bluuebunny/crossref_metadata_2025 huggingface dataset:
Microdeformations of domain walls in (210)-oriented garnet films (abstract)
Authors: Ilyicheva E. N. , Klushina A. V. , Shirokova N. B. , Nyenhuis J. A.
Published: July 2002

For appropriate values of perpendicular and in-plane magnetic fields, Hn and Hp, respectively, domain walls in (210) garnet films exhibit zig-zag and sinusoidal distortions along their lengths. Microdeformations of domain walls (DW) near these “instability loss lines”1 in the Hn, Hp plane were investigated in [1̄20]-oriented stripe domain structures by a dark-field magneto-optical technique. Changes of brightness and contrast of the image along and across the DW occur in response to an in-plane field Hp. Figure 1 shows a stripe domain structure with Hp=120 Oe along [001]. The analysis of the images2 confirms the presence of alternating DW parts inclined at angles ±α of about 3°–5° from the film normal. The domain-wall displacement varies through the film thickness as the result of the DW being pinned to the transitional level of the film–substrate interface. In the completely aligned stripe array, in-phase microdeformations have been observed for neighboring domain walls. With an increase of Hp, the DW parts with one direction of tilt are lengthened and the walls are reoriented from the [1̄20] to the [1̄21̄] direction. These results provide information on the spatial configuration of the deformed DW and give the possibility to create a more precise model of the domain and the domain wall in (210) garnet films.
Effects of spin vacancies on the correlated spin dynamics in La2Cu1−xZnxO4 from 63Cu nuclear quadrupole resonance relaxation
Authors: Carretta P. , Rigamonti A. , Sala R.
Published: July 2002

63Cu nuclear quadrupole resonance (NQR) relaxation measurements in La2CuO4 doped Zn are used in order to investigate the temperature dependence of the in-plane magnetic correlation length ξ2D and the effects associated to spin vacancies in two dimensional quantum Heisenberg antiferromagnets (QHAF). The relaxation rates T1−1 and T2−1 have been related to the static generalized susceptibility χ(q,0) and to the decay rate Γq of the normal excitations. By using scaling arguments for χ(q,0) and Γq, the relaxation rates have been expressed in close form in terms of ξ2D(x,T) and its dependence on temperature and spin doping x thus extracted. The experimental findings are analyzed in light of the renormalized classical (RC) and quantum critical (QC) behaviors predicted for ξ2D by recent theories for S=1/2 HAF in square lattices. It is first shown that in pure La2CuO4, ξ2D is consistent with a RC regime up to about 900 K, with tendency toward the QC regime above. The spin vacancies reduce the Néel temperature according to the law TN(x)≈TN(0)(1–3.5x). From the temperature dependence of 63Cu NQR relaxation rate T1−1, T2−1 and from the composition dependence of TN it is consistently proved that the effect on ξ2D can be accounted for by the modification of the spin stiffness in a simple dilutionlike model, the system still remaining in the RC regime, at least for T⩽900 K.
Microscopic theory of spin-wave interactions and relaxation in ferromagnetic films (abstract)
Authors: Costa Filho R. N. , Cottam M. G.
Published: July 2002

A diagrammatic perturbation method is employed to study the nonlinear dynamics of spin waves in thin ferromagnetic films, including the effects of the short-range exchange coupling and the longer-range magnetic dipole-dipole coupling between the spins. It is well known1 that, in the linear approximation, the spin-wave spectrum of a finite-thickness film may consist of several discrete branches describing the localized surface modes and the quantized (or standing) bulk modes. When higher-order effects are taken into account, we obtain a description of interactions between these modes where the dominant relaxation terms are due to three- and four-magnon scattering processes, by analogy with infinite ferromagnets.2 However, in the film geometry, the interaction terms may involve spin waves from either the same or different discrete branches, and so the temperature and wave-vector dependence of the spin wave energy shift and damping are modified. Our results represent a generalization of previous calculations for semi-infinite Heisenberg ferromagnets3 to include the dipole-dipole terms and finite film thickness. We employ a microscopic approach with a Hamiltonian, by contrast with previous theories for dipole-exchange spin-wave interactions, which have generally employed a macroscopic (or continuous-medium) approach using Maxwell’s equations. This enables us to obtain results applicable for ultrathin films and/or for all wave vectors.
Effect of readout magnetic-field direction on trilayer magnetically induced super resolution media (abstract)
Authors: Tamanoi K. , Tanaka T. , Sugimoto T. , Matsumoto K. , Shono K.
Published: July 2002

Among the proposed magnetically induced super resolution media, double-mask rear aperture detection (RAD) has the greatest potential for use in high-density land/groove recording.1 We proposed a trilayer double-mask RAD media that does not require a large initializing magnetic field.2 In this paper, we report the land/groove recording on the trilayer media for a 0.4 μm mark length and 0.7 μm track pitch. We found that crosstalk drastically changed depending on the direction of the readout magnetic field, and that the crosswrite is related to crosstalk. When applying the readout magnetic field in the erasing direction, the value of crosstalk was about −25 dB and a large crosswrite effect was observed. Conversely, the crosstalk was below −45 dB and no crosswrite effect was observed when applying the magnetic field in the writing direction. CNRs had almost the same value of 48 dB for both the above cases. To investigate the mask formation while applying the readout field in the writing direction, we precisely observed the wave form of the isolated marks. The carrier level rose twice with increasing readout field. However, the position of the leading edge mainly changed when increasing the field. We think that the low crosstalk is attributable to the enhancement of the front mask area. The trilayer media enables an areal density of 3 Gbit/in.2
Process optimization studies of high performance recordable minidiscs
Authors: Choe G. , Ishii J. , Gupta S.
Published: July 2002

