bluuebunny/crossref_metadata_2025 huggingface dataset:
Light-induced magnetization of gold measured by spin polarized photoemission
Authors: Pescia D. , Meier F.
Published: February 2003

The (111)-surface of a gold single crystal was irradiated by circularly polarized light and the spin polarization of the photoemitted electrons was measured in the light energy range 2.0 eV?hν?9.5 eV and for different work functions. Several interband energies have been accurately derived; they agree satisfactorily with existing band structure calculations. The symmetry character of the bands near Ef has been unambiguously assessed: in particular, experimental evidence of their sp-d hybridization properties has been obtained.
Fermi surface measurements of lutetium
Authors: Johanson W. R. , Crabtree G. W. , Schmidt F. A.
Published: February 2003

We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101̄0) and (112̄0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.
Abstract: A unified approach to some transport and EPR properties of noble metals with rare-earth impurities
Authors: Lacueva G. , Levy P. M. , Fert A.
Published: February 2003

Both magneto-transport and EPR experiments have shown the importance of the anisotropic character of the k-f interaction between conduction and 4f electrons. For noble metals with rare-earth impurities the magnitude of the anisotropic terms can be understood in terms of the hybridization of the conduction electrons with the outer 5d electrons of the rare-earth impurities. To obtain a consistent description of the magnetotransport properties, we have included the spin-orbit coupling of the 5d electrons as well as their crystal field splitting. The various parameters entering our model have been determined by fitting the isotropic transport properties as well as the anisotropic magnetoresistance arising from quadrupole scattering and the Hall effect due to skew scattering. We have used this model to calculate the 5d virtual bound state contribution to the g-shift and linewidth of rare-earth impurities in noble metals. After estimating the 6s contribution, we obtain a consistent fit for the g-shift and linewidth of several rare-earths in noble metals.
Volume mismatch substitution in two Ce compounds (invited)
Authors: Croft M. , Levine H. H.
Published: February 2003

The crossover from a γ-Ce-like state to an α-Ce state in Ce compounds has been subject of great interest in recent years. Here, we discuss two Ce compounds, CeAl2 and CePd3, which can be driven through a γ-like to an α-like transition via volume mismatch alloying. A nonlinear volume collapse coupled to two-phase behavior is common to both alloy systems. In the γ-like phase just before the volume collapse, spin fluctuations (probed by resistance measurements) with a characteristic energy scale TSF in the 10–50 K range are also common to both systems. For the CeAl2 based alloys, TSF is seen to increase rapidly and systematically with decreasing volume from well within the γ-like to well into the α-like phase.
Electronic structure and magnetic properties of CeAl2
Authors: Jarlborg T. , Freeman A. J. , Koelling D. D.
Published: February 2003

Self-consistent electronic energy band calculations have been performed utilizing the LMTO method for CeAl2 in assumed paramagnetic, induced ferromagnetic, and antiferromagnetic states. The paramagnetic Ce f band is roughly 1 eV wide and is located primarily above the Fermi energy with a leading edge extending down and producing a very high density of states at the Fermi energy. The induced ferromagnetic calculation shows large enhancement of the field but appears to decay when the field is removed. We have approximated the observed antiferromagnetic structure by the simple two sublattice form which does not enlarge the unit cell. The f level density of states is sharply narrowed in this state. Further, the state is self-consistently stable; after the fictitious driving field is removed, it does not decay away and results in a moment of 0.88 μB in good agreement with the neutron results of Barbara et al.
Thermodynamic scaling theory for the two-impurity Anderson model
Authors: Jayaprakash C. , Krishna-murthy H. R. , Wilkins J. W.
Published: February 2003

We present results of a study of the two-impurity Anderson model using a thermodynamic scaling theory developed recently. The model is characterized by the Coulomb energy U, the orbital energy εd, the d-level width Γ, and the separation between impurities R. If Γ≪−εd≪U, the low-temperature physics maps onto that of the two-impurity Kondo problem, discussed by us elsewhere; the main difference is that the RKKY interaction can acquire an antiferromagnetic contribution with a (kFR)−2 envelope over a restricted range of kFR. In this case impurity-impurity interactions can be substantial. The other interesting case is when the impurities have a ’’fluctuating valence’’ with the singlet lying lower in energy, i.e., εd≳Γ. Here we find that the single-impurity physics dominates the low-temperature behavior, and impurity-impurity interactions are perturbative. The qualitative features of the temperature-dependent susceptibility are discussed.
Magnetic ordering in cerium hexaboride CeB6
Authors: Burlet P. , Rossat-Mignod J. , Effantin J. M. , Kasuya T. , Kunii S. , Komatsubara T.
Published: February 2003

Neutron diffraction experiments have been performed on single crystals of CeB6 to investigate the magnetic ordering of this compound. The magnetic phase diagram derived from neutron diffraction is very comparable to those determined by specific heat, magnetization, and magnetoresistance measurements. Three magnetic phases are evidenced: a high temperature phase I which is probably paramagnetic; an intermediate phase II which may be ferromagnetic; and a low temperature, low field helical phase in which the structure results from a double modulation. This double modulation is interpreted as the coexistence of exchange interactions and of the Kondo effect.
Stability of spin-glass phases versus space dimensionality
Authors: Benyoussef A. , Boccara N.
Published: February 2003

