bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropy dispersion effects on the high frequency behavior of soft magnetic Fe–Co–N thin films
Authors: Sun N. X. , Wang S. X.
Published: May 2003

The high frequency behavior beyond 1 GHz of a Fe–Co–N film and a NiFe\Fe–Co–N film [NiFe stands for Ni81Fe19(wt. %)], shown as promising magnetic write head materials previously, has been investigated using a pulse inductive microwave magnetometer in this work. The NiF\Fe–Co–N film, which has a smaller dispersion angle (∼0.8°) than the Fe–Co–N film (∼2°), shows a smaller damping parameter and a higher ferromagnetic resonance frequency when longitudinally biased. When the Fe–Co–N film is transversely biased, the damping parameter of the Fe–Co–N film shows a diffuse peak at a transverse field of 1.76 kA/m (22 Oe), and its ferromagnetic resonance frequency shows a small local maximum at 1.76 kA/m (22 Oe). In contrast, the damping parameter of the NiFe\Fe–Co–N film shows a sharp peak at a transverse field of 1.4 kA/m (18 Oe), and its ferromagnetic resonance frequency displays a sharp local maximum also at a transverse field of 1.4 kA/m (18 Oe) too, which is very close to the dc anisotropy field. The sharp peak in the ferromagnetic resonance frequency and the damping parameter of the NiFe\Fe–Co–N film is due to the generation of a higher order (very close to the second order) ferromagnetic absorption when the ac field is large compared to the net in-plane dc magnetic field.
High-Bs Fe–Co–Al–O soft magnetic films
Authors: Shintaku Kazuhiko , Yamakawa Kiyoshi , Ouchi Kazuhiro
Published: May 2003

Fe–Co and Fe–Co–Al–O films were prepared by rf magnetron sputtering in an Ar-gas atmosphere. The coercivity (Hc) of the Fe–Co films was greatly decreased by a small amount of Al2O3 addition. However, a film thickness of more than 500 nm is necessary to obtain minimum the Hch (Hc in the hard-axis direction) of 5 Oe. Hch was greatly decreased by using a Ni–Fe underlayer of 0.5–12 nm, and was less than 1 Oe with film thicknesses ranging from 50 to 600 nm for Fe–Co–Al–O films. An amorphous Co–Zr–Nb soft magnetic underlayer was also examined to investigate influence of underlayer crystal structure. A Hch less than 1 Oe was realized for the samples with Co–Zr–Nb underlayer thickness of about 2 nm. Amorphous underlayer films were also effective in improving the soft magnetic properties of Fe–Co–Al–O films. It is finally concluded that combination of a small amount of Al2O3 addition and a soft magnetic underlayer film is essential to obtain small Hch with high saturation magnetic flux density of 2.4 T in a wide range of film thicknesses.
Evidence of a topological antiferromagnetic order on ultrathin Cr(001) film surface studied by spin-polarized scanning tunneling spectroscopy
Authors: Kawagoe T. , Suzuki Y. , Bode M. , Koike K.
Published: May 2003

Imaging of the surface magnetic structure of Cr(001) films epitaxially grown on Au(001) film was performed by using spin-polarized scanning tunneling spectroscopy and Fe-coated W tips. It is shown that two-step growth of a 4-nm-thick Cr layer having two different growth temperatures results in a chemically clean surface and makes it possible to observe distinct spin contrast. The spatially resolved maps of dI/dV signals taken at room temperature indicated that the topological antiferromagnetic order on the thin Cr(001) film surface that is subject to high-density steps and screw dislocations.
Hysteresis modeling of anisotropic and isotropic nanocrystalline hard magnetic films
Authors: Cornejo D. R. , Azevedo A. , Rezende S. M.
Published: May 2003

In the Hauser model, the magnetic state of a system is obtained by minimizing the so-called total energy function for a statistical set of magnetic domains. In this article, this energetic model of ferromagnetic materials is used in order to calculate hysteresis loops of isotropic and anisotropic nanocrystalline SmCo films at room temperature. A qualitative very good agreement between the calculated and experimental curves is obtained, mainly in the anisotropic case. Also, it has been verified that, under suitable approximations, the free parameters of the model can tie with intrinsic characteristics of the reversal magnetization process.
Modeling the interrelating effects of plastic deformation and stress on magnetic properties of materials
Authors: Lo C. C. H. , Kinser E. , Jiles D. C.
Published: May 2003

A model has been developed that describes the interrelating effects of plastic deformation and applied stress on hysteresis loops based on the theory of ferromagnetic hysteresis. In the current model the strength of pinning sites for domain walls is characterized by the pinning coefficient keff given by keff=k0+k′σ. The term k0 depicts pinning of domain walls by dislocations and is proportional to ρn, where ρ is the number density of dislocation which is related to the amount of plastic strain, and the exponent n depends on the strength of pinning sites. The second term k′σ∝−3/2λs/2mσ, where m is magnetization and λs is magnetostriction constant, describes the changes in pinning strength on a domain wall induced by an applied stress σ. The model was capable of reproducing the stress dependence of hysteresis loop properties such as coercivity and remanence of a series of nickel samples which were pre-strained to various plastic strain levels. An empirical relation was found between the parameter k0 and the plastic strain, which can be interpreted in terms of the effects on the strength of domain wall pinning of changes in dislocation density and substructure under plastic deformation.
Preisach modeling of magnetization and magnetostriction processes in laminated SiFe alloys
Authors: Dupré L. , De Wulf M. , Makaveev D. , Permiakov V. , Melkebeek J.
Published: May 2003

