bluuebunny/crossref_metadata_2025 huggingface dataset:
Hall effect for Kondo systems
Authors: Levy P. M. , Guo Wei , Cox D. L.
Published: July 2002

We have calculated the variations with temperature of the skew scattering contribution to the Hall effect for a Kondo-type ion. The conduction electron t matrix is calculated by using the single-ion Anderson model, and the 4f electrons’ Green’s function is evaluated by self- consistently solving a set of integral equations. Except for the asymptotic region T/Tk≫1, the Hall constant is not proportional to the susceptibility, nor does the constant change sign for realistic values of the parameters entering the theory.
Magnetic order and superconductivity in heavy fermion systems (invited) (abstract)
Authors: Aeppli G.
Published: July 2002

The neutron scattering technique, which directly probes magnetic correlation functions, has been used to identify the magnetic order in several heavy fermion systems, notably U2Zn171 and U1−xThxPt3.2 Our measurments3 show that pure UPt3, which is superconducting, is also a weak antiferromagnet with an ordered moment of 0.02 μB and a Néel temperature of roughly 5 K. We also find that the onset of superconductivity affects the magnetic correlations in UPt3. The relation between magnetism and superconductivity in compounds containing copper oxides is compared to that in the heavy fermion systems.
Nonlinear magnetization in magnetostrictive amorphous metal ribbons
Authors: Mermelstein M. D. , Dandridge A.
Published: July 2002

Measurements are presented of the quadratic field and stress contributions to the nonlinear magnetization in a field-annealed amorphous metal ribbon. The magnetization process is characterized by the Stoner–Wohlfarth model for a uniaxial single domain with magnetostriction. Parameter values for the model are deduced from the experimental data.
Simulation of bit jitter in magneto-optic recording
Authors: McDaniel T. W.
Published: July 2002

The interplay of several writing and reading phenomena that influence bit-position accuracy has been analyzed with a computer model of the magneto-optic (MO) recording process. A micromagnetics simulation determines a minimum energy magnetization state of a MO storage film following local laser heating in an externally applied bias magnetic field. Bit jitter is assessed by measuring the length, width, and position of written domains, and by analyzing the modeled readout signal and its derivative. The influence of variation in the magnetization, anisotropy, and exchange in an amorphous rare-earth–transition-metal film on the position and size of recorded marks has been simulated by specifying random variations of a film’s magnetic properties in the thermomagnetic writing step. Variations in medium thermal sensitivity and the reading laser spot size were also considered. Histograms showing the effects of write-read imperfections on bit-position accuracy in MO recording were developed. Comparisons with experiment and separation of other system noise effects have enabled model validation.
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7Fe-YIG: Narrow x-ray linewidth epitaxial layers on Gd3Ga5O12
Authors: Gualtieri D. M. , Lavender W. , Ruby S. L.
Published: July 2002

Epitaxial layers of 81% 57Fe-enriched Y3Fe5O12 were grown on thick, (100)-oriented substrates of Gd3Ga5O12 for experiments in resonant nuclear diffraction. Layers up to 10 μm thick were grown on each side of 32-mm-diam, 5-mm-thick wafers using techniques common for the growth of magnetic bubble materials, but with the use of a PbO-V2O5 flux in place of the usual PbO-B2O3 flux. The PbO-V2O5 flux offers a lower solubility of YIG which allows a reduction in the amount of 57Fe oxide required for layer growth. Thick substrates were used to reduce possible bowing from lattice constant mismatch. Lead incorporation onto yttrium lattice sites was controlled by adjusting the growth temperature, and this allowed a close lattice constant match between the layers and the substrate. Layer thickness was essentially uniform across the layer diameter with the edges 5% thicker than the center. Curie temperature and Faraday rotation measurements of the equivalent (111)-oriented material indicate as a formula unit (Y2.96Pb0.04)Fe3(Fe1.94Y0.06)O12. YIG/YIG double-crystal diffraction by tungsten L-γ1 irradiation of a 5×7-mm rectangular area of the first crystal gave a composite linewidth of 13 arcsec for the {400} reflection. This same linewidth was observed in synchrotron illumination of the central 80% of the area of the first layer. The possibility of linewidth reduction in this material is discussed.
Missing magnetic moment in spinel iron oxide films (abstract)
Authors: Ortiz C. , Vurens G. , Chen M. M. , Salmeron M.
Published: July 2002

This work studies the influence of oxygen flow and substrate temperature on the physical properties of reactive sputtered thin films of iron oxide spinels. We have focused on the variations of the magnetic moment, which can be as low as 20% of the bulk value, for certain experimental conditions. We present a model which attributes the missing moment to a mispopulation of Fe moments on the A and B sites. Direct experimental evidence to prove this model is obtained from conversion electron Mössbauer spectroscopic experiments, which correlate the missing moment with increased A-site population compared with the ‘‘textbook’’ population (only 8 A sites out of 64 are filled). For example, samples deposited at room temperature have always a low moment and are found to have a large A-site population. When the samples are annealed in vacuum under specific conditions to maintain the oxygen ratio and to give kinetic energy to the atoms to reach their spinel positions, an increase of the magnetic moment is observed.
Performance of magneto-optical recording media with direct overwrite capability
Authors: Schultz M. D. , Shieh H-P. D. , Kryder M. H.
Published: July 2002