We study the existence of spin-glass phases for site dilute frustrated Ising models with nearest-neighbor interactions for various space dimensionalities. For d = 4, phase diagrams of such systems exhibit a stable spin-glass domain at finite temperature. For d = 3 the spin-glass phase is only stable at T = 0.
Abstract: Microscope and magneto-optical rotation (MOR) studies of Eu0.54Sr0.46S in ferromagnetic (FM) and spin glass (SG) states
Authors: Dillon J. F. , Chen E. Yi , Maletta H.
Published: February 2003

The zero-field magnetic phase diagram of EuxSr1−xS as presently understood is based on neutron diffraction and susceptibility measurements. (1) The nature of the FM-SG boundary is not clear. We have used measurements of MOR as well as microscope examination to contrast the gross magnetic behavior of an X = 0.54 single crystal specimen in the FM and SG regions. Our findings include: (a) Plots of MOR versus field Φ(Ha) in the FM region after cooling in H = 0, initially show a linear increase with Ha, i.e., Φ = AHa, and then saturation at successively higher levels as T is decreased. To our great surprise, this behavior continues smoothly into the SG regime. (b) We measure a remanent rotation at various temperatures ΦR by subjecting the sample to ±16 kOe, then measuring Φ(Ha) in 1 kOe⩽Ha⩽2 kOe. We find Φ(Ha) = ±ΦR+AHa. ΦR is zero for T≳3.6 K. Below this it increases to a maximum, then in SG again increases. (c) We clearly see fine domain structure just below 3.6 K. This very strikingly disappears on cooling below about 1.8 K. We note that these are the first observations of magnetic behavior in the SG regime for a composition which is ferromagnetic at a higher temperature.    (1) H. Maletta and W. Felsch, Z. Phys. B 37, 55 (1980).
On the theory of the ferromagnetic phase transition in crystalline and amorphous materials
Authors: Fähnle M. , Herzer G. , Egami T. , Kronmüller H.
Published: February 2003

The ferromagnetic phase transition is determined by the interaction of spin clusters which are strongly coupled together. In the time-dependent Ginzburg–Landau theory (TDGL) this coupling is described by a nonlinear term in the equation of motion for the magnetization, and therefore the theory of phase transitions is mathematically rather complicated. We present a molecular field theory with correlations in space and time, which neglects the nonlinear coupling term, but which takes into account implicitly the effect of coupled spin clusters when constructing an appropriate linear equation of motion. The theory holds as long as the nonlinear term in the TDGL is not the dominant one, and it improves the conventional molecular field theory in a rather large range of temperatures, in which the couplings between the fluctuations are small enough but still important. It therefore may be successfully applied to the case of amorphous ferromagnets, which show deviations from the conventional molecular field behavior in a temperature range which is much larger than the range of critical behavior in crystalline Fe or Ni. Results for the critical slowing down and for the paramagnetic susceptibility are given.
Magnetic observations of austenite-martensite transformations induced by torsional strain
Authors: Garshelis I. J. , Fiegel W. S.
Published: February 2003

Wire specimens of a TRIP steel and several commercial austenitic stainless steels were torsionally strained both by continuous monotonic twist to fracture and by following various pause and reverse twist regimens. Progress of the phase transformation to ferromagnetic martensite, induced by the extensive plastic strain, was monitored by in situ dynamic measurements of the cyclic axial magnetizations due to alternating circular and alternating axial magnetic fields. By these means, various anisotropic features, as well as the relative concentration of the transformation products, were indicated. In the TRIP steel the dominant anisotropy is found to be magnetoelastic, whereas the Cr-Ni steels are found to develop a helical magnetic anisotropy, interpreted as resulting from the shape of the emergent martensite. While the TRIP steel transformation followed closely upon the advent of plastic strain, the Cr–Ni steels showed strain thresholds. Measurements following incremental surface metal removal of post fracture specimens indicated a negative radial gradient in martensite concentration from the surface, correlating with the similar gradient in accumulated strain.
Growth rate dependence of rare-earth segregation in the liquid-phase epitaxy of magnetic garnet films
Authors: Gualtieri D. M. , Tumelty P. F.
Published: February 2003

Epitaxial films of the archetypical bubble garnet (R, Y)3Fe5O12, where R is a rare earth, were grown on (111) Gd3Ga5O12 substrates from a 200:1 by weight PbO:B2O3 flux using the horizontal dipping technique with rotation. Growth rate was varied by adjusting supercooling and rotation rate, and the equilibrium segregation coefficients of the dodecahedrally crystallizing cations KR = Rxtal/Rmelt were determined with reference to the film-lattice constant and the segregation of these cations on octahedral sites. KR was found to obey the growth model of Burton, Prim, and Slichter [J. Chem. Phys. 21, 1987 (1953)], KR = KR0/[KR0+(1−KR0)e−kf], where f is the growth rate, KR0 is the segregation coefficient at zero growth rate, and k is a parameter which is a function of the thickness of the growth interface and the diffusion constant. The parameter k was found to be independent of the species R and to have the value 1.18 sec μm−1 for the particular growth condition. A strong correlation was found between KR0 and the partial molar heat of mixing of the R2O3 oxide and the flux, as calculated from regular solution theory [D. M. Gualtieri, J. Appl. Phys. 50, 2170 (1979)].
Changes in magnetic parameters due to annealing of the implanted epitaxial garnet-metal interface
Authors: Andersen Mark A. , Sethna P. P. , Fontana R. E. , Bullock D. C.
Published: February 2003

