bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave solitons in magnetic films (invited) (abstract)
Authors: Boardman A. D. , Xie K. , Mehta H. , Nikitov S. A.
Published: July 2002

Nonlinear waves in the form of solitons in magnetic films are attracting attention because of the interesting possibility of making novel spatial, and temporal, soliton devices that will operate in the technologically important microwave (GHz) frequency window. Some fascinating pioneering experimental work has been performed in this area and there is now every possibility that manipulation of solitonlike microwave pulses will be the basis of an entirely new range of devices. Both theory and experiment show that solitons are extremely robust and behave rather like particles. Magnetic films look set to become as successful as optical fibers in supporting bright envelope solitons; yet soliton behavior can often seem hard to comprehend. While they are subtle in their behavior they can be understood from many points of view that are physically, or mathematically, based. This presentation will explain what bright microwave envelope solitons are, drawing upon as much physical insight and analogy as possible. The necessary and sufficient conditions for soliton existence will be carefully set out, especially with respect to their relationship to the input conditions of a device. A substantial number of numerical examples will be used and the prospects for major expansion in the experimental area will be assessed. In the latter part of the presentation some important applications for solitons will be addressed. These will include the analysis of a switching device but logic devices, and various forms of pump–probe arrangements, will also be retrieved. Finally, the optimistic view that solitons in magnetic materials are now realistic tools will be expressed and the opportunities provided by dark and higher-dimensional solitons will be discussed.
Measurements of magnetization dynamics and magnetoimpedance in FeCoSiB and FeSiB amorphous wires
Authors: Masuda S. , Komatsu K. , Takemura Y. , Yamada T. , Kakuno K.
Published: July 2002

A technique to observe magnetization dynamics in amorphous wires is described. When an ac current passes through the amorphous wire, voltages induced between both ends of the wire and in a pickup coil wound around the wire are observed. These voltages indicate circumferential and axial components of magnetization changes in the wire, respectively. Observations in a Co-rich wire having slightly negative magnetostriction and an Fe-rich wire having positive magnetostriction under various bias fields showed quite different wave forms which indicate their domain structure.
Magnetization of HgBa2CuO4+δ with 0.03≤δ≤0.4
Authors: Xiong Q. , Afonso S. , Tang Y. Q. , Chan F. T. , Salamo G. , Xue Y. Y. , Chu C. W.
Published: July 2002

HgBa2CuO4+δ (Hg1201) samples with 0.03≤δ≤0.4 have been obtained. The magnetization of the powdered Hg1201 samples was determined using a Quantum Design SQUID magnetometer. It was observed that while the magnetization of Hg1201 increased with δ in the underdoped region, the magnetization decreased with δ in the overdoped region. These results suggest an increase of ns/m* with oxidation in the underdoped region and a decrease in the overdoped region, similar to that reported in underdoped HTSs and overdoped Tl2201 and Tl1201.
Submicron characterization of recording media using magnetic force microscopy (invited) (abstract)
Authors: Babcock K. , Manalis S. , Elings V. , Dugas M. , Challener W.
Published: July 2002

Magnetic force microscopy is finding widespread use in the analysis of magnetic structure at length scales relevant to modern storage densities. We present a new technique which uses the extremely localized stray fields of MFM tips to probe submicron media characteristics. The tip is brought into contact with the magnetized media, and a uniform external field Hext is momentarily added to the tip’s stray field. If the net field exceeds the local media coercivity, the magnetization is reversed locally, and a ‘‘bit’’ is written. High-resolution MFM imaging of the results is done immediately using the same probe. Bit arrays of several Gbit/in2 can be produced with the lithography software of a commercial MFM. Using the external field Hext as a parameter, the threshold for bit writing can be determined, giving a measure of the local, or ‘‘point’’, coercivity of the media on a 100 nm scale. Results for perpendicular Co–Cr and magneto-optical media can deviate significantly from conventional bulk hysteresis measurements, in some cases reversing the bulk coercivity ranking. Intermediate values of Hext reveal spatial variations in the point coercivity due to fluctuations in composition or microstructure. In square media, sufficiently strong fields Hext cause existing bits to grow, leading to bulk reversal via front propagation, and allowing a direct measurement of wall motion coercivity. Possible extensions to longitudinal media will be discussed. In general, combining the imaging and writing capabilities of MFM probes gives a direct assessment of media response to very localized fields, and leads to a powerful method for relating microstructure to bulk hysteresis properties.
Magnetic dichroism in the soft x-ray regime for magnetic domain imaging by total yield microscopy (abstract)
Authors: Hillebrecht F. U. , Kinoshita T. , Roth Ch. , Rose H. B. , Spanke D. , Dresselhaus J. , Kisker E.
Published: July 2002

Among the techniques for studying magnetic materials, methods utilizing magnetic dichroism in the soft x-ray region are receiving particular attention because of the unique feature of chemical specificity introduced by probing core levels. In soft x-ray absorption of linearly polarized light, the dichroism is proportional to the square of the magnetization M. The transverse magneto-optic Kerr effect is characterized by a change of the specular reflectivity when M is reversed, thus it is linear in M. Due to the relationship between reflected and transmitted radiation, a dichroism may also be expected in the absorption. We confirmed this by quasi-simultaneous measurement of the reflectivity and total yield around the Fe and Co 3p thresholds, using p-polarized light at oblique incidence: Switching the magnetization between the two directions normal on the plane of incidence indeed shows a magnetic dichroism. The relationship between the dichroisms in total yield and specular reflectivity was investigated as function of incidence angle.

