bluuebunny/crossref_metadata_2025 huggingface dataset:
XANES spectroscopy of CdFeTe and hypothetical zinc-blende FeTe (abstract)
Authors: Kisiel A. , Burattini E. , Lee P. M. , Dalba G. , Fornasini P.
Published: July 2002

Experimental measurements and studies of x-ray absorption edges have been carried out in Cd(1−x)FexTe with x=0.055 for the L edges of Cd and Te and the K edges of Fe using the synchrotron radiation at ADONE Wiggler facility in Frascati and utilizing the Si/111/ channel-cut crystal monochromator. Experimental results are presented and compared with theoretical calculations based on electronic density of states obtained from results for an ordered ferromagnetic alloy of CdFeTe. Agreement between the experimental results and those based on the theoretical calculations is found to be good. Using a virtual crystal model for the L edges of Te we have extracted the p and s,d projected contributions of FeTe in CdFeTe. The maximum values of these contributions are found to be situated at an energy equivalent to the conduction band edge in CdTe and about 4 eV above this band edge, respectively.
Neutron diffraction on the diluted magnetic semiconductor Sn1−xMnxTe
Authors: Vennix C. W. H. M. , Frikkee E. , Swagten H. J. M. , Kopinga K. , de Jonge W. J. M.
Published: July 2002

In the diluted magnetic semiconductor Sn1−xMnxTe, magnetic ordering occurs at low temperature when the charge carrier density p exceeds a critical value. By means of single-crystal neutron diffraction on samples with x=0.03, p = 7 × 1020 cm−3 and x=0.06, p = 11 × 1020 cm−3, we have shown that this ordered phase is ferromagnetic. For the 6% Mn crystal indications were found for magnetic fluctuations just below the ordering temperature. The experimental results rule out the existence of a (reentrant) spin-glass phase at these Mn concentrations and charge carrier densities.
A study on the Kerr effect enhancement by the multidielectric layer structure
Authors: Kim K. C. , Kim Y. S. , Kim J. H. , Moon H. , Hong K. M. , Ahn D. H.
Published: July 2002

Many types of magneto-optical structures have been investigated to improve the MO Kerr effect. We have studied the enhancement of the MO Kerr effect in the Tb21Fe79 amorphous film having a multidielectric structure in which the TiO2 layer is sandwiched by SiNx layers. The variations of Kerr angle and reflectivity with the thickness of dielectric layer are calculated by using the reiterative formula [M. Mansuripur, G. A. N. Connel, and J. W. Goodman, J. Appl. Phys. 53, 4485 (1982)]. Experiment and simulation results are discussed.
Magneto-optic and optical characterization of Tb/Co compositionally modulated amorphous films
Authors: Chen Liang-Yao , He Ping , Nafis Suraiya , McGahan William A. , Woollam John A. , Sellmyer D. J.
Published: July 2002

Amorphous Tb/Co compositionally modulated films were deposited on Si substrates with different modulation layer thicknesses ranging from about 2.5 to 15 Å. The nominal Tb to Co layer thickness ratios were systematically varied and the complex refractive index (n and k) and polar magneto-optical Kerr effects (rotation and ellipticity) were measured in the 3000–8000-Å spectral range as well. The samples were divided into two groups. In one group, the thickness of the Co layers was fixed, the Tb layer thickness varied. In the second group, the thickness of the Tb layer was fixed, and that of the Co layer thickness varied. The Kerr rotation and the coercivities of the samples showed very consistent and interesting changes. X-ray diffraction and x-ray fluorescence were also performed on the samples, which revealed layered structures, or compositional modulation, and provided information on the Tb to Co atomic ratios in the samples.
Nuclear-spin relaxation in S=1 Heisenberg antiferromagnetic chains in high field
Authors: Gaveau P. , Boucher J. P. , Regnault L. P. , Goto T. , Renard J. P.
Published: July 2002

The proton spin-lattice relaxation rate 1/T1 has been measured in the two compounds Ni(C2H8N2)2NO2 (ClO4) (NENP) and [Ni(NO2)3N(CH3)4] (TMNIN), which provide good examples of S=1 antiferromagnetic chains. Both the field H and the temperature dependencies are well analyzed in the framework of the Haldane conjecture. The prediction of a mode whose energy decreases with H is confirmed. The energy damping of this mode is observed to be also reduced by H. For both compounds, a possible energy renormalization is suggested as H approaches the critical field, where the spin system is expected to recover a magnetic behavior.
Separation of spin and orbital moments by synchrotron x-ray scattering (invited) (abstract)
Authors: McWhan D. B.
Published: July 2002

X rays are becoming an important probe of magnetism largely due to the unique properties of synchrotron radiation, namely the high flux, polarization, and tunability. The x-ray scattering cross section contains terms which depend on the electronic spin and angular momentum densities, and the two terms have different polarization dependencies unlike the corresponding terms in the neutron scattering cross section.1 The ratio of the orbital to spin contributions can be obtained from measurements of the change in linear polarization on scattering from an antiferromagnet. This effect was demonstrated for the basal plane spiral structure of holmium metal.2 More recently measurements on the type IA phase of UAs have demonstrated the existence of an orbital contribution approaching the free ion value of uranium even though the observed magnetic moment is only two-thirds of the free ion value.3
The sensitivity of magnetoacoustic emission to defects and coupling in the context of stress measurement
Authors: Ng D. H. L. , Jakubovics J. P. , Briggs G. A. D. , Scruby C. B.
Published: July 2002