In this article, magnetization loops under mechanical stress and magnetostriction loops under quasistatic magnetic excitation conditions are discussed. In both cases, the hysteresis loops are modeled using the Preisach theory. The identification procedure of the material parameters is described. The article discusses first the shape of the Preisach distribution function for the study of magnetostriction loops. Next, a Preisach model is proposed for the description of magnetization loops under mechanical stress starting from the magnetization loop obtained without applying mechanical stress. A setup has been constructed for the measurement of magnetization loops under compressive or tensile stress. Also, a measuring system based on a single sheet tester and on optical displacement measurement techniques is used to establish the magnetostrictive behavior of laminated SiFe alloys. It is shown that a good correspondence between the calculated and measured magnetization and magnetostriction loops is obtained.
Proposal for a standard problem for Preisach based models
Authors: Morentı́n Francisco J. , Alejos Oscar , Muñoz José M. , Torres Luis , López-Dı́az Luis
Published: May 2003

Preisach based models have been usually considered as very convenient tools to simulate both the static and the transient behavior of the irreversible magnetization. In the present work, a very simple physical system consisting of a square array of aligned magnetic particles has been considered in order to be characterized by means of Preisach parameters. A uniform magnetic field is applied in the direction of the easy axis of the particles so that the system has only one dimension. Results reveal that, despite the simplicity of this system, it cannot be successfully defined by means of Preisach parameters. The distribution of interaction fields in the system does not follow a simple Gaussian function. A distribution composed of three balancing peaks is found instead.
Modeling the irreversible response within the ferromagnetic phase of La0.7Sr0.3MnO3
Authors: Roshko R. M. , Xi L.
Published: May 2003

The magnetic response of a ferromagnetically ordered perovskite La0.7Sr0.3MnO3 with a critical temperature TC=325 K has been measured as a function of applied field ha over the interval −4 kOe⩽ha⩽+4 kOe, and as a function of temperature T over the interval 5 K⩽T⩽350 K which spans the ordered phase, and analyzed within the framework of a model which reduces all magnetic systems to an ensemble of temperature dependent, asymmetric double well subsystems. The model is able to replicate the field and temperature dependence of the measured zero field cooled moment, the field cooled moment, the isothermal remanent moment, the thermoremanent moment, the initial magnetizing curve, the magnetizing remanence, the major hysteresis loop, and the demagnetizing remanence, and yields the spectrum of double well dissipation barriers and level splittings which represent the Barkhausen excitations between metastable domain configurations.
Micromagnetic study of nonlinear effects in soft magnetic materials
Authors: Mohler G. , Harter A. W. , Moore R. L.
Published: May 2003

Numerical simulation is used to study the linear and nonlinear effects of increasing incident power density on soft magnetic materials at the microscale. A magnetic field pulse with Gaussian time dependence and variable strength is numerically applied to a magnetic particulate in an equilibrium state. The field-dependent dynamic susceptibility (M/H) is calculated from the Fourier transform of the magnetization response. Calculations show that as the magnitude of the excitation field exceeds a critical value, the system becomes nonlinear. At this point, the ferromagnetic resonance should become suppressed and span a wider range of frequencies. Two systems are simulated in the linear and nonlinear regimes; one system shows complete agreement with established nonlinear theory, while the other shows unusual behavior. Both systems agree with linear theory at low fields, and vanishing susceptibility at excessively high fields is observed for both.
Modeling a perpendicular recording medium using a variational method
Authors: Ridley P. H. W. , Spargo A. W. , Hines G. V. , Roberts G. W.
Published: May 2003

A micromagnetic model is used to investigate the dynamic behavior of a perpendicular recording medium which consists of a hard data layer and a soft underlayer. A variational finite element form of the Gilbert equation of motion is used to simulate the magnetization dynamics without thermal fluctuations. A computationally efficient variational approximation is used for the magnetization dynamics. The demagnetizing field calculation uses a hybrid finite element/boundary element calculation or a hybrid wavelet/boundary element method. The variational scheme is particularly suited to reducing numerical errors in areas of the material where magnetic inhomogeneities occur such as in the data layer during the nucleation of domains. Perpendicular recording media presents a viable alternative to the conventional longitudinal type in extending the superparamagnetic limit. Higher field strengths allowing higher densities have been shown to be sensitive to the characteristics of the soft underlayer. The dynamic effects of the soft underlayer are investigated for thicknesses between 65 and 80 nm. Interaction effects between the data layer and soft underlayer are observed to be more prominent in the 65 nm thickness.
Low switching current flux-closed magnetoresistive random access memory
Authors: Zheng Y. K. , Wu Y. H. , Li K. B. , Qiu J. J. , Shen Y. T. , An L. H. , Guo Z. B. , Han G. C. , Luo P. , You D. , Liu Z. Y.
Published: May 2003