In this study, the effect of process parameters on magnetic and recording properties of MiniDiscs is reported. Processes have been tailored to optimize the recording performance of MiniDiscs, such as carrier-to-noise ratio (CNR) at low magnetic fields, recording power margin, and recording power threshold. At higher deposition pressures or lower deposition rates of TbFeCoCr, the external bias field sensitivity of the carrier becomes worse but the noise at high bias fields (>200 Oe) decreases, resulting in improved CNR at high bias fields. Disks with TbFeCoCr sputtered at low pressure or high deposition rates produce a high error rate at high recording power (>4.5 mW), due to jitter noise caused by interference of neighboring magnetic domains. The power margin of the disks is strongly affected by the pressure and deposition rate of TbFeCoCr. When the Curie temperature of the TbFeCoCr layer is lowered by 30 °C (alloy change), the power margin decreases significantly and CNR is decreased by ∼2 dB because of low Kerr rotation. CNR values well above 49.5 dB are easily achieved on MiniDiscs with optimized TbFeCoCr and SiN layers.
Exchange decoupling of grains in polycrystalline CoPt alloy films (abstract)
Authors: Heimel J. , Kleinefeld Th. , Weller D.
Published: July 2002

Thin films of CoPt alloys in the thickness range of 5–50 nm were investigated using magnetic and nanostructural characterization methods. These compounds are suitable candidates for magnetic and magneto-optic recording applications due to their excellent perpendicular anisotropy and stability of very small magnetic domains in the nanometer regime. We have intensively studied the influence of thermal treatment on the magnetic behavior as well as on the nanostructure of the alloy films. The films were prepared under UHV conditions at elevated substrate temperature. X-ray measurements reveal a preferential fcc (111) texture with very small dispersion of the c axes. From scanning tunneling microscopy studies a typical grain size of the order of 10–20 nm was determined. The as-grown films exhibit only little surface roughness. MOKE measurements and domain visualization by means of Kerr microscopy reveal an almost perfect perpendicular magnetic orientation.
Spin dynamics studies of single Fe and Ni impurity in bcc iron (abstract)
Authors: Sabiryanov R. , Jaswal S. S. , Antropov V. P. , Harmon B. N. , Liu S.
Published: July 2002

Spin dynamics based on a quasiclassical approximation1 is used to study a single Fe or Ni magnetic impurity in ferromagnetic bcc iron. The optimization of the magnetic structure of the impurity includes quantum effects such as spatial spin inhomogeneity and different orbital contributions. The Pauli equation for noncollinear magnetic configuration is solved for each impurity. When rotated from ferromagnetic ordering, Fe and Ni impurities show different behavior. The Fe moment remains almost unchanged through a rotation of 0.6π radians and drops to zero when the rotation is increased to 0.72π radians. This behavior is primarily due to the interplay of more localized eg states and itinerant t2g states. On the other hand, the Ni moment drops continuously with rotation, going to zero at 0.5π radians. The different degrees of localization of Ni and Fe moments are analyzed in terms of different spatial anisotropy of magnetization density. The inhomogeneous spin space configurations are presented and analyzed using corresponding space dependent exchange integrals.
A spectroscopic study of the nonlinear magneto-optical response of garnets
Authors: Pavlov V. V. , Pisarev R. V. , Kirilyuk A. , Rasing Th.
Published: July 2002

In magnetic garnet films crystallographic χijk(2)(2ω) and magnetization-induced χijkl(3)(2ω) electric-dipole type contributions to the nonlinear optical susceptibility may coexist due to a simultaneous breaking of space and time-reversal symmetry. A spectroscopic study shows different behavior of these two contributions as a function of the photon energy.
Magnetization and Shubnikov-de Haas effect in diluted magnetic semiconductors (Cd1−x−yZnxMny)3As2
Authors: Laiho R. , Lisunov K. G. , Lähderanta E. , Stamov V. N. , Zakhvalinskii V. S.
Published: July 2002

The results of the Shubnikov-de Haas (SdH) effect and magnetization of single crystals of (Cd1−x−yZnxMny)3As2 (CZMA) are presented. Specimens with x+y=0.3 and y=0.04, 0.06 and 0.08, subjected to long-time thermal annealing, were studied. SdH effect was investigated in fields B up to 11 T in the temperature range T=4.2–20 K. Magnetization was measured at B⩽5. 5 T and 5 K⩽T⩽20 K. SdH oscillations were analyzed taking into account (i) the anomalous magnetic field dependence of the cyclotron mass observed recently in CZMA, and (ii) influence of the s−d interaction to the effective g-factor (geff) of conduction electrons. The dependence of geff on B and T was introduced in the analysis of the SdH oscillations by fitting the magnetization data with the effective Brillouin function. Values of the exchange-independent part of geff, the exchange constant in the conduction band and the spin-dependent part of the Dingle temperature were determined.
Interfacial effects in Fe/4d TM multilayers (abstract)
Authors: Tomaz M. A. , Antel W. J. , Harp G. R. , O’Brien W. L.
Published: July 2002