The feasibility of directly overwriting certain magneto-optical recording materials without the use of an external magnetic field has recently been demonstrated in our laboratory. In this report experiments to evaluate the beam positioning accuracy necessary for successful direct overwrite, the effects of static bias fields on the direct overwrite process, and the possibility of writing and erasing domains of arbitrary length on direct-overwrite materials are discussed. The data show that an error in beam positioning of at least 75% of the nominal domain diameter is tolerable for complete erasure without an external applied field. Application of particular values of dc bias field is shown to decrease the pulse width required to write while only slightly narrowing the allowed margin of erase pulse width, thus raising the allowed data rate.
Dielectric and magnetic properties of polycrystalline cobalt-substituted LiTi ferrites
Authors: Kuanr B. K. , Singh P. K. , Kishan P. , Kumar N. , Rao S. L. N. , Singh Prabhat K. , Srivastava G. P.
Published: July 2002

The electric, dielectric permittivity, loss tangent, microwave power absorption, and hysteresis loop parameters were studied on a series of cobalt-substituted lithium titanium ferrites. The experimental results indicate that cobalt substitution affect all these parameters. The observed dispersion in conductivity and dielectric permittivity with frequency and temperature are in accordance with Maxwell–Wagner model while the microwave and hysteresis loop properties can be interpreted with the help of Dionne’s exchange isolation model.
A novel low-temperature preparation of Ni-Zn ferrite and the properties of the ultrafine particles formed
Authors: Chen C. J. , Bridger K. , Winzer S. R. , PaiVerneker V.
Published: July 2002

Ultrafine particles of nickel-zinc ferrite have been formed from solutions of metal nitrates by coprecipitation with hydrazine, followed by aging at 90 °C. The crystallites either aggregate into much larger clusters or form single particles, depending upon the preparation conditions, and vary in size from 30 to ≊300 Å. Saturation magnetizations (Ms) of the ferrites varied from 40 to 65 emu/g and the coercivities from 1 to ≊100 Oe. Increasing hydrazine concentrations tended to produce particles with lower Ms. However, for hydrazine/metal ratios below unity, decreasing the hydrazine concentration dramatically lowered the Ms value. Particles formed without hydrazine (e.g., by aging hydroxides precipitated with potassium hydroxide) did not appear to be magnetic. Variations of the magnetic properties and lattice parameters as a function of preparation conditions will be discussed.
An NMR study of tetragonal Nd2Fe14B and Nd2Fe14−xCoxB
Authors: Zhang Y. D. , Budnick J. I. , Potenziani II E. , Pedziwiatr A. T. , Wallace W. E. , Panissod P.
Published: July 2002

1 0B, 11B, 57Fe, and 59Co spin-echo NMR experiments have been performed for naturally abundant and 10B-enriched Nd2Fe14B and Nd2Fe14−xCox B (x≤0.7) at 1.3 and 4.2 K for frequencies from 10 to 300 MHz. The Fe hyperfine field (HF) values in the Nd2Fe14B compound and their assignment to the six iron sites are the following: 302(e) 320(c) 325(k1), 334( j1), 352(k2), and 378( j2) kOe. The substitution of Co for Fe decreases the HF at the Fe nuclei at j2, k2, j1, k1, and c sites while no obvious change in the HF at the e site nor at the B nuclei has been found. The spin-echo amplitude corresponding to the Fe(k2) site line decreases with increasing Co content. A complex 59Co spectrum is found in the frequencies between 150 and 260 MHz with a strong peak around 250 MHz. These results confirm that Co atoms have a strong preference to enter the k2 site.
Small-angle neutron scattering from amorphous ErFe2 and HoFe2 alloys
Authors: Spano M. L. , Rhyne J. J.
Published: July 2002

Small-angle neutron scattering measurements (SANS) have been made an amorphous ErFe2 and HoFe2 alloys as a function of temperature. These alloys show strong ‘‘subcritical’’ scattering as the temperature is lowered below their SANS-determined transition temperatures (Tf’s) of 105 K (±1 K) and 185 K (±5 K), respectively. The SANS line shapes are Lorentzian above Tf, but become increasingly non-Lorentzian below Tf and are consistent with a Lorentzian plus Lorentzian-squared cross section which is appropriate for these random anisotropy systems. The correlation lengths for ErFe2 and HoFe2 at low T are in the range of 60–70 Å. Near Tf ErFe2 shows a sharp peak, while for HoFe2 ξ is resolution limited over a range of 25 K below Tf.
Microwave susceptibility and effective linewidth of iron-carbonyl powders
Authors: Naziripour G. A. , Patton C. E. , Kogekar M. V.
Published: July 2002

The effective linewidth technique has been applied to study the microwave response and effective linewidth of iron carbonyl powders. The frequency and Q of a high-Q microwave cavity containing small powder samples was measured over a field range of 0–12 kOe at 10 GHz. The frequency data for high field (9–12 kOe) were used in conjunction with magnetization data and theory to calibrate the microwave system. The calibration parameters were then used in conjunction with the Q data to determine the negative imaginary part of the powder microwave permeability μ″ vs field. The μ″ results at high field were then fitted to theory to estimate the operational effective linewidth parameter for the powders. The procedure provided clear microwave evidence for (1) magnetic saturation of the powders in the expected field range of 7–8 kOe, (2) the operational validity of a model which treats the powder particles as noninteracting spheres, and (3) an off-resonance effective linewidth of about 500 Oe at 10 GHz.
Electronic structure of the light actinide oxides from electron spectroscopy (invited)
Authors: Gunnarsson O. , Sarma D. D. , Hillebrecht F. U. , Schönhammer K.
Published: July 2002