A spin valve magnetoresistive random access memory with a flux-closed structure is presented. The flux-closed structure prevents the disruption to magnetization of the recording layer and increases the thermal stability. Simulation results show that the switching field increases under the uniform external field, however, the switching field has no change under the bit current field. Only the bit current that flows mostly at the center is used to switch the cell. Experimental results show that the bit current of 10 mA is sufficient to switch the 1 μm×4 μm cell.
Performance of current-in-plane pseudo-spin-valve devices on CMOS silicon-on-insulator underlayers
Authors: Katti R. R. , Zou D. , Reed D. , Schipper D. , Hynes O. , Shaw G. , Kaakani H.
Published: May 2003

Prior work has shown that current-in-plane (CIP) giant magnetoresistive (GMR) pseudo-spin-valve (PSV) devices grown on bulk Si wafers and bulk complementary metal-oxide semiconductor (CMOS) underlayers exhibit write and read characteristics that are suitable for application as nonvolatile memory devices. In this work, CIP GMR PSV devices fabricated on silicon-on-insulator CMOS underlayers are shown to support write and read performance. Reading and writing fields for selected devices are shown to be approximately 25%–50% that of unselected devices, which provides a margin for reading and writing specific bits in a memory without overwriting bits and without disturbing other bits. The switching characteristics of experimental devices were compared to and found to be similar with Landau–Lifschitz–Gilbert micromagnetic modeling results, which allowed inferring regions of reversible and irreversible rotations in magnetic reversal processes.
Magnetic properties of patterned tunnel junctions
Authors: Warot Benedicte , Petford-Long Amanda K. , Anthony Thomas C.
Published: May 2003

Patterned magnetic tunnel junctions are being actively studied for their application in magnetic random access memory (MRAM) and read-heads. For MRAM application purposes, a clean magnetization reversal is one of the required properties. Various parameters such as junction size, shape or layer sequence are being investigated to optimize element properties. In this article, we report the results of Lorentz transmission electron microscopy used to study the magnetization reversal mechanism of (Ta/NiFe/MnFe/NiFe/Al2O3/NiFeCo) tunnel junction elements. Single layer NiFeCo element properties have also been investigated for comparison with the tunnel junctions. The results on tunnel junctions show the influence of size and aspect ratio of the patterned elements on magnetic properties. For the wider elements, domain formation and propagation is the dominant reversal mechanism and no asymmetry is observed between the antiparallel (AP) to parallel (P) and P–AP reversal measured as a function of aspect ratio. Single-domain reversal is the main process for narrower elements and there is an asymmetry in reversal field between the AP–P and P–AP reversals as a function of aspect ratio. Many energy terms (such as Néel coupling, stray field coupling, and the internal demagnetizing field) need to be taken into account to explain this behavior.
Magnetic nanowire arrays: A study of magneto-optical properties
Authors: Peng Yong , Shen Tiehan-H. , Ashworth Brian
Published: May 2003

Nanocomposite films of highly ordered magnetic nanowires embedded in anodic aluminum oxide templates were fabricated and magneto-optical properties were studied. Following our previous work, studies on Co nanowire arrays were carried out, where the MO properties in relationship with nanowire lengths and diameters were investigated. The results were found to be considerably different from corresponding bulk metal. We demonstrated that the Faraday effect was a convenient and useful probe for the study of the magnetic properties of these semitransparent nanocomposite films. A preliminary study on the photon energy dependence of the magneto-optical properties of Fe nanowire arrays was also conducted in the visible spectrum regime.
Magnetic properties of Fe nanocubes with magnetostatic interactions
Authors: Lee H. K. , Schulthess T. C. , Brown G. , Landau D. P. , Sorge K. D. , Thompson J. R.
Published: May 2003

Recent experiments indicate that the magnetic properties of single domain Fe nanoparticles (dispersed in an insulating matrix) may be dominated by magnetostatic interactions at packing fractions as low as 10%, where the separation between particles is of the same order as the particle size [Sorge et al., IEEE Trans. Magn. 37, 2197 (2001)]. We use extensive Monte Carlo simulations to calculate the temperature dependence of the remnant magnetization as a direct test of this hypothesis [Sorge et al., IEEE Trans. Magn. 37, 2197 (2001)]. The particle distribution is constructed with a computer model that imitates the experimental system for which data were obtained from transmission electron microscopy images, and the Fe particles are modeled as point dipoles with cubic anisotropy. Using bulk values for the anisotropy and the Fe magnetization, our simulations reproduce very well the experimental remnant magnetization. Furthermore, we find that the magnetic properties are dominated by the effects of dipole–dipole interactions and that the experimental results cannot be reproduced with noninteracting particles.
Coercivity and remanence in self-assembled FePt nanoparticle arrays
Authors: Schrefl T. , Hrkac G. , Suess D. , Scholz W. , Fidler J.
Published: May 2003