We have studied Fe/TM multilayers (TM=Mo, Nb, Ru, Rh, Pd) using x-ray magnetic circular dischroism, magneto-optical Kerr effect, and x-ray diffraction. A diverse set of magnetic behaviors emerges from the analysis. We focus on the behavior which can be attributed to the existence of a physical interface between different chemical species. In particular, we have measured an enhanced Fe moment in some cases (TM=Ru, Mo, Rh, Pd) yet not in others (TM=Nb). These results will be discussed, including the relative orbital and spin moments and the effects of alloying at the interface. The measured induced moments in the TM layer will be presented as well where applicable.
Preparation of soft magnetic and thermally stable Fe–Co–Ta:N/Ti multilayered films by sputter deposition
Authors: Nakagawa Shigeki , Suemitsu Katsumi , Naoe Masahiko
Published: July 2002

Although the as-deposited Fe–Co–Ta:N single layer films with a thickness of 200 nm possessed large 4πMs of about 16 kG, they revealed low μr. [Fe–Co–Ta:N/Ti]n multilayers were prepared with the aim to improve soft magnetic characteristics of Fe–Co–Ta:N films. The [Fe–Co–Ta:N(50 nm)/Ti(10 nm)]4 multilayered films exhibited relatively high μr of about 400 even in the as-deposited state. Furthermore, they exhibited better thermal stability of their soft magnetism. For example, the multilayered films postannealed at TA of about 300 °C lost only 20% of their moment, compared to as-deposited films, and maintained a relatively high μr. By contrast, a Fe–Co–Ta:N(200 nm) single layer film lost, at the same temperature, nearly 50% of its moment. X-ray diffractometry indicates that the postannealed multilayered films did not include such paramagnetic ζ-Fe2N crystallites. It seemed that the Ti insertion layers worked as barrier layer for N diffusion to prevent the formation of such nitride crystallites.
The effect of magnetic interaction in barium hexaferrite particles
Authors: Garcı́a del Muro M. , Batlle X. , Labarta A. , González J. M. , Montero M. I.
Published: July 2002

The effect of interactions on the magnetic relaxation of nanocrystalline hexagonal barium hexaferrite BaFe10.4Co0.8Ti0.8O19 is discussed. We had previously shown that according to the T ln(t/τ0) scaling, an enhancement of the lowest-energy barriers was detected when demagnetizing interactions were dominant. Also, the Henkel plots obtained for particles of about 10 nm of mean diameter showed that the overall interactions were demagnetizing. In the present work, we have modified the interactions by milling the particles with a nanosized SiO2 powder. Dipolar interactions are modified by breaking the particle aggregates. The observed overall interactions resulted to be also demagnetizing for the milled sample. The time dependence of the magnetization was analyzed according to two different procedures: the fluctuation field and activation volume analysis and the T ln(t/τ0) scaling. Activation volumes were found to increase with demagnetizing interactions and the leading demagnetizing mechanism appeared to shift from an individual particle mode for the unmilled sample to a collective one for the milled sample. The second approach showed larger relaxation rates at short times for the milled sample. The effective energy barrier distribution obtained from the scaling suggested that demagnetizing interactions increased in the milled sample, which led to an enhancement of the amount of the lowest-energy barriers.
Molecular dynamic model of the magnetic properties and microstructure of advanced metal particle dispersions
Authors: Coverdale G. N. , Chantrell R. W. , Satoh A. , Vietch R.
Published: July 2002

A molecular dynamic model of the properties of a strongly interacting particulate dispersion is described. The model is applied to the study of the properties of a dispersion of advanced metal particles from the intrinsic magnetic behavior through the effects of shear and orientation during the coating process to a final description of the microstructure of the coated medium. The predicted magnetic properties of the dispersion, calculated from the physical properties of the particles and medium, give excellent agreement with experiment. Initial predictions of the effects of shear show the model to be a useful basis for the interpretation of shear magnetometry. Following the “model” coating process the model gives realistic predictions of the microstructure of coated media.
Rheological and cryogenic-transmission electron microscopy probing of the structure of magnetic paints
Authors: Potanin Andrei A. , Shrauti Suresh M. , Arnold David W. , Lane Alan M.
Published: July 2002

Rheological measurements and cryogenic transmission electron microscopy are used to probe the structure of model magnetic paints which contain ferrimagnetic pigment particles of barium ferrite, a wetting resin, and a solvent. As the resin concentration c increases, the storage modulus goes through a minimum. At low c, a flocculated network is developed in the paint. Milling of the paint at insufficient resin concentration does not improve its dispersion quality, but instead results in the formation of a stronger network. Milling at higher c effectively disrupts the network into small aggregates. The resin concentration required to provide effective milling is lower for paints containing the larger iron oxide particles.
An assessment of alternative soft magnetic materials in rotary variable differential transformers
Authors: Midgley G. W. , Howe D. , Mellor P. H.
Published: July 2002

Position sensors are a key technology for controlled actuation systems, which are required to meet increasingly exacting dynamic performance specifications. Of the various sensing technologies, variable differential transformers are capable of satisfying stringent performance criteria, in terms of resolution, repeatability, and stability of output, while operating in the harshest of environments. They utilize the variation of mutual inductance which occurs between a primary and two secondary coils as a ferromagnetic core is moved by the object whose position is to be measured. The article is concerned with rotary variable differential transformers, which currently use high permeability magnetic alloys, such as nickel–iron, either solid or laminated. However, since they are being required to operate at increased excitation frequencies, up to 5 kHz, there is interest in the use of powder composite magnetic materials, which, although having a lower permeability, have a higher electrical resistivity, and hence reduced eddy current effects. The potential for such materials is investigated by steady-state ac finite element analysis, and shown to be promising.
Nonlinear optical investigations of magnetic heterostructures (invited)
Authors: Crawford Thomas M. , Rogers Charles T. , Silva Thomas J. , Kim Young K.
Published: July 2002