In addition to this new form of magnetic dichroism, other forms have been explored for imaging near-surface magnetic domains of elemental and compound materials in a total yield microscope. By using different light polarizations different components of the magnetization are detected. p- and circular polarization yield magnetization components parallel to the surface, normal to and in the plane of light incidence, respectively. With linearly s-polarized light, images similar to those with circularly polarized light were obtained. This is evidence for a sizeable Faraday rotation, leading to a significant degree of circular polarization before the optical transition takes place. The helicity of the Faraday-induced ellipitical polarization depends on the local sample magnetization, thereby generating the magnetic contrast in an analogous fashion as does circularly polarized light. This mechanism is expected and found to be effective also for p-polarized light, however, with contrast smaller than that related to the transverse MOKE. Finally, we report first results for an antiferromagnet, where domains were observed via the M-quadratic Voigt effect in the soft x-ray region.
Change of magnetoresistance characteristic and crystal structure by ion bombardment to interfaces in [Ni81Fe19/Cu] multilayers (abstract)
Authors: Miyamoto Y. , Yoshitani T. , Nakagawa S. , Naoe M.
Published: July 2002

Many practical applications using giant magnetoresistance (GMR) have been developed, such as read-out heads and spin valve devices; however, the origin of GMR is not still fully understood. The GMR effect seems to be originated from the spin scattering mechanism whether at the interfaces or at the layer bodies. Therefore, it is necessary to investigate the spin scattering behaviors at the interfaces in GMR multilayers. It is regarded that the mixing and the diffusion of atoms at the interfaces in multilayers can be well promoted by ion bombardment to the interfaces at proper energy in dual ion beam sputtering (DIBS) method. In this study, change of magnetoresistance (MR) and crystallographic characteristics induced by interfacial mixing of atoms were investigated. Specimen films were deposited by DIBS. Additional ion bombardment to the growing surfaces arranges the mixing effect at the interfaces between Ni-Fe and Cu layers. Acceleration voltage of sputtering ion source Vmg were set at 500 V and that of bombarding ion source Vsg was varied in the range of 0–300 V. Si wafers were used as substrates. Ni–Fe/Cu multilayers with GMR were deposited on 50 Å thick Fe buffer layers.

Only two monolayers at the interfaces in Ni–Fe/Cu multilayers were exposed to ion bombardment to cause the local interfacial mixing. X-ray diffraction diagrams, showed that (111) orientations of Ni–Fe and Cu crystallites are obtained at Vsg below 200 V and that, on the contrary, (100) orientation became dominant in the films deposited at Vsg above 200 V. There is no apparent differences in MR ratio with increase of Vsg. However, the field sensitivity and saturation field properties were drastically degraded at Vsg above 200 V, while the crystal structure seemed to be changed. These results indicate that spin scattering were mainly occurred at the layer bodies in Ni–Fe/Cu multilayers. These results implied that the interfacial mixing is not so effective for changing MR ratio of Ni–Fe/Cu multilayers. However, the behavior of magnetization vectors are much influenced by change of local structure at the interfaces. These results seem to confirm the proposed theory; i.e., the spin scattering in layer bodies is the dominant mechanism on GMR in Ni–Fe/Cu multilayers.
Metal-insulator transition in dirty Kondo insulators
Authors: Schlottmann P. , Hellberg C. S.
Published: July 2002

We consider arbitrary clusters of Kondo holes in a Kondo insulator described by the nondegenerate symmetric Anderson lattice with a nearest-neighbor tight-binding conduction band on a simple cubic lattice. The f-electron self energy is considered within the local approximation. Each Kondo hole introduces a boundstate in the gap. The quantum interference in the scattering off the impurities gives rise to interactions among the Kondo holes. The spectral weight of the bound states is predominantly localized on the sites neighboring the Kondo holes. Clusters of impurities separated by more than one lattice site are disconnected for boundstates at the Fermi level. On a simple cubic lattice the metal-insulator transition in the impurity band then reduces to the site percolation of Kondo holes with first, second and fourth nearest neighbors. We use the low density mean cluster size expansion and a small cell renormalization to estimate the critical concentration. Hopping in the conduction band beyond nearest neighbors reduces the percolation threshold. Hence, 9.9% of Kondo holes is an upper bound for the insulator to become a metal.
Interfacial roughness of Fe–Cr GMR superlattices (abstract)
Authors: Dmowski W. , Egami T. , Kelly D. , Schuller I.
Published: July 2002