Magnetoacoustic emission (MAE) is under development as a technique for the nondestructive measurement of stress in magnetic materials. However, structural defects create additional boundaries which alter the magnetic domain configuration and could perturb the MAE response of the material. MAE is therefore employed to investigate the effect of additional surfaces on the domain structure close to and some distance from artificially implanted holes in a mild steel bar. The MAE profile, a result of non-180° wall motion, obtained before the hole drilling, shows two outer peaks of equal height one at each knee of the magnetization curve. This suggests that the energies dissipated by the domain nucleation and annihilation processes are the same. However, the MAE profile obtained near an 8 mm hole shows a large initial peak and a small final peak, indicating that the enlargement of reverse domains is mainly due to the unpinning of trapped walls at the edges of the hole. This process is discrete and sudden and, therefore, the initial signal peak is large. In the largest field applied, the reverse domains are not completely annihilated, causing the final peak to be small. A further practical problem is that variations of magnetic coupling can have a significant effect on the MAE profile. This is also investigated, and it is concluded that using a spacer of optimal thickness between the magnet and the specimen could reduce the sensitivity to this effect.
New data-acquisition system for spin-polarized scanning electron microscopy (abstract)
Authors: Matsuyama H. , Koike K.
Published: July 2002

A new data-acquisition system suitable for spin-polarized scanning electron microscopy used in magnetic domain observation has been developed. The system is composed of a primary-electron-beam scan controller, four counters of two pairs of output signals coming from a spin polarization detector, an image processor with two high-speed digital signal processors calculating the polarization-components Px and Py from the detector outputs, 32 frame memories (512×512×16 bit) for the detector outputs, Px, Py, sample absorbed current, etc., as well as a 1280×1024 pixel monitor. The system enables not only high-speed scanning (21 s/image) for a quick view but also very slow-speed scanning (≳1 h/image) for a high-quality image. With this variable-speed scanning, it is possible to promptly obtain a homogeneous quality image even when the secondary-electron intensity distribution is inhomogeneous due to the surface topography. By calculating the magnitude and direction of magnetization from Px and Py, magnetization vectors can be represented as arrows in the domain image. The system has been successfully applied to domain observation of an iron single crystal and a magnetic recording head having a three-dimensional surface structure as well as side plane observation of multilayered films for a magnetic recording head.
The topography of iron oxide thin films (abstract)
Authors: Zhou Zeng-Jun , Yan Jun Jue
Published: July 2002

The surface mophology of thin-film recording media is important for recording characteristics. STM analysis was done for iron oxide thin films prepared by a water vapor added rf-sputtering process.1 They were oxidized in an open air in the temperature range 300–350 °C in order to transfer magnetite thin films to gamma iron oxide thin films. The STM image of gamma iron oxide thin film is not much different from the as-sputtered thin film, although the surface roughness increased a little; it is less than 200 Å.
Examination of the interaction between eddy currents and magnetoelasticity in Terfenol-D
Authors: Kvarnsjö L. , Engdahl G.
Published: July 2002

When an electrically conducting magnetic material is magnetized dynamically, eddy currents will be induced inside the material. The eddy currents give rise to a decrease of the flux density obtained at quasistatic conditions at a specific magnetizing field and hence, for a magnetostrictive material such as Terfenol-D, also a decrease in the magnetostriction. Because of the magnetoelastic interaction in magnetostrictive materials, it is difficult to analytically predict the influence of these eddy currents. By solving the equation for the radial field distribution inside the rod numerically, a model which takes the eddy currents into account can be formulated. This radially resolved model makes it possible to calculate the local eddy current distribution inside the rod, and by choosing the appropriate boundary conditions, the ‘‘effective’’ behavior of the rod can be calculated. Results obtained from a radially resolved model are compared with corresponding results from experiments. Also, a comparison is made between the radially resolved model and an analytical model for handling the influence of eddy currents in magnetostrictive materials.
Numerical computation of the magnetostriction effect in ferromagnetic materials
Authors: Delince F. , Genon A. , Gillard J. M. , Hedia H. , Legros W. , Nicolet A.
Published: July 2002

This paper describes a model of the magnetostriction by a finite element scheme for magnetostatic cases. Given a structure, the magnetic field is first computed taking into account the ferromagnetic saturation. Magnetic induction over elements is then used to compute the magnetoelastic energy and the minimization of the mechanical functional leads to the determination of displacement, strain, etc., due to the magnetostriction process.
Thermal renormalization of the helix wave vector in the planar model
Authors: Rastelli E. , Tassi A.
Published: July 2002

Helical configurations play an important role as equilibrium configuration for a number of rare-earth-metal and transition-metal compounds. The source of spiralling spin patterns in continuous symmetry models is the competition between the exchange coupling between spins localized at different distances. Experimental data and several approximated arguments suggest that the helix pitch is temperature dependent. Here, we give the first controlled proof of this behavior on the basis of a low-temperature expansion of the free energy for the planar chain.
Demagnetization effects on forward and reverse thresholds of M-R memory elements
Authors: Pohm A. V. , Comstock C. S.
Published: July 2002