FePt-based nanostructured materials are excellent candidates for high density recording beyond 1 Tbit/in2. We calculate remanence, coercivity, and loop shape of annealed monodisperse FePt nanocrystals, using a modified Stoner–Wohlfarth model. To justify the simplifications of a Stoner–Wohlfarth model detailed finite element micromagnetic simulations were performed. Magnetic measurements on arrays of chemically synthesized FePt nanoparticles show remanence ratios of about 0.6 which is greater than that predicted for a series of noninteracting Stoner–Wohlfarth particles. A small fraction of the particles (5%) is assumed to remain in the disordered fcc phase with low magnetocrystalline anisotropy. Both remanence and coercivity are highly sensitive to the strength of the exchange interactions within a multiple twined nanocrystal. The calculated values are in the range from Jr/Js=0.52, Hc=0.77 MA/m to Jr/Js=0.61, Hc=1.2 MA/m. The results of the modified Stoner–Wohlfarth model are confirmed by finite element micromagnetic simulations taking into account magnetostatic interactions and allowing nonuniform magnetic structures within a particle.
Defect related switching field reduction in small magnetic particle arrays
Authors: Donahue M. J. , Vértesy G. , Pardavi-Horvath M.
Published: May 2003

An array of 42 μm square, 3 μm thick garnet particles has been studied. The strong crystalline uniaxial anisotropy of these particles results in the stable remanent state being single domain with magnetization parallel to the film normal. Magneto-optic measurements of individual particles provide distribution statistics for the easy-axis switching field Hsw, and the in-plane hard-axis effective anisotropy field, Heff, which induces the formation of a metastable stripe domain structure. Both Hsw and Heff are much smaller than the crystalline anisotropy field. Micromagnetic simulations show that the small Hsw cannot be attributed to shape anisotropy, but is consistent with smooth, localized reductions in the crystalline anisotropy caused by defects in either the particles or the substrate.
Competitive effects of dipolar interactions and a bias magnetic field on the magnetic relaxation times of Co clusters
Authors: Luis F. , Bartolomé J. , Petroff F. , Garcı́a L. M. , Vaurès A. , Carrey J.
Published: May 2003

We have investigated, by means of ac susceptibility experiments, the magnetic relaxation of layers of Co nanoclusters (D≃2.6 nm) embedded in Al2O3. Superparamagnetic blocking takes place at higher temperatures as the number of layers increases. These results are interpreted using a simple model in which dipole–dipole interactions between nearest neighbor particles increase the relaxation time. The influence of interactions is affected by the application of bias magnetic field H. As the magnetic moments of the particles become polarized by H, the blocking temperature approaches the behavior expected for noninteracting particles.
Variation of the magnetic domain structure with reversal field (invited)
Authors: Woodward R. C. , Lance A. M. , Street R. , Stamps R. L.
Published: May 2003

A rate dependence of the magnetic domain structure has been observed in a Pt/Co multilayer. The form of the domain structure as a function of the rate of change of magnetization was studied using nanosecond pulsed magnetic fields. At low fields the magnetization pattern consists of a dendritic like growth of the domains. As the magnitude of the pulse field is increased the patterns change to a more circular structure with smooth boundaries. The change in structure can be quantified and is discussed in terms of a field dependence where different behaviors can be clearly identified. The structure observed results from a narrowing of the distribution of energy barriers to reversal as the field is increased.
Micromagnetic and Preisach analysis of the First Order Reversal Curves (FORC) diagram
Authors: Stancu Alexandru , Pike Christopher , Stoleriu Laurentiu , Postolache Petronel , Cimpoesu Dorin
Published: May 2003

The First Order Reversal Curve (FORC) diagrams of interacting single-domain ferromagnetic particle systems have been found experimentally to contain negative regions. In this paper, we use micromagnetic and phenomenological (Preisach-type) models to help explain the occurrence of these negative regions. In Preisach-type modeling, the position of the negative region is correlated with the sign of the mean-field interactions. In micromagnetic modeling, the position of the negative region is correlated with the spatial arrangement of the particles in the model.
Reversible magnetization and Lorentzian function approximation
Authors: Azzerboni B. , Cardelli E. , Della Torre E. , Finocchio G.
Published: May 2003

The paper proposes the use of a Lorentzian function to describe the irreversible component of the magnetization of soft materials with hysteresis using the Everett’s integral. We will derive an analytical formula to compute the irreversible magnetization, and compute the reversible component by the measurements of the major loop. We shall compare the numerical results with experiments on not-oriented-grain magnetic irons.
Combined Preisach–Mayergoyz-neural-network vector hysteresis model for electrical steel sheets
Authors: Makaveev Dimitre , Dupré Luc , De Wulf Marc , Melkebeek Jan
Published: May 2003

Three versions of a vector hysteresis model for electrical steel sheets are presented, based on the function approximation capabilities of feed-forward neural networks and the memory mechanism of vector hysteresis proposed by Mayergoyz. The first model handles arbitrary vector magnetization patterns, but requires a very extended data set for the training of the neural network. The second model is suitable for convex induction loci and allows a reduction of the required training set. The third model handles the features of the considered magnetization pattern in an alternative way and relaxes the convexity requirement. The choice of the specific model, its parameters, and the network training set depends on the types of magnetization patterns concerned. Arbitrary high accuracy can be reached by extending the complexity of the model and/or the size of the training set. Experimental results for the third model are presented and show the good accuracy of the approach. Standard neural network algorithms are used.
First order approximation for interactions in particulate single-domain particle systems
Authors: Cimpoesu Dorin , Postolache Petronel , Stancu Alexandru
Published: May 2003