Fe–Cr superlattices exhibit giant magnetoresistance effect which can be utilized in magnetic recording heads. There are many studies indicating the role of the interfacial structure on the magnetoresistance effect. To elucidate this point we have performed x-ray diffraction study of three [Fe(30 Å)/Cr(12 Å)]10 superlattices which had been sputtered in 4, 7, and 10 mTorr of Ar. We used position sensitive detector in horizontal setup to collect simultaneously specular scattering intensity (z component of the scattering vector Q perpendicular to the film) and off-specular intensity with y parallel to the plane of the sample. This technique allows to evaluate interfacial roughness at various length scales. Short range roughness may be due to interdiffusion, while some medium range roughness is also present, and could have effects on transport phenomena. In conventional low angle diffraction analysis these contributions are intermixed. From the Fourier transform of the scattered intensity distribution in Qx−Qy plane the interfacial height fluctuation function g(r)can be obtained (r is a lateral spacing). Figure 1 presents g(r) obtained for three samples of Fe–Cr. It is apparent that 4 mTorr sample is very different than 7 and 10 mTorr in terms of interfacial roughness. We will discuss in detail results of the diffraction studies together with the magnetization and magnetotransport data.
The influence of Ni on the microstructure and GMR of the Co–Cu alloy granular films (abstract)
Authors: Zhang S. Y. , Cao Q. Q.
Published: July 2002

The microstructure and Giant Magnetoresistance (GMR) in Co–Cu and Co–Ni–Cu alloy granular films prepared by dc magnetron sputtering technique was discussed. The microstructure of Co–Ni–Cu alloy granular films observed by XRD, SEM, and HRTEM examinations showed even microscopic tissue in which nanoparticles of Co–Ni were well-distributed, much different than that of Co–Cu alloy granular films in which full-grown microparticles of Co were embedded in Cu matrix. By Magnetic Hysteresis Measurement and Neel’s superparamagnetism theory, the mean size of the Co–Ni particles in Co–Ni–Cu alloy granular films was estimated to be 2 to 4 nm, much smaller than that in Co–Cu alloy granular films. These results indicated that owing to the existence of Ni in Co–Ni–Cu alloy granular films the phase segregation was not a nucleation and growth process as that of Co–Cu alloy granular films but due to spinodal decomposition which was reported for the first time in granular films. It was also found that when samples dropped from room temperature to low temperature, the GMR boomed in Co–Ni–Cu alloy granular films, on the contrary to the behavior of Co–Cu alloy granular films. This fact meant that the Co–Ni–Cu alloy granular films with proper Ni content might have no response to the temperature change. Furthermore, the GMR as a function of magnetic density in Co–Ni–Cu alloy granular films is of much better linearity than that in Co–Cu alloy granular films.
Spin glass behavior of Zn1−xMnxTe
Authors: Shand P. M. , Christianson A. D. , Martinson L. S. , Schweitzer J. W. , Pekarek T. M. , Miotkowski I. , Crooker B. C.
Published: July 2002

We have performed ac susceptibility and dc magnetization measurements on the diluted magnetic semiconductor Zn1−xMnxTe. The measurements clearly indicate spin glass behavior. For an x=0.4 sample, the data for the imaginary part of the complex susceptibility (χ″) was analyzed according to conventional power-law dynamics and good scaling was obtained with Tc=13.4±0.2 K, zν=10.5±1.0, and β=0.9±0.2. These values of zν and β are consistent with results obtained in other spin glass systems. The scaling of the χ″ data was not as good when analyzed within the activated dynamics model. Magnetization measurements of an x=0.5 sample also showed a spin glass-like transition. Scaling of the nonlinear magnetization just above the transition gave Tc=20.8±0.2 K, and the critical exponent values β=0.8±0.2 and γ=4.0±1.0. This confirms the β value obtained from the ac measurements and the γ value is in fair agreement with reported values for other diluted magnetic semiconductor spin glass systems. We conclude that Zn1−xMnxTe and similar systems undergo equilibrium phase transitions to a spin glass state at low temperatures.
Observation of spin-glass freezing in the S=1 linear-chain Heisenberg antiferromagnet NENP
Authors: Hagiwara M. , Katsumata K. , Sasaki S. , Narita N. , Yamada I. , Yosida T.
Published: July 2002

We have observed spin-glass freezing in a nominally pure single crystal of the S=1 linear-chain Heisenberg antiferromagnet Ni(C2H8N2)2NO2(ClO4)(NENP) by direct current (dc), linear alternating current (ac), and nonlinear ac susceptibility measurements. A possible origin of this spin-glass freezing is discussed.
The energy loss per cycle in bar domain Si–Fe
Authors: Lorenz Bryen E.
Published: July 2002

Theoretical investigations into the average energy loss per cycle of oriented, bar domain silicon–iron samples, has been typically carried out by treating the static hysteresis and eddy current losses separately. Since all losses ultimately are related to the motion of the domain walls in soft magnetic materials, this differentiation is at best artificial and at worst misleading. A simple model is proposed in this paper, based on the empirical properties of silicon iron, which when incorporated into the loss calculation yields results that predict the presence of both contributions to the total loss. In addition, the model places a limit on the frequency dependence of the domain widths (domain refinement). The implications of this constraint are investigated.
180° domain wall with the coordinate dependent azimuthal angle of magnetization
Authors: Sobolev V. L. , Teh C. T. , Huang H. L.
Published: July 2002

