bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic effects in Cr-Mn alloy single crystals containing 0.05 and 0.1 at. % Mn
Authors: Smit P. , Alberts H. L.
Published: July 2002

Measurements of the thermal expansion, ultrasonic wave velocity, and ultrasonic attenuation are reported for very dilute Cr-Mn alloy single crystals. The threshold Mn concentration needed to drive the first-order antiferromagnetic transition in Cr to second order is found to be smaller than 0.05 at. % Mn. This result is discussed in terms of recent theories. The critical behavior of the sound velocity and ultrasonic attenuation of Cr+0.1 at. % Mn is well described by a power law near TN but not for the thermal expansion.
Energetics of bcc-fcc lattice in Fe-Co-Ni compounds (abstract)
Authors: Moroni E. G. , Jarlborg T.
Published: July 2002

The linear muffin tin orbital method is applied to compute the energy properties of several ordered binary Fe-Ni, Fe-Co, and ternary Fe-Ni-Co compounds near the bcc-fcc transition, from first principles. The calculations use the local spin density and the Perdew–Wang gradient corrected approximation to treat exchange and correlation. We address the importance of the gradient corrected approximation for the calculation of the fcc-bcc energetics for these 3D Fe-based systems near the Fe rich region. By adding Co to the Fe-Ni alloy it is possible to reduce the volume expansion accompanying the fcc to bcc transition. To study these effects we have considered the energetics in several ordered ternary systems with a fcc and bcc lattice. When increasing the e/a ratio from 8.5 (Fe3Ni) to 8.75 (NiFe2Co) and to 9 (Co or FeNi) one finds increased stability of the FM fcc phase compared to the bcc phase. We observe also that by increasing the e/a ratio the magnetic moment of the fcc lattice becomes more stable; this induces an augmentation of the spontaneous magnetostriction and a decrease of the volume change accompanying the fcc-bcc transition. A comparison of the different computed magnetic and ground-state properties with experimental data is provided.
Giant magnetoresistance in Fe0.95Cr0.05/Cr multilayer films
Authors: Chen L. H. , Jin S. , Tiefel T. H. , Van Dover R. B. , Gyorgy E. M. , Fleming R. M.
Published: July 2002

We have studied the effect of Cr alloying addition to the Fe layers on the magnetoresistance behavior of the Fe/Cr superlattice films [Fe(15 Å)/Cr(8–20 Å)]30. The alloyed superlattice films Fe0.95Cr0.05/Cr exhibited significantly improved giant magnetoresistance effect (ΔR/R∼12.2% at 4.2 K), as compared to the unalloyed Fe/Cr multilayer films (ΔR/R∼6.9%). The M–H loops indicate that antiferromagnetic coupling exists in both films, which is believed to be responsible for the observed giant magnetoresistance. The improvement in ΔR/R in the Cr-alloyed superlattice films is attributed to the stronger spin-dependent scattering of conduction electrons caused by the introduction of Cr impurities in the ferromagnetic layers. The alloyed superlattice films also exhibit reduced coercivity and saturation magnetization.
Thermal stability of NdGd/FeCo multilayers
Authors: Yu X. Y. , Suganuma T. , Watabe H. , Iwata S. , Tsunashima S. , Uchiyama S.
Published: July 2002

Thermal stability has been investigated for the structure and the perpendicular anisotropy Ku of Nd44Gd56/Fe89Co11 multilayer films with the bilayer period of 1 nm, where Ku becomes the maximum. From the results of isothermal annealing at temperature Ta, it has been found that the saturation magnetization Ms scarcely changes up to Ta=400 °C, while Ku is almost constant up to Ta=200 °C but decreases rather quickly for Ta above 200 °C. The decrease in Ku for Ta≳260 °C is accompanied by the decrease in the peak intensity of low angle x-ray diffraction, namely by the deterioration of the layered structure.
Electronic structure and spin-density distribution in Y2Fe17 (abstract)
Authors: Huang Ming-Zhu , Ching W. Y.
Published: July 2002

We have calculated the spin-polarized band structure of the Y2Fe17 compound in the rhombohedral structure using the first-principles self-consistent orthogonalized linear combination of atomic orbitals method in the local spin-density approximation. Using a real space integration scheme, we have obtained the site-decomposed magnetic moments as follows: −0.28μB on Y-6(c), 2.54μB on Fe-6(c), 2.08μB on Fe-9(d), 2.28μB on Fe-18(f), and 2.10 on Fe-18(h). Similar values are obtained when the more traditional Mulliken scheme is used. The calculated spin magnetic moments are in good agreement with Mössbauer data but are somewhat larger than these obtained by Coehoorn using the linear muffin-tin orbitals (LMTO) method.1 The calculated density of states are similar to that of Coehoorn’s. In order to have a better insight on the magnetic structure of Y2Fe17, the real space spin density distributions are plotted and it is shown that the negative spin density on the Y site extends to a fairly large region. We will extend our calculation to Nd2Fe17 crystal and to cases in which the Fe atoms are selectively substituted by Al, Si, and Ga, as well as the effect of the N addition. Previous OLCAO calculations2,3 on Nd2Fe17N systems were nonself-consistent and therefore less reliable.
Effects of pole flux distribution in a homopolar linear synchronous machine
Authors: Balchin M. J. , Eastham J. F. , Coles P. C.
Published: July 2002

