bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic properties of U2Pt2Sn
Authors: Prokeš K. , de Boer F. R. , Nakotte H. , Havela L. , Sechovský V. , Svoboda P. , Winand J. M. , Rebizant J. , Spirlet J. C. , Hu X. , Gortenmulder T. J.
Published: July 2002

U2Pt2Sn is crystallizing in an ordered version (space group P42/mnm) of the tetragonal U3Si2 type of structure. Clear anomalies in the magnetic susceptibility, specific heat, and electrical resistivity around 15 K indicate that U2Pt2Sn orders antiferromagnetically below this temperature. As expected for an antiferromagnet, the susceptibility and specific heat anomalies are shifted to lower temperatures upon application of external magnetic field. The specific-heat coefficient γ=327 mJ/mol f.u. K2 remains unchanged in fields up to 5 T. The antiferromagnetic ground state of U2Pt2Sn can be concluded also from the metamagnetic transition around 22 T in the magnetization at 4.2 K and from magnetic reflections in the neutron-diffraction pattern at low temperatures.
Oblique electron transport in the presence of collinear and noncollinear magnetizations
Authors: Camblong Horacio E.
Published: July 2002

The nonlocal real-space Kubo approach to electron transport in magnetic multilayers is applied to a new geometry, ‘‘oblique transport,’’ whose complexity is traced back to a combination of the layering, of the nonlocal character of the linear response, and of the oblique direction transport in this new geometry. The problem is dealt with by applying a condition on the average current density vector or on the average electric-field vector, depending upon the external driving conditions. Its solution exhibits a characteristic anisotropy and it yields the global oblique conductance and magnetoresistance as simple trigonometric expressions in terms of the in-plane and vertical conductances and magnetoresistances, for arbitrary noncollinear-magnetization configurations.
Giant magnetoresistance in magnetic granular systems
Authors: Sheng L. , Gu R. Y. , Xing D. Y. , Wang Z. D. , Zhu Jian-Xin
Published: July 2002

Based on a semiclassical model, the transport properties in systems of cylindrical or spherical magnetic granules are investigated analytically. It is shown that the conductivities as well as the magnetoresistance of these systems depend strongly on the size of the granules. In particular, there is always an optimum granular size for the magnetoresistance.
Real-space analysis of inhomogeneous scattering versus superlattice-potential effects for magnetotransport (abstract)
Authors: Camblong Horacio E.
Published: July 2002

Spin-dependent scattering has usually been regarded as the basic mechanism for giant magnetoresistance (GMR), following the seminal quasiclassical work of Camley and Barnás. When this mechanism is considered, the correct quantum-mechanical treatment of magnetotransport in multilayers is provided by the real-space Kubo approach. In addition, band-structure effects due to imperfect matching of the Fermi surfaces of the constituent materials of the superlattice have been regarded as another source of GMR. It turns out that a real-space approach to superlattice effects is both straightforward and intuitive. In effect, a solution of this unified model of inhomogeneous scattering and superlattice potentials is accomplished by deriving the real-space Green’s function, which is a direct generalization of that of Ref. , but with a wavevector that is obtained by solving the dispersion relation for a Kronig-Penney model. It is shown that spin-dependent scattering remains the dominant mechanism, even though it is somewhat modified by the presence of superlattice potentials; that is, GRM is mainly due to a ‘‘short-circuit effect’’ rather than due to a ‘‘channeling effect.’’ The corresponding ‘‘internal quantum size effects’’ (due to potential barriers) are not easily observable because of, among other factors, the exponential suppression of the one-particle propagator in the presence of the relatively short mean free paths in multilayers; this ‘‘geometrical effect’’ is an outstanding feature of magnetic multilayers as their giant magnetoresistance is governed by strong scattering at the interfaces. Finally, due to interdiffusion, the standard usage of reflection coefficients is shown to be incorrect.
Superconductivity and magnetic properties of Fe/Nb multilayers (abstract)
Authors: Mühge Th. , Zoller I. , Westerholt K. , Zabel H. , Goryunov Yu. V. , Garif’yanov N. N. , Khaliullin G. G. , Garifullin I. A. , Tagirov L. R.
Published: July 2002

The interplay between superconductivity (SC) and ferromagnetism (FM) in dilute magnetic alloys and intermetallic compounds attracted considerable attention during the last 30 years. Usually the ferromagnetic state is more stable and therefore tends to suppress SC. On the other hand, the magnetic state can be changed due to a modification of the RKKY interaction in the SC state. Mutual influence of SC and FM may acquire new peculiarities in such artificial systems as FM/SC multilayers. This work is focused on the study of Fe/Nb multilayered system, prepared on Al2O3(112̄0) substrates by rf-sputtering and by molecular beam epitaxy (MBE) techniques. The Nb thickness tNb was varied from 150 to 500 Å and the Fe thickness tFe was changed from 5 to 100 Å. The sputtered samples were highly layered with sharp interfaces as revealed by x-ray reflectivity and were textured in the [110] direction. The epitaxial MBE samples showed (110) growth of Nb and Fe with a coherence lengths comprising the total film thickness. Surface and interface roughnesses were very small. The dependence of the ferromagnetic resonance (FMR) spectra parameters on the direction of the dc magnetic field rotating in the plane of the samples show sixfold anisotropic behavior indicating the well known three-domain in-plane structure of Fe layers on sapphire substrates.