The 4f core level spectra of ThO2, UO2, and NpO2 are shown to be well described in the Anderson impurity model. The O(2p)-actinide (5f ) hybridization is found to be very large. This leads to a new interpretation of the 7-eV satellite in the 4f spectrum, which corresponds to an antibonding 5f n−5f n+1 final state, where n=0,2, and 3 for ThO2, UO2, and NpO2, respectively. The resonance photoemission 4f spectrum is studied, and it is found that interference between different intermediate states is crucial for its interpretation. In particular, the photon energy dependence (CIS spectrum) is strongly influenced by these interference effects. In the 5f valence spectrum of UO2 the theory gives a satellite, which is due to a split-off state caused by the large hybridization.
Magnetization measurements on (Ce,Gd)Al3
Authors: Edelstein A. S. , Holtz R. L.
Published: July 2002

Ce1−xGdxAl3 exhibits an interesting interplay of heavy-fermion, spin-glass, and antiferromagnetic behavior. Magnetization measurements were undertaken to further our understanding of this system and to estimate the fraction of the magnetization involved in the spin-glass and antiferromagnetic transitions. By making a linear extrapolation of the magnetization data to H=0, one defines the spontaneous magnetization, Ms. At T=2 K, we find that Ms is approximately proportional to x for x≤0.4 and equal to approximately 10% of the maximum possible contribution from just the Gd moments. Ms increases at a much faster rate between x=0.40 and 0.50, but then decreases to zero at x=0.635 where the system is antiferromagnetic. For x=0.635 and T=1.5 K, the magnetization is proportional to H for H≤80 kOe. Using this linearity, we suggest that nearly all the spins are correlated at low temperatures for x≥0.635.
A CaCu5-type samarium-iron phase stabilized by zirconium addition
Authors: Lin Chin , Sun Yun-Xi , Lou Zheng-Hua
Published: July 2002

Light rare-earth metals are not assumed to form compounds of the CaCu5-type structure with iron. When zirconium was not added, the Th2Zn17-type rhombohedral structure existed in the samples of nominal composition SmFe5 and SmFe7. Samples of nominal composition (Sm1−xZrx)Fe5 and (Sm0.65Zr0.35)Fey were studied by x-ray diffraction and thermomagnetic analyses. Thermomagnetic analyses showed the existence of a new phase besides Sm2Fe17. X-ray diffraction analyses showed the new phase has a CaCu5-type structure. Lattice parameters and Curie temperatures of these samples were measured.
Studies of the magnetization densities in Pu compounds; determination of the degree of localization
Authors: Lander G. H. , Wulff M. , Rebizant J. , Spirlet J. C. , Brown P. J. , Vogt O.
Published: July 2002

The electronic configuration of trivalent Pu is nominally a 5f5 state in which there is a strong cancellation of the L (orbital) and S (spin) components in the J=5/2 ground state. This leads to small g factors and magnetic moments, and to unusual neutron magnetic form factors f(Q) with maxima at Q values greater than zero. We present here the results of form-factor measurements (taken on the polarized-neutron diffractometer at the ILL) on single crystals of PuSb, PuTe, and PuFe2. These results show that the form factor, which is a measure of the magnetization density of the 5f electrons around the Pu nucleus, is sensitive to the degree of localization of the 5f electrons. For example, in PuSb the 5f electrons are well localized and the form factor is in good agreement with the predictions of intermediate coupling and crystal-field theory. In PuTe f(Q) falls monotonically from a maximum at Q=0, indicating an almost spin-only system. This is produced by wide 5f bands, which give rise to the observed T-independent magnetic susceptibility. In PuFe2, however, a large maximum occurs in f(Q). We believe this arises from strong hybridization of the 5f and 3d Fe electrons, which leads to a reduction in the Pu orbital component.
Thermodynamics of the diluted classical spin Heisenberg chain with single ion anisotropy (abstract)
Authors: Dong X. Y. , Ahmed S. , McGurn A. R.
Published: July 2002

The thermodynamics of a one-dimensional diluted Heisenberg magnet of classical spins in the presence of single ion anisotropy is calculated. This model is representative of systems such as (CD3)4NMnxCu1−xC13 and CsMnxMg1−xBr3. The magnetization susceptibility, energy, and specific heat are determined as functions of the magnetic concentration and single ion anisotropy for both ferromagnetic and antiferromagnetic couplings. Spin-spin correlation functions and the elastic scattering function are also calculated for various values of anisotropy and spin concentration in these systems. The solutions presented are obtained as sums over the properties of finite length chains weighted by their probabilities of occurrence in the diluted system. UFaipxr UFc15xr UFRULEF a)Permanent address: Department of Physics, Nankal University, Tianjin, People’s Republic of China.
A resistance minimum in an alloy of only ‘‘impurity’’ atoms (abstract)
Authors: Henry Warren E.
Published: July 2002

Ever since the discovery of a resistance minimum1 in alloys dilute in 3d magnetic metals, there has been interest in the physical mechanism involved.2 A Kondo model3 was worked out on the basis of small to vanishing concentration of magnetic atoms in a ‘‘normal’’ metal host, i.e., s-d interaction. This research is on the limiting case of an alloy containing only 3d magnetic atoms (Ni, Fe, Cr, and Mn). It has been found that the depth of the resistance minimum has the absolute value which is of the order of magnitude as the resistance minimum of alloys dilute in magnetic atoms. The depth of our minimum is Δρ=4×10−2 μΩ cm. The implication is that the change in scattering is the same in cause for the alloys dilute in magnetic atoms as the alloy with only magnetic atoms. The resistance minimum is at about 2.5 K in this alloy. The resistance of this sample is 875 Ω at the temperature of liquid helium. The resistance measurements are precise to six significant figures through a special potentiometric facility. A discussion will be given of the application of various theories to these results.
Variational ground state for the periodic Anderson model
Authors: Bowen Samuel P. , Mancini Jay D.
Published: July 2002