A refinement in the way hard-axis demagnetizing effects are treated in multilayer M-R memory elements brings experimental and calculated results into agreement for both the forward and reverse switching thresholds. In the improved model, the nonuniform rotation of the magnetization in the elements because of edge pinning is taken into account. The demagnetizing fields are treated as corrections to the hard-axis word field rather than an addition to the anisotropy constant.
Major line operation in vertical Bloch line memory
Authors: Wu J. C. , Katti R. R. , Stadler H. L.
Published: July 2002

The operation of a major line in a vertical Bloch line memory using a partial garnet grooving architecture was studied experimentally and numerically. The major line was fabricated on a 5-μm bubble garnet using three conductor layers and a 10% garnet grooving. The major line contains a bubble generator, a bubble propagation track, a bubble expander for bubble detection, and a bubble annihilator. The minimum current for bubble generation was 350 mA, at 50 ns pulse width. The bubble propagation track was a typical dual conductor design with a 5-μm-wide conductor and a 20-μm circuit period. The minimum drive current was 5 and 10 mA at an operating frequency of 250 and 500 kHz, respectively. The bias field margin was from 84 to 100 Oe. The bubble expander was a modification of the propagation track. The meandering conductor and the groove width were gradually increased to stretch the bubble into a stripe. The bias field margin was from 82 to 84 Oe. The numerical model includes the effect of the garnet grooving, and the simulation results agree with the experimental data.
Magnetization and thermal expansion of single-crystal Er and Tm
Authors: Willis Frank , Ali Naushad
Published: July 2002

The magnetization and ac susceptibility data of single-crystal Er show the antiferromagnetic ordering of the c axis and basal plane moment components at TN∥ = 87 K and TN⊥ = 53 K, respectively. In addition, we observe anomalies at 51, 40, 34, 29, and 27 K. These anomalies correspond to the commensurate spin-slip structures observed by Gibbs et al. [Phys. Rev. B 34, 8182 (1986)] in x-ray synchrotron scattering studies. From the thermal expansion study of single-crystal Er, we find that the phase transitions at TN∥ and 51 K are second order, whereas the transitions at TN⊥, 27, and 18 K are first order. The order of these transitions are in poor agreement with earlier studies of single-crystal Er. The magnetization measurements of single-crystal Tm show anomalies at TN = 57 K, Tc = 30 K, and an anomaly at 41.5 K.
Forced magnetostriction and pressure dependence of the magnetism of weakly ferromagnetic Y(Co1−xAlx)2 and Sc3In
Authors: Riedi P. C. , Armitage J. G. M. , Graham R. G.
Published: July 2002

The Curie point and spontaneous magnetization of weakly ferromagnetic Y(Co1−xAlx)2 alloys with x∼0.15 is shown to decrease rapidly with increasing pressure, in agreement with the theory of weak itinerant ferromagnetism. Forced magnetostriction measurements on Sc3In, however, confirm that the magnetization at 4.2 K in a field of ∼2 T increases with pressure.
Magnetism in expanded 3d transition metals
Authors: Schwartzman K. , Fry J. L.
Published: July 2002

For sufficiently large expansion of the lattice, transition metals will eventually exhibit ferromagnetism in accordance with Hund’s rule. This problem has been reexamined on the basis of calculations of the paramagnetic susceptibility to determine instabilities of the paramagnetic phase. Comparison of predictions using this method for the critical lattice constant for ferromagnetism are in good agreement with previous total energy calculations. However, this study also yields new predictions of antiferromagnetism for a range of lattice constants less than that for onset of ferromagnetism. The susceptibility is formulated in a multiband generalization of the Stoner approach with many-body effects incorporated within the local-density approximation in density functional theory. Slater–Koster band structures are employed which permit lattice constant variation to be realized through a relatively simple scaling scheme. Both many-body effects and the distribution of primarily single-electron states associated with Fermi surface nesting combine to produce the antiferromagnetic instability under expansion. Nesting is probably necessary for incommensurate antiferromagnetism, and its decrease in importance as the lattice constant continues to increase contributes to the incipient ferromagnetic instability.
Magnetic coupling in CaCu5-type rare-earth cobalt compounds
Authors: Liu J. P. , Zhong X. P. , de Boer F. R. , Buschow K. H. J.
Published: July 2002

The composition of rare-earth cobalt compounds of the hexagonal CaCu5-structure type varies from RCo5 to approximately RCo6 when passing through the lanthanide series. We have studied the field dependence (up to 35 T) at 4.2 K of the magnetization of several compounds of this series, including various pseudobinary compounds of the type R1−xYxCo5+δ and GdCo5−rNir. The magnetic isotherms at 4.2 K were analyzed with a mean-field model. The magnetic coupling constant JRT between the moments of the rare-earth (R) and 3d (T) element in the Hamiltonian H = −Σ2JRTSR⋅ST derived from these measurements was found to have a tendency to decrease with increasing atomic number of the lanthanide involved.
Impurity effects in superconducting UPt3
Authors: Aronson M. C. , Vorenkamp T. , Koziol Z. , de Visser A. , Bakker K. , Franse J. J. M. , Smith J. L.
Published: July 2002

Superconducting UPt3 is characterized by a novel and complex magnetic field-temperature phase diagram, with two superconducting transitions at Tc1 and Tc2 in zero field. We have studied the effects of Pd and Y impurities on the zero field superconducting properties of UPt3. Resistance measurements show that both dopants increase the residual resistivity and decrease the spin fluctuation temperature in the normal state. Tc1 is depressed by both dopants, but more effectively by Pd. ‖Tc1 − Tc2‖ is essentially unaffected by Y doping, but increases dramatically with Pd doping.
The temperature relationship of the fluctuation field and coercivity in NdFeB alloys
Authors: Ferguson G. B. , O’Grady K. , Popplewell J. , Chantrell R. W.
Published: July 2002