FMR and SQUID measurements showed that FM of Fe layers survived down to tFe=10 Å. The out-of-plane FMR measurements also showed that the easy axis of magnetization lies in the plane of the samples down to this thickness. The superconducting transition temperature Tc was determined by measurements of the electrical resistivity and by SQUID measurements. It was established that there is a critical thickness of the Fe layer tFecrit above which SC was not detected for temperatures down to 1.5 K. This value was dependent on tNb. Thus, for example, it was found that for tNb=300 Å the value of tFecrit=30 Å and for tNb=350 Å—tFecrit=50 Å. For constant tFe with increasing tNb up to a certain thickness, SC was not detected; then Tc started to increase, and, finally, it approached the constant value of the order of 6 K above a certain tNb which depended on tFe. The critical magnetic field HC2 obtained from the resistivity measurements, strongly decreased with increasing tFe or decreasing tNb. The temperature dependences of HC2 were typical for two-dimensional superconductors. For the interpretation of the data obtained, various theories were employed.
A comparison of structure and magnetoresistance in Fe/(Ag–Cu) films (abstract)
Authors: Kwon S. J. , Choi S. J.
Published: July 2002

Films of 12 Fe/(Ag–Cu) bilayers were prepared to have either granular or multilayer structures on glass substrates with a 50 Å Cu buffer layer. A magnetic Fe layer of 15 Å was deposited by e-beam evaporation, and a nonmagnetic Ag–Cu layer of 20 Å by thermal coevaporation with various Ag/Cu ratio. As the nonmagnetic layer composition changed from Ag to Cu, roughness of the film surface varied from more than 100 Å to less than 10 Å, measured with atomic force microscopy. Regularity of multilayer structure was evident in the Fe/Cu film from a superlattice peak at around 2theta=2.5 deg by Cu Kα x-ray diffraction. The peak weakened as the Ag content increased in the nonmagnetic layer, and completely disappeared at Ag/Cu≳1, which indicated that granular structure became dominant. Pendelloesung peaks at 2theta=1 to 2 deg had a similar composition dependency. The structural change was confirmed with cross-sectional transmission microscopy, too. The deposited structure is explained in terms of surface tension and wettability of each element. Increasing Cu content decreases the surface tension and increases the wettability of the nonmagnetic layer. Heat treated film structures are explained with identical terms. Change of magnetoresistance is discussed in part by connectivity of the nonmagnetic layer. From the discussion, a reasoning is given to the effect of annealing on the magnetoresistance of the films.
Nonlinear dynamics in microwave driven coupled magnetic multilayer systems
Authors: Rezende S. M. , de Aguiar F. M.
Published: July 2002

Conventional microwave ferromagnetic resonance (FMR) techniques have proven very useful in the investigation of coupled magnetic multilayer systems. Here we show theoretically that with sufficiently high powers, a microwave magnetic field applied either parallel or perpendicular to the dc field, can drive nonlinear effects. The Landau–Lifschitz equation is used to obtain the nonlinear equations of motion for the two normal modes of a coupled two-layer system. In the usual FMR configuration, only the acoustic mode is coupled to the driving field. However, for driving fields above a critical value, energy can be transferred to the optic mode, in a process similar to the subsidiary resonance observed in spin-wave systems. At higher driving the system may display well-known transitions to chaos.
Magnetization and dynamics of reentrant ferrimagnetic spin-glass [MnTPP]::+[TCNE].−⋅2PhMe
Authors: Brinckerhoff W. B. , Morin B. G. , Brandon E. J. , Miller Joel S. , Epstein A. J.
Published: July 2002

We present direct current (dc) magnetization M(T,H) and alternating current (ac) susceptibility χac(T,H,f) data for the quasi-one-dimensional molecule-based ferrimagnet [MnTPP]::+[TCNE].−⋅2PhMe (TPP=meso-tetraphenylporphyrinato, TCNE=tetracyanoethylene). Static scaling of the real part χ′ of the ac susceptibility and data collapse of M(T,H) over a limited reduced temperature range above Tc≊13 K lead to the critical exponents γ≊1.6, β≊0.5, and δ≊4.2. Below Tc, χac depends sensitively on frequency and exhibits a striking double-peak structure similar to that found in reentrant spin glasses. Possible models for the frequency dependence of the peaks observed in χac are discussed.
λ-MnO2, a new frustrated antiferromagnet with the defect spinel structure (abstract)
Authors: Greedan J. E. , Liu Guo , Raju N. P. , Reimers J. N. , Tun Zin
Published: July 2002

MnO2 exists in a number of crystalline modifications. λ-MnO2, prepared by electrochemical delithiation of the spine Li2Mn2O4, has Mn4+, S=3/2, occupying the octahedral (16c) sites in Fd3m. The magnetic sublattice consists of a pyrochlore-type array of corner-shared tetrahedra and is thus a candidate for frustrated antiferromagnetism. The dc susceptibility data indicate, for very low applied fields of 45 G, a sharp maximum at 32 K but this is smeared to a broad maximum at 25 K for fields as modest as 300 G. Zero-field neutron diffraction data show long range order with K=(1/2 1/2 1/2) and Tn=32 K. Surprisingly, the long range order is robust to applied fields of 1.0 T and higher. Prominent diffuse scattering persists up to greater than 60 K due to short range order which is indicative of frustration. The properties of λ-MnO2 are compared with those of the spin-glass-like pyrochlore, Y2Mn2O7, which has the same magnetic species on the same sublattice.
Enhancement of piezomagnetic response of highly magnetostrictive rare earth-iron alloys at kHz frequencies
Authors: Pulvirenti P. P. , Jiles D. C. , Greenough R. D. , Reed I. M.
Published: July 2002