We report second-harmonic magneto-optic Kerr effect investigations of magnetic heterostructures. The heterostructures studied are multilayers of Si/Al2O3/Cu(50 nm)/Ni81Fe19(x), Si/Al2O3/Cu(50 nm)/Co(2 nm)/Ni81Fe19(x), and Si/Al2O3Cu(50 nm)/Ni81Fe19(x)/Cu(5 nm), where x ranges from 1 to 30 nm. For films thinner than the optical penetration depth, the transverse second-harmonic Kerr effect experimentally separates and distinctly identifies each of these multilayered structures. We find that the addition of the 2 nm Co layer between Cu and Ni81Fe19 increases the magnetic signature in the second-harmonic intensity by more than a factor of two. This increase correlates with the observed magnetoresistance increase in spin valves with the addition of Co. For films thicker than the penetration depth, the structures with air-exposed Ni81Fe19 are identical, but they differ significantly from Ni81Fe19 films capped with Cu. We used spectroscopic ellipsometry to determine the linear optical properties of each film in the structure. Modeling of both Cu(50 nm)/Ni81Fe19 and Cu(50 nm)/Ni81Fe19(x)/Cu(5 nm) suggests that the buried magnetic interfaces are better generators of second-harmonic than the air-exposed Ni81Fe19 surface. There is a distinct decay in the magnetic component of the second-harmonic intensity for film thicknesses below 2 nm.
Magnetic force microscopy image of Co–Cr–Ta layer in perpendicular magnetic tape at high linear recording density
Authors: Ishikawa K. , Taguchi R. , Miyashita E. , Numazawa J. , Ohshima H.
Published: July 2002

In this study, magnetic force microscopy (MFM) was used to investigate the recording capability of a perpendicular magnetic tape at a higher linear recording density. Perpendicular magnetic tapes with polyimide base sheets 10 μm thick were fabricated by a facing-target sputtering system [H. Yoshimoto, K. Kuga, Y. Yoneda, and J. Numazawa, J. Magn. Magn. Mater. 148, 357 (1995)]. A Co–Cr–Ta (200 nm) monolayered tape with a base sheet of excellent surface roughness was fabricated. A complete recorded bit pattern of 250 kfci was observed as a MFM image on the tape. A recorded bit pattern of 300 kfci was also observed. A Co–Cr–Ta/Ni–Fe (150/50 nm) multilayered tape was also fabricated. The remnant magnetization state on this tape at 50 kfci was improved by the presence of an underlayer (Ni–Fe) only 50 nm thick. The MFM image at 250 kfci was the same as with a monolayered tape.
Double gap in the spin-Peierls compound CuGeO3
Authors: Aïn M. , Regnault L. P. , Dhalenne G. , Revcolevschi A. , Lorenzo J. E. , Jolicoeur Th.
Published: July 2002

We report on inelastic high resolution neutron scattering measurements in the spin-Peierls compound CuGeO3. We observed the sharp dispersive mode which is gapped throughout the whole Brillouin zone. We also observed that this mode is separated by an unexpected second gap of ≈2 meV from a continuum of magnetic excitations that extends to higher energy. The first gap (or “triplet gap”) and its associated dispersive mode are due to the breaking of a singlet dimer into a delocalized triplet as illustrated by polarized neutron under magnetic field. We propose that the second gap (or “solitonic gap”) and the continuum correspond to dissociation of the triplet into two unbound spin-1/2 solitons that are separated by a dimerized region of arbitrary length.
Field dependent neutron scattering from Cu–Mn (abstract)
Authors: Hicks T. J. , Cable J. W.
Published: July 2002

Advantage was taken of the high magnetic susceptibility of Cu–Mn alloys in the range 12–22 at. % Mn to observe field dependent magnetic neutron scattering. A single crystal containing 21.3 at. % Mn was mounted on the HB1 spectrometer at the HFIR reactor with its 〈001〉 axis vertical. Scattering was measured with unpolarized neutrons at low angles and between the (100) and (1120) positions in reciprocal space using a neutron energy of 14.8 meV. Small angle scattering with a half-width of 0.1 Å−1 was observed as well as the scattering maxima at the (1,12-δ,0) and the (1,12,0) positions. The magnetic scattering was approximately uniformly reduced by about 10% at 4.2 K after warming above the glass temperature and cooling again to 4.2 K in a field of 4.25 T. Reduction of the intensity of all magnetic features by the application of the field indicates that all the magnetic periodicities are intimately connected to the uniform magnetic response. A model which assumes that the alloy contains entities with both a ferromagnetic moment associated with the (0,0,0) scattering and an antiferromagnetic periodicity associated with the (1,12-δ,0) scattering yields a ferromagnetic moment for the entity of 36 μB estimated from the reduction in scattering. This compares with 42 μB estimated from the intensity and width of the low angle scattering.
Thermal stability of longitudinal and perpendicular recording media obtained by Monte Carlo simulation (abstract)
Authors: Uesaka Y. , Nakatani Y. , Hayashi N. , Fukushima H.
Published: July 2002