An aluminum-copper cover layer on implanted magnetic garnet causes a change in certain magnetic parameters, having a direct effect on the device parameters of a bubble memory chip. This change is NOT seen in nonimplanted garnet slices. After 2 h of annealing at 350 C in vacuum, there was a difference in bubble collapse field between the metal-covered garnet and the bare garnet. This difference in some cases was more than 10 Oe, and it was then simple to create a region depleted of bubbles surrounded by a region of densely packed bubbles. The depth of the interaction was 1300 Å, determined by successive ion-beam machining and collapse field measurements. This interaction depth was independent of the total annealing time. Since no aluminum has been detected in the garnet after anneals, an oxygen depletion mechanism is suggested.
Laser annealing in ion-implanted garnets
Authors: Madore M. , Gerard P. , Jouve H. , Auvert G. , Bensahel D.
Published: February 2003

H+ ion-implanted garnet films with a composition of (Y, Sm, Lu, Ca)3 (Fe, Ge)5O12 have been laser annealed in ambient air. Annealed films were studied using ferromagnetic resonance (FMR) and X-ray techniques. A thermal model is proposed suitable with the experimental data. Emphasis on the differences of the laser annealing compared to a classical furnace annealing are presented. Hydrogen trapping has been observed to result from the high velocity of the quenching process.
Magnetic properties of substituted Sm2Co17−xTx compounds (T = V, Ti, Zr, and Hf)
Authors: Satyanarayana M. V. , Fujii H. , Wallace W. E.
Published: February 2003

Ternary Sm2Co17−xTx systems in which Co is replaced by V, Ti, Zr, and Hf have been studied to ascertain the efficacy of these elements in improving the permanent magnet characteristics of Sm2Co17-based magnets. Single phase materials were obtained for 0?x?1.0. X-ray diffraction measurements indicate that these compounds exhibit either the hexagonal-Th2Ni17 or the rhombohedral-Th2Zn17 structure. The lattice parameters are found to increase with x and in the order Hf<Zr<Ti<V, indicating that these elements are probably substituting for Co. Permanent magnet characteristics such as easy directions of magnetization, saturation magnetizations (M2), and anisotropy fields (HA) were measured at 295 and 77 K along with the Curie temperatures (TC). All compounds studied retain the uniaxial magnetic behavior of Sm2Co17, both at 295 and 77 K. The Curie temperatures are found to decrease with replacement of Co by V, Ti, Zr, and Hf at an approximate rate of 180, 150, 90, and 50 deg/atom, respectively. The saturation magnetic moments also decrease, with increasing x, in the order Zr<Ti<V<Hf. The striking effect of these substituents is in improving the anisotropy field, the improvement being in the order Zr≳Ti≳V≳Hf. Among all the substituents studied, Zr appears to be the most promising for permanent magnet applications.
Thermal stability and temperature coefficients of four rare-earth-cobalt matrix magnets heated in dry air
Authors: Strnat R. M. W. , Liu S. , Strnat K. J.
Published: February 2003

Flux-loss characteristics during long-term air aging of four rare-earth-cobalt matrix magnet types were measured. Irreversible losses and reversible temperature coefficients on heating above room temperature are reported. Purely magnetic and permanent microstructure-related changes during aging were differentiated by measuring hysteresis curves before and after long-term exposure. Three commercial polymer-bonded magnets using different rare-earth-cobalt-transition metal alloys and a solder-matrix magnet with Sm(Co, Cu, Fe, Zr)7.4 were studied. They were cycled between 25 °C and maximum temperatures to 150 °C (25 ° intervals) as applicable. Aging data at 50 and 125 °C for an exposure time of 3300 h are reported. The 2–17 samples have a stability far superior to bonded 1–5. The soft metal binder imparts significantly better aging behavior on precipitation-hardened 2–17 magnet alloys above 100 °C than an epoxy resin matrix.
Bubble film characterization for process control (invited)
Authors: Washburn H. A. , Schechter B. D.
Published: February 2003

Considerations for characterization techniques of liquid-phase epitaxial magnetic garnet films are to (a) maximize process control information, (b) correlate with device performance, and (c) satisfy manufacturing constraints. Magnetization, anisotropy, film thickness, and their temperature dependencies are important device parameters and also determine process constraints. Optical film thickness, domain stripe-out field, and its temperature coefficient, anisotropy field, and stripe-width or susceptibility satisfy the characterization requirements. The ac susceptibility technique provides easily automated data collection for susceptibility and stripe-out field and the speed and precision to maximize process control information. Using the Maartense magnetometer, this method can separate films on the two sides of the substrate, thereby allowing use of one-side polished wafers and not constraining the LPE process. Susceptibility shows dependencies similar to the optically measured static stripe-width while more realistically employing wall motion.
One megabit bubble memory operation over extended temperatures
Authors: Washburn H. A.
Published: February 2003