The coercivity Hc and fluctuation field Hf are intrinsic properties of any magnetic system exhibiting hysteresis. They are measures of the energy barriers resisting magnetization reversal and may be used to probe the nature of the magnetization processes. The variation of coercivity as a function of temperature and of the fluctuation field as a function of field and temperature have been studied for sintered and melt-spun NdFeB. The fluctuation field has been found to vary with field in the sintered material indicating that interactions play an important role in the nucleation of reverse domains while it remained constant in the melt-spun sample. The relationship between the coercivity and fluctuation field has been studied and found to be consistent with the Barbier plot though some deviation from the expected curve was found.
The effect of Laves phase on the magnetic properties of Fe-Co-Nd-B alloys
Authors: Yang C. J. , Choi S. D. , Lee W. Y.
Published: July 2002

The formation of a Laves phase, Nd(Fe,Co)2, in Nd(Fe0.92−xCoxB0.08)5.5 magnets prepared by powder metallurgical processing of melt-spun powders has been confirmed. The Laves phase forms after crystallization in melt-spun alloys when x is larger than 0.17, and is likely to occupy 15 vol % of the sintered magnet when the Co content x is 0.22. ‘‘Two-phase’’ magnets of Fe77Nd16B7+(5–20 wt. %) NdFe2 were prepared by rapid solidification and powder metallurgy. As the volume fraction of rapidly solidified Laves phase NdFe2 (actually a mixture of NdFe7 compound plus Nd-rich phase) increased, the magnetic properties, particularly for coercivity, were found to decrease.
Self-consistent-field calculations for the Anderson impurity model
Authors: Chen Chu-Xin , Luo Qiang , Bickers N. E.
Published: July 2002

A variety of self-consistent-field techniques have recently been used to calculate correlation functions of the two-dimensional Hubbard model. Such techniques extend Hartree–Fock theory by including a large class of fluctuation processes. The computational requirements of the self-consistent-field approach decrease in lower dimensional systems. For this reason, a thorough test of techniques may be performed by examining the Anderson impurity model, the zero-dimensional limit of the Hubbard model. Using the fluctuation exchange and pseudopotential parquet approximations applied previously in two dimensions, we calculate static and dynamic correlation functions for the Anderson model and compare with quantum Monte Carlo results.
Effect of magnetic domain configuration on read-back amplitude variations in inductive film heads (abstract)
Authors: Kasiraj P. , Holmes R. D.
Published: July 2002

Narrow track width, high-performance inductive film heads exhibit a noise phenomenon in which the read-back peak amplitude varies after writing with the head. This noise phenomenon was studied in 6- to 8-μm track width, 31-turn double layered coil, film heads using a scanning Kerr effect microscope. These heads, made from electroplated permalloy films with a magnetostrictive coefficient of − 1.6 × 10−6, were specially selected for the study to have varying levels of read-back amplitude variation by using the percent variation in the peak amplitude after repeated writes as a quantitative noise figure. A statistical sampling method was used to quantitatively measure the magnetic domain patterns in the top NiFe layer of the heads under simulated operating conditions. Quantitative correlation was found between the read-back variation and the magnetization orientation in the narrow-sloped pole region. The images show that a single 180° domain wall orientated longitudinally to the flux conduction direction in the narrow pole piece is the major source of read-back variation in these types of heads. The statistical sampling method shows that the pole domain configurations are reproducible in both the low-noise and high-noise heads. Patterned NiFe films on planar alumina substrates have the desired transverse oriented 180° domain wall configuration in the pole-shaped region, as found in the low-noise heads.

These results imply that the variation of the domain configuration in the pole region is caused by easy axis reorientation due to variation in the stress-induced magnetic anisotropy in that region. We also find that the read-back noise is not sensitive to the longitudinal 180° walls found near the back closure region of the heads. This is probably due to the lower flux densities found in the back closure as compared to the pole region and the existence of other flux paths that circumvent the domain walls in the back closure region. We conclude that read-back distortion noise in 6-μm track width heads can be drastically reduced by maintaining a transverse magnetic easy axis in the sloped pole piece by either employing fabrication methods that control the stress state of the pole region or by using very small magnetostriction values in the NiFe films.1
Avalanches and self-organization in the dynamics of cellular magnetic domain patterns (invited)
Authors: Westervelt R. M. , Babcock K. L. , Vu M. , Seshadri R.
Published: July 2002

Cellular magnetic domain patterns in magnetic garnet films are an example of a spatially-extended metastable system whose evolution is limited by topological constraints. For sufficiently large applied magnetic fields, the entire pattern is under tension and can respond to local perturbations via large collective motions. In this regime disordered cellular patterns respond to small increases in applied field or to manual cell breakage via avalanches of sequential cell destruction which sweep through the pattern via the motion of cell walls. After one avalanche has stopped another can be started by a small increase in field or by another manual cell breakage; the system thus tends to self-organize into barely stable states. The measured distributions of avalanche size and duration are best fit by power laws. These features suggest that cellular avalanches may be an example of self-organized criticality.
Electrical resistivity, magnetization, and grain-boundary precipitate in nickel-rich nickel-indium alloys
Authors: Yao Y. D. , Chen Y. Y. , Chuang T. H. , Kung C. , Lin C. J.
Published: July 2002