Linear forms of synchronous electrical machine are at present being considered as the propulsion means in high-speed, magnetically levitated (Maglev) ground transportation systems. A homopolar form of machine is considered in which the primary member, which carries both ac and dc windings, is supported on the vehicle. Test results and theoretical predictions are presented for a design of machine intended for driving a 100 passenger vehicle at a top speed of 400 km/h. The layout of the dc magnetic circuit is examined to locate the best position for the dc winding from the point of view of minimum core weight. Measurements of flux build-up under the machine at different operating speeds are given for two types of secondary pole: solid and laminated. The solid pole results, which are confirmed theoretically, show that this form of construction is impractical for high-speed drives. Measured motoring characteristics are presented for a short length of machine which simulates conditions at the leading and trailing ends of the full-sized machine. Combination of the results with those from a cylindrical version of the machine make it possible to infer the performance of the full-sized traction machine. This gives 0.8 pf and 0.9 efficiency at 300 km/h, which is much better than the reported performance of a comparable linear induction motor (0.52 pf and 0.82 efficiency). It is therefore concluded that in any projected high-speed Maglev systems, a linear synchronous machine should be the first choice as the propulsion means.
Barkhausen transitions in single layer and bilayer thin permalloy films
Authors: Farrell G. P. , Hill E. W.
Published: July 2002

The low coercivity of uniaxial thin nickel-iron multilayer films, prepared according to E. W. Hill, J. P. Li, and J. K. Birtwistle [J. Appl. Phys. 69, 4526 (1991)], makes them attractive for magnetic sensor applications. Barkhausen jumps, causing noise, limit the performance of such sensors. It has been reported [R. F. Soohoo, J. Appl. Phys. 69, 5871 (1991)] that, for any given sample under identical initial conditions, these Barkhausen jumps are deterministic rather than noisy in nature. This is consistent with the fact that the defect structure of a given sample is deterministic. This study compares power spectra and coercivity distributions from Barkhausen pulses obtained by applying varying alternating fields to thin permalloy films. The effect of an orthogonal bias field is also examined. The samples under examination consist of both single layer and bilayer films, produced as continuous layers by vacuum evaporation and ion milled into 40 mm diameter discs. The permalloy is of 80/20 composition and has a total thickness of 100 nm. The bilayer films have a nonmagnetic tantalum interlayer of thickness 5 nm. The rate of change of the applied field was varied between 2918.4 and 11.4 Oe/s, at an initial amplitude of 90 Oe. The results show that the Barkhausen pulses have a strong deterministic trend, but also contain a smaller nondeterministic component. As the frequency and amplitude are decreased, this random effect becomes larger. As might be expected when an orthogonal bias field is applied to the samples, the amplitudes of the pulses are decreased. The films also exhibit a corresponding reduction in coercivity.
Magnetic shielding from alternating magnetic field by NbTi/Nb/Cu superconducting multilayer composite cylinder
Authors: Otsuka Hiroaki , Itoh Ikuo
Published: July 2002

Magnetic shielding from alternating magnetic field by a NbTi/Nb/Cu superconducting multilayer composite cylinder was investigated at liquid-helium temperatures. The specimen employed in this study was a slender seamless cylinder about 15 mm in diameter and having an aspect ratio of 6. The frequency of the alternating magnetic field was in the range of 40–500 Hz, and the maximum amplitude was 1000 G rms at 40 and 50 Hz owing to the capacity of the ac generator. The magnetic shielding efficiency of this cylinder, defined as the ratio of the magnetic field strength with and without the cylinder, was found to be of the order of 10−4. It was also found that the magnetic shielding effect depends upon the frequency investigated in this study. These shielding effects were mainly due to the shielding current originating from the superconductivity, which turned out to give superior shielding effect than that of a Cu cylinder.
Interpretation of magnetic force microscopic images (abstract)
Authors: Kikukawa Atsushi , Awano Hiroyuki , Hosaka Sumio , Honda Yukio , Imura Ryo
Published: July 2002

The authors have developed a magnetic force microscope (MFM) which works in a vacuum. By detecting the cantilever resonance frequency directly, it takes full advantage of the improved cantilever resonance quality, lowered noise level, and improved resolution, due to reduction of the air resistance that the cantilever suffers. Detailed observations on various magnetic recording media were made employing this instrument. An obstacle in interpreting the MFM images is that they contain both the magnetic image and the surface corrugation (directly related to the atomic force) since the cantilever detects both magnetic and atomic force at the same time. One solution for this is to compare the images of the same region observed at different tip to sample spacings because the contrast due to the magnetic force decreases as the tip to sample spacing reduces. We confirmed that this decrement in magnetic contrast occurs due to the effects of the atomic force by predicting the MFM image theoretically, utilizing a model which has taken in the effect of the atomic force estimated by an experiment. An example among the analyses on various magnetic recording media is the analysis of the magneto-optical (MO) disks which have undergone the heat cycle test. The MFM revealed the existence of irregular shaped domains, which were not observed with the conventional methods (Kerr effect microscopes) in the badly damaged regions. This information was helpful in detecting the deterioration that occurred to the magnetic layer. The authors are convinced that MFM would become a powerful and convenient tool for analyzing magnetic recording media.
Giant magnetoresistance and induced exchange anisotropy in mechanically alloyed Co30Ag70
Authors: Ounadjela K. , Herr A. , Poinsot R. , Coey J. M. D. , Fagan A. , Staddon C. R. , Daniel D. , Gregg J. F. , Thompson S. M. , O’Grady K. , Grieves S.
Published: July 2002