One megabit bubble memories have been characterized for error rate and parametric margins over a wide ambient temperature range. The field access Permalloy devices employed a block replicate/swap architecture, replicate generation, multiplexed detection, and 50-KHz drive frequency. Margins of bias, drive, pulser parameters, and detector signals indicate that adequate temperatures and parametric guardbands are available to assure reliable operation without compensation from −20 to +85 °C ambient. Functional limitations beyond that temperature range are related to the temperature dependencies of the garnet magnetization (and its mismatch with the bias magnets), anisotropy, and capping layer effect. Factors important for the enhanced temperature range are conservative design (including low field rate, large elements, and replicate generation), low defect and low stress processing, and control of the garnet film properties.
Annihilation of vertical Bloch lines during creep in magnetic bubble materials
Authors: Han B. S. , Keezer D. , Humphrey F. B.
Published: February 2003

Additional motion of a magnetic bubble following a gradient field pulse may be induced through the application of a relatively small uniform z-field pulse. This phenomenon, known as ’’creep,’’ is studied in detail using a high-speed optical sampling microscope. Results for a (YGdTm)3(FeGa)5O12 sample indicate that the distance through which the bubble may translate during creep is roughly quantized in units of about 0.6 μm. This distance is attributed to the annihilation of a single pair of oppositely wound vertical Bloch lines (VBL’s). Observed motions of 1.2, 1.8, 2.4, ... μm correspond to the annihilation of 2, 3, 4, ... VBL pairs, respectively. Based on the Bloch curve model, corresponding theoretical values are obtained and show close agreement with experiment. In addition, experimental values for the rate of VBL annihilation are obtained. In each case the annihilation time for a single VBL pair is between 40 and 65 ns. All experimental results support the assertion that VBL annihilation must be accompanied by radial motion of the bubble wall.
Effect of heat treatment on magnetic properties and morphology of iron particles
Authors: Sueyoshi T. , Tashita K. , Hirai S. , Kishimoto M. , Hayashi Y. , Amemiya M.
Published: February 2003

Acicular iron particles with high coercivity and high saturation magnetization were prepared by reduction of the hematite particles which were obtained by dehydration of the silica-coated goethite particles in the process of heat treatment in air. Variations in specific surface area, micropore distribution, crystallite size, and magnetic properties with the dehydration temperature were measured. For the iron particles prepared by reduction of the silica-coated hematite particles obtained by dehydration at 800 °C, a maximum coercivity of 1250 Oe was obtained, and the crystallite size reached the minimum value of 220 Å which was close to the critical value of single domain particle. The highly acicular iron particles consisting of the closely packed small crystallites were obtained.
Fabrication of a multitrack, thin-film head
Authors: Noro Y. , Ohshima I. , Saito M. , Yamada M. , Tanaka K.
Published: February 2003

Thin-film magnetic heads with a high track density of 25 tracks per 3.81 mm have been fabricated. The write current density is the same as that of the conventional sendust audio head. The head consists of a two-layer, high aspect ratio coil, formed by the reactive plasma etching method, and spin-coated PIQ varnish layers as the insulation layers to provide a smooth surface for subsequent coil layers and the Ni-Fe alloy layer.
A powder neutron diffraction study of the LaNi4.5Al0.5D4.5 structure at 298 and 77 °K
Authors: Crowder C. , James W. J. , Yelon W.
Published: February 2003

Recently, there has been some controversy over the structure of hydrides of the La(Ni5−xAlx)5 system. One of the proposed structures belongs to the P6/mmm space group and contains five deuterium sites.4,5 The other proposed structure belongs to the P31m space group and contains two deuterium sites.6 In an attempt to resolve this conflict, a powder neutron diffraction study has been carried out for LaNi4.5Al0.5D4.5 at 298 and 77 °K. A modified Rietveld profile analysis technique was used to interpret the data. It is found that a two-site model using P6/mmm symmetry adequately describes the structure at 298 °K. At 77 °K, there is no evidence of magnetic ordering and the structure shows only slight changes from that given at 298 °K. The lattice parameter a contracts from 5.341 to 5.331 Å, while c remains constant at 4.236 Å.
Surface analysis by magnetization measurements on FeTi and Fe0.85Mn0.15Ti
Authors: Stucki F.
Published: February 2003

Surface composition and chemistry of binary hydrogen storage compounds are studied by means of magnetic susceptibility measurements. FeTi and Fe0.85Mn0.15Ti decompose at the surface forming superparamagnetic Fe particles which dominate the magnetism of powders. The surface decomposition, e.g., as a consequence of a number of hydrogenation cycles, results in an increase and the oxidation of the Fe particles, e.g., by impurities, results in a decrease of the magnetization. In this way the surface composition may be monitored. We found that FeTi is more susceptible to posioning by impurities than (FeMn)Ti because of a smaller segregation rate.
Abstract: Magnetoelastic modes in amorphous ribbons
Authors: Cullen J. R.
Published: February 2003