A variational calculation of the ground state of the Anderson lattice model is discussed. The calculation creates a finite Hamiltonian matrix for many-electron states, which are appropriate for the thermodynamic limit. A simple 14×14 truncation is discussed for finite U and a smaller 3×3 is used for the large U limit. Both approximations indicate that the spin configurations of the localized f orbitals are antiferromagnetically correlated for nearest neighbors in the ground state. This antiferromagnetic correlation is mediated by an RKKY interaction and thus offers a variety of spin orderings as a function of lattice and density.
A meaningful post-processing method based on a locally orthogonal discretization
Authors: Saito Y. , Ikeguchi S. , Hayano S.
Published: July 2002

A locally orthogonal property between the side of a Delaunay triangle and the edge of a Voronoi polygon is applied to the post-processing scheme. Our post-processing scheme explicitly satisfies a governing equation in the electromagnetic fields so that it removes the discontinuities appearing at the edges of the first-order triangular finite element. Furthermore, when the vector obtained by our post-processing scheme is used as a starting vector for the iterative matrix inversions, e.g., the successive overrelaxation and conjugate gradient methods, then covergence to a correct solution vector is extremely accelerated in our test examples.
Analytical solutions for the three-dimensional side-fringing field of magnetic recording heads
Authors: Mayergoyz I. D. , Bloomberg Dan S.
Published: July 2002

Using conical coordinates, and in the limit of small gap length, the three-dimensional boundary value problem for the side-fringing field of beveled recording heads is reduced to two dimensions. This makes it possible to use analytic functions of a complex variable, and find simple expressions, in terms of elementary functions, for the scalar potential and three-dimensional magnetic fringing field. For a given bevel angle, the spectral response for side reading from in-plane and perpendicular magnetization depends on a single dimensionless parameter, and a quasi-exponential falloff of this response is calculated as a function of the bevel angle.
Second-order term effect on the dispersion characteristics of a magnetostatic delay line
Authors: De Gasperis P. , Marcelli R. , Miccoli G.
Published: July 2002

This work reanalyzes the methods of calculation of the dispersion characteristics of a dispersive magnetostatic wave delay line. It turns out that the analytical approach, commonly developed in a first-order approximation, leads to erroneous results when exploited to derive the variation of the group velocity as a function of the wave vector k (or of the frequency), particularly for k values lower than 100–200 cm−1. To get a more accurate response, higher-order terms have been introduced in the analysis of the dispersion relation. To describe their effect, the inferred analytical results are compared to the numerical ones and to the experimental responses of a magnetostatic wave delay line. Furthermore, the method has been exploited to evaluate the power threshold levels (Pthr) in the excitation of magnetostatic solitons. It gives the correct order of magnitude of values when compared to the experimental ones.
Magnetic and crystallographic characterization of Zn0.78Fe0.22Se and FeSe films on GaAs (001)
Authors: Jonker B. T. , Krebs J. J. , Qadri S. B. , Prinz G. A. , Volkening F. , Koon N. C.
Published: July 2002

We have grown single-crystal (001) epilayers of the diluted magnetic semiconductor Zn1−xFexSe with 0≤x≤1 on GaAs(001) substrates by molecular-beam epitaxy. The films retain the zinc-blende structure for thicknesses up to at least 2 μm for x≤0.22, while epilayers with higher Fe concentrations can be stabilized up to some decreasing critical thickness. SQUID magnetometry data obtained for x=0.22 indicate Van Vleck paramagnetic behavior accompanied by a decrease in the fraction of magnetically free Fe2+ ions with increasing x. Conversion electron Mössbauer spectra of the FeSe epilayers show a dominant paramagnetic central peak at both 300 and 13.5 K, with small contributions from Zeeman-split components at low temperature. The samples were further characterized with x-ray rocking curve, θ-2θ, and topography measurements.
A coupled field finite element for magnetostructural analysis
Authors: Ostergaard Dale F.
Published: July 2002

Advances in the design and application of high magnetic field devices such as particle accelerators, magnetic levitators, actuators, and electromagnetic launchers may often necessitate analysis of the coupled field interaction between magnetic forces and elastic structural deformation. A finite element formulation for two-dimensional planar and axisymmetric application that directly couples magnetomechanical interaction is presented. The formulation is verified by comparison of finite element solutions and analytic solutions for two problems.
Magnetic field generated by lightning protection system
Authors: Geri A. , Veca G. M.
Published: July 2002

A lightning protection system for today’s civil buildings must be electromagnetically compatible with the electronic equipment present in the building. This paper highlights a mathematic model which analyzes the electromagnetic effects in the environment in which the lightning protection system is. This model is developed by means of finite elements of an electrical circuit where each element is represented by a double pole circuit according to the trapezoidal algorithm developed using the finite difference method. It is thus possible to analyze the electromagnetic phenomena associated with the transient effects created by the lightning stroke even for a high-intensity current. Referring to an elementary system comprised of an air terminal, a down conductor, and a ground terminal, numerical results are here laid out.
Magnetic aftereffect in textured Ni/Cu compositionally modulated alloys (abstract)
Authors: Atzmony U. , Swartzendruber L. J. , Bennett L. H. , Lashmore D. , Watson R. E. , Rubinstein M. , Lubitz P.
Published: July 2002