Giant magnetoresistance of 7.7% at 5 K is observed in bulk mechanically alloyed Co30Ag70. Our recently defined δ(Δρ/ρ) technique used to determine the predominant interactions within the system indicated that negative interactions dominate between the particles. Exchange anisotropy and metastable magnetization processes characterized by large Barkhausen jumps are observed at low temperatures on a small volume of the sample.
Magnetization and ferromagnetic resonance studies on amorphous films of Fe2O3-Bi2O3-Li2O
Authors: Chen J. , Cheney S. , Srinivasan G.
Published: July 2002

This report is on magnetic properties of samples of 0.5 Fe2O3-(0.5−x)Bi2O3-xLi2O (x=0.1–0.4) prepared in oxygen atmospheres by rf sputtering techniques. The films develop a spontaneous moment M only when annealed in air at temperatures Ta≥675 K. The room-temperature M vs Ta data show a maximum in M for Ta=775–875 K even though x-ray diffraction data do not show the precipitation of any crystalline ferromagnetic or ferrimagnetic phases. The spontaneous moment could be attributed to the presence of ordered clusters in the amorphous film. The magnetization is found to be dependent on the concentration of nonmagnetic Li2O: M increases with increase in x. An in-plane anisotropy in the films is evident from ferromagnetic resonance studies (FMR) at x-band frequencies. The anisotropy field increases with increasing x. The room-temperature in-plane FMR linewidth decreases with increasing x.
Origin of high coercive force in rare-earth–transmission-metal thin film
Authors: Callaby D. Roy , Lorentz Robert D. , Yatsuya Shigeki
Published: July 2002

A sequence of rare-earth/transmission-metal (RE-TM) films have been sputter coated and an increase in the coercive force of over six times has been measured for a change in argon pressure from 2 to 10 mTorr. By using small-angle x-ray scattering measurements, a strong correlation has been found between the number or volume of voids and the coercive force in sputtered coatings of RE-TM materials, especially Tb-Fe-Co. A transmission electron microscopy technique has shown that the majority of these voids accumulate in the observed gaps between columns.
Recording characteristics of Kr-sputtered Tb/FeCo multilayer magneto-optical disks
Authors: Karube Hiro , Matsumura Kunihiko , Nakada Masafumi , Okada Osamu
Published: July 2002

Recording magnetic-field sensitivity and readout stability for Tb/FeCo multilayer magneto-optical (MO) disks, made by sputtering with Kr and Ar gas, were studied. The 100 Oe recording magnetic-field sensitivity for Kr disks was obtained. The readout stability for Kr disk is superior to that for Ar disk. It seems that high readout stability for Kr disks is caused by the large wall coercivity and the large ratio of wall coercivity to nucleation coercivity.
LiNiO2: Quantum liquid or concentrated spin glass?
Authors: Rosenberg M. , Stelmaszyk P. , Klein V. , Kemmler-Sack S. , Filoti G.
Published: July 2002

From the magnetic and Mössbauer spectroscopy study of LiNi1−xFexO2 with x=0, 0.01, 0.05, and 0.10 evidence for strong ferromagnetic correlations and spin freezing at low temperatures was found, reminding many characteristic features of spin glass behavior in variance with models describing the ground state of LiNiO2 as a quantum liquid.
A model for the Barkhausen noise power as a function of applied field and stress (abstract)
Authors: Sablik M. J.
Published: July 2002

The model of Alessandro et al.1 is used to derive the Barkhausen noise power in terms of permeability μ, which is really the irreversible permeability, since the Barkhausen noise is produced by the irreversible motion of domain walls. From the model expression, it is shown that the peak in the Barkhausen noise power as a function of applied field coincides with the peak in the irreversible permeability. From the magnetomechanical hysteresis model,2 an expression for the irreversible permeability is found and shown to peak at a higher magnetic field than the total permeability. Using the magnetomechanical hysteresis model and the derived expression from the Alessandro model, the Barkhausen noise power peak value is computed and found to increase almost linearly from negative (compressive) to positive (tensile) stress, with slightly decreased slope at high positive and negative values of stress, in agreement with trends in experimental observations.3,4 Dependence of the Barkhausen noise power on Ḣ, the time rate of increase in the linearly increasing ramp function used for H, is also investigated and found to increase moderately sharply for intermediate ranges of Ḣ and to saturate at larger Ḣ.
Magneto-optical properties of Al and In-substituted CeYIG epitaxial films grown by sputtering (abstract)
Authors: Gomi M. , Abe M.
Published: July 2002

Cerium substitution to iron garnet strongly enhances magneto-optical (MO) effect in the visible region around hν=1.4 and 3.1 eV. We have previously proposed a Ce3+(4f)-Fe3+ (tet.) charge transfer model as an electronic transition inducing the strong MO effect. In this study, we have measured Faraday spectra of CeYIG films in which Fe ions were diluted with Al or In ions. These ions, respectively, are known to preferentially occupy tetrahedral and octrahedral iron sites in the garnet structure, giving us some information on the role of Fe3+ in the MO enhancement. The Y2Ce1Fe5−xMxO12 (M=Al, In; x=0–5) films were epitaxially grown in situ on (111)-oriented Gd3Ga5O12 (GGG) single crystal substrates by conventional rf diode sputtering. With the amounts of substitutions increasing, Faraday rotation and ellipticity of the films at hν=1.4 eV reduced at nearly the same rates for both ions of Al and In. We found from the analysis using molecular field theory that these reductions are in proportion to the magnetic moment of the tetrahedral iron sublattice. This indicates that the tetrahedral Fe3+ contributes to the electronic transition at 1.4 eV, supporting the proposed charge transfer model.
Enhancement of the magneto-optical quality of YIG films in a structure containing a thin metal film (abstract)
Authors: Boardman A. D. , Voronko A. I. , Vetoshko P. M. , Volkovoy V. B. , Toporov A. Yu.
Published: July 2002