Structure of 180° one-dimensional domain wall (DW) in a uniaxial ferromagnet in the presence of an external magnetic field arbitrarily oriented with respect to the DW has been investigated. Solutions of the system of equations which describe the behavior of the magnetic moment inside the DW in the case when the magnetization azimuthal angle is dependent upon the coordinate normal to the DW have been obtained and influence of magnetic field on the structure of the DW analyzed. Dependences of the effective widths of the distributions of both the polar and azimuthal angles of magnetization across the DW proper have been obtained. The effective width due to the azimuthal angle variation along the DW normal was found to increase with increasing transverse field.
Magnetic force microscope study of domain wall structures in magnetite
Authors: Pokhil Taras G. , Moskowitz Bruce M.
Published: July 2002

Domain walls (DW) in a small multidomain grain (≊20 μm) of magnetite (Fe3O4) exhibiting a planar domain pattern were studied using a magnetic force microscope (MFM). Most walls were subdivided with one or two Bloch lines and all walls displayed asymmetric MFM responses. Domain walls were observed to have small offsets either at the location of Bloch lines or at other locations without Bloch lines. The experimental data were described by a model in which (1) the easy axis of magnetization is not exactly parallel to the grain surface but is slightly inclined, and (2) there is also some plane dividing the grain in two parts with slightly different inclined easy axis directions. The inclined easy axis produces asymmetric spin distributions across the DW and wall offsets occur to reduce the surface magnetostatic energy of the wall.
A new magnetic bar code system based on a magnetic anisotropy detection (abstract)
Authors: Sasada I. , Watanabe N.
Published: July 2002

Magnetic bar codes can be used in unclean environments, where widely used optical bar code systems cannot be applied. Readout system for magnetic bar codes can also be made much simpler than optical ones. A new magnetic bar code system is proposed, in which binary information is coded in the sign of tilted angles of magnetic strips from a given standard direction. This scheme is unique compared to the conventional optical bar code, where width or space of the parallel pattern carries information, or an already reported magnetic bar code, where cross sectional shapes of pattern engraved in a ferromagnetic body carries information. Each of the magnetic strips brings about magnetic anisotropy due to its shape effect, hence angular dependent permeability in the proximity of the strip. The sign of the tilted angle of each magnetic strip is detected inductively through the angular dependent permeability by using a magnetic pickup head with a pair of cross-coupled figure-eight coils, where the sign of mutual inductance between the primary and the secondary figure-eight coil has one to one relationship to the sign of the tilted angle.

Because the detection of the tilted angle is independent of scanning speed, variation in the scanning speed of the readout head does not affect the performance. In our preliminary study, the proposed magnetic bar code system was examined using pickup head consisting of a pair of cross-coupled 10-turn figure-eight coils which was embedded in a rectangular ferrite rod with cross-shape groove on the top surface of 6.5×3 mm dimension. The head was made thinner in the scanning direction to allow dense alignment of the pattern. Two kinds of pattern were made: the one was by aligning short amorphous wires (5 mm in length and 120 μm in diameter) on the plastic film and the other by using a thin (10 μm in thickness) copper film with tilted slits backed by an amorphous ribbon. These samples of magnetic bar code patterns were scanned with lift-off of 1 mm under the operating condition of 120 kHz and 200 mA. Amplitudes of the positive and the negative peak of the output voltage well exceeded 10 mV. Density of the pattern in the preliminary study was 7 bits for the bar code length of 2.6 cm. We will discuss several factors to make density of the pattern higher. Because the pickup coils can be assembled with planar coils and because the magnetic bar code itself is thin, the total system of this bar code scheme can be realized in thin form.
Annealing and geometric effects in the magneto-impedance of amorphous Co70.4Fe4.6Si15B10 alloys
Authors: Sommer R. L. , Chien C. L. , Hasegawa R.
Published: July 2002

Giant magneto-impedance effects in different measuring geometries (longitudinal and transverse) of amorphous Co70.4Fe4.6Si15B10 ribbons under different field annealing have been studied at various frequencies (0.1 Hz–2 MHz). For suitably annealed samples, rich peak features have been observed in longitudinal MI measurements. For transverse MI measurements, a large effect magnitude has also been found. These results are discussed in terms of the effects of the magnetic annealing and measurement geometries on the effective permeability.
Resonant near-sound reorientation of the domain wall plane in yttrium orthoferrite
Authors: Chetkin M. V. , Kurbatova Yu. N. , Akhutkina A. I.
Published: July 2002

The dynamic orientation of the moving domain wall (DW) inclined at the static at an angle of about 50° to the surface of the plate of the orthoferrite cut perpendicularly to the optical axis was investigated. In the process of the increase of the domain wall velocity a very sharp decrease of the visible thickness of DW takes place near the transversal sound velocity. The moving domain wall changes its orientation plane and becomes almost perpendicular to the plate. This result may be caused by renormalization of anisotropy or dynamic minimization of domain wall energy. The solitary defection wave can propagate along self-organizing structure in the domain wall as a result of supersonic instability.
Approach to the anhysteretic surface
Authors: Sablik M. J. , Langman R. A.
Published: July 2002