The existence of a magnetic aftereffect (‘‘magnetic viscosity’’) in textured Ni/Cu multilayered alloys was established1 using a vibrating sample magnetometer at room temperature and at 86 K. It was shown that the effect is strongly dependent on the step field, H2 (i.e., the value the field is reduced to after the magnetic moment has been aligned in high field), and exhibits a maximum relaxation rate for values of H2 around the reverse coercive field, Hc. Aftereffect behavior of this type has been observed in other materials, though most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation is enhanced at low temperature in the present situation. Several questions remain open from this earlier work. Among these are: is the effect a property of a thin Ni film or is it attributable to the compositional modulation of the alloy?; what is the exact form of the time decay and what is the mechanism that causes this effect? In order to resolve some of these issues the magnetic aftereffect has been measured in more detail and for longer periods of time at both temperatures (room and 86 K) in a new set of [111]-textured, layered Cu/Ni alloys of varying thicknesses. The slab thickness of the Ni, dNi, was varied between 6 and 30 Å, and the ratio dNi/(dNi+dCu) between 0.1 and 0.8.
Anisotropy of the linear magnetic birefringence in erbium iron garnet
Authors: Guillot M. , Le Gall H. , Feldmann P. , Marchand A.
Published: July 2002

Linear magnetic birefringence (LMB or the Cotton–Mouton effect) measurements have been performed on single crystals of erbium iron garnet (ErIG) in the 4.2–300-K temperature range at 1.15 μm wavelength in magnetic fields up to 20 kOe, applied along the three cubic crystallographic directions. Light propagation was parallel to the [1̄10] direction. Except for the [110] direction at low temperatures the LMB is proportional to the internal field, and a strong anisotropy is observed in the whole temperature range. At the compensation temperature (80 K) the ‘‘LMB susceptibilities’’ change sign and are found to be proportional to the inverse of the temperature square in a wide range of temperatures. A macroscopic analysis is presented in terms of electric dipole contributions: Thesecond-order magneto-optical coefficient of the Er3+ is deduced in the spontaneous state.
Unusual finite size effects on critical temperature in fcc Ising antiferromagnets
Authors: Pommier J. , Diep H. T. , Ghazali A. , Lallemand P.
Published: July 2002

A new multispin coding technique is presented for Monte Carlo simulation of antiferromagnetic Ising spin systems on an fcc lattice. The nearest- and next-nearest-neighbor interactions J1 and J2 are included. This technique allows a considerable gain in CPU time and computer memory. As a first application, we have studied samples of 4L3 spins with L up to 48. An unusual behavior of the critical temperature with increasing L is found in the case of nearest-neighbor interaction in zero field. Finite size effects on the locations of tricrical points in the (T,J2/J1) plane are discussed.
Mean-field treatment of three component spin Hamiltonian with high-order cubic anisotropy: Generic phases and sequences of order-order transitions (abstract)
Authors: Pawlowska Z. , Oliker J. , Kventsel G. F. , Katriel J.
Published: July 2002

A three-component spin system involving cubic anisotropy of fourth, sixth, and eighth degree was studied using the Landau theory and mean-field approximation. The last method involves solving of the recently proposed infinite-ranged magnetization equation, which was previously applied only to the systems with quartic anisotropy.1 Both approaches result in five possible ordered phases. Two of them, X and XYZt, are the only possible ordered phases if the sixth and eighth-order terms are not taken into account, they correspond to the ordering along an axis and along the main diagonal, respectively. In the XYt phase, which is unstable in ‘‘quartic’’ approximation but can be stabilized by higher-order terms, the resultant magnetization is directed along the diagonal in the XY plane. In the remaining two phases, XYg and XYZg, the magnetization vector rotates continuously in the XY plane and in space, respectively, upon varying the temperature; these phases resemble the ‘‘generic’’ phase found by Galam and Birman2 in the two-component system. It is shown that these new phases can be approached from the isotropic (I) phase via a sequence of second-order transitions; the longest possible sequences are found to be I-X-XYg-XYt and I-XYZt-XYZg-XYt.
Magnetic properties of the copper trimer chains 4-picolinium2 Cu3Cl8 and 4-picolinium2 Cu3Br8
Authors: Zaspel C. E. , Rubenacker Gerald V. , Hutton Stuart L. , Drumheller John E. , Rubins R. S. , Willett R. D. , Bond Marcus R.
Published: July 2002

(4-pic)2Cu3Cl8 and (4-pic)2Cu3Br8 contain planar, bibridged copper halide trimers. The trimers are then stacked with longer semicoordinate Cu–halide–Cu bonds between adjacent trimers. The magnetic susceptibilities show that trimers are in a spin-1/2 ground state at low temperatures with coupling constants J/k=30 and −100 K, respectively, determined by fitting the data to a new high-temperature expansion with only exchange constants and external field as expansion parameters. We show that even though the spin-1/2 trimers are antiferromagnetically exchange coupled along the chain, they order ferromagnetically at low temperature providing examples of pseudo-one-dimensional, S=1/2, Heisenberg ferromagnets. Electron paramagnetic resonance measurements at the X band were also performed and confirm the susceptibility measurements.
Mössbauer spectroscopy studies of molecular magnets (invited)
Authors: Reiff William Michael
Published: July 2002