The effects of Al and Si additions on the frequency response of highly magnetostrictive Tb–Dy–Fe alloys have been studied. These elements reduced the electrical conductivity of the material, thereby increasing the depth of penetration of ac magnetic fields and extending the operational frequency range. Complex permeability measurements were made on doped and undoped polycrystalline samples with the objective of studying the improvement in energy conversion efficiency at kilohertz frequencies as a result of the alloying additions. The resulting complex permeability was compared with the values for single crystal specimens of Tb0.3Dy0.7Fe1.92 at a range of frequencies from 10 Hz to 50 kHz.
Frequency mixing phenomena in a bistable system
Authors: Grigorenko A. N. , Nikitin P. I. , Roschepkin G. V.
Published: July 2002

A response of a bistable system subject to several periodic and random forcing is discussed. It is shown that spectrum components of the response on mixed frequencies demonstrate a noise-induced enhancement typical for stochastic resonance. The quenching of the spectrum harmonics due to an application of a constant force that destroys symmetry of the potential is calculated. The theory is checked on a simple bistable magnetic system: a local part of a domain wall in a thin ferrit–garnet film.
Magneto-optic and microwave properties of epitaxial garnet thin film heterostructures and superlattices (abstract)
Authors: Ramesh R. , Venkatesan T. , Lofland S. , Dominguez M. , Bhagat S. M. , Simion B. M. , Thomas G.
Published: July 2002

We report on the growth and magnetic characterization of epitaxial garnet thin films and heterostructures by pulsed laser deposition. Thin films and heterostructures consisting of yttrium iron garnet (YIG) interleaved with rare earth substituted bismuth iron garnet (BIG) have been deposited on single-crystal GGG substrates. These heterostructures exhibit strong polar magneto-optic Kerr effects with rotation angles of better than 5×104 °/cm at 533 nm. Microwave measurements at 10 GHz suggest that the Eu-substituted BIG layer has a preferred out-of-plane magnetization while the YIG layer is still magnetized in-plane. The implications of the magneto-optic and microwave results will be discussed in light of the heterostructure periodicity and film microstructure.
Mössbauer effect and electronic transport studies of icosahedral Al50Pd10Mn25−xFexB15 alloys
Authors: Yewondwossen M. , Jagger J. E. , Koziol Z. , Dunlap R. A.
Published: July 2002

The temperature and applied magnetic field dependence of the resistivity of icosahedral Al50Pd10Mn25−xFexB15 (x=0 and 5) alloys has been measured between 4.2 and 300 K. At low temperature, T<30 K, the resistivity showed a rapid decrease with increasing temperature and may be described by a combination of weak localization (WL) and magnetic scattering effects. At higher temperatures the resistivity is adequately described by the temperature dependence of the structural and magnetic effects as described by Boltzmann-type transport. The measured magnetoresistance of both samples is consistent with theoretical predictions based on WL. The room temperature Mössbauer effect spectrum of the x=5 sample showed a well resolved doublet with mean isomer shift (relative to room temperature α-Fe) and quadrupole splitting of +0.22 mm/s and 0.36 mm/s, respectively. These results indicate that the Fe probe nuclei do not carry a magnetic moment in these alloys.
Superconducting metastable phase in rapid quenched Y–Pd–B–C borocarbides
Authors: Ström Valter , Kim K. S. , Grishin A. M. , Rao K. V.
Published: July 2002

Rapid quenched (RQ) palladium-based borocarbides with large fractions of the superconducting phase (Tc≳20 K) have been obtained. Superconductivity is found to exist only in the RQ state. Thus, while the as cast YPd2B2C is nonsuperconducting, the RQ material superconducts and has an x-ray diffraction (XRD)-pattern characteristic of a face-centered cubic fcc lattice with a lattice parameter of 4.15 Å. A sequential annealing study shows decay of the superconducting phase above 750 °C which correlates well with the reduction in the integral intensities of the XRD fcc peaks. A tentative phase diagram for superconductivity in the Y–Pd–B–C systems is presented.
Micromagnetics of dual spin-valve GMR heads
Authors: Zhu Jian-Gang , Ye Xiao-Guang , Yuan Samuel W. , Tong Hua-Ching , Rottmayer Robert
Published: July 2002

Micromagnetic simulations were performed to study the biasing characteristics and playback performance of actual dual spin-valve GMR heads. Both symmetric and asymmetric dual spin valve heads were analyzed. The study shows that the symmetric dual spin-valve head is not properly biased in its patterned form, without any additional transverse biasing schemes. On the other hand, the asymmetric dual spin valve head is self-biased since in this form, the free layer is free from the demagnetizing fields arising from the pinned layers. However, opposite GMR effects with similar magnitudes would be required for the two spin valve structures in the same multilayer film.
Soft magnetic properties of nanocrystalline FeRuGaSi-Hf alloy films and head characteristics for the embedded thin film tape head
Authors: Ohmori H. , Shoji M. , Kobayashi T. , Yamamoto T. , Sugiyama Y. , Hayashi K. , Hono K.
Published: July 2002