In this paper, we have investigated experimentally the approach to the anhysteretic surface in M–H–σ space. In particular, for a 0.5 wt% carbon steel specimen, we have applied 73 MPa tension and a bias field H and determined the end flux density after superimposing an ac field of amplitude gradually decreasing to zero. We find that the point on the anhysteretic curve for 73 MPa tension and field H is not approached unless the initial amplitude of ac field is sufficiently large to overcome domain wall pinning, which restrains redistribution of the domains. A similar experiment in which stress is cycled was also done. Stress was cycled discretely between 0 and 140 MPa, with the discrete changes about 73 MPa eventually decreasing to zero in bias field H. It was found that the loci of (B,H) end points did not approach the anhysteretic, suggesting that larger amplitude changes in stress and perhaps more continuous changes are needed to overcome domain wall pinning.
An investigation on the magneto-optical enhancement in Ni-substituted barium ferrites
Authors: Zhang Xijuan , Xu You , Duan Mingqian , Guillot Maurice
Published: July 2002

The calculation of the contribution of the intraionic electric-dipole transitions between the 3d8 and 3d7 4p configurations of Ni2+ ions doped in barium ferrites to the Faraday effect is presented. It is shown that such transition is an important origin of the Ni contribution to the Faraday effect in the Ni-substituted barium ferrite. The energy difference between the mean energies of the 3d8 and 3d7 4p configurations is large. So the 496-nm wavelength (photon energy 2.5 eV) is far from the resonance frequencies. However, since the molecular field upon the Ni2+ ions is very large, the Faraday rotation at 496 nm produced by such transition is still large. Other possible origins are discussed briefly.
Surface-induced miscibility gap in vapor deposited Co1−xPtx (abstract)
Authors: Tran M. Q. , Shapiro A. L. , Rooney P. W. , Hellman F.
Published: July 2002

We have deposited (100) and (111) oriented single-crystal Co1−xPtx films (x=0.65, 0.75, and 0.86) over a range of growth temperatures from −50 to 800 °C. The Curie temperature is increased by up to 200 °C over the value expected for the homogeneous, chemically disordered alloy in the as-deposited films (of both orientations) grown near 400 °C. Measurements of the onset of magnetic ordering below the Curie temperature indicate separation into Co-rich and Pt-rich regions. High resolution x-ray measurements show no shift in the lattice constant or broadening of the x-ray peaks, and no observable strain for x=0.75, suggesting that the separated regions are small and epitaxially coherent. We interpret this as evidence for a previously unobserved miscibility gap. The bulk phase diagram shows no phase separation, but magnetic energy tends to drive the system toward immiscibility as demonstrated by the calculations of several workers. We suggest that the observed miscibility gap is an equilibrium surface effect, trapped into the bulk film by low bulk mobility. Preliminary work by Rosengren and Kundrotas supports this idea. Large perpendicular magnetic anistropy is found in those films that exhibit an anomalously high Curie temperature (films grown near 400 °C). This anisotropy is likely related to the phase separation. After annealing at high temperatures, the Curie temperature approaches the homogeneous values and the anisotropy relaxes.
Synthesis and physical properties of RNi2B2C and related materials (invited) (abstract)
Authors: Cava R. J.
Published: July 2002

Copper oxides have dominated superconductivity research since 1987. The interplay between superconductivity and magnetism lies at the center of the controversy concerning the appropriate microscopic model for their superconductivity. We have recently been exploring a broad new family of materials which represent the first true quaternary intermetallic superconductors. Although their superconducting Tc’s are not competitive with the copper oxides, several of the members of the family have Tc’s equivalent to the highest Tc’s ever reported for intermetallic compounds. The materials are especially surprising in that they are not based on niobium alloys, but rather are based on the borides of nickel, palladium, and platinum. The presence of square planes of the normally magnetic transition metals nickel and palladium suggests that magnetism might play some role in the superconducting mechanism. There are experimental results on both sides of the magnetic/conventional mechanism question, and although at this time the community is leaning largely toward a conventional mechanism, this should still be considered an open question. The presence of superconductivity for some of the magnetic rare earth analogs results in interesting phenomena, especially in the case of HoNi2B2C where the magnetic transition on the Ho sublattice is very close to the superconducting Tc. This talk will serve as an introduction to the chemistry, structure, and basic physical properties of these new materials, and will draw on the results of other groups, as well to present a summary view of these materials.
Neutron scattering studies of the magnetic order in RNi2B2C
Authors: Lynn J. W. , Huang Q. , Sinha S. K. , Hossain Z. , Gupta L. C. , Nagarajan R. , Godart C.
Published: July 2002

Neutron diffraction has been used to investigate the magnetic order of RNi2B2C. For R=Er the system orders antiferromagnetically at TN=6.8 K, and this long range order coexists with superconductivity (Tc=11 K). The magnetic structure is an incommensurate, transversely polarized spin-density-wave state, with the modulation wave vector δ along the a axis and the moments along b. δ has a temperature-independent value of 0.5526 (2π/a), with the structure squaring up at low temperatures. For R=Ho the moments also prefer to reside in the a–b plane, but initially an incommensurate c-axis spiral state forms upon cooling, with TN≊TC≊8 K. This c-axis spiral consists of ferromagnetic sheets of holmium moments in the a–b plane, but with each sheet rotated by ∼163° as one proceeds along the c axis. Small a-axis peaks are also observed above the reentrant superconducting transition over a narrow temperature range, but the c-axis peaks dominate. Just below the reentrant transition at ∼5 K the magnetic system locks-in to a simple commensurate antiferromagnetic structure, which permits superconductivity to be restored. The c-axis spiral, the a-axis component, the commensurate antiferromagnetic structure, and the superconducting phase are all in a delicate balance energetically, and this balance may be easily shifted by subtle changes in composition, magnetic field, and pressure. DyNi2B2C orders antiferromagnetically at TN=11 K, with the same commensurate antiferromagnetic structure as found for the holmium material at low temperature. The existence of superconductivity in some samples of DyNi2B2C is consistent with the antiferromagnetic structure observed.
Theory, fabrication and testing of dual track complimentary type of thin-film recording heads for perpendicular magnetic recording system
Authors: Ichihara T. , Nakagawa S. , Matsushita N. , Naoe M.
Published: July 2002