A variety of new organo-molecular magnets have been characterized in our and colleagues’ laboratories in recent years using classic susceptibility measurements. In this effort, iron-57 Mössbauer spectroscopy has proven a particularly useful additional tool in elucidating charge transfer and interesting, unprecedented magnetic behavior for magnets based on electron donation from decamethylferrocene to polycyanide electron acceptors, e.g., tetracyanoethylene, tetracyano-quino-dimethane, hexacyanobutadiene. Examples of Mössbauer spectra of such systems are presented with emphasis on (a) slow paramagnetic relaxation at low spin ferric sites as a probe for spin on the polycyanide electron acceptor units; (b) large orbital contributions to internal hyperfine fields concommitant with highly anisotropic magnetic behavior; and (c) onset of multiple hyperfine pattern spectra signifying complex magnetostructural transformations.
Domain wall pinning in sputtered soft amorphous magnetic thin films
Authors: Ho Wing Kei , Humphrey Floyd B.
Published: July 2002

Domain wall pinning in sputtered soft amorphous thin films has been observed similar to that seen in rapidly quenched amorphous ribbon. The pinning is induced by annealing samples in their nonsaturated state. The easy-axis hysteresis loop of such a sample shows a characteristic stop in the change of magnetization at a nonsaturated magnetization value for both an increase and decrease of applied field, corresponding to the field value when the domain walls are pinned. An abrupt increase of magnetization is observed when the pinning is overcome by a large enough applied field, called wall pinning force (Hp). Sputtered amorphous Fe5.85Co72.15Mo2B15Si5 thin films with coercivity of about 0.06 Oe and thickness of about 6500 Å gave a wall pinning force as high as 0.6 Oe. The general mechanism of the wall pinning was confirmed by domain viewing. For different annealing temperatures, the wall pinning force increases as the annealing duration increases and approaches a maximum value. A linear relation between the maximum value of wall pinning force and the field-induced magnetic anisotropy field was obtained.
Magnetic imaging by atomic force microscope (invited) (abstract)
Authors: Grütter P. , Meyer E. , Heinzelmann H. , Rosenthaler L. , Hidber H. R. , Güntherodt H.-J.
Published: July 2002

A new method of imaging the surface of magnetic samples on a submicron scale is described and the observation of magnetic domain walls is presented. Measurements in air on a Co-Ni recording media, polycrystalline Ni foil and rapidly quenched alloys are shown. This magnetic microscope is based on the idea of measuring magnetic forces with the recently developed atomic force microscope (AFM). Forces acting on a tip are recorded by the measurement of the deflection of a lever to which this tip is attached. In order to measure ultra small forces (less than nN), the spring constant of the lever has to be small and the deflection of the lever has to be measured with great sensitivity, i.e., by using interferometry or scanning tunneling microscopy (STM). The lever is made from ferromagnetic Ni foil with an integrated, electrochemically etched tip. Different measuring modes of the AFM are described. The images obtained by the AFM using a para- or ferromagnetic tip and by the STM are compared. Furthermore, the results obtained by the magnetic AFM on Co-Ni recording media are compared with previous studies by scanning electron microscopy with polarization analysis (SEMPA).
Doping of InP and GaInAs during organometallic vapor-phase epitaxy using disilane
Authors: Woelk E. , Beneking H.
Published: July 2002

Disilane (Si2H6) is presented as a new silicon doping source in the organometallic vapor-phase epitaxy of InP and GaInAs. The doping characteristics of disilane were studied under a range of growth conditions used to obtain device quality layers. Silicon incorporation by means of disilane shows a different behavior in InP and GaInAs doping. The slope of the log N vs log (disilane flow) plot is 0.75 for InP and 1 for GaInAs. A variation of doping level with growth temperature was observed revealing an activation energy of 1.2 eV in the case of InP. Electrical measurements on disilane-doped InP and GaInAs yield the same high mobilities as obtained in otherwise doped films, indicative of low compensation.
Generation of high intensity cw stimulated Raman scattering in a single-mode fiber
Authors: Irrera Fernanda , Mattiuzzo Lamberto , Pozza Davide
Published: July 2002

The first two orders of stimulated Raman scattering have been observed by pumping a single-mode fiber with a cw Nd:YAG laser. Broadband first Stokes with intensity of up to a few watts has been observed as a function of the input power. The critical powers have been measured.
Magnetic properties and microstructure of Co-Cr-Pr vertically magnetized films
Authors: Suzuki T. , Yoshida N. , Hwang U. , Uchiyama Y. , Ishibashi K.
Published: July 2002

The effect of Pr on both the magnetic properties and microstructure of Co-Cr alloys is discussed. The saturation magnetization Ms and perpendicular magnetic anisotropy Ku at room temperature is found to increase with Pr, becoming maximum at about 0.5 wt. % Pr, and then decreases monotonously. The microstructure is also changed with Pr, leading to a less-defined columnar structure. However, no significant change is found in the Auger spectra for various contents.
Structural and magnetic properties of pseudoternary Nd2(Fe1−xCux)14B compounds
Authors: Chen S. K. , Duh J. G. , Ku H. C.
Published: July 2002