The Hf-added FeRuGaSi alloy film has an amorphous structure in the as-deposited state and becomes nanocrystalline after annealing. Due to this structure change from crystalline to amorphous by the addition of Hf, soft magnetic degradation of the film deposited on the slant grooved substrate, which is necessary for the sophisticated embedded thin film (ETF) head structure, is greatly suppressed and the undesirable film stress is relieved. The FeRuGaSi-Hf alloy film has higher resistivity and permeability at high frequencies than those of sendust film, and the read/write characteristics of this alloy film show better performance than sendust film.
Magnetization reversal and small lancettes calculated by statistic domain behavior (abstract)
Authors: Fulmek Paul L. , Hauser Hans
Published: July 2002

The energetic model of ferromagnetic hysteresis calculates the magnetic state of anisotropic ferromagnetic materials by minimizing the total energy function ET=EH+EM. The energy of the material EM is divided into reversible (statistic domain behavior) and irreversible terms. The applied field H (energy EH) causes reversible domain wall displacements si until an individual Barkhausen jump starting position sA is reached. The probability density pa(sA) is assumed to be decreasing with increasing sA: pa=(Ka/Kc)exp [−(Ka/Kc)sA] (adaptive constant Ka). Kc describes the influence of the total magnetic state on pa at points of magnetization reversal; Kc=1 for the initial magnetization curve. The losses Er during an irreversible Barkhausen jump (wall friction Kr) are increasing with si: Er=Kr[si−sA−(Kc/Ka)(Kc−1)] and Kc depends on the covered displacements si at a point of field reversal: Kcnew=2−Kcboldexp[−(Ka/Kcold) si]. This follows from the condition of steadiness at these points. The physical constants of this model are derived from anisotropic energy contributions, initial susceptibility, coercivity, and saturation magnetization. The approach shows a good agreement to measurements to the stability of small lancettes of (110)[001] 3.5% FeSi steel sheets, magnetized in the rolling direction.
Characterization of minor loops using Preisach-based models
Authors: Vajda Ferenc , Della Torre Edward
Published: July 2002

This paper gives a theoretical analysis of recently reported experimental hysteresis data by O’Grady and Greaves [J. Magn. Magn. Mater. 138, L233 (1994)] performed on a variety of thin film and particulate recording samples. Using recently developed hysteresis models, it is shown that the nonzero area of their measured minor loop is due to hysterons in the media that switch to the up state in negative field. Using the accommodation model, it is shown that, when cycling the applied field, the computed magnetization drifts up or down and approaches a stable minor loop. The direction of the drift depends on the accommodating magnetizing process.
Environmental effects on the pause mode performance of metal-evaporated and metal-particle tapes
Authors: Patton Steven T. , Bhushan Bharat
Published: July 2002

A commercial Hi-8 VCR was instrumented to measure the friction force between the rotary heads and tape and rms head output. Pause mode experiments using metal-evaporated (ME) and metal-particle (MP) tapes were performed at design tension under equilibrium conditions inside of an environmental chamber at various temperatures and specific humidities (SH is the ratio of the weights of water vapor to dry air in the mixture). ME tape performed well only at high humidity [on the order of 80% relative humidity (RH)] in the operating temperature range of 15.6–32.2 °C. Under all conditions, lubricant was removed from the ME tape surface, which resulted in increased signal amplitude (due to decreased head medium spacing) and friction during individual experiments. For fixed temperature, increased SH reduced both the lubricant depletion rate and the number and magnitude of spacing loss signal dropouts. The thicker water film maintained on the interface components acted as an additional replenished lubricant, which reduced the displacement of the perfluropolyether lubricant from the tape surface and acted as a mediator for solid debris to traverse the contact region of the head and tape. For fixed SH, reduced temperature led to the same improvements due to increased lubricant viscosity at lower temperatures. Increased lubricant viscosity reduced the displacement of lubricant from the tape surface, and displaced lubricant remained on the tape contact region of the head surface and acted as a mediator for solid debris to traverse the contact region of the head and tape. Tests with MP tape showed a relative insensitivity to the environment.
The role of impurity scattering in Co/Cu (111) M.B.E. multilayers (abstract)
Authors: Wellock K. P. , Hickey B. J.
Published: July 2002

The origin of spin-dependent scattering (sds) within magnetic/nonmagnetic systems is a controversial issue which has attracted much attention in recent years. There is now a consensus of opinion that sds is necessary for the giant magnetoresistance (GMR) and most work suggests that this scattering occurs at the interface, but the details have yet to be discovered. Numerous studies have been performed placing impurities within the multilayer and in nearly all cases a reduction in MR is observed. The only exceptions to this are the cases where magnetic impurities are used. We have observed the first enhancement of MR for the Co/Cu system using nonmagnetic impurities. In the case of a simple trilayer system up to an eightfold increase in MR is observed while for a multilayer system up to 40% increase is recorded. Impurities have been introduced during sample growth in a controlled manner using a shutter arrangement such that a direct comparison of impurity-doped and an undoped sample can be made. In previous impurity studies changes in coupling have given rise to confusing results. In order to avoid this we have used relatively thick Cu spacer layers and very small levels of impurities so that no magnetic coupling changes are induced by doping. All samples were characterized by x-ray diffraction and in situ RHEED where we found no evidence of structural changes induced by the Au impurities. We discuss these results in the light of current theories of spin-dependent scattering.
Relaxation in NiFe/Ag giant magnetoresistive devices
Authors: Cross R. W. , Kos A. B.
Published: July 2002