A new type of recording head for a perpendicular magnetic recording system, a dual track complimentary (DTC) type of thin-film head, was proposed in this study. The magnetic core of the head has a ‘‘U’’ character shape which is provided with ‘‘a pair of’’ recording tracks and the efficiency to detect flux reversal in the media will become high enough to achieve high linear density. The two-dimensional analysis of DTC heads implied that the perpendicular component of the head field should become larger by using the double-layered media under a narrower spacing condition. Recording characteristics using conventional ring head were evaluated in order to determine the principle of DTC configuration. Several DTC heads were prepared using photolithography technique and their performances were examined. A typical DTC head has inductance of about 500 nH, which is relatively low, and constant up to 10 MHz. DTC heads seems to be one of the most hopeful candidates as the heads useful for perpendicular magnetic recording systems.
Three-dimensional analysis of the magnetization process of thin-film media
Authors: Miyashita E. , Yoneda Y. , Numazawa J.
Published: July 2002

A calculation model in which the medium is considered as a set of many fine magnetic particles is applied to thin-film media. The magnetic characteristics are calculated for a particle with an initial layer, a particle without an initial layer, and media composed of the particles of either type. The results show that the switching mode of both particles is a quasi-coherent rotation but the switching field dependence of the particle with an initial layer has curlinglike characteristics. The perpendicular medium with an initial layer is over corrected by 4πMs demagnetization correction.
Nanoindentation study of the mechanical properties of metal evaporated magnetic tapes
Authors: Deng Hong , Barnard John A.
Published: July 2002

Nanoindentation techniques have been used to examine hardness (H), Young’s modulus (E), and strain rate sensitivity (m) in three types of commercial unaged and aged metal evaporated (ME) magnetic tapes. The aged tape samples were aged at 75 °C for 60 weeks at 5% and 90% humidity. The hardness of the ME layer can be determined at a depth of 30–50 nm, but for deeper penetrations the hardness value is increasingly affected by the soft polymer substrate. H and E are essentially the same for the unaged samples and the samples aged at 5% humidity but greatly decreased for the tapes aged at 90% humidity. The creep behavior (the time-dependent deformation) of these tapes was also characterized for the first time using the nanoindenter. Strain rate sensitivity increases with maximum applied load. On the other hand, a decrease in the strain rate sensitivity is observed for the tapes aged at 5% humidity. For the tapes aged at 90% humidity it is very difficult to obtain the strain rate sensitivity due to the excessive brittleness of the samples. Nanoindentation creep measurements appear to be quite sensitive to the degradation of ME tape caused by adverse environmental conditions.
A micro-remote centered compliance suspension for contact recording head (abstract)
Authors: Nakao M. , Sugiyama S. , Hatamura Y. , Hamaguchi T. , Watanabe K.
Published: July 2002

Nowadays contact recording has become one of the most important mechanisms for high-density recording of HDD. The contact recording head is always subject to friction when sliding. If the friction causes vibration on the sliding head, the swaying of the head is likely to lead to some undesirable bit shifts. The authors previously measured the head movement in sliding with a Watrous-type suspension where it was verified that the front edge of the head fell down to the disk surface because the rotational center of the pitching motion of the head was located above the sliding surface, inducing a heavy sticking. In order to prevent the sticking from occurring, we have already proposed RCC (remote centered compliance) suspension (15 mm in thickness) which consists of a pair of inclined plates. With this suspension, the front edge of the head is raised up because of the enhanced location of the rotational center which is now below the sliding surface. In this article we present a newly designed micro-RCC suspension (125 μm in thickness) for an acutal small MR head (1×1×0.5 mm) of the contact recording. It has two pairs of the inclined plates structure for two-axis frictions which are caused by seeking and tracking motions of the head, respectively.

This suspension is fabricated from a 125 μm thick sheet of polyimide using the ultraviolet laser beam. We evaluate its movement in sliding at low speed (50 μm/s) and at high speed (2 m/s) under a 10 mN load on a sputtered disk, respectively. The normal and frictional forces are measured by a micro two-axis force sensor (0.01 mN resolution) with parallel-plate structure and the pitching motion of the head is measured by an inclination sensor by means of laser reflection angle measurement (10 μrad resolution). From the experiment at low speed, we have clarified that the head yields a stable friction (0.15±0.02 mN) and has the nose-up attitude (0 to + 100 μrad). In addition, from the evaluation at high speed, we have observed the stable read-back signal (±7% modulation) because of the stable motion without any sticking. As a reference suspension, we prepare a micro-Winchester-type suspension. From the similar evaluation, we have identified that the reference head shows unstable friction (0.25±0.1 mN) with the nose-down attitude (0 to −500 μrad) and an unstable signal (±50% modulation). We have confirmed through these observations that the micro-RCC suspension will be an indispensable tool for contact recording in order to realize a stable recording against the friction.
Rough surface contact analysis and its relation to plastic deformation at the head–disk interface
Authors: Poon Chin Y. , Bhushan Bharat
Published: July 2002