TE/TM polarized light reflection from a multilayer structure containing a magneto-optic (MO) and a metal film is investigated theoretically and experimentally. A metal film is used whose thickness is chosen to support long-range surface polaritons (SP). This is to use their sharp resonance for tuning the whole structure. It was shown that if the MO layer is placed in a multilayer structure consisting of a thin metal film that supports a long-range surface polariton, the resonance couples to the off-diagonal element of the YIG-film dielectric tensor. This means that this process exhibits a nonreciprocal property, as well as a Faraday rotation in the MO film. A combination of these two effects enhances the value of the magneto-optic quality (Faraday rotation divided by the losses incurred by the light) and the nonreciprocity of the light reflection from the structure. Theoretical and experimental optimization of these effects at a wavelength equal to 0.5 μm has been carried out for thin monodomain single crystal YIG films, saturated by a magnetic field of the order 1 Oe. It has enabled the design of a high frequency operation circulator to be developed. These results will be reported in this paper.
Magnetic properties of amorphous Cr–Fe alloys prepared by thermal evaporation and mechanical milling
Authors: Xia S. K. , Baggio-Saitovitch E. , Larica C. , Sarkissian B. V. B. , Cunha S. F. , Tholence J. L.
Published: July 2002

Cr100−xFex amorphous alloys have been prepared through two different routes: thermal coevaporation and mechanical milling. The Mössbauer measurements on the materials show that the amorphization leads to a dramatic reduction of Fe magnetic moment as compared to the crystalline bulk samples. On the other hand, the magnetic ac susceptibility and the magnetization measurements indicate a dominant ferromagnetic intracluster interaction with a competing intercluster interaction. Such a competition could give rise to a spin-glass-like behavior.
Four-spin exchange in Bi2CuO4 (abstract)
Authors: Petrakovskii G. , Val’kov V. , Sablina K. , Fedoseev B. , Furrer A. , Roessli B. , Fischer P.
Published: July 2002

Magnetic properties of Bi2CuO4 single crystals are of interest owing to their relationship to the high-Tc superconductor problem. Earlier we carried out the magnetic and neutron scattering investigations on high quality large single crystals. The Bi2CuO4 crystal belongs to the space group P4/ncc and the magnetic group is the collinear plane antiferromagnet with a Neel temperature of 45.8 K. The three-dimensional character of the antiferromagnetic ordering is reflected by the value of the critical magnetization exponent 0.352. The sublattice magnetization depends very little on temperature up to about 15 K. The spin-wave spectrum contains two branches with energy gaps of 2.1 and 3.4 meV. The theoretical interpretation of the experimental data shows the necessity of introducing the tensor four-site exchange in the S=1/2 spin Hamiltonian with the tetragonal anisotropic bilinear exchange. This provides the gap characteristics of the acoustic branch of spin waves and the correct temperature dependence of the sublattice magnetization. This result shows the importance of the four-site exchange for the formation of Bi2CuO4 magnetic properties. From the similarity of magnetic subsystems, Bi2CuO4, and high-Tc superconductors it is suggested that the four-site exchange is responsible for magnetic ordering of the square spin S=1/2 lattice. We also suggest a thermodynamic theory of the temperature dependence of magnetic properties of Bi2CuO4.
The superconducting transition temperature of layered S
i −J
ij−S
j superconductors (abstract)
Authors: Cherenkov Valery A.
Published: July 2002

The Si−Jij−Sj multilayered superconductor structures containing different superconductors (Sij) with an isolated layer are investigated. There is a theoretical model of a tunneling Hamiltonian for the defect Josephson lattice. There are the Ising magnetic and resonance valence band models between the layers. The ‘‘saturation’’ of Tc(N) is determined. The analogy has been present for Tc(N) in the representation of a plane (high-Tc) structure and the Kosterlitz–Thouless transition.
Magnetism and superconductivity in heavy-fermion compounds (abstract)
Authors: Goltsev A. V.
Published: July 2002

The mean-field theory based on an extended high degeneracy model is derived to describe an interplay between the Kondo effect, magnetism, and superconductivity in heavy-fermion compounds. The competition and coexistence of the Kondo effect and ferro- or antiferromagnetic orders of localized moments are considered depending on the local exchange interaction. It is shown that an antiferromagnetic order arising in the coherent Kondo state can have an anomalously small antiferromagnetic moment per f atom (∼0.01μB) and stimulate superconductivity with an anisotropic superconducting gap that vanishes along lines on the Fermi surface. We apply the theory for studying thermodynamic peculiarities of the antiferromagnetic and superconducting transitions, and the microscopic structure of the antiferromagnetic and superconducting states in URu2Si2 and UPt3. The theoretical estimation (0.035μB) of the antiferromagnetic moments of U atoms in URu2Si2 is in good agreement with the experimental result (0.04μB). We also study the microscopic origin of the double superconducting transition in UPt3. The superconducting gap in the successive superconducting states is strongly anisotropic. In the former state the gap vanishes on part of the Fermi surface, while in the following state the gap vanishes on lines only.
Magnetic properties of an isolated ferromagnetic bond embedded in Heisenberg antiferromagnets
Authors: Ting S. T. , Haas S. , Crow J. E.
Published: July 2002