Giant magnetoresistance was measured as a function of time and device size for patterned NiFe/Ag multilayer films. The sputtered NiFe/Ag multilayers were postannealed at 340 °C for 5 min in order to produce a change in resistivity Δρ/ρ of 5% in a saturating field of 4 kA/m (50 Oe). The microstructure of these films is believed to be discontinuous due to Ag bridging through the NiFe grain boundaries after the anneal. The films were fabricated into rectangular stripes with Au current lead, and then exposed to a magnetic field pulse to measure the time response of the resistance, characterized by a time constant τ, from the relation ΔR(t)=ΔR0e−t/τ. An apparatus was developed to produce a magnetic field pulse up to 8 kA/m (100 Oe) with a turn-on/off time constant of 10 μs. The response of the NiFe/Ag devices saturated quickly with the turn-on step with a time constant nearly equal to that of the field pulse. The response to the turn-off step, however, had a time constant of nearly 300 μs. When the field is first applied, the torque on the magnetic moments quickly aligns the magnetization. When the field is shut off, however, the torque due to the field drops to 0, so interacting magnetostatic fields from the grains and thermal energy dominate the relaxation process. The average time constant depends on the device size and the applied current density. Relaxation may be detrimental for using this type of material for read heads where very high data rates are required.
Simulation of magneto-optic readout signal spectrum using digitized mark and beam patterns (abstract)
Authors: Jo S. , Sohn J. W. , Lee S. K. , Kim S. G.
Published: July 2002

This paper describes a simple and convenient simulation method, which uses analytical models for mark and beam patterns. The readout signal of optical disk system is obtained by two-dimensional convolution of Gaussian intensity beam pattern and elliptical mark pattern. Then, signal spectrum is obtained by executing a fast Fourier transform algorithm after adding quantitative MO noise sources within bandwidth. For simulation, the two-dimensional distributions of mark reflectivity and beam intensity were digitized, which enabled us to use easily available algorithm routines in digital signal processing. The resolution of the beam and mark patterns can easily be adjusted by changing the number of bits representing the patterns. Also, various noise sources in the MO disk system can be selectively added using random function generator. Simulated signal spectra were compared with experimental results. The parameters used were as follows: laser beam width was 780 nm, NA was 0.55, signal frequency was 9.4 MHz, duty ratio was 38%, and minimum mark dimension was 0.6 μm by 0.75 μm. Simulated C/N ratio was 50 dB, which was very close to the experimental value of 52 dB.
Comparison of the magneto-optical figure of merit of NdFeCo and TbFeCo alloys
Authors: Challener W. A.
Published: July 2002

Due to the magneto-optical (MO) activity of light rare earths, NdFeCo alloys have been suggested as candidates for use in future high density MO media designed for use at shorter wavelengths. We have measured the MO indices of refraction and computed the maximum Kerr rotation figure of merit as a function of wavelength from 400 to 900 nm for a wide range of NdFeCo and TbFeCo alloys. Only a marginal gain in MO media performance is expected by incorporating NdFeCo into optimized TbFeCo thin film stacks.
The rate of domain growth in magneto-optic recording media (abstract)
Authors: Earl J. , Lyberatos A. , Chantrell R. W.
Published: July 2002

The magnetization reversal in magneto-optic media occurs in general by a process of nucleation followed by domain growth. The rate of domain growth is of importance in thermomagnetic recording. Under steady external field conditions, a slow thermoactivated domain growth is observed and the time dependence curves M(t) are often described using a theory by Fatuzzo. The Fatuzzo theory assumes a constant rate of expansion v of cylindrical domains; however, it does not consider the dispersion in the energy barriers or the formation of dendritic domain structures that may arise, for example, from the spatial and temporal variations of the demagnetizing field. Monte Carlo simulations of domain growth were performed using a model that considers distinct intrinsic energy barriers for nucleation and wall motion and incorporates the contribution of the demagnetizing and domain wall energy in the computation of the energy barriers. The rate of domain expansion, v=dRg/dt, where Rg is the radius of gyration, was found to be constant during the initial stage of the growth process but decreases for large Rg as a result of the reduction in demagnetizing strength. Small fluctuations in v are observed arising from the variation of the domain shape during the growth process. The simulations have also shown that the dependence on the applied field is exponential, v=v0 exp(H/Hf), where Hf is the fluctuation field, in good agreement with experiment. The exponential dependence was found to be valid even in the case of dendritic domain growth, suggesting that the Fatuzzo theory may be useful in the description of the growth of domains of irregular shape.
Characteristics of microstrip directional coupler on magnetized ferrites
Authors: Albuquerque E. L. , Albuquerque M. R. M. L. , d’Assunção A. G.
Published: July 2002

We have studied the physical properties of a high directivity microstrip directional coupler on a single-layered ferrite substrate under the influence of an external dc magnetic field H0. We also present an analysis of the coupled microstrip lines on a ferrite-dielectric substrate. Our method of calculation, which is done in the spectral domain, is based upon a combination of the Hertz vector potentials and the Galerkin numerical technique. The dyadic Green functions for the coupled microstrip lines are also obtained. We consider the even and odd modes of propagation, with the characteristic impedances and normalized phase constants of these artificial structures obtained as a function of their geometry. Special attention is given to the determination of a high directivity for the coupler, by equating the phase velocity of the even and odd modes of propagation which, in turn, is obtained throughout the variation of the applied magnetic field H0.
Magnetism and structure of ultrathin fcc FexCo1−x films on Cu(001) (abstract)
Authors: Dittschar A. , Zharnikov M. , Kuch W. , Schneider C. M. , Kirschner J.
Published: July 2002