Ni–P coated Al–Mg (Ni–P) and glass–ceramic (GC) substrates for magnetic recording are measured by an atomic force microscope (AFM) using different scan sizes and sampling resolution. AFM measurements of the Ni–P and GC surfaces at smaller sampling intervals reveal finer details. The GC surface contains more high frequency details than the Ni–P surface. The correlation length β*, a spatial parameter, is used in addition to the rms roughness Rq to characterize the surfaces. Contact analysis using a three-dimensional elastic-plastic rough surface contact model shows that the asperity pressure of the GC surface increases more rapidly than the Ni–P surface as the sampling interval decreases. For both surfaces, asperity contact starts from plastic deformation, the scale of which depends on different surface topographical structures. The GC surface is shown to have higher asperity pressure because it has higher frequency structures. The high frequency structure will facilitate plastic deformation, and it can help explain previously published results why the disk with Ni–P substrate has better durability than the disk with GC substrate in different environments.
Theoretical predictions of magnetic interface anisotropy in (Pd/Co/Pd)/X superlattices
Authors: MacLaren J. M.
Published: July 2002

We present first principles electronic structure calculations of the magnetic interface anisotropy for several (1Pd/1Co/1Pd)/nX superlattices with X=Pt, Pd, Ag, or Cu. The calculated anisotropies are compared to those found in Co/X and (1Pt/1Co/1Pt)/nX superlattices. The predicted anisotropies for monolayer spacers of Ag or Cu are similar in magnitude to those computed for Co/Pd or Co/Pt multilayers. In the case of (1Pd/1Co/1Pd)/1Pt, the anisotropy is enhanced when compared to either Co/Pt or Co/Pd superlattices, though to a lesser extent than that computed for (1Pt/1Co/1Pt)/1Pd. Surprisingly, increasing the number of spacer layers to three, results in a suppression of the perpendicular anisotropy in (1Pd/1Co/1Pd)/3X and (1Pt/1Co/1Pt)/3Cu superlattices. This result is inconsistent with a near-neighbor Neel model, which would predict little sensitivity to the number of X layers. The Neel model has been shown to work quite well on average for many fcc-based Co/Pt and Co/Pd multilayers. This suggests that the details of the superlattice electronic structure are important in these systems.
Origins of giant biquadratic coupling in CoFe/Mn/CoFe sandwich structures (abstract)
Authors: Koon Norman C.
Published: July 2002

Recently Filipkowski et al. reported extremely strong, near 90 degree coupling of 2.5 erg/cm2 for epitaxial sandwiches of CoFe/Mn/CoFe, where the CoFe composition was chosen to be a good lattice match to Mn. Both CoFe and Mn have the bcc structure, but Mn is antiferromagnetic while CoFe is ferromagnetic. It was found that the data were very well described by a simple model due to Slonczewski, in which the interlayer coupling is given by Fc=C+(φ1−φ2)2+C−(φ1−φ2−π)2. While this model describes the data much better than the usual biquadratic form, it still does not connect directly to the microscopic origins of the effect. In the present work we seek to explain the results in terms of normal bilinear exchange and magnetocrystalline anisotropy, together with reasonable assumptions about the structure of the interfaces. We obtain excellent agreement with both the experimental results and the Slonczewski model under the assumptions that at least one of the two CoFe/Mn interfaces is smooth (i.e., atomically flat) on a length scale comparable to or greater than the thickness of the Mn layer and at least one interface is rough on a scale less than approximately a domain wall thickness.
Magnetic parameter control for high-density quadrivalued MO recording (invited) (abstract)
Authors: Ohta N. , Shimazaki K. , Yoshihiro M. , Nagai N. , Ohnuki S.
Published: July 2002

To increase recording density of MO media, several schemes have been proposed. Among them, magnetic multivalued (MMV) recording is one of the most promising methods. We have first realized the quadrivalued MMV media using a field modulation method. Such media is composed of an exchange coupled TbFeCo/PtCo bilayer. By switching the external field in four levels, the separated signal corresponding to the each field is obtained as a four leveled output. For the acutal device application for high-density and high-speed recording, it is necessary to reduce the external field as small as possible. In the previous experiment, about ±900 Oe was necessary to record the whole levels. For such MMV media, the quadrivalued signal response depends on the magnetic characteristics of the TbFeCo/PtCo bilayer, which is so called dual write state. The higher field level on the MMV media is defined by the threshold field of the dual write state. It is found that the threshold field is controllable to tune the magnetic parameter, especially the exchange coupling force between the TbFeCo and PtCo. As a result, the reduction of the recording field less than 350 Oe is realized on a new media. Using such tuned media, high-density quadrivalued recording is experimentally carried out.
A study on the Kerr angle enhancement by the magnetic image effect (abstract)
Authors: Chang S. P. , Lee Y. P. , Huang D. R.
Published: July 2002

