show mild oscillations superimposed on a broad background. Due to a barrier in the entrance channel, the cross sections increase with energy with clear thresholds and the rate constants vary with temperature in the Arrhenius form. The calculated canonical rate constant is in good agreement with the experimental measurements. Our results also indicate that the quasiclassical trajectory method underestimates the rate due to the neglect of tunneling, while the quantum statistical approach overestimates because of the short lifetime of the reaction intermediate.
Quantum key distribution at telecom wavelengths with noise-free detectors
Authors: Rosenberg Danna , Nam Sae Woo , Hiskett Philip A. , Peterson Charles G. , Hughes Richard J. , Nordholt Jane E. , Lita Adriana E. , Miller Aaron J.
Published: January 2006

The length of a secure link over which a quantum key can be distributed depends on the efficiency and dark-count rate of the detectors used at the receiver. We report on the first demonstration of quantum key distribution using superconducting transition-edge sensors with high efficiency and negligible dark-count rates. Using two methods of synchronization, a bright optical pulse scheme and an electrical signal scheme, we have successfully distributed key material at 1550 nm over 50 km of optical fiber. We discuss how use of these detectors in a quantum key distribution system can dramatically increase range and performance.
Transfer fabrication technique for embedded and inverted micro/nanostructures
Authors: Seo Soon-min , Kim Joon H. , Kim Tae-il , Lee Hong H.
Published: January 2006

A transfer fabrication technique is developed to construct embedded and inverted micro/nanostructures that cannot be readily built by other methods. Transfer patterning/printing is used for the fabrication, which involves transferring a patterned layer on a flat substrate to another substrate that has a higher work of adhesion with the layer than the flat substrate. The technique is relatively simple and fast (∼10s). Inversion of a shape that is made possible by the transfer is the basic concept. This inversion allows fabrication of three-dimensional embedded structures through multiple stacking. The technique could open new avenues for various applications.
Two-photon absorption cross-section spectrum of a π-conjugated polymer obtained using the white-light continuum Z-scan technique
Authors: Oliveira S. L. , Corrêa D. S. , De Boni L. , Misoguti L. , Zilio S. C. , Mendonça C. R.
Published: January 2006

We have used the white-light continuum (WLC) Z-scan technique to determine the degenerate two-photon absorption (2PA) cross-section spectrum of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene). The results obtained show good agreement with those employing a single-wavelength source, although much faster because of the wavelength multiplexing introduced by the use of a broadband source. The improved spectral resolution of the WLC Z-scan allowed the observation of a 2PA peak around 675nm, a subtle feature in the nonlinear spectrum that could be fitted using a sum-over-states model. The WLC Z-scan technique has proved to be an important tool to determine the 2PA spectrum of polymers.