Magnetic and crystallographic measurements have been made on new pseudoternary compounds Nd2(Fe1−xCux)14B in order to study the systematic variation of magnetic properties with Cu substitution. X-ray powder diffraction data indicate that the tetragonal Nd2Fe14B-type phase exists only for x≤0.05. Partial replacement of Fe by nonmagnetic Cu significantly decreases the saturation magnetization value with little change in ferromagnetic Curie temperature TC. Low-temperature spin orientation temperature (Tsr) decreases from 135 K for x=0.00 to 130 K for x=0.03, and 122 K for x=0.05, and the tilt angle of the easy magnetization direction from the tetragonal c axis decreases accordingly.
Reconstruction mechanisms in ion-implanted yttrium iron garnet films
Authors: Balestrino G. , Lagomarsino S. , Milani E. , Gerard P. , Tucciarone A.
Published: July 2002

Yttrium iron garnet films implanted with Ne+ ions at two different doses have been analyzed by x-ray double-crystal diffractometry and conversion electron Mössbauer spectroscopy after thermal treatment at different temperatures. The strain profile, paramagnetic fraction, hyperfine fields of both the paramagnetic and magnetic fraction, and the full width at half-maximum of the Mössbauer peaks have been measured for the different temperatures. The reconstruction mechanism of the crystalline lattice has been studied. It appears that at least two different mechanisms are involved with two activation energies. The first one, which starts at nearly 150–200 °C and is completed at nearly 500–600 °C, is on a short-range scale and is driven by oxygen diffusion, while the second one, which has a higher activation energy, is on a long-range scale. There is clear evidence that, at least for the lower dose implanted sample, the reconstruction mechanism is not an epitaxial regrowth.
Switching performance of a cryogenic silicon photoconductive power switch
Authors: Petr R. A. , Nunnally W. C. , Smith C. V.
Published: July 2002

The silicon photoconductive power switch has the potential to replace gaseous discharge switches like thyratrons, krytrons, ignitrons, and spark gaps, that are commonly found in high-voltage and high-current pulse circuits. This offers the possibility of developing advanced laser and radar drive circuits that are all-solid state, and which enjoy the advantages of improved efficiency, compactness, and life expectancy. Silicon operating at liquid-nitrogen temperature is especially attractive as a power switch because at 77 K it displays an extremely low coefficient of thermal expansion, a large optical absorption depth for 1.06-μm light, and a large thermal conductivity. These factors allow low-temperature silicon to switch power levels an order of magnitude greater than at 300 K, and an experimental cryogenic silicon photoconductive power switch (PCPS) has been made to switch pulses of 15-kV, 1.2-kA, 0.5-μS duration at 100-Hz recurrent frequency. Temperature and thermal stress profiles generated in the switch during operation have been calculated and experimentally verified, and the upper power limits for this switch technology are established. It is shown that the silicon switch compares favorably with thyratrons in terms of electrical ratings and energy transfer efficiency, and should be considered in advanced pulser designs.
Structure and optical properties of plasma-deposited fluorinated silicon nitride thin films
Authors: Livengood Rhett E. , Petrich Mark A. , Hess Dennis W. , Reimer Jeffrey A.
Published: July 2002

The deposition chemistry, optical properties, and structure of plasma-deposited fluorinated silicon nitride films are studied and compared to available results of other researchers. Fluorinated films show an increase in deposition rate and optical band gap, and a decrease in refractive index and film stress compared to unfluorinated silicon nitride films. Fluorine concentration in the films ranges from 5 to 25 at. %. The total hydrogen concentration of fluorinated films is lower than that of unfluorinated films. The improved thermal stability of fluorinated films as compared to unfluorinated films is explained by a significant decrease in hydrogen bonded to silicon. All films hydrolyze to some extent and films with large fluorine concentrations hydrolyze rapidly to silicon dioxide. The microstructure of fluorinated films consists of clustered silicon-fluorine and nitrogen-hydrogen regions within an amorphous silicon-nitrogen matrix.
Raman scattering characterization of the microscopic structure of semi-insulating polycrystalline Si thin films
Authors: Olego D. J. , Baumgart H.
Published: July 2002

Raman scattering experiments were carried out to study the microscopic structure of semi-insulating polycrystalline Si (SIPOS) thin films prepared by low-pressure chemical vapor deposition. The samples contain 18, 25, and 30 at. % of oxygen and after growth they were annealed at 900 and 1000 °C for 30 min. The Raman spectra show in the vibrational region of the optical frequencies of Si two bands, which arise from scattering in crystalline grains and disordered forms of Si. The behavior of these bands as a function of oxygen content and annealing temperatures was established in detail. The crystallinelike band peaks below the transverse optical frequency of Si at zone center and is broadened with respect to the Raman line of a Si wafer. From the broadenings, estimates of grain sizes are obtained. The band due to the disordered form of Si appears at frequencies above those of an extended network of amorphous Si. A model for the SIPOS microscopic structure is proposed in which the disordered Si corresponds to the surface layers of the crystalline grains. The latter are embedded in an amorphous SiO2 matrix. Quantitative estimates of the contributions of the ordered and disordered phases of Si to the SIPOS structure are attempted. The Raman results provide additional experimental evidence that the crystallization temperature of Si increases under the presence of oxygen.
Energy enhancement and volume effect between parallel and transverse gas flow N2 laser
Authors: Saito Y. , Nomura A. , Kano T.
Published: July 2002