In most cases the interparticle interactions are essential in the evaluation of the magnetic properties of the ferromagnetic particulate systems. Usually, in first approximation, a mean interaction field linearly dependent on the magnetic moment of the sample is considered and other interactions are neglected. Using micromagnetic simulations on a system of interacting uniaxial single-domain particles we have shown that both the mean interaction field and interaction fields distribution dispersion depend on the magnetic moment of the sample. When the magnetic moment of the sample is small the statistical interactions are more important than the mean field ones and cannot be neglected.
Numerical modelling in the time domain of dynamic hysteresis of soft materials in cylindrical coordinates
Authors: Cardelli Ermanno , Torre Edward Della , Pinzaglia Enrico
Published: May 2003

This paper deals with the numerical analysis of soft magnetic materials with hysteresis in dynamic axial symmetric problems. We present a procedure based on a 1D Finite Difference Time Domain (FDTD) algorithm where there are implemented magnetization dependent Preisach based models. Experimental measurements of the virgin curve and the major loop are used to identify the models. The numerical scheme in the time domain proposed is discussed and a probe of its intrinsic stability is given. Numerical codes based on the above algorithm are used to show some of the possibilities of this numerical tool for the dynamic magnetic analysis.
Computing the surface impedance in nonlinear materials with hysteresis
Authors: Bertoncini F. , Cardelli E. , Di Fraia S. , Tellini B.
Published: May 2003

A numerical model in time domain for describing the energetic magnetic behavior of hysteretic materials is here proposed. Parallelogram shaped hysteresis loops have been used for simplifying the calculation. Equivalent major loops have been defined starting from the measured ones. Measurements have been done in our laboratory on different magnetic material cores. Both soft Mn–Zn ferrites and not oriented magnetic irons have been tested. Comparison with other numerical procedures based either on rectangular shaped hysteresis loops, or on the implementation of a scalar Preisach model is presented and discussed.
Remanent head field study of single pole-type head based on micromagnetics
Authors: Mochizuki Masafumi , Ishikawa Chiaki , Ide Hiroshi , Nakamoto Kazuhiro , Nakatani Yoshinobu , Hayashi Nobuo
Published: May 2003

The magnetization configurations within the pole tip of the single-pole-type head have been examined through a micromagnetic computer simulation based on the Landau–Lifshitz–Gilbert equation. The aspect ratio, including the effect of the exchange length (Lex), was defined as the ratio of the throat height (Th) to the write-track width (Tww) and the thickness (Tp), which is given (Th×Lex)/(Tww×Tp). It was found that the magnetization configuration and the perpendicular component of remanent head field (Hr) are strongly dominated by this aspect ratio at any value of Tww. It was also found that there is a characteristic aspect ratio at which Hr starts to decrease. These results show that decreasing the aspect ratio is an effective way to reduce the intensity of the remanent head field.
High anisotropy CoCrPt(B) media for perpendicular magnetic recording
Authors: Lu Bin , Weller Dieter , Sunder Ashwin , Ju Ganping , Wu Xiaowei , Brockie Richard , Nolan Tom , Brucker Charles , Ranjan Rajiv
Published: May 2003

CoCrPt(B) media with high magnetic anisotropy have been fabricated at a thin magnetic layer thickness (10 nm) and a thin interlayer thickness (4 nm). The hard magnetic properties of the CoCrPt enable addition of boron, which aids to magnetically decouple the grains. These media are thermally stable and have an enhanced signal-to-noise ratio.
ΔM
study of perpendicular recording media
Authors: Wu X. W. , van de Veerdonk R. J. M. , Chantrell R. W. , Weller D.
Published: May 2003

A significant source of media noise in thin-film granular systems is intergranular exchange coupling. This important interaction between grains in longitudinal recording media has been studied by well-established ΔM(H) techniques. In this study, micromagnetic calculation using a Monte Carlo simulation has been carried out to confirm the validity of such a technique for perpendicular media. A recently developed demagnetization correction method is applied to a series of alloy perpendicular media, and subsequently, the exchange interactions in these films are studied using the ΔM(H) technique. With increasing film thickness, ΔM(H) changes from positive to negative, indicating a reduction of the exchange interaction in thicker films. This reduction is attributed to a stronger exchange coupling between grains at the initial stage of the film growth.
Recording characteristics of perpendicular magnetic media with CoZrNb, NiFeNb, and exchange-pinned NiFeNb soft magnetic underlayers
Authors: Zheng Min , Chekanov Albert , Choe Geon , Johnson Kenneth E. , Gao Lan , Liou Sy-Hwang
Published: May 2003

The recording performance of perpendicular media with amorphous CoZrNb, nanocrystalline NiFeNb, and exchange-pinned FeMn/NiFeNb soft magnetic underlayers (SULs) has been studied. A method has been proposed to quantify the spike noises from the SUL. We found that media with higher permeability NiFeNb SULs showed 4 db higher signal-to-noise ratio than media with lower permeability CoZrNb SULs. The exchange-pinned NiFeNb SUL suppresses spike noise and offers good recording performance. Furthermore, the recording frequency dependence of dynamic coercivity (Hc) was strongly affected by the use of different SULs. The increase in dynamic Hc with linear density is negligibly small for media with NiFeNb SULs, whereas dynamic Hc sharply increases with increasing density for media with CoZrNb SULs.
Media tribology design to improve flyability at low flying height
Authors: Li Z. F. , Chen C. Y. , Liu J. J. , Pirzada S. A.
Published: May 2003