The thermal stability of longitudinal and perpendicular recording media was investigated using Monte Carlo simulation method.12 In longitudinal recording, the easy directions of the grains are distributed randomly in the film plane. In perpendicular recording, the easy directions are aligned almost perpendicular to the film plane. The material parameters, Ms=400 emu/cm3, Ku=2 ×106 erg/cm3, and α=1, were used. The exchange stiffness constant between adjacent grains was assumed to be zero. The effects of thickness, grain size in-plane, and distribution of grain size in-plane of the media on decay of the magnetic properties and on decay of the output signal with time were calculated. The rate of signal decay of a longitudinal medium is similar to the decay rate of the squareness and it is much smaller than the decay rate of the coercivity. The same relationship holds for a perpendicular medium. In longitudinal recording, a high density signal is more affected by thermal fluctuation than a low density signal, but in perpendicular recording, a low density signal is more affected than a high density signal. Signal decay is larger in longitudinal recording than in perpendicular recording when the thickness is larger than the grain size in-plane. On the other hand, it is smaller in longitudinal recording than in perpendicular recording when the grain size in-plane is larger than the thickness. The distribution of the grain size in-plane decreases coercivity and squareness of the media at a finite temperature and it also decreases the signal.
Robust design of a permanent magnet stabilized high areal density magnetoresistive head
Authors: Fernandez-de-Castro J. J. , Mowry G. S. , Ding J. , Giusti J. , Saunders D.
Published: July 2002

As the recording industry increases areal density every year, a magnetoresistive-soft adjacent layer (MR-SAL) head design is desirable with the following qualities: easy to be fabricated in large volume, capable of consistent and stable device-to-device performance, and enough signal to noise ratio to perform at high recording densities and data rates. A new type of MR head with these attributes is described for an areal density equal to 1444 Mb/in.2. The off-track characteristics of this MR head are determined by the sensor edge design which is defined by a permanent magnet (PM) layer. Improved off-track performance was achieved by substituting the spacer layer with the PM outside of the active sensor area. Excellent boundary control stabilization was obtained by the ferromagnetic exchange coupling between the PM and, the SAL and the MR layers. The bit error rate and electrical test results showed acceptable performance at 175 kbpi and 8250 tpi. The above MR head had average values of low frequency amplitude (LFA), PW50, read width and write width equal to 900 μV, 12.4, 72, and 107 μin., respectively. The low frequency symmetry (LFSYM) was 1.1 (Vpos/Vneg) and the position error off-track capability was 26 μin. Finally, the LFA covariance (σ/avg) was found to be 0.22% and the microtrack had no bumps or side lobes. These results indicate that this design and its implementation produce stable heads that can perform on and off track at 1444 Mb/in.2.
Microstrip resonator for GHz measurements of microscale magnetic objects (abstract)
Authors: Valanju A. P. , Win W. , Yun E. J. , Walser R. M.
Published: July 2002

The integration of thin ferromagnetic films for applications above 1 GHz is expected to require micron scale, thin film objects (∼100 μm×100 μm×0.1 μm) with volumes less than ∼10−15 m3. With maximum relative susceptibilities of ∼100, the measurement of these micro-objects by small perturbative techniques is experimentally challenging. Here, we describe the design, calibration, and performance of a microstrip resonator with a cavity volume of <10−6 m3 and a cross-sectional area <1 mm2. We have designed and built a gap-coupled, transmission-type, linear microstrip resonator. At even (odd) harmonics of the fundamental resonance, maxima of the electric (magnetic) field are established at the midpoint of the linear resonator. This resonator was designed to measure the magnetic responses of ensembles of micron scale ferromagnetic objects in the 0.4–10 GHz frequency range. The lowest resonant frequency (400 MHz) intentionally overlapped the upper operating frequency range of our lower frequency measurement systems, to permit comparison and calibration. The center conductor of the microstrip was photolithographically patterned in a 6 μm thick gold film electroplated on a high quality microwave alumina substrate. A quasi transverse electric mode (TEM) was launched on the microstrip from a well-matched transition to a 3.5 mm coaxial connector. The microstrip resonator was excited by coupling to the microstrip transmission line through two 50 μm capacitive gaps (∼0.07 pF) in the center conductor. The measurements were performed with HP 8510 network analyzer. The equivalent circuit of the microstrip transmission resonator and coupling capacitors were used to compute the 22 transmission resonances expected in the 0.4–10 GHz range. The results compare well with the measured resonances indicating the applicability of the quasi static approximation to 6 GHz. A perturbation theory for calculating the permeability from the measured cavity parameters was formulated for the microstrip resonator. Initial measurements on microscale magnetic objects are in good agreement with those obtained from other measurements.
Computer simulation of neutron diffraction from coupled and uncoupled magnetic superlattices (abstract)
Authors: Goldman K. I. , Kepa H. , Giebultowicz T. M. , Sinha S. K.
Published: July 2002