Ultrathin films of 3d-transition metal alloys, and in particular FeCo alloys, currently receive considerable interest because of their potential technological application and the possibility to adjust magnetic properties via the variation of composition and structure. To study magnetic and structural properties of the otherwise unstable fcc phase of FeCo, this structural phase was stabilized by epitaxial growth on Cu(001). Ultrathin FexCo1−x films were deposited at room temperature by coevaporation from two separate Knudsen cells, operated under stabilized conditions. The film thickness was varied between 2 and 9 monolayers (ML) and the Fe concentration between x=0.2 and x=0.95. The growth process was monitored by medium energy electron diffraction (MEED). Auger electron spectroscopy and low energy electron diffraction (LEED) were employed to analyze the composition and structure of the films. A nearly perfect layer-by-layer growth up to at least 9 ML, as seen by MEED, is encountered for x≤0.7. For higher Fe concentrations and thicknesses greater than 4 ML, deviations from the layer-by-layer growth are observed, indicating a structural rearrangement. LEED-I(V) curves reveal the coexistence of two structural phases with different interlayer spacings, the relative amount of which depends on the composition. Magnetic properties were characterized by the magneto-optical Kerr effect (MOKE). The remanent magnetization was found to lie within the film plane over the whole range of thicknesses and concentrations investigated.

A linear increase of the Kerr signal at saturation magnetization with increasing thickness indicates that practically the whole film is magnetic. As a function of composition, the saturation Kerr signal develops continuously with increasing Fe content. This suggests that in fcc FeCo alloys the contribution of Fe and Co to the total magnetic moment is nearly constant over the whole compositional range.
Nonlinear magneto-optical Kerr effect study of quantum-well states in a Au overlayer on a Co(0001) thin film
Authors: Koerkamp M. Groot , Kirilyuk A. , de Jong W. , Rasing Th. , Ferré J. , Jamet J. P. , Meyer P. , Mégy R.
Published: July 2002

We have measured the polar nonlinear magneto-optical Kerr rotation and the total generated second harmonic intensity from a perpendicularly magnetized Co(0001)/Au(111) thin film (6 ML) versus the thickness of a Au overlayer. For both experiments we find a clear oscillation with a period of about 13.5 ML. This behavior can be interpreted as arising from quantum-well states (QWSs) in the Au overlayer, though interestingly, the observed period is twice the expected one. Especially for the reflected intensity this oscillation is very pronounced: the intensity changes by a factor of 10 when the Au overlayer thickness changes from 7 to 13 ML. These strong effects make this nonlinear technique very suitable for the study of these QW oscillations.
Quantum well states and interlayer coupling: Co/Cu(100)
Authors: Nordström L. , Lang P. , Zeller R. , Dederichs P. H.
Published: July 2002

The electronic states that mediate the interlayer exchange coupling and the corresponding coupling strengths are calculated for Co/Cu(100). It is found that some states are strongly confined within the spacer layer. This is shown to lead to a strong RKKY-like coupling, but also to some weak contributions from higher harmonics. Weaker confined states only contribute by a rather weak RKKY coupling.
Effects of write current switching time on recording characteristics (abstract)
Authors: Tomiyama F. , Takano H. , Shiroishi Y. , Suzuki M. , Sugita Y.
Published: July 2002

High-frequency recording is essential for a recording channel with both a high data rate and a high linear recording density, and this study examined the ways in which performances are affected by the switching time of the write current, ts, and the disk velocity, v. The switching time, defined as (tr+tf)/2, where tr and tf are the rise time and the fall time of the write current, was changed from 5 to 20 ns, while v was changed from 12 to 26 m/s. Co-based thin-film media with a coercivity of about 2.5 kOe and a remanence-thickness product of about 100 G μm were used for recording the data. The flying height of the head was maintained at 50 nm regardless of disk velocity. This study confirmed that the overwrite characteristics are strongly related to the product of ts and v. Overwrite here was defined as the ratio of the residual fundamental frequency component amplitude of a 21 kFCI signal to the original one after overwriting with a 86 kFCI signal. Suitable overwrite characteristics were obtained when t*sv was smaller than πa, where a is the transition parameter derived from the equation proposed by Williams and Comstock. The transition length on the medium was determined primarily by πa when t*sv was smaller than πa, but was determined by t*sv when t*sv was larger than πa. Linear density characteristics and noise characteristics and their relationship to the medium properties will also be addressed in this talk.
Coercivity and remanence of amorphous and nanocrystalline Fe–(Cu,Ta)–SiB ribbons
Authors: Murillo N. , González J. , Blanco J. M. , González J. M.
Published: July 2002

We report on the evolution, with the thermal treatment parameters, of the remanence and coercive force of amorphous melt spun ribbons having compositions of Fe77.5Si13.5B9, Fe76.5Cu1Si13.5B9, and Fe74.5Ta3Si13.5B9. The thermal treatments were carried out by using the current annealing technique with and without the simultaneous application of a tensile stress along the axis of the samples. Our results show that upon low temperature (low current), short time treatments both the remanence and the coercive force are basically determined by the characteristics of the effective anisotropy induced during the treatment. In contrast, high temperature (high current) treatments result in values of both quantities that are linked to the (partial or total) accomplishment of the first stage of the crystallization process of the samples.
Magnetic garnet film epitaxy on nonsingular faces (abstract)
Authors: Gorelik S. S. , Letyuk L. M. , Morchenko A. T.
Published: July 2002