Certain kinds of amorphous ribbons (2605SC, for example) are known to undergo huge modulus changes with applied magnetic field at kilohertz frequencies and below. It is to be expected that relatively large changes in ultrasonic velocity will also occur. In order to analyze the field dependence of the ultrasonic velocity and attenuation, an understanding of the nature and dispersion of the normal magnetoelastic propagating waves must be obtained. Magnetoelastic plate-wave dispersion and attenuation have been calculated for models of magnetically saturated insulators. For a description of ribbons, however, the effect of a finite conductivity must be concluded. It is probably necessary to include the effect of the random nature of the parameters determining the velocity, as well. In a future publication we will present the results of calculations of the effect of eddy currents and random magnetic anisotropy on the velocity of ultrasonic waves in ribbon-like amorphous magnetoelastic alloys.
Light scattering determination of magnetic moments of magnetotactic bacteria (invited)
Authors: Rosenblatt Charles , de Araujo F. Flavio Torres , Frankel Richard B.
Published: February 2003

Light scattering is used to determine the average lengths and magnetic moments of magnetotactic bacteria in culture. The results are consistent with estimates made from electron micrographs.
Tracking pyritic sulfur in the microwave desulfurization of coal
Authors: Jacobs I. S. , Zavitsanos P. D. , Golden J. A.
Published: February 2003

Magnetic desulfurization is an attractive physical method of coal cleaning which has been studied for a quarter century. High-frequency selective heating of coal to convert nonmagnetic pyrite to moderately magnetic pyrrhotite has been suggested to enhance separation. Despite predicted feasibility, some successes have only recently been attained. We report on the use of Mössbauer spectroscopy and magnetization to follow indirectly the amounts of inorganic sulfur in coal. We observe significant conversion (≳10%) to pyrrhotite by microwave treatment of coarse coal granules at 915 MHz and 2.45 GHz at power levels of a few kW for about 1 min. Analysis of phase distribution allows independent calculation of the inorganic desulfurization resulting from microwave treatment and magnetic separation.
A reactive sputtering method for preparation of berthollide type of iron oxide films
Authors: Naoe M. , Hoshi Y. , Yamanaka S.
Published: February 2003

In order to prepare berthollide type of iron oxide (i.e., nonstoichiometric magnetite; FeOx:1.34<×<1.5) thin films, iron targets were sputtered in pure water vapor at the pressure of 2×10−3 Torr by using a high rate sputtering apparatus with faced targets. The composition and crystal structure of the obtained films strongly depend on input power Pt and substrate temperature T2. The increase of Pt and Ts lead to the reduction of oxygen content in the films. The films deposited at Pt above 300 W and Ts of 200 °C exhibit a spinel type of crystal structure. Their lattice constant a0 and resistivity ρ change monotonically from a0 and ρ for γ-Fe2O3 to those for Fe3O4 with an increase of Pt from 300 to 800 W. On the other hand, when Pt is kept constant at 300 W, berthollide type of iron oxide films was deposited at Ts of 220–270 °C. The optical spectra of glow discharge reveal the existence of a large amount of ionic species such as H+ and OH+ in the space between targets. They seem to be effective for the formation of the berthollide type of iron oxide.
Pulsed power switching using saturable core inductors
Authors: Stockton M. , Neau E. L. , VanDevender J. P.
Published: February 2003

We have investigated some of the problems involved in switching fast, high-power pulses using single-turn saturable core inductors constructed of Metglas 2605SC. These include hold-off voltages and times, output pulse risetimes, B-H curves of the material under fast pulse conditions, and propagation of the saturation field through the core. Experiments were done at Sandia on the RAMSES I accelerator which uses a 200-kV Marx generator to provide a 200-ns pulse to a 1 Ω coaxial water transmission line.
Calculation of magnetic domain wall bowing and eddy current losses in an infinite sheet of bar-like domains
Authors: Del Vecchio R. M.
Published: February 2003

An analytic solution has been obtained for the magnetic field distribution and eddy current losses associated with an infinite array of regularly spaced 180° domain walls which are allowed to bow during their motion. Wall motion was constrained to satisfy a sinusoidal total flux boundary condition. The field solution was solved self-consistently with the domain wall equation of motion. Calculated losses were always lowered relative to the plane wall case. Difficulties were encountered in the numerical iteration scheme as the degree of bowing increased. Using an approximation for the high bowing case, a physical instability occurred before bowing became too severe.
Abstract: Cubic anisotropy measurements of ion-implanted layers on magnetic bubble garnets
Authors: Maartense I. , Searle C. W.
Published: February 2003