The variations of the electrical resistivity, the magnetization, and the grain-boundary precipitates of a Ni-rich Ni-In alloy system with In concentration up to 7.5 at. % have been investigated as functions of annealing time at 773 K. For samples homogenized at 1225 K, clear grain boundaries are observed. However, for these aged samples, we observed both grain-boundary precipitates and variations of the electrical resistivity and the magnetization; and the binary alloy with higher In concentration has the higher variation rate in the decrease of the electrical resistivity, the increase of the magnetization, and the growth of the grain-boundary precipitates.
Observation of short-range spin correlations in Fe-doped GdBa2Cu3O7−δ superconductors
Authors: Tang H. , Qiu Z. Q. , Walker J. C.
Published: July 2002

The effects of Fe doping on the superconducting and magnetic properties of GdBa2Cu3O7−δ superconductors have been thoroughly examined. Fe doping not only depresses the global superconducting transition temperature Tc, but also locally destroys superconductivity in small regions around the Fe dopants. Mössbauer measurements at 4.2 K revealed magnetic hyperfine structure for samples doped with ≥3% of Fe. Its origin is determined here to be Fe-induced short-range spin correlations of the Cu spins in the nonsuperconductive regions. Upon oxygen depletion, the short-range spin correlations evolve into the familiar long-range 3D antiferromagnetic ordering.
Domain wall contrast in magnetic recording media (abstract)
Authors: Proksch R. B. , Dahlberg E. Dan
Published: July 2002

A compact, low noise magnetic force microscope has been constructed. It utilizes an ac interferometric detection scheme sensitive to the magnetic force gradients above a sample. It is similar to the design proposed by Rugar et al.1 A variety of magnetic recording medias, both longitudinal and vertical with written patterns, have been investigated. The studies have been made using etched Ni cantilevers. Contrast and resolution of the microscope as a function of cantilever scan heights will be discussed.
Dynamic periodical distortions of stripe domains in garnet films (abstract)
Authors: Zharkov G. Yu. , Yurchenko S. E. , Chetverikov V. M.
Published: July 2002

One of the problems arising in the development of VBL memory is to make stripe domains (SD) resistant to bending distortions. The paper considers a theoretical and experimental study of the mechanism of bending sinusoidal distortions of isolated SD caused by the sequence of bias fields (Hz) spatially homogeneous pulses compressing SD. The SD distortion dynamics was studied by the method of high speed photography with exposure of 10 ns. The SD critical width has been discovered. When reached, it first causes small distortions of the domain wall (DW). Further effects of the Hz pulses increases them, and after 10–12 field pulses the irreversible statically stable sinusoidal distortions of SD are finally formed. After that each subsequent Hz pulse just inverts the spatial structure of the distortions (i.e., transfers it from one bistable sin kx-type state to another: −sin kx). The performed theoretical analysis shows that the above effect is connected with the DB structure transformation observed when some critical SD width w* is reached. It has been experimentally discovered that the formed bending distortions of SD remain stable during the effect of the Hz pulse where SD width w≳w*, and tend to straighten when width w<w* is reached. The sequence of the above changes in the DW structure leads to the transition from one bistable state to another through an intermediate state with a small SD width. Experimentally found has been a close-to-linear dependence of spatial amplitude of distortions on the value of Hz. It has also been discovered that the distortions period and amplitude linearly increase together with the duration of Hz. The relation between the time of reaching w* and time of bending formation has been established.
Magnetic properties of Fe-N/Al-N multilayered films prepared by ion-assist sputtering
Authors: Kubota K. , Naoe M.
Published: July 2002

Fe-N/Al-N multilayered films have been prepared by dual-ion-beam sputtering. The influences of nitrogen incorporation into Fe/Al multilayered films and the effects of postannealing on the soft magnetic properties have been investigated. For the multilayered films composed of Fe-N and Al-N layers with thickness of 100 and 20 Å, respectively, coercivity of about 1 Oe and relative permeability of 2500 was attained by incorporating the proper content of nitrogen into each layer during deposition and then postannealing the films at 150 °C. Fe-N/Al-N multilayered films prepared by the ion-assist sputtering technique used in this study may be useful as excellent soft magnetic materials.
Effect of spacer material on the magnetic surface anisotropy in ultrathin Fe70B30 multilayer films
Authors: Hicken R. J. , Rado G. T. , Chien C. L.
Published: July 2002

It has been found recently that the magnetic surface anisotropy Ks in Fe70B30/Ag multilayer films decreases monotonically with magnetic layer thickness (2L) for 2L<16.5 Å. In order to determine possible effects of the spacer material on the surface anisotropy in the aforementioned system, Ag has been replaced with Al2O3 and ferromagnetic resonance (FMR) measurements have been made on these films. These Fe70B30/Al2O3 films were fabricated by magnetron sputtering and were characterized by x-ray-diffraction and vibrating sample magnetometer (VSM) measurements in addition to FMR. In the region where Ks depends upon 2L, the data is insufficient to confirm the thickness dependence of Ks that was observed in Fe70B30/Ag, while in the region where Ks is independent of 2L, the values of Ks deduced for Fe70B30/Ag and Fe70B30/Al2O3 are in good agreement. The latter is particularly interesting in light of the enormous difference in conductivity between Ag and Al2O3.
FMR in ferromagnetic films with coupled layers
Authors: Guslienko K. Yu. , Lesnik N. A. , Mitsek A. I. , Vozniuk B. P.
Published: July 2002