Recently, new mechanisms have been proposed to explain the giant enhancements of M-O Kerr effect. In this work, we use magnetic image effect to explain the Kerr angle enhancement of M-O media on Co-base amorphous films. The M-O layer and reflection layer were produced by using conventional dc magnetron sputtering processes. The Kerr hysteresis loops of M-O films were measured with wavelength from 500 to 860 nm, and the peak applied field was 9 kOe. We have studied the enhancements of Kerr angle in TbFeCo amorphous film which sandwiched by AlN layers and backed with Co-base amorphous film. There is a remarkable increase of Kerr angle with value 1.85° at wavelength 640 nm. At wavelength 780 nm, the Kerr angle of magneto-optic medium on Co-base amorphous ribbon has been significantly enhanced by a factor of 3.1 as compared to that on Al foil. Because of its high permeability and low coercivity, the Co-base amorphous film serve as a magnetic shielding material which can induce the magnetic image effect for M-O film. Theoretical calculations show that the Kerr angle can be enhanced by the image magnetic field. The calculated values of Kerr angle are in good agreement with experiment results. An explicit equation to calculate the Kerr angle will be discussed.
The low-temperature rate of electron capture beta decay in magnetic materials
Authors: Folan L. M. , Tsifrinovich V. I. , Sheverev V. A.
Published: July 2002

Electron capture β-decay in 54Mn2+ ions in solids is analyzed. It is shown that the decay rate of 54Mn2+ should decrease significantly at low temperatures, approaching a limit of 35% of its room temperature value. It is also shown that the decay rate at low temperatures can be manipulated using resonant electromagnetic fields and the rate can be modulated by a factor of four. Extension to other species is suggested and potential applications are described.
Characteristic analysis of coupled microstrip patch resonators on ferrimagnetic substrates
Authors: Sun Kunquan , Chen Yinchao , Barry Walter , Corlett John
Published: July 2002

This paper is to use the spectral-domain technique to perform characteristic analysis of coupled microstrip patch resonators on ferrimagnetic substrates. Our formulation has been validated by comparing our result with the published data and showing an excellent agreement between them. Numerical computations have been performed to obtain dependence of resonant frequency on patch dimensions, offset and separation between the two patches, thicknesses of ferrimagnetic film and substrate. It has been seen that as the length of the patch increases the resonant frequency decreases. The larger the offset between the two patches the lower the resonant frequency. The separation between the two patches strongly affects the resonant frequency. It is also found that the resonant frequency increases as the width of the patch decreases. For the fixed dimensions, separation and offset, a thinner substrate results in a higher resonant frequency, and in contrast, a thinner ferrimagnetic film results in a lower resonant frequency.
Jitterbug spin channel mixing in heterogeneous giant magnetoresistive material
Authors: Gregg J. F. , Allen W. , Thompson S. M. , Watson M. L. , Gehring G. A.
Published: July 2002

A mechanism is described which considers the effect of small magnetic particles on the spin diffusion length in a granular giant magnetoresistive material. Spin depolarization occurs by precession of the spin orientation of the carrier due to the s–d exchange interaction within a magnetic particle. Numerical simulation of this jitterbug effect is found to generate a temperature and field dependence of the distance a carrier may travel within the sample without losing its spin memory.
Structural evolution in sputtered Co90Fe10/Ag giant magnetoresistance multilayers
Authors: Jarratt J. D. , Barnard J. A.
Published: July 2002

The thermal evolution of structure, giant magnetoresistance (GMR), and magnetic properties in two sequences of sputtered (Co90Fe10/Ag) multilayers is presented. Granular-type and ‘‘discontinuous’’ GMR is observed depending on layer thickness.
The soft magnetic properties of stripes fabricated using laser ablation of multilayer thin films
Authors: Grimes Craig A. , Lumpp Janet K.
Published: July 2002

We examine the low frequency BH loop and complex permeability spectra of multilayer permalloy films laser processed to define samples consisting of stripes parallel to the as-deposited hard axis. We begin by examining different laser energy densities for groove definition in films of different thickness. We observe that for well coupled multilayer films with thin, 15 nm, spacer layers the demagnetizing field, which is a function of groove depth, is able to reorient the easy and hard axes from the initial orientation. As the groove becomes more clearly defined the hard axis permeability increases, while the easy axis permeability decreases. The role of stripe width and ambient processing atmosphere are also investigated.
Magnetic fluctuation spectrum of CuGeO3: Raman scattering
Authors: van Loosdrecht P. H. M. , Boucher J. P. , Martinez G. , Dhalenne G. , Revcolevschi A.
Published: July 2002

Raman spectra of the magnetic fluctuation spectrum of CuGeO3 are presented for 4<T<300 K and B≤20 T. For B=0 the results show good agreement with theoretical expectations for a one-dimensional isotropic Heisenberg antiferromagnet which exhibits a spin–Peierls transition. In the presence of a magnetic field the phase transition to the incommensurately modulated phase is observed around B=12.8 T at T=4.2 K. The spectra obtained in the high field phase clearly show evidence for a well-defined spin fluctuation spectrum, which appears to present an intermediate case between the dimerized phase and the short-range order regime of the uniform phase.