As the head media separation (HMS) continues to decrease with increasing areal density, maintaining good flyability performance is crucial to ensure the robustness of the head-disk-interface. Carbon wear and lubricant pickup on the slider surface are found to be the main contributors to flyability degradation. The effects of carbon overcoat and lubricant on load/unload flyability were investigated at the near-contact flying height by either reducing the environmental pressure or slowing down the disk rotating speed. Changing lubricant process and X-1P additive amount can affect lubricant pickup. In order to reduce the head wear, a thin layer of softer functional carbon layer was applied on the top of plasma-enhanced chemical vapor deposition carbon. However, carbon and lubricant modification has some limitations on improving flyability as HMS continues to drop. As an alternative approach to minimizing slider pickup at low flying height, landing the head in the laser textured contact-start-stop zone serves the function of cleaning the head and removing head smear.
Improvement of soft magnetic properties of Fe–Co–B underlayer with large saturation magnetization by Ni–Fe–O seedlayers
Authors: Kong Sok-hyun , Okamoto Takeshi , Nakagawa Shigeki
Published: May 2003

Fe–Co–B layers were investigated for a soft magnetic underlayer with large saturation magnetization 4πMs in perpendicular magnetic recording media. The addition of B was examined to see the decrease of in-plane coercivity Hc∥ in the Fe–Co layer. The surface morphology of the films observed by atomic force microscopy revealed that each of the grains in the Fe–Co–B layer seemed to be separate. These separate grains seemed to cause the suppression of exchange coupling between grains in polycrystalline ferromagnetic films. A Ni–Fe–O seed layer was effective in reducing the grain size of the Fe–Co–B layer and inducing high uniaxial in-plane magnetic anisotropy. The grain size of the Fe–Co–B layer deposited on the Ni–Fe–O seedlayer was about 73% that of a Fe–Co–B single layer. The magnetic anisotropy field Hk was as high as 255 Oe in the Fe–Co–B/Ni–Fe–O layer. Furthermore, the relative permeability μr of Fe–Co–B/Ni–Fe–O was about 200 and the resonance frequency fr was above 3 GHz. Insertion of a Ni–Fe–O interlayer was also effective in decreasing Hc∥ of the Fe–Co–B layer. A [Fe–Co–B/Ni–Fe–O]8 multilayer exhibited Hc∥ as low as 11 Oe in the hard axis of magnetization.
Write field gradient effect on perpendicular recording
Authors: Shukh Alexander , van Ek Johaness
Published: May 2003

An effect of the write field gradient on perpendicular recording has been studied by three-dimensional finite-element method and micromagnetic modeling. Two conceptual writer designs were compared: the conventional trailing pole (TP) writer with the main pole serving as the trailing pole and the leading pole (LP) writer, where the main pole operates as the leading pole. Both writers record transitions on double-layer media by the trailing edge of the main pole. The LP writer allows effective control of the write field gradient by positioning the trailing edge adjacent to the write gap. The dependencies of the perpendicular HPERP and longitudinal HLONG components of the write field along with a gradient of the perpendicular component HPERP/dx and write angle on write gap length g and write current IW were computed. The LP writer revealed higher HPERP/dx than the TP writer at g⩽2 μm. The HPERP/dx has a maximum at IW=15–20 mA for both writers and decreases with the current increase. The LP writer exhibited higher HPERP/dx and write angle Θ, as well weaker dependence of these parameters on write current than the TP writer in all ranges of current. Micromagnetic modeling of recorded patterns has shown that the LP writer provides better writeability, and a sharper and less curved transition. Both writers demonstrated the best performance at IW=15–20 mA where HPERP/dx and the write angle have the maximum. Severe transition distortion was observed for the TP writer at IW>30 mA.
Domain wall pinning and controlled magnetic switching in narrow ferromagnetic ring structures with notches (invited)
Authors: Kläui M. , Vaz C. A. F. , Bland J. A. C. , Wernsdorfer W. , Faini G. , Cambril E.
Published: May 2003

We present a magnetoresistance study of controlled spin switching and domain wall pinning effects in mesoscopic narrow ferromagnetic Permalloy ring structures containing notches. It is found that notches create an attractive potential well for the transverse domain walls present in these structures. The strength and size of this potential well is measured and found to stretch far beyond the physical dimensions of the notch. Measuring the resistance, a minimum at remanence is found to occur when a transverse domain wall is pinned at the notch, in agreement with the results of numerical simulations of the anisotropic magnetoresistance. Applying a field in the direction corresponding to a potential well edge, a magnetic state with a very wide domain wall is stabilized, leading to a dip in the magnetoresistance at such angles. Using notches of different sizes, it is demonstrated that controlled switching is achieved, which means that the circulation direction of the vortex state can be selected.
Micrometer-scale magnetometry of thin Ni80Fe20 films using ultrasensitive microcantilevers
Authors: Chabot Michelle D. , Moreland John
Published: May 2003