The theory of FMR in double-layer coupled films suggested is compared with experimental data on resonance field angular dependencies in the T/Permalloy (T=Co,Ni) films. The angular dependence of FMR has been studied at 9.05 GHz at room temperature. The external magnetic field H is directed at an angle φ to the film plane. It has been found that 1,2,3, or 4 resonance peaks exist that depend on layer thickness. The results have been explained by a theoretical model assuming exchange and dipole interlayer coupling. The latter depend upon the film thicknesses and the critical layer thickness dcrj ∼ δj (domain-wall halfwidth) is introduced. Only the case dj < dcrj (homogeneous magnetic state of the film) is considered. Numerical calculations are used for finding the equilibrium dependencies of the polar angles θj(H,φ) of the magnetization directions from the thermodynamic potential which corresponds to the Hamiltonian used. The experimental FMR spectra of all samples reveal two resonance lines: ‘‘Kittel’s peak’’ and an ‘‘exchange peak.’’ The theoretical predictions and the experimental results are in good agreement. The interlayer coupling energy obtained is about 3 erg/cm2.
Out-of-plane ferromagnetic resonance study of magnetically coupled Fe/Cr/Fe films (abstract)
Authors: Oliver S. A. , Vittoria C. , Krebs J. J. , Lubitz P. , Prinz G. A.
Published: July 2002

Magnetically coupled single-crystal Fe/Cr/Fe (001) sandwiches have been studied by ferromagnetic resonance (FMR) techniques. Such films have been previously shown to be antiferromagnetically coupled for a chromium layer thickness range 12 Å<tCr<25 Å by variable frequency ferromagnetic resonance measurements along principal crystallographic axes, and other techniques.1 These measurements have been extended to include oblique angle application of the applied magnetic field (H) between principal crystallographic axes in the film plane and the film normal. Measured films had tCr=13, 16, 17, and 28 Å. Ferromagnetic resonance measurements were taken using a fixed frequency 9.5-GHz cavity. Resonances corresponding to the in-phase and out-of-phase precession of film moments M1 and M2 were observed for the three thinnest films with H lying in the film plane. These resonances could be tracked to high (∼85°) oblique angles before disappearing, with the in-phase resonance strengthening near perpendicular. Perpendicular FMR measurements on the tCr=13-Å-thick sample show a weaker resonance ∼680 Oe above the in-phase resonance, corresponding to the out-of-phase precessional mode. This value can be directly compared to 4J/Ms∼540 Oe result from earlier work,1 perhaps indicating some anisotropic exchange. An extension of the model presented in Ref. 1 is presented to explain the resonance behavior as a function of angle.
Magnetic anisotropy of ferromagnetic Fe and Co thin films (invited) (abstract)
Authors: Freeman A. J. , Li Chun
Published: July 2002

The observation of transition-metal (TM) magnetic moments in thin films aligned perpendicular to the surface has focused theoretical and experimental attention on the origin of magnetic anisotropy in these exciting low-dimensional materials. In this paper we report on a study of the magnetic anisotropy of Fe and Co thin films originating from the spin-orbit interaction term of the fully relativistic Dirac equation. We employ a total energy second variation FLAPW method in which: (i) the electronic charge density is determined with the semirelativistic (no spin-orbit) FLAPW method; (ii) relativistic eigenvalues are calculated via a variational procedure using the semirelativistic wave functions as basis. The magnetic anisotropy energy of free-standing Fe(001) and Co(001) monolayers yields in-plane orientation of the spin moment. Semirelativistic calculations determined the magnetic moments of 1Fe/1Au, 1Fe/1Ag, or 1Fe/1Pd−all (001) slabs; the results agree well with those of monolayer Fe on thicker substrates. Magnetic anisotropy results1 for Fe monolayers on Au, Ag, and Pd(001) substrates give perpendicular anisotropy for these films, in agreement with experiment. Magnetic anisotropy calculations of Co thin films on CuPd and (001) and (111) substrates will also be presented. The origin of the magnetic anisotropy is discussed from a detailed analysis of the electronic structure (electronic bands, Fermi surface). Comparisons are given to the work of Gay and Richter and Fritsche et al.
Order parameter distribution of the random bond Ising ferromagnet with antiperiodic boundary conditions
Authors: Hetzel R. E. , Bhatt R. N.
Published: July 2002

The two-dimensional random bond Ising ferromagnet with antiperiodic boundaries in one direction has been studied by Monte Carlo simulations. From the overlap distribution function P(q), the scaling behavior of P(q) near q=0 with linear dimension L has been obtained. In contrast to recent simulations of the four-dimensional Ising spin glass, our results are consistent with the predictions of the droplet model.
Temperature dependence of barrier heights in spin glasses
Authors: Lederman M. , Orbach R. , Hammann J. , Ocio M.
Published: July 2002

One of the characteristics of spin glasses (SG) below the glass temperature Tg is aging. It is a direct consequence of the ‘‘rugged’’ and highly degenerate nature of the free-energy landscape in configuration space. We have determined the temperature dependence of the height of a given barrier Δ(T) in the ‘‘canonical’’ spin glass AgMn2.6%. Our results show that the rate of change, ‖δΔ/δT‖, increases linearly with increasing Δ in the range of Δ we explore experimentally.
The peak in the TRM in a fine particle system
Authors: El-Hilo M. , O’Grady K. , Popplewell J.
Published: July 2002