Effective cubic anisotropy fields of 100 keV Ne+ implanted layers on (111) garnet films can be directly measured by monitoring the in-plane ac susceptibility or loss while a dc in-plane field is varied along the projection of a cubic hard axis. The effective field is defined by the onset of irreversibility in the in-plane rotation of the magnetization. In the presence of various perpendicular bias fields, the effective field boundary can be plotted for magnetization directions from ∼10° to 90° out-of-plane, with the 90° orientation defining the uniaxial anisotropy field, as reported previously. The effective fields have been measured as a function of temperature for (YSmLuCa)3(FeGe)5O12 films subjected to several implantation dosages and annealing temperatures. The measurement technique is described in an accompanying paper. In a uniform layer, the in-plane effective cubic field should vary as sin ϑM cos2 ϑM, with the magnetization angle given approximately by sin ϑM = Hb/ Hku, where Hb is the applied bias field and Hku is the effective in-plane uniaxial anisotropy field of the layer. The effective-field boundary of a lightly implanted film (8×1013 ions/cm2) behaves generally as expected. The maximum in-plane cubic anisotropy occurs near ϑM = 35°, the direction of a 〈100〉 cubic hard axis and shows relatively little change with annealing, whereas the uniaxial anisotropy field drops rapidly with annealing. The temperature dependence of the uniaxial effective field clearly reflects the variation of the cubic anisotropy. With an implantation dosage of 2×1014/cm2, the cubic hard axes are defined only after annealing. In the as-implanted film, the out-of-plane hard axis directions cannot be located. A heavily implanted film (6×1014 ions/cm2) shows completely anomalous behavior: The cubic hard-axis maximum has totally disappeared, as if the out-of-plane structure has been randomized, although the three-fold symmetry of the in-plane hard directions remains well defined. Annealing has little effect on this behavior, except that after a 600 °C anneal the cubic anisotropy shows a large decrease and the in-plane directions are split off from the original 〈211〉 directions. Similarly, the uniaxial anisotropy gives evidence of a breakup of the layer into regions as described earlier. Long-range diffusion of neon atoms is presumed to be responsible for this behavior. We plan to present a more detailed account of this work at a later date. 1 I. Maartense, C. W. Searle, and H. A. Washburn, J. Appl. Phys. 52, 2361 (1981). 2 I. Maartense, J. Appl. Phys. 53, xxxx (1982).
Series evidence for a fluctuation-induced first-order transition in a bcc Ising model with competing interactions
Authors: Velgakis M. J. , Ferer M.
Published: February 2003

Landau theory predicts that the bcc, spin 1/2 Ising model with nearest-neighbor ferromagnetic interaction K1 and next-nearest-neighbor antiferromagnetic interaction K2 has a continuous transition with a two component order-parameter (n = 2) between the paramagnetic and the type two antiferromagnetic phases for K1/K2<3/2. For K1/K2≲3/2, we show that this system has a transition temperature, determined from matching high- and low-temperature free-energy series, which is well above the temperature at which the susceptibility diverges. This supports the conclusion, also drawn from renormalization group and Monte-Carlo calculations, that the transition is driven first-order by fluctuations.
Transport in hydrogenated amorphous silicon p-i-n solar cells
Authors: Crandall Richard S.
Published: February 2003

Measurements of the voltage dependence of the photocurrent in hydrogenated amorphous silicon p-i-n solar cells are presented along with a simple physical model of the transport. For the conditions of weakly absorbed light, the photocurrent-voltage curve can be completely specified by the light intensity and electron and hole drift lengths. Furthermore, the carrier with the longer drift length determines the solar cell current-voltage curve.
The superconducting transition temperature as a probe for ion-beam induced precipitate dissolution
Authors: Hofmann A. , Ziemann P.
Published: February 2003

The system Indium+Mn precipitates has been irradiated with 275 keV Ar+ ions at low temperatures (T<15 K). By using the depression of the superconducting transition temperature Tc as a probe for dissolved Mn atoms, it could be demonstrated that an ion-beam induced precipitate dissolution occurs even at small Ar fluences (<1015 cm−2). The maximum amount of Mn atoms which can be forced into metastable solution by irradiation depends on the preparation conditions of the samples. For high Ar fluences the dissolution effect is overlapped by the influence of the simultaneously produced radiation damage on Tc .
Nucleation of thin film Pt2-Si
Authors: Aly El-Saied M. , Stark J. P.
Published: February 2003

Thin platinum films are rf sputtered onto a clean, cold, n type (4-10) ohm-cm and (100) oriented single crystal silicon substrates. Thin platinum films in the equivalent thickness range 10Å⩽t⩽35Å produce amorphous semiconducting surface regions as shown by transmission electron diffraction and Auger electron spectroscopy and sheet resistance measurements. The present experiments indicate that the stability of this layer is dependent on the thickness of the deposited platinum layer, the glass is stable for thicknesses equal or less than 35 Å and unstable with respect to the nucleation of α-Pt2Si for greater thicknesses at room temperature with no applied field during deposition. Polycrystalline α-Pt2Si diffraction rings are found at a minimum deposited metal thickness of 40 Å. In studying the reaction path in the same system while applying a dc current parallel to the thin film during sputtering, our measurements show that the applied field stimulates the solid state transition to the crystalline (α-Pt2Si). The silicide α-Pt2Si is formed consistently at platinum layer thicknesses of about 25 Å as compared to 40 Å with no applied dc field.
A size effect on the mobility of slow electrons in microcrystalline AgBr
Authors: Hirano Akihiro , Masumi Taizo , Takada Shunji
Published: February 2003

Measurements of galvanomagnetic effects on AgBr microcrystals dispersed in insulating gelatin layers (photographic emulsion grains) were performed at 4.2–40 K as a function of the grain size (50 nm–1.3 μm) using a fast pulse technique with blocking electrodes. The value of the mobility of slow electrons was determined to be about 103 cm2/V s for 400-nm cubic crystals at 4.2 K, much smaller than that in pure bulk crystals, and decreases with decreasing size of the microcrystals. Additional results obtained from various specimens eliminate the possibility that this size effect is due to differences of impurity concentration. Possible mechanisms of this size effect on the mobility of slow electrons are discussed from the point of view of surface effects.
Application of the Onsager theory to thermally stimulated currents
Authors: Plans J. , Zieliński M , Świderski T. , Kryszewski M. , Ulański J.
Published: February 2003