The magnetic properties of an isolated ferromagnetic bond of coupling constant K embedded in a layered spin-1/2 Heisenberg antiferromagnet with interplane coupling strength J⊥=αJ∥ (0≤α≤1.0) have been studied using linear-spin-wave (LSW) theory. In the pure lattice, the sublattice magnetization 〈Szi〉 is 0.304 at α=0 and saturates to 0.422 at α=1.0. The spin correlations 〈SxiSxj〉 decrease with increasing α within the plane and increase along the interplane direction. The introduction of an isolated ferromagnetic bond into the host lattice tends to enhance 〈Szi〉 at lattice sites joining the bond as K approaches zero. Increasing K will drastically suppress 〈SxiSxj〉 across the bond. Whereas, 〈SxiSxj〉 is enhanced between the neighboring sites close to the impurity link resulting in the suppression of 〈Szi〉. This behavior persists for all α values. The LSW theory breaks down at a certain K value. Increasing α, the critical value of K extends to a larger number.
Studies of the Verwey transition in Fe3O4/NiO superlattices by SQUID magnetometry and neutron diffraction techniques (abstract)
Authors: Berry S. D. , Borchers J. A. , Erwin R. W. , Lind D. M. , Shaw K. A. , Lochner E.
Published: July 2002

Single crystal superlattices of Fe3O4 and NiO, grown on MgO(100), provide a means to study the competition between interfacial exchange coupling effects and epitaxial strain induced by these closely, but not perfectly, lattice matched materials. Both induce profound macroscopic magnetic effects in the superlattices, especially for films with very thin (<80 Å) modulation thicknesses. The Fe3O4 Verwey conductivity transition in the bulk (∼120 K) is highly sensitive to both the exact stoichiometry of the iron oxide and the presence of strain and is accompanied by a structural and magnetic anisotropy change. X-ray diffraction measurements show that these superlattices are tetragonally distorted (up to 1%), with the increased strain associated with superlattices composed of thin bilayers. By tracking the magnetic evidence of this phase transition using SQUID magnetometry techniques, we observe attenuation of the effect in superlattice films as the iron oxide layers grow thinner and the nickel oxide layers are thickened, which suggests that the presence of strain in the iron oxide layers is highly important. The small structural distortion is observable in neutron diffraction measurements of a Fe3O4 film. Studies of the diffuse and critical scattering associated with this transition in strained iron oxide films and Fe3O4/NiO superlattices and a comparison to previous work on bulk Fe3O4 single crystals will be discussed.
Studies of magnetic interactions between Gd granules in copper matrix
Authors: Hsu J. H. , Huang Y. H.
Published: July 2002

Ultrafine Gd particles in the Cu metallic material have been obtained by rapid annealing of sputtered metastable GdxCu1−x alloys. The particle shape and size were measured by a transmission electron microscopy. The evolution of crystal structure with annealing temperature has been investigated by x-ray diffraction and electron diffraction. It has been found that the Gd granules have formed following annealing above 300 °C and the granular size increases with rising annealing temperature. The magnetic data show that the as-sputtered metastable Gd0.1Cu0.9 and Gd0.2Cu0.8 alloys obey a Curie–Weiss law at high temperature with a negative value of θ. After annealing, the θ value varies with annealing temperature according to an oscillatory function. The evolution of the magnetic properties and microstructure during annealing are described in detail.
Preparation and magnetic properties of Mn4N films by reactive facing targets sputtering
Authors: Nakagawa Shigeki , Naoe Masahiko
Published: July 2002

Ferrimagnetic Mn4N films have been successfully prepared at low process temperatures using the facing targets sputtering apparatus. The mixture gas of Ar and N2 with the ratio of N2 in pressure to total gas RN2 of 10% was optimal as the reactive working gas for depositing Mn4N films, since the deposition at excessive RN2 tended to cause the formation of Mn3N2 crystallites. In fact, they appeared in films deposited at RN2 higher than 30%. The film deposited at the substrate temperature Ts of 200 °C exhibited saturation magnetization 4πMs of about 300 G. The films prepared at Ts of 350 °C exhibited 4πMs and an in-plane coercivity Hc∥ of 450 G and 300 Oe, respectively. The films annealed at 400 °C in vacuum furnace exhibited 4πMs larger than about 510 G. However, the film annealed at temperature above 500 °C exhibited 4πMs smaller than 80 G.
Structural and magnetic characteristics of Co81Cr19/Al multilayers deposited by plasma-free sputtering with Kr gas (abstract)
Authors: Takahashi Takakazu , Naoe Masahiko
Published: July 2002

In multilayers deposited by sputtering, interfaces between each layer are necessary to be extremely sharp and flat. Therefore, the kinetic energy and number of sputtering gas atoms and ions recoiled from the target plane must be satisfactorily decreased. So, in this study, Kr, which is heavier than both Co and Cr in atomic weight, was used as a sputtering gas, while Ar used in conventional sputtering is lighter than them. The Co81Cr19/Al multilayers have been prepared on plasma-free glass slide substrate at room temperature by alternately depositing Co81Cr19 and Al layers, using the facing targets sputtering (FTS) apparatus. The thickness of Co81Cr19 layer lCo-Cr was varied in the range of 45–140 Å, while the thicknesses of Al layer lAl were approximately 7 and 14 Å. The total layer thickness was in the range of 1450–1530 Å. It has been found from the small angle x-ray diffraction diagrams and the scanning electron microscope (SEM) images that the clear periodic structure could be formed in all specimen multilayers. In the multilayers with lal of 7 Å, the Co81Cr19 layers were intrinsically composed of hcp phase crystallites with c-axis orientation Δθ50 normal to the layer plane ranging from 5.4 to 8.4. In the multilayers with lAl of 14 Å, the Co81Cr19 layers seemed to be composed of hcp phase crystallites with very large Δθ50 of which value could not be estimated. However, for all specimen multilayers, the interplanar spacing between (002) planes d(002) were in the range of 2.033–2.038 Å. These values were nearly equal to those of Co81Cr19 single layer films (2.035 Å).