From measurements of the thermoremanent magnetization (TRM) curve, at different times of measurement we have found that the peak in the TRM for a system of Fe3O4 particles curve only develops after 15 s. This indicates that this phenomenon is due to time dependence of the remanence. The time variation of the TRM was found to fit the stretched exponential test over the whole range of time examined.
Synthesis and magnetization of a reentrant Ni-Mn thin-film system
Authors: Abdul-Razzaq W. , Wu M.
Published: July 2002

Ni-Mn disordered alloys in the bulk form are known to have a reentrant phase for a range of Mn percentages that are <24 at. % Mn [W. Abdul-Razzaq and J. S. Kouvel, Phys. Rev. B 35, 1764 (1987)]. By a sputtering technique, we have synthesized thin films of Ni–Mn (22.2 at. % Mn) of different thicknesses that undergo a transition from a ferromagnetic state to a spin-glass (reentrant) state with decreasing temperature. After initial cooling in zero field from room temperature to 5 K, the magnetization M was measured in an applied field of 100 G as the temperature was raised to 200 K. A peak in the magnetization was observed for all the films at about the same temperature. We found that this temperature represents the transition from a ferromagnetic-like state to a spin-glass state. The magnetic hysteresis loop obtained by cooling from 200 to 5 K in a 10-kG field was also measured and found to be asymmetrical and displaced from the origin for every film. The displaced loops indicate that these films have a unidirectional anisotropy corresponding to the Dzyaloshinsky-Morria interactions. The transition temperature from the ferromagnetic state to the paramagnetic state was determined by observing the temperature at which the thermoremanent magnetization vanished.
Light rare-earth substitution and the ‘‘reentrant’’ magnetic properties of amorphous melt-spun Fe93Zr7a) (abstract)
Authors: Nicolaides George K. , Rao K. V.
Published: July 2002

It is well known that the ‘‘ferroglass’’ or the so-called ‘‘reentrant’’ magnetic property of Fe-rich amorphous Fe-Zr alloys is extremely sensitive to the Zr content. We have successfully amorphized by melt spinning Fe93.5Zr6.5, which is found to have all the characteristics of a typical spin-glass alloy in the vicinity of the multicritical point. These x-ray amorphous ribbons, whose composition has been determined by inductively coupled plasma (ICP) and energy dispersive x-ray analysis (EDAX) techniques, have been characterized by ac susceptibility [determining both χ′(T) and χ″(T)] as well as the essential dc magnetic measurements to confirm their spin-glass character. On substituting Fe with 1, 2, and 3 at. % Nd (also confirmed by ICP and EDAX analyses) our detailed magnetic studies of these Fe93.5−xNdxZr6.5 alloys indicates that (1) Nd couples ferromagnetically with Fe, and (2) the finite-range ferromagnetic ordering temperature increases with x, while the spin-freezing phenomenon is suppressed to lower temperatures (see figure). As far as we know, this is the first time such a systematic Fe-Zr-based alloy series with a crossover through the multicritical point has been obtained. Detailed studies and interpretation of the data in the framework of the presence of local anisotropy in a matrix of statistical fluctuations of the competing exchange interactions will be presented elsewhere.
Spectral measurements of the magneto-optical Kerr rotation and ellipticity in the media of optical recording
Authors: Zhou Feng Lei , Erwin J. Kevin , Mansuripur M.
Published: July 2002

Spectral measurements of Kerr rotation and ellipticity for TbFe and superlattice Co/Pt and Co/Pd samples are obtained by a novel technique. The results of measurements are accurate over a wavelength range of 350 to 1100 nm. The interference effect on the Kerr spectra of the TbFe samples are studied by applying the multilayer analysis program. The reflectivity and Kerr spectra of Co/Pt and Co/Pd superlattice samples are studied to understand the interference effect and the magneto-optic interactions.
A high-performance permeance meter and its application to measuring the complex permeability of thin Fe-Si-Al-N films for perpendicular magnetic recording heads
Authors: Yoneda Yoshiro , Hayashi Naoto , Numazawa Junji
Published: July 2002

A high-performance permeance meter has been developed to measure the permeability of thin films for perpendicular magnetic recording heads. The instrument is able to determine small permeance (about 20 μm) with a good signal-to-noise ratio in the frequency range of 0.5–120 MHz and, moreover, to reduce the conventional error in the high-frequency region. The complex permeability of an Fe-Si-Al-N film 200 nm thick for perpendicular magnetic recording heads was measured, and the real part of the permeability was about 3500 with a −1-dB frequency of about 80 MHz.
Power losses versus stress and temperature in soft amorphous alloys
Authors: Appino C. , Fiorillo F.
Published: July 2002