As it has been shown recently, the thermally stimulated current (TSC) technique may be successfully applied to investigate the effect of charged centers on electrical phenomena in organic solids. The Onsager theory of dissociation is applied to obtain a theoretical description of the field-dependent TSC spectrum, which appears as an effect of charged centers. Appearance of a TSC peak is considered in two cases: (a) due to ionization of donor or acceptor centers, and (b) due to thermal release of photogenerated and frozen at low temperature carrier pairs. It is shown that in the first case the maximum temperature of the TSC peak depends on the square root of the applied electric field. This dependence is linear in the intermediate range of fields (this is the case described by a simple Poole-Frenkel formalism), and tends to saturation for both low and high fields. In the case of photogenerated carrier pairs, for the range of trap parameters commonly accepted for amorphous solids, the TSC peak position is field-independent. The effect of charged centers on the activation energy found from the initial rise of TSC current is also discussed. The theoretical predictions are illustrated by the results of TSC experiments performed for poly/N-vinylcarbazole/ and its mixtures with polycarbonate.
An alternate way of looking at maser noise
Authors: van der Ziel A.
Published: February 2003

The earlier theory of maser noise was based on Nyquist’s expression for thermal noise. We present here an alternate approach based on the Callen-Welton expression for thermal noise. It is shown that available noise power measurements in high-gain masers cannot discriminate between the two approaches. The noise figure and the system noise temperature are calculated for the two points of view.
On recent studies about sources of acoustic emission in technical superconductors
Authors: Pasztor G. , Schmidt C.
Published: February 2003

Discrepancies exist in the literature about the interpretation of acoustic emission (AE) experiments with technical superconductors. At least three different origins of AE in short sample experiments have been identified: (1) shear transformation during mechanical strain, (2) friction by wire motion, and (3) flux motion during current or field sweep. This last origin, however, has been disputed recently. The paper discusses the published results and shows that flux motion is clearly an origin of AE. Further data are also presented to support this conclusion.
Analytic solutions to superconductor-insulator-superconductor quantum mixer theory
Authors: Smith A. D. , Richards P. L.
Published: February 2003

Three-port quantum mixer theory for superconductor-insulator-superconductor tunnel junctions is solved for several simple cases of practical interest. Closed form solutions are derived for the conversion gain in the low local oscillator power limit, and also the general conditions for zero and infinite gain. These results are useful in understanding more general computer calculations of predicted performance. Practical limits to gain and dynamic range are analyzed both for series arrays and single junctions.
Temperature coefficients of the open-circuit voltage of p-n junction solar cells
Authors: Wu Ching-Yuan , Chen Jenn-Fang
Published: February 2003

An analytic expression for the tempoerature coefficient of the open-circuit voltage has been derived in general, which may be applied to different kinds of p-n junction solar cells. Based on the dominance of the saturation dark current density, the simplified expression have also been developed and justified by experimental measurements. It has been shown that the negative temperature coefficient of the open-circuit voltage is decreased with the increasing light level and the interaction between minority carriers and the high-low junction. Hence, the temperature coefficient of the open circuit voltage is good measure for providing a guide to test the effectivness of a high-low junction in a back-surface-field (BSF) solar cell. Moreover, based on the measured temperature coefficient of the open-circuit voltage from the BSF solar cells fabricated on thin epitaxial substrate, a new method for measuring the effective energy-gap narrowing in the highly doped emitter has been proposed and studied. It has shown that the effective energy-gap narrowing measured is in good agreement with the eempirical expression proposed by Slotboom.
Diffusion coefficient of 195Au in the liquid Au0.81Si0.19 alloy
Authors: Bruson A. , Gerl M.
Published: February 2003

Using the shear cell technique the diffusion coefficient DAu of 195Au in liquid Au0.81Si0.19 has been measured in the temperature range 663–1773 K. The experimental values are compared with an estimation of D made in the framework of the Enskog approximation. The relative enhancement of DAu below 1100 K is attributed to short-range order effects in the liquid.
Grain-boundary diffusion of Sn in Pb
Authors: Kim K. K. , Gupta D. , Ho P. S.
Published: February 2003

Grain-boundary diffusivities of a Sn119 radioactive tracer have been measured in polycrystalline Pb specimens in the temperature range 70–200 °C. The combined diffusion parameter δDb is expressed by the Arrhenius relation δDb = 7.3×10−9 exp(−0.41±0.02 eV/kT) (cm3/sec). The Sn impurity diffusivities are larger than Pb self-diffusivities in the grain boundaries, which has been confirmed by codiffusion measurements of the two species. The lattice diffusivities reported in the literature for the Sn and Pb tracers also show a similar trend. In both situations the effect appears to be related to the physical characteristics of the two diffusing species.
Effect of top electrode deposition rate on tunnel junction characteristics
Authors: Ocampo M. A. , Heiras J. L. , Will T. A.
Published: February 2003

We have found that the rate of deposition of Pb when fabricating thin film Al-oxide-Pb tunnel junctions has a small but reproducible effect on tunneling characteristics. Zero bias junction conductance is typically increased by a factor of 2 or more when the top electrode deposition rate is raised from 10 to 100 Å/s. This change is associated principally with a reduction of the effective barrier height at the Pb interface.
Reducing noise in photoamplifier circuits with low noise artificial resistors
Authors: Forward Robert L.
Published: February 2003