Neutron diffraction is a powerful tool for investigating interlayer coupling phenomena in magnetic superlattices. In the absence of interlayer spin coherence the diffraction spectrum has the form of a broad smooth maximum, i.e., it essentially reproduces the shape of the single-layer structure factor. In contrast, spectra from correlated superlattices exhibit characteristic fringe patterns. However, doubts are sometimes expressed as to whether the presence of fringes indeed provides meaningful evidence for interlayer coherence; such opinions are usually based on results of computer simulations that produce “fringelike” features even though the magnetization in consecutive layers changes in a random fashion. Clarity in this issue is certainly of importance, especially in studies of systems with antiferromagnetic layers, in which neutron diffraction is practically the only experimental tool capable of detecting interlayer spin coherence. We report the results of thorough computer modeling studies that show that the “pseudofringes” obtained from simulations on uncoupled superlattice models disappear after averaging the data from a sufficiently large number of random configurations. It is a reasonable expectation that in a real superlattice each magnetic layer breaks into a large number of domains, so neutrons passing through the sample “see” different situations. Hence, realistic modeling does require averaging over many random configurations, and our results point out that in following such a procedure, the “fringelike” features eventually wash out, and the simulated spectra become fully consistent with the analytical single-layer structure factor. However, there is still the possibility that in special situations the spectra from uncoupled systems may exhibit fringes. Suppose that the system symmetry allows discrete domain states (e.g., corresponding to in-plane easy axes), and that the average domain size and the superlattice period are both small in comparison to the coherence length of the incident neutron wave (since the coherence length in a typical experiment is of the order of 1000 Å, this is not an unusual situation). Then, arguably, there is always a finite probability that equivalent domains located in different layers will fall into the “coherence volume,” and give rise to constructive interference, even though the domains are not coupled by any interactions. In view of that, our work included simulations on several different model systems that might, in principle, exhibit such an effect. Again, the averaged data from many thousands of runs showed no anomalies at the expected fringe positions, providing more evidence that neutron diffraction allows a fully reliable distinction of coupled and uncoupled superlattice systems.
Thermal 1/f noise in Cu90Co10: Effect of grain size
Authors: Maraner A. , Toninato F. , Vitale S. , Tiberto P.
Published: July 2002

We report on the thermal magnetic noise with 1/f spectrum and the related ac linear response susceptibility measured at liquid helium temperatures in the bulk granular system Cu90Co10. The thermal magnetic noise and the related linear response, ac susceptibility have been shown to be the close analogue at thermal equilibrium of the magnetic viscosity. The measurements have been performed on a set of samples where various size distributions of the nanostructured magnetic clusters have been produced by annealing the ribbons by the Joule heating technique. The thermal equilibrium, low temperature magnetic viscosity has been found to depend on the heating current in the same way as the room temperature giant magnetoresistance. We discuss how this analogy relates magnetic viscosity to the barrier energy distribution resulting from grain size distribution.
Influence of bending stresses on the magnetization process in Fe-rich amorphous wires (abstract)
Authors: Vázquez M. , Gómez-Polo C. , Theuss H. , Kronmüller H.
Published: July 2002

We report a systematic investigation of the domain structure as well as the magnetization reversal in bent Fe-rich amorphous wires. The samples consisting of the composition Fe77.5Si7.5B15 were prepared by the water quenching technique leading to bistable magnetic behavior (square hysteresis loops) above a critical sample length of 60 mm. The outstanding magnetic properties of such wires are due to their intrinsic stress distribution frozen in during the fabrication process and their high magnetostriction constant λ>10−5.1 Bending these wires provides an elegant method of introducing additional external tensile and compressive stresses in the halves of the wire exerted to convex and concave curvature, respectively. Domain structures of accurately polished bent wires were recorded by means of magneto-optical Kerr microscopy. Due to the magnetostrictive coupling the stress distribution in the samples is clearly reflected by the domain structure: In zero applied field we observe a single domain in the convex part of the wire with the magnetization being aligned parallel to the wire axis. The concave half of the sample reveals a transversal multidomain structure. Observation of the evolution of the domain structure with external circular fields applied parallel to the bent wire axis reveal the process of the magnetization reversal. We obtain two processes corresponding to the nucleation of a reversed domain in the center of the wire where the stresses are minimum, or alternatively, at the surface of the wire, where the surface of the reversed domain exhibits a minimum. Both processes can qualitatively be explained within a simple micromagnetic consideration. This theory reveals the estimate ΔE≅2–3×10−8 J/m for the first nucleation of the reversed domain.
Batch-processed close-track array heads (abstract)
Authors: Tang D. D. , Santini H. , Lee R. E. , Ju K. , Krounbi M.
Published: July 2002

This article describes novel array heads for close packed track recording. The heads are batch fabricated on wafers in a linear fashion (Fig. 1). These 60-turn thin-film inductive heads are designed with 6 μm pitch helical coils and planar side-by-side P1/G/P2 yoke structures. The linear head array is placed along the upstream-to-downstream direction of the track. By skewing the array slightly off the track direction, each head of the array aligns to an individual track (Fig. 2). In this case, the track pitch is about 5 μm, which is the yoke height. With this head arrangement, even though thermal expansion causes the head-to-head distance to increase along the upstream–downstream direction, it does not cause a thermally induced track misregistration problem. The increased head-to-head distance only affects the timing of signals between tracks, which can be compensated by the channel electronics. Thus, the thermally induced track misregistration problem is eliminated using this design. The guardbands between tracks are not necessary and a close-packed track recording is possible. A state of the art head impedance of the 60-turn head is obtained: 11 Ω and 0.40 μH. The gap-to-gap pitch is 100 μm. The overall head-to-head isolation is greater than 50 dB at 10 MHz. Such a large isolation is realized by suppressing the capacitive coupling between lead wires using a ground plane and grounded wall structures. The tight winding of the helical coils reduces the magnetic coupling between the heads.
Crystallographic texture determinations from inverse susceptibility measurements
Authors: Lewis L. H. , Welch D. O.
Published: July 2002