M s and Hc were significantly varied in the range of 500–1150 emu/cc and 35–260 Oe, respectively. In the multilayers with lAl of 7 Å, (Mr/Ms)1 was in the range of 0.28–0.36 and the perpendicular magnetic anisotropy was rather remarkable. On the other hand, in the multilayers with lAl of 14 Å, (Mr/Ms)1 was in the range of 0.61–0.7 and the in-plane magnetic anisotropy was significantly dominant. Co-Cr grains for lAl of 14 Å were finer than those for lAl of 7 Å. These results may indicate that the kinetic energy and number of atoms and ions recoiled from the target plane were significantly decreased by using Kr instead of Ar. So, the multilayers deposited by sputtering with Kr gas had excellently sharp and flat interfaces suitable for use of the apparent magnetoresistance effect.
Temperature dependence of interlayer exchange coupling in Co/Ru/Co trilayer structures
Authors: Zhang Z. , Zhou L. , Wigen P. E. , Ounadjela K.
Published: July 2002

The temperature dependence of the interlayer exchange coupling field Hex and the effective anisotropy field Heff within ferromagnetic layers was investigated for Co/Ru/Co trilayer structures using the angular dependence of ferromagnetic resonance (FMR). It was found that both Hex and Heff increase with decreasing temperature. The dependence of Hex on temperature follows roughly the relationship Hex∝(T/T0) sinh(T/T0) predicted by Edwards et al., and the characteristic temperature T0 decreases with increasing Ru spacer thickness as predicted.
Magnetothermopower of Co/Cu1−xNix multilayers
Authors: Shi Jing , Kita E. , Parkin S. S. P. , Salamon M. B.
Published: July 2002

We studied the magnetothermopower of Co/Cu1−xNix multilayers (with x=0.37 and 0.42) at various temperatures. Both systems have negative thermopower and the magnitude of the thermopower increases as the magnetic field increases. We found that as the ferromagnetic component of the magnetization becomes larger at lower temperatures, both the magnetothermopower and the magnetoresistance decrease. The inverse relationship between the thermopower and the resistance, when the field H varies, holds well at different temperatures. We interpret the results in terms of the two-current model, with an emphasis on the spin-split density of states.
Ferromagnetic resonance studies of Py bilayers for the system (Permalloy/Al2O3) (abstract)
Authors: Hurdequint H. , Bouterfas N. , Vaurés A.
Published: July 2002

We report a detailed ferromagnetic resonance study, performed at X band and room temperature, of magnetic permalloy (Py) bilayers (Py1/Al2O3/Py2) deposited by rf sputtering on mica substrates. We will present and discuss results relative to two series of Py bilayers characterized by an ultrathin Py layer thickness and corresponding to the two following sets of spacer thickness ts: (40;30;19 Å) and (15;12;9 Å). These films have been deposited at room temperature and subsequently annealed (at T=220 and 190 °C, respectively, for these two sets). The resonance spectrum is studied as a function of the orientation [ΘH=(N,H) with respect to the film normal N] of the applied dc field H in a plane perpendicular to the film. (i) For the three samples of the first series the resonance spectrum is composed of two resolved lines which can be attributed to the resonances of the individual layers (Py1 and Py2) dynamically uncoupled. As for a single Py layer, the angular variation Hres(ΘH) of each line observed is well accounted for in terms of a unique parameter (4ΠM−HA), where HA is a uniaxial perpendicular anisotropy field arising from the interface-induced anisotropy. The anisotropy fields HA1 (for Py1) and HA2 (for Py2) are found slightly different (HA2−HA1=500 G), reflecting some differences in the structural characteristics of the (Py/Al2O3) interfaces in the two Py layers. (ii) In the second series of lower ts values, by contrast, the observed resonance spectrum is more complex revealing for a given orientation ΘH two main modes (with a more intense one) and for specific geometries (around ΘH=0) the presence of other resonance modes of much weaker intensities. For these samples the angular variation Hres(ΘH) of the different modes observed, by comparison to the behavior found in the Py single-layer control sample, provides clear evidence for the presence of a dynamical coupling between the magnetizations of the two Py layers. The main mechanisms, likely responsible for this intermagnetic layer coupling, will be discussed: dipolar coupling and exchange coupling (either direct through pinholes or indirect).
Comparison of the electron-spin-resonance linewidth in multilayered CuMn spin glasses with insulating versus conducting interlayers
Authors: Leslie-Pelecky D. L. , VanWijland F. , Hoff C. N. , Cowen J. A. , Gavrin A. , Chien C.-L.
Published: July 2002