The single crystal films of magnetic garnets are widely used in various microelectronics devices. The yttrium–iron and bismuth–gallium-substituted magnetic garnet films were grown by liquid phase epitaxy from supercooled solutions on the basis PbO+B2O3. As substrates for films the gadolinium–gallium garnet wafers crystallographically oriented in the range from (111)- to (110)-directions are used. In experiments such growth process parameters as supercooling temperature and angular velocity of substrate rotation were varied too. The parameters to be examined were thickness, growth rate, crystallografic, magnetic, and magnetooptical characteristics of the as-grown films. To analyze the growth process kinetics it was developed the model, including the terms (supersaturation CL−CE) of the first and second orders for description of surface crystallization reaction. The following expression was derived for epitaxial growth rate: f=D/ρδ [(CL−CE)+k1δ+D/2k2δ−√ (k1δ+D)2+4k2δD(CL−CE)/2k2δ], where D is diffusion coefficient, δ is diffusion boundary layer thickness on the solid–liquid interface, ρ is film density, CL is concentration of garnet phase in the melted solution, CE is equilibrium concentration, km is surface reaction constant (kinetic coefficient) of order m in D ∂C/∂x (0,t)=km[C(0,t)−CE]m. A selected parameters are given for (YBi)3(FeGa)5O12 films grown under the same conditions: Orientatio−−−−−−−0°(110) 30′ 2° 30′ 2° 30′ 7° 30′ 90° (111) Growth rate, μm/min ...  0.1   0.075      0.08       0.16        0.26 Specific Faraday rotation, deg/cm...1526  1804    1713   1439     1953 The peculiarities of domain structure and properties of obtained films are discussed.
Dependence of energy dissipation on annealing temperature of melt–spun NdFeB permanent magnet materials
Authors: Gao Z. , Jiles D. C. , Branagan D. J. , McCallum R. W.
Published: July 2002

A model of magnetic hysteresis which was developed originally for soft magnetic materials has been applied to melt–spun ribbons of Nd2Fe14B-based material. The crucial ideas in the model description of hysteresis center on a dissipation of energy due to hysteresis which is proportional to the change in magnetization. The Nd2Fe14B material was melt–spun amorphous and then annealed for a period of 24 h at temperatures ranging from 700 to 950 °C. This resulted in different grain sizes, depending on annealing temperature. Consequently the hysteresis curves represent the properties of the material as a function of both annealing temperature and grain size. It was found that the magnetic properties varied systematically with annealing temperature, and hence grain size, as would be expected. When modeling the magnetic properties it was found that the model parameters also varied systematically, in particular, the energy dissipation parameter k was to a first approximation a simple linear function of the annealing temperature and decreased with increasing annealing temperature as a result of grain growth. Therefore, this study revealed a basic relationship between materials processing conditions, microstructure, model parameters, and magnetic properties.
Structural and magnetic studies of Er2Fe17−xMxCy (M=Ga and Al) compounds
Authors: Chang W. C. , Lu S. L. , Chen S. K. , Yao Y. D.
Published: July 2002

The effect of Ga and Al substitution for Fe on the structural and magnetic properties of the Er2Fe17−xMxCy (M=Ga, Al; x=0–4, y=0–2) compounds was investigated. It was found that Ga is superior to Al in stabilizing the single-phase Er2Fe17−xMxCy compounds. The hexagonal Th2Ni17-type structure persisted in almost all alloys with the exception of Er2Fe13Ga4C and Er2Fe13Ga4C2. These two compounds exhibited a rhombohedral Th2Zn17 structure. Both the Curie temperature and magnetization can be enhanced with a certain amount of Ga or Al substitution. But they decreased almost monotonically with the increase of Ga or Al content in Er2Fe17−xMxCy (x≳1, y≳0). The spin reorientation temperature, Tsr, was influenced by both carbon interstitial and Ga or Al substitution for Fe and ascribed to the increase of the c-axis uniaxial anisotropy of the Er3+ sublattice by the modification of electron structure around it. The highest Tsr of 241 K appears in the compound Er2Fe14Ga3C.
Experimental observation of the longitudinal resonance mode in ferromagnets with random anisotropy
Authors: Suran G. , Boumaiz E. , Youssef J. Ben
Published: July 2002

We report here the first experimental observation of the longitudinal resonance mode in ferromagnets with a wandering axis (FWA). The mode is detected in amorphous Co93−xZr7(RE)x thin films with RE=Pr,Nd,Tb, and Dy, 0≤x≤4, but only if the film exhibits a very well defined in-plane uniaxial anisotropy field Hk. The experimental identification and some of the main properties of the longitudinal mode are reported and compared with theoretical predictions.
Electrical transport and optical properties of tetraanilinobenzene Langmuir–Blodgett films
Authors: Paloheimo J. , Pal A. J. , Stubb H.
Published: July 2002