Microcantilever torque magnetometry is used to measure quantitative M-H curves on patterned Ni80Fe20 films. The dynamic deflection method is employed, in which a small film is deposited onto a microcantilever and placed in an external magnetic field. A small orthogonal ac torque field is applied at the cantilever's resonant frequency, and the resulting torque is measured as a function of external field. Film patterning and deposition have been integrated with cantilever fabrication. Results are presented for a 5 μm×5 μm×30 μm Ni–Fe film. The measured saturated magnetic moment of the sample is 5.1±0.2×10−13 A m2 for a 100 A/m torque field. The M-H curves for the smaller films show hysteretic switching consistent with a series of stable multi-domain states. Values of the saturation magnetization are within 3% of the value measured on similar samples by ferromagnetic resonance, indicating this is a sensitive method for measuring magnetic reversal in small ferromagnetic samples.
Magnetization switching in Permalloy square ring magnets
Authors: Vavassori P. , Grimsditch M. , Novosad V. , Metlushko V. , Ilic B.
Published: May 2003

We present the results of a study of magnetization switching in Permalloy square rings using the diffraction magneto-optic Kerr effect combined with numerical micromagnetic simulations. Diffracted loops show a two-step switching process as the external field is swept along both the ring edge and the diagonal. The hysteresis loops calculated from micromagnetic simulations show that switching should occur via a single step transition from a one onion to the reversed onion state for both directions of field applied. We have found that in order to reproduce the observed two-step reversal slight asymmetry has to be introduced into the ring shape. In this case a stable intermediate states appear during switching, accounting for the shape of diffracted loops.
Noise in magnetic tunnel junction devices
Authors: Klaassen K. B. , van Peppen J. C. L. , Xing X.
Published: May 2003

The noise expected from an ideal magnetic tunnel junction (MTJ) head is thermal noise at low bias voltages (≪50 mV, thermally assisted barrier crossings) and shot noise at higher bias voltages (≫50 mV, field-assisted barrier crossings). The shot noise is larger than the thermal noise, therefore, at 200 mV, the signal of an MTJ head has to be a factor of 2 larger than that of a GMR head with the same resistance to realize the same SNR. This paper reports MTJ noise measurements up to the ferromagnetic resonance (1–2 GHz). An ultra low-noise pre-amplifier system is described that allows electrical biasing of the devices. Wide-band 1/f noise is observed in devices without proper hard bias. Saturation is used to assess the magnetic fluctuation noise and the resonance therein. These wide-band noise measurements demonstrate that one can electronically read out MTJ heads up to the ferromagnetic resonance and down to the noise floor.
Microwave and magnetic properties of barium hexaferrite films having the c-axis in the film plane by liquid phase epitaxy technique
Authors: Yoon S. D. , Vittoria C.
Published: May 2003

We report the growth of thick barium hexaferrite (BaFe12O19,BaM) films on m-planes ([11_00] or [101_0]) sapphire (Al2O3) substrates by the liquid phase epitaxy deposition technique. The procedure entailed the deposition of seed layers of BaFe12O19 onto the substrate by the pulsed laser ablation deposition and then dipping the substrate into a molten flux for 2 h. The total thickness ranged from 60 μm to 200 μm. The vibrating sample magnetometer (VSM) measurement data showed that the film exhibited magnetic uniaxial anisotropy axis in the film plane. The coercive field was relatively small, range of Hc was from 0.007 kOe to 0.08 kOe, and the saturation magnetization (4πMs)≅4.42 kG. The ferrimagnetic resonance (FMR) linewidth (ΔH) at 59.9 GHz was ∼0.08 kOe. This value of ΔH should be contrasted with previous FMR linewidth measurement of films deposited by the PLD technique which showed a ΔH of ∼1.20 kOe.
Metastable antiferromagnetic domain configurations in exchange biased bilayers
Authors: Thomas Luc , Negulescu Béatrice
Published: May 2003

We report on exchange bias relaxation in NiO/FeNi bilayers. FeNi films have been sputtered on top of NiO films, previously grown on quartz substrates using pulsed laser deposition. As-prepared bilayers show enhanced coercivity but no bias. Their hysteresis loops are essentially isotropic within the sample plane. Exchange bias relaxation is observed after the samples have been magnetized once, and let in their remanent state: exchange bias progressively builds up in zero external magnetic field, over a few days timescale. This behavior may be related to the reorientation of antiferromagnetic domains triggered by the exchange coupling with the ferromagnetic domains throughout the interface. Relaxed samples are exchange biased along the magnetization direction, which becomes an easy axis. Along the perpendicular direction, a two-step magnetization reversal is observed. This two-step process is erased when the samples are field-annealed at elevated temperatures, and it is replaced by the rotation process usually observed along the hard axis. These results suggest that two different antiferromagnetic domain structures can be stabilized at room temperature, both giving rise to exchange bias. This may be related to the competition between the field-induced exchange bias direction, and the antiferromagnetic anisotropy easy axis within the NiO layer.
Magnetic relaxation in exchange-coupled Co/CoO bilayers measured with ac-anisotropic magnetoresistance
Authors: Venus D. , Hunte F. , Krivorotov I. N. , Gredig T. , Dahlberg E. Dan
Published: May 2003