The temperature-dependent electron-spin-resonance linewidth ΔH(T) may be used to investigate the effect of the geometry and interlayer material on the magnetic properties of multilayered systems. We compare ΔH(T) in CuMn/Al2O3 multilayers with previous measurements of CuMn/Cu samples. CuMn/Al2O3 samples with CuMn thicknesses, WSG, from 40 Å to 20 000 Å obey the same form as the CuMn/Cu system, but show quantitative differences in the fitting parameters. The linewidths of the CuMn/Al2O3 samples, even in the bulk, are systematically larger than the linewidths for the CuMn/Cu samples, suggesting that the ESR linewidth is sensitive to differences in sample growth and structure. The value of the minimum linewidth decreases with decreasing WSG in the CuMn/Al2O3 series, but remains constant in the CuMn/Cu series. Although susceptibility measurements of the freezing temperature Tf do not differentiate between samples with WSG≥5000 Å, the ESR linewidth is sensitive to changes at larger length scales. This experiment emphasizes the importance of considering both the total sample thickness, as defined by the range of the conduction electrons, and the spin-glass layer thickness in analyzing the ESR linewidth in multilayers.
Low-dose implantation of Sb in Si1−xGex epitaxial layers: Correlation between electrical properties and radiation damage
Authors: Atzmon Z. , Eizenberg M. , Shacham-Diamand Y. , Mayer J. W. , Schäffler F.
Published: July 2002

Pure Si(100) and Si1−xGex (x<0.20) layers, epitaxially grown on Si(100) substrates, were implanted at room temperature with Sb+ ions at an energy of 100 keV and a dose of 1013 cm−2, which was found to be below the critical value for amorphization. Spreading resistance profiling and Hall-effect measurements show that a p-type region was formed in the Si1−xGex alloy layers upon annealing at 500 °C, in spite of the fact that the implanted ion (Sb) is a donor. Only higher-temperature anneals transformed the implanted layer into the expected n-type doping. A p-type region was also formed following Xe implantation, indicating that these results can be attributed to the radiation damage without dependence on the electronic structure of the ion. This phenomenon does not exist at all in pure Si. Rutherford backscattering (channeling) measurements show that the amount of defects formed in the Si1−xGex alloy layer during the implantation process increased with the Ge content, in good agreement with Monte Carlo simulations. These results can explain the observation that the level of the p-type doping increased with the Ge content in the alloys.
Magnetic properties of Y3−x−yPrxLuyFe5O12 garnet films
Authors: Azevedo A. , Cinbis C. , Kryder M. H.
Published: July 2002

In this work we report on the magnetic and low-field ferromagnetic resonance properties of iron garnet films of general composition Y3−x−yPrxLuyFe5O12 for 0≤x≤0.3 and 0≤y≤0.7. The films were grown onto [111] gadolinium gallium garnet substrates by liquid phase epitaxy. Both growth-induced and cubic anisotropies were investigated by means of torque magnetometry and ferromagnetic resonance at room temperature. The growth-induced anisotropy constant Ku and the first order magnetocrystalline cubic constant K1 exhibit a linear dependence with the praseodymium content. The addition of Lu with Pr enhances both Ku and K1 dependence on the doping, yielding ΔKu/x∼−2.4×105 erg/cm3 and ΔK1/x∼−1.1×105 erg/cm3. The addition of praseodymium in the garnet films significantly improves the soft magnetic properties. In-plane coercivity is about 0.1 Oe and there is a negligible anisotropy in the plane of the film. The effect of the doping by praseodymium and lutetium on the saturation magnetization is insignificant at room temperature.
Interpreting logarithmic decay
Authors: Klik Ivo , Chang Ching-Ray , Lee J.
Published: July 2002

We consider an array of thermally relaxing single domain particles with lognormal distribution of nucleation fields. At a constant applied field we calculate the mean magnetization and the magnetic viscosity and irreversible susceptibility due to thermal activation, and analyze the existence conditions of logarithmic decay and the time interval on which it can be observed. For very narrow distributions multiexponential decay is obtained. An approximate relation between magnetic viscosity and irreversible susceptibility is proposed and the influence of activation volume distribution is included.
Effect of a nonpenetrating electron beam on enhancing photoelectron yield
Authors: Yadlowsky Edward J. , Hazelton Robert C.
Published: July 2002

The photoelectron yield from polyethylene, Kapton H, and Teflon samples was measured using a Xenon flash lamp with UV spectrum extending down to 190 nm (6.5 eV). These measurements indicated a dramatic increase in the yield when the samples were irradiated by a nonpenetrating electron beam. The photoelectron yield rose with both dose rate and total dose deposited in the insulator. Observations of the yield revealed persistent enhancement even after turning off the electron beam. This delayed component is reminiscent of the delayed conductivity observed in insulators after the ionizing radiation is turned off. Studies showed that this enhancement was not due to precharging of the dielectric surface. Instead, it was attributed to an increase in the population of carriers, generated by the electron beam, which had been in localized traps within the forbidden band. These trapped electrons, lying just below the conduction band absorbed the xenon radiation and were emitted from the sample materials. Enhanced photoelectron yield has importance in determining the surface potential of insulators on spacecraft exposed to the plasma environment for extended periods of time.
GaAs bidirectional bistability switch using double triangular barrier structures
Authors: Yarn Kao-Feng , Wang Yeong-Her , Chang Chun-Yen
Published: July 2002

We report on the experimental results of a new bidirectional bistability switching device using GaAs double triangular barrier structures prepared by molecular beam epitaxy. Bidirectional switching has been predicted experimentally in n+-n−-δ(p+)-n−-p+-n−-δ(p+)-n−-n+ structure. The significant S-shaped negative differential resistance characteristics are obtained due to the voltage-induced avalanche breakdown and potential barrier redistribution. A large on/off voltage ratio of ∼ 6.5 is observed in either direction of two-state at room temperature. In addition, the device can be expected to operate as a three-terminal triggered triac.
Guided optical waves in a ferroelectric liquid crystal layer
Authors: Ito Shinzaburo , Kremer Friedrich , Aust Emil , Knoll Wolfgang
Published: July 2002