Determination of the quantitative relationship between crystallographic texture and magnetic properties in advanced permanent magnets may be hampered by complex microstructures, which complicate methods that rely on diffraction, or by interparticulate interactions, which adversely affect methods based on magnetic remanence measurements. To this end, new techniques in the determination of texture of bulk permanent magnets are being explored to overcome these inherent experimental difficulties. The analysis of inverse paramagnetic susceptibility measurements constitutes a new method to investigate crystallographic texture. Such measurements also provide Curie temperature data, which are sensitive to chemical changes that may have occurred in the magnetic phase during processing. The mathematical formalism underlying the analysis of inverse susceptibility measurements is outlined, and is used to evaluate magnetic measurements taken from a series of Nd2Fe14B magnets that have been processed by different means, and thus contain different degrees of texture. While this method does provide qualitative information concerning the relative crystallographic alignment of magnet samples, it needs calibration to obtain an explicit value for a texture order parameter.
Using ferromagnetic resonance to measure magnetic moments of ultrathin films (abstract)
Authors: Celinski Z. , Urquhart K. B. , Heinrich B.
Published: July 2002

We developed a technique to measure the saturation magnetizatiaon of ultrathin ferromagnetic films using ferromagnetic resonance (FMR). By employing it we determined the ratios of total magnteic moments of ultrathin Fe films located in Ag/Fe/Ag, Au/Fe/Ag, Cu/Fe/Ag, Pd/Fe/Ag, and Ni/Fe/Ag structures relative to that of an Au/5.7 ML Fe/Ag reference film. The ratios obtained using our method have the total measurement error of 1%. All FMR measurements, carried out at 77 K, confirmed theoretical predictions that Fe atoms located at or near interfaces possess enhanced magnetic moments compared with those of Fe atoms in the bulk. In particular, the total magnetic moment ratio for Ag/5.5 ML Fe/Ag and Ag/10.9 ML Fe/Ag (thick Fe) samples was determined to be of 1.06. This compares well to the total magnetic moment ratio of 1.05 calculated for these two films using the results obtained from first principles calculations. The total magnetic moment ratios for Pd/5.6 Fe/Ag, Pd/5.7Fe/Ag, 2(bcc Ni)/5.7 Fe/Ag and 3(bcc Ni)/5.7 Fe/Ag samples using the thick Fe sample were found to be of 1.11, 1.12, 1.15, and 1.24, respectively. The FMR measured magnetic moment ratios were nearly identical with the results obtained from the neutron spin polarized reflection measurements.1 All measured magnetic moment ratios in Fe films surrounded by the above wide range of interfaces were in excellent agreement with the ratios obtained by using published first principles calculations, and that allows one to determine the enhancement of magnetic moments at the interfaces.
Using magnetoresistance to investigate magnetic interface anisotropy
Authors: Hickey B. J. , Wellock K. P. , Walker M. J.
Published: July 2002

The ability to grow high quality thin metallic layers has brought about the discovery of the giant magnetoresistance (GMR) in multilayers and equally the perpendicular anisotropy exhibited by certain ferromagnetic thin films such as Co. In this article, we will describe magnetoresistance and magneto-optical Kerr effect (MOKE) measurements of molecular beam epitaxy-grown multilayers of Co/Cu(111). It is demonstrated that by controlled doping of the interface between the Co and Cu with submonolayer amounts of Au we are able to increase the magnitude of the GMR. Analysis of MOKE data shows that there is an increase in the perpendicular anisotropy of the Au-doped samples compared to those without Au which can account for the increase in the GMR.
Effects of interfacial relaxation on the magnetic coupling of Mn/Fe(111)
Authors: Zhong Lieping , Wu Ruqian , Freeman A. J. , Olson G. B.
Published: July 2002

The structural, electronic, and magnetic properties of monolayer Mn on an Fe(111) substrate are determined using the local spin density total energy full potential linearized augmented plane wave method and atomic force approach. A strong interplay between magnetism and atomic structure is found, e.g., the interfacial Fe layer undergoes a large downward relaxation by 0.59 a.u. from the ideal bcc position. As was found previously for bulk fcc Mn and Mn/Fe(001), the equilibrium Mn–Fe bond length is larger in the ferromagnetic state (4.47 a.u.) than that in the antiferromagnetic (AFM) state (4.31 a.u.). The AFM coupling between Mn and Fe is the ground state. The interplay between the interfacial magnetic coupling in the Mn/Fe(111) and the multilayer relaxation is discussed.
Lattice, Ce-L3valence, transport, and magnetic results on mixed-valent/Kondo system Ce1−xLaxMn2Si2
Authors: Liang G. , Xi H. , Roberts E. , Binford T. , Mochizuki K. , Markert J. T. , Croft M.
Published: July 2002

Lattice, Ce-L3 edge, resistivity, and magnetic susceptibility measurements have been carried out on the polycrystalline Ce1−xLaxMn2Si2 system (0⩽x⩽1) to study the interplay between Mn 3d-host magnetism and Kondo-type Ce-spin fluctuations. As x increases, the system varies gradually from a Ce mixed-valent system with 3d-host antiferromagnetism (at x=0) to a nearly trivalent system with strong 3d-host ferromagnetism (near x=1). In the antiferromagnetic (AF) phase region (0⩽x⩽0.5), the Neel temperature TN decreases with the increase of x, manifesting the weakening of the host AF field. Impurity Kondo behavior is observed at x=0.05, indicating that the low-temperature coherence state in CeMn2Si2 can be destroyed by “Kondo holes” which are created by very small substitution of La for Ce. The susceptibility and resistivity results suggest that the impurity Kondo effect in the 0.1⩽x⩽0.5 samples is partially suppressed by a nonvanishing ferromagnetic (FM) field component; whereas the phononlike behavior of the resistivity curves in the Mn-host FM-phase region (0.5<x⩽1.0) supports our previous proposal that the Kondo-type Ce-spin fluctuations can be effectively quenched by a strong 3d-host FM field.
On the relationship between crystal structure and magnetism in U2Pd2Sn and U2Ni2In (abstract)
Authors: Nakotte N. , Purwanto A. , Robinson R. A. , Von Dreele R. B. , Havela L. , Prokeš K. , Sechovsky V. , Pereira L. C. J. , Spirlet J. C. , Rebizant J.
Published: July 2002