The effect of gas flow parallel and transverse to the optical path and of the volume of the laser tube on N2 laser energy and pulse width was experimentally investigated. Energy enhancements of more than a factor of 2 are clearly seen in transverse flow as compared with parallel flow. Gas flowrate affects the energy more in lasers with a large volume. Pulse widths in lasers with transverse flow are shorter than those with parallel flow by about 2 ns. These results show that both the direction of gas flow and the volume of the laser tube are important parameters to adjust to increase energy and power.
Ion mixing and thermochemical properties of tracers in Ag
Authors: Ma E. , Kim S.-J. , Nicolet M.-A. , Averback R. S.
Published: July 2002

Very thin films of Ni, Ta, W, Pb, and Bi in a Ag matrix were irradiated at 77 K with 330 keV Kr ions at doses from 3 to 7×1015 ions/cm2 and analyzed at room temperature by backscattering of 1.9 MeV He+. The measured mixing efficiencies, Dt/φFD, for the various tracers correlate with their respective tracer impurity diffusion coefficients and impurity-vacancy binding energies in Ag. The results concur with previous ones with a Cu matrix and further support the idea that the parameters that are important for thermal diffusion are also important for ion mixing in a thermal spike.
Analysis of the effects of recombination and leakage on the static properties of GaInAsP/InP stripe geometry lasers
Authors: Chik K. D.
Published: July 2002

The static properties of stripe geometry gain guided lasers have been analyzed using a model that unifies the Auger recombination and the energetic carrier leakage mechanisms. Theoretical results show that the Auger recombination and carrier leakage could modify the gain profile and the optical intensity distribution in the laser cavity significantly, and could account successfully for the difference in the threshold behavior observed experimentally between GaInAsP/InP and AlGaAs/GaAs lasers.
Field-induced transition in the conductivity mechanism of polycrystalline silicon films
Authors: Ada-Hanifi M. , Sicart J. , Dusseau J. M. , Robert J. L.
Published: July 2002

Current-voltage characteristics of polycrystalline silicon films highly doped with phosphorus and boron were studied over a wide range of temperatures (40–300 K) and applied electric fields (up to 5 kV cm−1). After the usual ohmic regime, we observed a large increase in dc current versus applied voltage. Moreover, at higher electric fields, a new ohmic conduction regime appeared which has not yet been reported in polycrystalline silicon. Thermoemission-based models cannot fully interpret our results. We present a new interpretation of current-voltage characteristics based on a model previously used to interpret the electrical properties of these films at low electric fields. This model takes into account the existence of fluctuations both in intergranular potential and in the grain boundary barrier heights. They result from all of the macroscopic inhomogeneities due to the growth conditions of the material. The high electric field detraps carriers from grain boundaries and extracts the carriers located in the valleys of potential created by the fluctuations, thus inducing transition in conductivity.
The automatic determination of cadmium-mercury telluride composition
Authors: Micklethwaite W. F. H.
Published: July 2002

This paper describes the use of a fully automated Fourier-transform infrared spectrophotometer system to scan the composition of bulk slices of CdxHg1−xTe for the range 0.15<x< 0.35 and its calibration to analytically determined X values. The most useful correlation established is for the n type, between the 300 K IR cuton defined by the zero-transmission intercept of a line tangent to the transmission curve at 1/e of its maximum and the composition parameter X as determined by wet chemical analysis. The overall prediction accuracy of true X is better than 0.005. Other cuton definitions, implementation pitfalls, and X correlations with both p-type transmission and 300 K carrier concentration are also discussed.
Optical studies of Cd0.9Mn0.1Te doped with Au, As, Cu, and P acceptors
Authors: Misiewicz J. , Becla P. , Isaacs E. D. , Wolff P. A. , Heiman D. , Ram-Mohan L. R. , Wrobel J. M.
Published: July 2002

Optical absorption and photoluminescence measurements were made on Cd0.9Mn0.1Te doped with As, P, Cu, and Au. Shallow acceptor ionization energies were determined as: 108 meV for P; 115 meV for As; 170 meV for Cu; and 180 meV for Au. These energies are larger than those for CdTe due to the formation of bound magnetic polarons. Self-consistent numerical calculations of the bound magnetic polarons are made for As and P dopants. The absorption spectra below 0.5 eV were separated into contributions from acceptor photoionization, inter- and intraband transitions, and free-hole absorption. Acceptor concentrations in the 1017 cm−3 range were found for As and P doping; however, Cu and Au were found to produce high compensation (<1012 cm−3). Mechanisms for this behavior are discussed.
Photoconductivity of a modulation-doped GaAs/AlGaAs heterostructure induced by fast neutron irradiation
Authors: Wu Yong-sheng , Huang Yi , Li Yong-kang , Yang Zhong-xing , Zhou Jun-ming
Published: July 2002

We have studied the Shubnikov–de Haas (SdH) oscillation and the quantum Hall effect on a modulation-doped GaAs/AlGaAs heterostructure and found that there is no parallel conductivity and no failure in obeying the law μ∼nγ when the electron concentration in the interface is increased by exposing the sample to white light. The photoconductivity can persist for several days at room temperature if the sample is not annealed.
Signal generation in optically detecting thermal-wave instruments
Authors: Dóka O. , Miklós A. , Lórincz A.
Published: July 2002

It is shown that under usual conditions the photothermal interferometric method may measure signal combinations originating from both photothermal deformation and changes of the complex dielectric constant.
Fabrication and structure of Mo/Ta superlattices
Authors: Bennett Wayne R. , Falco Charles M.
Published: July 2002

Mo/Ta superlattices with superlattice wavelengths in the range 20–180 Å were made by alternately sputtering these components. We present the results of a variety of x-ray diffraction studies used to structurally characterize these samples.