The role of stress-induced anisotropy on magnetic power losses has been investigated in FeBSiC amorphous ribbons, in the ‘‘as-quenched’’ state and after annealing. Loss separation has been accomplished up to 400 Hz, under a wide range of applied tensile stresses (3.5 MPa≤σ≤300 MPa). It is found that, by increasing σ, the hysteresis loss component Wh is initially decreased and passes through a minimum around a critical stress σ0. Correspondingly, rearrangement of the maze domain structure associated with the unstressed state occurs and a longitudinally oriented pattern sets in. The dynamic loss exhibits a somewhat opposite trend, as it tends to monotonically increase with σ, thus attenuating the overall benefits of tensile stressing. Insight on the physical mechanisms responsible for these phenomena is obtained by measuring, at different stress levels, Wh versus temperature (20 °C≤T≤280 °C). Topological rearrangements of the domain structure and interaction of the Bloch walls with localized stress fluctuations are envisaged, in association with roughness of the ribbon surface, as the main sources of coercivity and losses. As to the relaxation aftereffect, this is shown to produce additional loss under fairly restricted conditions of temperature and magnetization rate.
Implementation of the total and reduced magnetic scalar potential technique using hierarchical finite elements
Authors: Rodger D.
Published: July 2002

The total and reduced scalar potential technique is a method for introducing source currents into magnetic scalar potential field models. If required, the magnetic scalars can be coupled to other field vectors in different regions in order to model eddy currents or may be used on their own in magnetostatics problems. This contribution shows how hierarchical finite elements which use shape functions based on Legendre-type polynomial expansions may be implemented in total and reduced scalar potential schemes.
On the calculation of magnetic-field perturbations caused by variations of material boundaries
Authors: Mayergoyz I. D.
Published: July 2002

A weak Galerkin form for the calculation of perturbations of the magnetic scalar potential caused by variations of material boundaries is derived. Finite-element discretizations of this Galerkin form are discussed.
New nonlinear algorithms for finite element analysis of 2D and 3D magnetic fields
Authors: Brauer J. R. , Larkin L. A. , MacNeal B. E. , Ruehl J. J.
Published: July 2002

New nonlinear algorithms are presented that use the given material B-H curve directly, rather than converting it to a reluctivity ν=(H/B) vs B2 curve as is common. In addition to full Newton–Raphson iteration, also discussed are modified Newton–Raphson iteration, quasi-Newton iteration, and line search algorithms. Full Newton–Raphson iteration with the new direct B-H algorithm is shown in most typical small 3D and 2D magnetostatic problems to achieve convergence in a much smaller number of iterations than the ν vs B2 algorithm.
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e model of orthogonal-core transformers
Authors: Ichinokura O. , Sato K. , Jinzenji T. , Tajima K.
Published: July 2002

This paper deals with a numerical model of orthogonal-core transformers for use in spice. The model was devised on the basis of the magnetic circuit of the orthogonal-core with the saturation and hysteresis effects. Using the numerical model, the behavior of the dc-ac converter constructed with the orthogonal-core transformers and square-wave transistor choppers was analyzed. The calculated values and measured ones show a good agreement. The method presented here is suitable for the circuit analysis and design optimization of the dc-ac converter taking account of nonlinear characteristics of the orthognal-cores and semiconductor devices used in the converter.
Modeling the write process in direct overwrite magneto-optic media
Authors: Perlov C. M.
Published: July 2002

A model for the write process in exchange coupled direct overwrite magneto-optic media is presented. The model has the flexibility to simulate poor overwrite with multiple domains. The exchange coupled interface between layers is accounted for with a domain wall energy when the transition metal spins in the top and bottom layer are not aligned. Magnetic layer properties suitable for direct overwrite are explored. Conditions under which overwrite fails or written domains are unstable are examined.
Adjacent track crosstalk in magneto-optical recording (abstract)
Authors: McDaniel T. W. , Finkelstein B. I.
Published: July 2002

As the areal density of future magneto-optical (MO) disk drives is increased, adjacent track interference on readout will become a more significant engineering problem. Many issues are involved in the analysis of this problem, including tracking servo misregistration, the transverse dimension of written domains, the reading laser beam intensity profile (especially aberrations), the nature of the optical-transfer function for reading information to each side of the track center, and diffraction effects involving disk grooves and the linearly polarized read beam. The change from pulse-position to pulse-width modulation significantly increases the recording system sensitivity to adjacent track crosstalk (ATC). We conducted a variety of experimental tests of ATC to separate and understand the above effects. Two numerical scalar diffraction models of MO readout have been used to make quantitative predictions of signal amplitude as a function of off-track displacement and written frequency. Sensitive measures of read-beam aberration have been developed from conventional disk tests involving ATC and on-track signal analysis. In this paper, we report on the closure of readout models with experimental measurements and the development of methods for choosing the appropriate balance of bit and track density for future MO drives.
Catalytic-active ferrite plating films with Au particles dispersed
Authors: Itoh T. , Demura M. , Abe M. , Tamaura Y.
Published: July 2002

We prepared ferrite films of Fe3O4 and α-Fe2O3 in which Au fine particles (which exhibit catalytic activity for CO→CO2 oxidation) are dispersed by ferrite plating in an aqueous solutions below 100 °C. We used as-reaction solution FeCl2 (Fe2+ + Cl−) and as oxidizing solution HAuCl4 (H+ + AuCl−4). The reduction-oxidation reaction between Fe2+ and AuCl−4 facilitates the ferrite formation and also Au-particle formation reactions. The Au particles were ∼30 nm in diameter. Among all the prepared films an α-Fe2O3 film containing Au fine particles at an atomic ratio Au/Fe=0.12 exhibited the highest oxidation activity, which appeared above 100 °C, and converted the CO gas to CO2 completely at 200 °C.