This article reports on the use of guided optical waves for investigating ferroelectric liquid crystals. Although the liquid crystal layer is highly anisotropic in the SmA and SmC* phases, every principle value of the refractive index ellipsoid has been determined by choosing an appropriate rotation angle of the prism with respect to the direction of molecular orientation. In the SmC* phase, an alternating electric field gives rise to the molecular swing around the rubbing direction. The induced alternation of refractive indices provides a high contrast of reflectivity of the incident light, involving the particular characteristics of ferroelectric liquid crystals.
Oxygen loss effect under both reducing and oxidizing thermal treatments on superconductivity of single-crystal Bi2Sr2CaCu2O8+y
Authors: Wu Wenbin , Wang Liangbin , Zhu Jingsheng , Li Xiao-Guang , Zhou Guien , Qian Yitai , Chen Zuyao , Zhang Yuheng
Published: July 2002

After annealing at 450–550 °C, in either flowing nitrogen or flowing oxygen atmosphere, the Bi2Sr2CaCu2O8+y single crystals with as-grown superconducting transition temperature Tc of 65–83 K all showed at Tc of ∼86 K with a transition width of 0.5–1 K. For the crystals annealed at 500 °C and in increasing oxygen pressure, however, the improvement of superconductivity was depressed. These results can be explained by oxygen loss under both reducing and oxidizing thermal treatments of the oxygen-doped Bi2Sr2CaCu2O8+y samples.
Universal expressions for range parameters of ions in solids
Authors: Hou Qing , Luo Zhengming , An Zhu
Published: July 2002

The detailed parametric analysis of the Boltzmann equation of ion transport shows that there is an approximately one-to-one correspondence between ion transport quantities and a characteristic parameter named the scaled transport cross section and defined earlier [Z. Luo, Nucl. Instrum. Methods B 48, 444 (1990)]. To attest to a significant conclusion, we have completed systematic calculations over numerous-ranges for ions implanted in solids. The systematic calculations include 3410 ion-target-energy combinations. The calculations show that range parameters present a good single-value dependence on the scaled transport cross section at low incident energies. Based on this result, universal expressions for range parameters have been obtained. To test the validity of the expressions, the range distributions of ions in solids have been calculated by universal expressions. The comparisons between the results of the universal expressions and experimental or Monte Carlo data show that the universal expressions given in the present article can give good predictions to range distributions of low energy ions implanted in solids.
Electron-wave phase-shifting interferometry in transmission electron microscopy
Authors: Lai Guanming , Ru Qingxin , Aoyama Kazuhiro , Tonomura Akira
Published: July 2002

A phase-shifting interferometry is described using a generalized algorithm for measuring the electron phase in a transmission electron microscope. This method makes the electron-wave phase-shifting interferometry suitable for practical applications by removing the restrictions on data acquisition and on the phase shifter. Calculating the initial phase of each interferogram from the interferogram itself greatly increases the precision of the measured phase distribution. Experimental application of this method demonstrated that it is capable of measuring electron phase distribution with both high spatial resolution and high precision.
Mesoscopic transport in Si metal-oxide-semiconductor field-effect transistors with a dual-gate structure
Authors: Matsuoka Hideyuki , Ichiguchi Tsuneo , Yoshimura Toshiyuki , Takeda Eiji
Published: July 2002

This article studies the mesoscopic transport of electrically controllable inversion layers of Si metal-oxide-semiconductor field-effect transistors that use a dual-gate structure. We have developed two kinds of devices: a quasi-one-dimensional device (1D-FET) and a Coulomb blockade device (CB-FET). In both devices, the field effect is used to change the channel structure by introducing potential barriers in the narrow inversion channel. The 1D-FET changes a long diffusive quantum wire into a short ballistic one. Strong oscillations in differential conductance, even negative differential conductance, have been observed at 4.2 K, indicating enhanced modulation of electron mobility by intersubband scattering suppression. The CB-FET, on the other hand, transforms a simple quantum wire into a coupled quantum-dot array. A clear change in transport properties is observed with changes in the barrier height at low temperatures. The experimental results are consistent with the theory of one-dimensional subbands and the Coulomb blockade of single-electron tunneling.
Electrical, optical properties, and surface morphology of high purity InP grown by chemical beam epitaxy
Authors: Rao T. Sudersena , Lacelle C. , Benzaquen R. , Rolfe S. J. , Charbonneau S. , Berger P. D. , Roth A. P. , Steiner T. , Thewalt M. L. W.
Published: July 2002

High purity InP layers have been grown by chemical beam epitaxy using H2 as the carrier gas for transporting the metal alkyl trimethylindium into the growth chamber. InP layers exhibiting Hall mobility as high as 238 000 cm2/V s at 77 K and with a peak value of 311 000 cm2/V s at 50 K and residual Hall concentration of 6×1013 cm−3 at 77 K were grown at 500 °C using a low V/III ratio (2.2) and a phosphine (PH3) cracking cell temperature of 950 °C. The 4.2 K photoluminescence spectra were dominated by donor bound exciton (D0,X)n up to n=6 and free exciton (X) transitions for InP layers grown above 500 °C. All the InP samples exhibited very weak acceptor related photoluminescence transitions indicating very low concentration of acceptors. The energy of these transitions suggests that Mg is the major residual acceptor. Donor impurity identification by high resolution magnetophotoluminescence indicated that S and Si are the major impurities. PH3 has been found to be the major source of S impurities in the present study.