We report a study of the electrical and optical properties of Langmuir–Blodgett films of tetraanilinobenzene. The optical absorption, peaking at 4.1 eV, is blue shifted by 0.2 eV, and photoluminescence, peaking at 3.0 eV, is red shifted by 0.4 eV compared to the material in solutions, indicating H aggregates. p-type doping by iodine gas or protonation in acidic solutions results in two polaronic subgap absorption bands and leads to an increase in conductivity from 10−10 to about 10−4 S/cm. The optical properties and doping mechanisms have been discussed and compared to those of vacuum-evaporated films. The oxidized units as well as polaronic states were found to act as nonradiative recombination centers for excitons. The conductivity σ of the protonation-doped samples has a temperature T dependence log σ∝T−1/2 indicating variable-range hopping in a quasigap, probably due to the Coulomb interactions between localized carriers in polaronic states. The nonohmic region was studied for moderately high electric fields up to 105 V/cm.
Superconductor-insulator transition and electric field effect of YyPr1−yBa2Cu3O7−x thin films
Authors: Kabasawa Uki , Tarutani Yoshinobu , Fukazawa Tokuumi , Sugii Nobuyuki , Hasegawa Haruhiro , Takagi Kazumasa
Published: July 2002

The transport characteristics of YyPr1−yBa2Cu3O7−x thin film systems were systematically investigated as a function of the Y concentration and film thickness. The films in the superconducting state changed their transport characteristics to those of the nonsuperconducting state when the film thickness was decreased beyond the value at which the film sheet resistance is equal to the quantized sheet resistance h/4e2. This phenomenon is a kind of superconductor-insulator transition. The resistance-temperature characteristics in the insulator phase are a result of the variable-range-hopping conduction between localized states. The electric-field effect was measured especially in the insulator phase. The resistance modulation ratio ΔR/R in the insulator phase was much greater than the carrier density modulation ratio ΔN/N. The ratio of ΔR/R to ΔN/N increased as the Y concentration increased. In particular, the (ΔR/R)/(ΔN/N) value reached as high as 50 for a Y0.9Pr0.1Ba2Cu3O7−x film in the insulator phase. Higher (ΔR/R)/(ΔN/N) values effectively enhance the performance of superconducting field effect transistors.
Magnetic and crystallographic properties of R2Fe14Si2 (R=Y, Gd, Dy, Er, and Tm) compounds (abstract)
Authors: Konno K. , Ido H. , Pourarian F. , Obermyer R. T. , Sanker S. G.
Published: July 2002

In connection with a previous work, magnetic and crystallographic properties of the off-stoichiometric compounds R2Fe14Si2 of the R2Fe17-type are studied. Magnetization curves at T=5 K are observed in a high magnetic field up to 15 T for loose powders as well as for field-aligned powders of the samples expressed in the title. Temperature dependencies of the spontaneous magnetizations are also determined in the temperature region from 5 K to the respective Curie temperature. Detailed x-ray analysis is carried out for Y2Fe14Si2. Conclusions are as follows: (1) the Si substitution brings about significant displacements of the 12j-site Fe as well as the dumbell-site Fe from their original positions, which is discussed in connection with other present experimental data such as the remarkable enhancement of the Curie temperature caused by the Si substitution; (2) averaged Fe moment reduction is strictly determined for the present samples; (3) all the samples have a planer anisotropy at room temperature, taking this fact the magnetization curves for the field-aligned samples are analyzed; (4) exchange interaction between R sublattice and Fe sublattice has been determined for all the samples.
Study of residual magnetization of hard steel samples
Authors: Saadi M. , Jellali F. , Delmas A. , Quichaud G.
Published: July 2002

This study forms part of a program trying to determine the position of a train on railway using magnetic spots. In this paper, we investigate the influence of the parameters of the exciting current pulse on the residual magnetization of a hard steel. In the case of a pulse of long duration and small amplitude, we show that the associated hysteresis problem can be reduced to the determination of a magnetic field distribution due to a fixed magnetization. We define this magnetic field distribution by means of a boundary integral equations method. For these conditions, the internal and external induction distributions are of the same order of magnitude. In contrast, for pulses of short duration (millisecond or less) and large amplitude, the eddy currents in hard steel lead to a remanent magnetization loop which is permanently trapped by the hysteresis phenomena. The residual external induction is always small, and is not representative of the large internal magnetization.
Magnetic reversal in perpendicularly oriented thin films subjected to picosecond magnetic fields (abstract)
Authors: Heidmann Juergen , Weller Dieter , Siegmann Hans C. , Garwin E. L.
Published: July 2002

The magnetic reversal mechanism in perpendicularly oriented, premagnetized Co based thin film alloys, induced by ultra short magnetic field exposure of a few picoseconds duration has been studied. Field pulses with a magnitude of several thousand Tesla were generated by the 50 GeV final focus electron beam at the Stanford Linear Accelerator Center (SLAC). Characteristic remanent domain patterns are observed in these films long after field exposure using polar Kerr microscopy. Complete reversal of the magnetization is found to occur during a single spin precession event of 6.0 ps duration where the inplane-field amplitude is greater or equal to the macroscopically determined perpendicular anisotropy field. Further, a wide transition range, dividing the reversed and nonreversed regions is observed which is broken into a quasi periodic stripe domain structure with stripe-width 0.3 μm. As a main result of this experimental study we find that magnetization reversal on this time scale is solely governed by the intrinsic effective field, i.e., anisotropy- and demagnetization-field contributions, rather then by complex curling and buckling mechanisms. Unique insight into fundamental spin reversal mechanisms and their ultimate speed in thin magnetic recording films is provided by these experiments.