Isostructural U2T2X compounds (T=transmission metal, X=p-electron element) offer a new perspective on the relationship between magnetic anisotropy and the geometrical arrangement of the elements, because (unlike most other uranium compounds) two approximately equal shortest interuranium distances are found. Our recent neutron diffraction indicate that the moment arrangement in magnetically ordered U2T2X compounds is extremely sensitive to the choice of the constituents.1 In order to get a deeper understanding of what finally determines the moment configuration in U2T2X compounds, we have studied two members of this large family, namely U2Ni2In and U2Pd2Sn. Both compounds have the shortest U–U links along the c axis and order antiferromagnetically at low temperatures. The exchange coupling along the shortest U–U link is antiferromagnetic in U2Ni2In, while it is ferromagnetic in U2Pd2Sn, though both compounds exhibit a noncollinear in-plane configuration of the U moments. Here, we present the results of our neutron-diffraction studies performed at various temperatures between 12 and 300 K, for temperatures above and below TN. Our analysis reveals that neither U2Ni2In nor U2Pd2Sn exhibit “normal” thermal-expansion behavior (linear contraction of the lattice with decreasing temperature). However, while deviations from the normal behavior in U2Pd2Sn occur only below TN (and may be attributed to magnetically driven distortions of the crystal lattice), unusual thermal expansion for U2Ni2In is found already at much higher temperatures (far above TN). We discuss, whether the unusual thermal expansion in U2Ni2In supports the formation of long-range magnetic order or whether short-range magnetic fluctuations above TN are responsible for the expansion behavior in this compound.
Increase conductivity in UNiSn with the application of magnetic fields
Authors: Ng H. K. , Love B. , Cope C. J. , Wang Y. J. , Yuen T. , Lin C. L.
Published: July 2002

We report on the frequency dependent conductivity of the modified Huesler alloy UNiSn in the antiferromagnetic state and in the presence of a magnetic field. UNiSn is paramagnetic above 43 K and has a semiconducting gap of about 65 meV. Below 43 K, the compound is in an itinerant antiferromagnetic state. The reflectance of UNiSn is measured from 4 meV to 0.4 eV and in fields up to 16 Tesla. At 5 K, there is a shift in spectral weight from the gap region to lower frequencies as the applied magnetic field is increased. This shift in spectral weight gives rise to increase conductivity with applied field in the metallic state. However, the gap value is unaffected by the field. No field dependence is observed for the isostructural compound, ThNiSn, which does not undergo an antiferromagnetic transition.
Photoluminescence study of the optical properties of SiGe quantum wells on separation by implanted oxygen substrates
Authors: Nayak Deepak K. , Usami Noritaka , Fukatsu Susumu , Shiraki Yasuhiro
Published: July 2002

A detailed experimental study of the optical properties of separation by implanted oxygen (SIMOX) substrates is performed using photoluminescence techniques. The photoluminescence properties of SIMOX substrates are compared with those of Si substrates. The silicon-on-insulator (SOI) layer is found to be free of any strain. High-quality SiGe quantum wells are grown on SOI using gas source molecular beam epitaxy. It is found that the photoluminescence properties of these quantum wells on SOI differ significantly from those of the SiGe quantum wells grown on a Si substrate under identical growth conditions. Intense photoluminescence and higher operation temperature are obtained for quantum wells grown on SOI substrates. It is shown that growth of a few hundred Å Si buffer layer on SOI is essential in order to achieve a high quality SiGe epitaxy on SOI. Finally, a SiO2/Si/SiO2 optical cavity is proposed on SIMOX substrates, and it is employed to further enhance the photoluminescence intensity of SiGe quantum wells on SOI.
Growth of FexNi1−x ultrathin films on Cu(100) near the invar concentration
Authors: Schumann F. O. , Wu S. Z. , Willis R. F.
Published: July 2002

We have grown ultrathin FexNi1−x films epitaxially on Cu(100) with different stoichiometry. Previous measurements showed a deviation of the thickness dependence of Tc for a Fe75Ni25 alloy, which was not observed for smaller Fe concentrations. Therefore, we investigated the growth near this invar concentration more closely. With a charge coupled device camera based acquisition system, we observed the evolution of the reflection high-energy electron diffraction pattern during growth near the invar concentration. This allows us to determine the in-plane lattice constant of the top layer. Up to 66% Fe content, we see in-plane lattice constant oscillations similar to the Co/Cu(100) system [Fassbender et al., Phys. Rev. Lett. 75, 4476 (1995)]. At 80% Fe content, these oscillations are suppressed and we observe also a lattice contraction as expected from recent calculations. We discuss these results in connection with our previous results on the magnetic properties of FexNi1−x ultrathin films.