A standard passive dissipative resistor in a photodiode circuit is replaced by a low-noise active artificial resistor. A room-temperature artificial resistor acts on a signal current from the photodiode in the same manner as the resistor, but the self-generated noise of the artificial resistor is that of a resistor at cryogenic temperatures. Because of its low noise, the artificial resistor can produce an improvement in the signal to noise of the photodetector system with minimum effect on the bandwidth. Analysis shows that the system signal to noise can approach that of the photodiode itself. An experiment designed to demonstrate the effect produced an improvement of 2.8 dB in a photoamplifier circuit.
Parity nonconservation experiments in radio-frequency cavities
Authors: Robiscoe R. T.
Published: February 2003

Several experiments proposed to detect parity non-conserving effects in atomic hydrogen study radio-frequency transitions induced in a resonance cavity. We point out that characteristics of the transition amplitudes, such as the resonance line shape and possible interference terms, can be affected substantially by the spatial variation of the fields in the cavity.
Coercivity mechanisms in Fe-Cr-Co magnet alloys
Authors: Jin S. , Brasen D. , Mahajan S.
Published: February 2003

The mechanism of coercivity in Fe-Cr-Co permanent magnet alloys has been investigated. An attempt has been made to separate the contribution to Hc of various mechanisms and microstructural variables by comparing spherical versus elongated particle morphology and aligned versus random distribution with varying particle diameters. It is shown that the particle morphology (shape anisotropy) is the dominant factor in determining the coercivity of the alloy rather than the particle size. Approximately 75% of the total coercivity is attributed to the shape anisotropy in the case of deformation-aged anisotropic Fe-33.7Cr-11.6Co alloy, and ∼55% in the case of isotropic alloy.
Amplification of frequency upshifted radiation by cold relativistic guided electron beams
Authors: Fruchtman A. , Friedland L.
Published: February 2003

An amplifier on cold, relativistic, guided electron beams is considered. The problem is reduced to a set of first-order, linear, ordinary differential equations. The dispersion relation governing the stability of the system is derived and its solutions are studied numerically. The results of the calculations show that in the submillimeter regime, the spatial growth rates in the system may be comparable to those predicted for Raman-free electron lasers.
The coherent and incoherent pumping of a gamma ray laser with intense optical radiation
Authors: Collins C. B. , Lee F. W. , Shemwell D. M. , DePaola B. D. , Olariu S. , Popescu I. Iovitzu
Published: February 2003

Both the coherent and incoherent pumping with intense optical radiation of electromagnetic transitions in nuclei were modeled in this work. In the first case the anti-Stokes upconversion of conventional laser radiation was shown to be a potentially viable means for pumping a γ-ray laser. With the most favorable possible arrangement of nuclear energy levels, the threshold for stimulated output at 10 keV might be reached at a few tens of Joules for isomeric media with lifetimes of the order of tens of years. Whether such an arrangement of excited states actually exists will require additional experimentation. In the case of the incoherent pumping of nuclear material, the resonant excitation of energetic states of nuclei by x radiation from laser plasmas or exploding wires was modeled with results similar to those for the case of coherent pumping. Thresholds for stimulated output could be as low as a few hundred Joules into the primary laser pulse producing the x-ray flash. Again the possibilities were found to be critically dependent upon unknown parameters, particularly upon the efficiency for the conversion of input energy into x rays. The overall possibilities for the excitation of a γ-ray laser with optical pumping were concluded to be reasonably encouraging and the need for additional spectroscopic data was clearly defined.
Silicides of ruthenium and osmium: Thin film reactions, diffusion, nucleation, and stability
Authors: Petersson C. S. , Baglin J. E. E. , Dempsey J. J. , d’Heurle F. M. , La Placa S. J.
Published: February 2003

The reactions of ruthenium and osmium thin films with their silicon substrates lead to the formation of the following phases: the isomorphous Ru2Si3 and Os2Si3, and OsSi2. Ru2Si3 forms by a diffusion controlled mechanism from approximately 450 to 525 °C; the activation energy is 1.8 eV. Os2Si3 grows by the same process and with the same activation energy as Ru2Si3, but at slightly higher temperatures (for equivalent rates). OsSi2 grows at about 750 °C by a nucleation controlled mechanism. With an alloy of ruthenium containing 33 at.% rhodium, one obtains RuSi, which forms by a diffusion controlled mechanism with an activation energy of 2.4 eV from 400 to 475 °C, and Ru2Si3. In the case of the ruthenium alloy, the formation of Ru2Si3 is not diffusion controlled; the controlling process is akin to a nucleation mechanism. Ru2Si3 and Os2Si3 form by silicon motion. This is also true of OsSi2, but the high formation temperature results in some metal motion also during the formation of that phase. The diffusion processes are discussed on the basis of simple ideas about diffusion in intermetallic compounds. The nucleation processes are shown to occur for the phases OsSi2 and Ru2Si3 (with rhodium), as in other nucleated phases, when the enthalpy contribution to the driving force is close to zero. The observation leads one to anticipate that for most (perhaps all) platinum-like metals the silicides with the highest silicon content should be unstable at low temperatures.