The complex ac-susceptibility of field-cooled Co/CoO bilayers has been measured by perturbing the magnetization with a small (5 Oe) ac field, and detecting the response through anisotropic magnetoresistance using a double modulation technique. Samples of Ta(3 nm)/Co(8 nm)/CoO(3 or 10 nm)/Cu(3 nm) grown by sputter deposition on an amorphous silicon nitride substrate have been studied using a frequency of 100 Hz. The relaxation of the exchange anisotropy in response to the perturbation allows the activation energies and relaxation times of the CoO grains to be investigated. Both the real and imaginary response show prominent thickness-dependent peaks at the blocking temperature, as well as a peak near 80 K which is insensitive to CoO film thickness. The measurements are well-described by a generic linear relaxation model of the anisotropy field, using a bimodal distribution of activation energies for the CoO grains.
Louis Néel: Retrospective (invited)
Authors: Coey J. M. D.
Published: May 2003

Louis Néel (1904–2000) was probably the most influential figure in applied magnetism in the 20th century. He pioneered or developed concepts such as antiferromagnetism, ferrimagnetism, superparamagnetism, magnetic viscosity, surface and induced anisotropy, domain walls, orange-peel coupling, and exchange anisotropy, many of which are of great importance in modern thin-film devices. A brief summary is given of his career and scientific contributions.
Magnetic property control by using a composite template for dual-layered perpendicular media
Authors: Ikeda Yoshihiro , Takano Kentaro , Do Hoa , Supper Natacha , Moser Andreas , Sonobe Yoshiaki , Rice Philip
Published: May 2003

Thin composite template layers for dual-layered perpendicular media have been studied. By combining a thin amorphous layer and a thin NiAl seed-layer, thermally stable and low noise media have been realized simultaneously. By changing the thickness ratio of the top amorphous layer and the bottom seed-layer, the magnetic properties of the recording layer can be controlled without changing the magnetic spacing between the soft underlayer and the write pole. Magneto-optical Kerr effect, transmission electron microscopy, and spin-stand measurements were performed to investigate the influence of different composite templates on the recording properties. It will be shown that the composite template allows the optimization of thermal stability and media noise in perpendicular media. The thermal stability of the media was measured by signal decay measurement using a spinstand and dynamic coercivity measurements using the Kerr effect. The KuV/kBT values, as obtained by the latter method, are consistent with the signal decay data. Those results demonstrate that the presented dynamic coercivity measurement is a very useful method for evaluating the thermal stability of dual-layered perpendicular media.
Evaluation of magnetic interactions in a double-layered perpendicular magnetic recording media using ferromagnetic Hall effects
Authors: Das Sarbanoo , Kong Sok-hyun , Nakagawa Shigeki
Published: May 2003

A new method for evaluating magnetic interactions among particles in the recording layer (RL) with a soft magnetic underlayer (SUL) in a double-layered perpendicular magnetic recording media has been demonstrated. Since the RL and SUL reveal Hall effect responses with different symmetries regarding the applied magnetic field, it is possible to not only detect the anomalous Hall voltage from the RL and the planar Hall voltage from SUL simultaneously, but also to extract and evaluate their properties individually. In order to evaluate the magnetic interparticle interactions in the RL, an evaluation index of the ΔV-plot, which corresponds to the ΔM-plot, estimated using a simple relation among the initial magnetization curve, the upper and lower branch of the major hysteresis loop, was introduced. The initial magnetization curve of Co–Cr–Ta RL in a Co–Cr–Ta(100 nm)/Ni–Fe(50 nm) double-layered thin film, can be evaluated from the Hall voltage in positive and negative range of applied magnetic field using the point symmetry of the anomalous Hall voltage revealed by the RL. The negative peak in the ΔV-plot of the double layer indicated the dominance of magnetostatic interaction in the Co–Cr–Ta layer. Measurements under the canted applied field revealed field direction dependence in the estimated ΔV-plot. Adjustment of the driving current direction with respect to the in-plane projection of the applied magnetic field was found to be effective for selective rejection of the contribution from the SUL to the total Hall effect signal.
Characterization to realize CoCr-based perpendicular magnetic recording media with high squareness and normalized coercivity
Authors: Saito Shin , Hoshi Fmikazu , Itagaki Norikazu , Takahashi Migaku
Published: May 2003

In an attempt to find a material guidance to realize CoCr-based perpendicular media with high squareness and normalized coercivity, we have performed systematic magnetic characterization to examine the effects of thermal agitation and magnetic exchange interaction. The main results are as follows: (1) With decreasing measuring temperature from R. T. to 4.2 K, normalized coercivity, Hc/Hkgrain, increases for the medium strongly influenced by thermal agitation, whereas changes slightly for the medium with strong intergranular exchange coupling. (2) All the media characterized in this study have a low value of Hc/Hkgrain equal to or less than 0.36 at R. T. (3) An exchange decoupled medium (α=1.0) tends to show a large positive Hn/Hkgrain, which results in a significant decrease of loop squareness S. On the other hand, it is possible to obtain a medium with S=1 for α>1.6 through the exchange interaction. (4) To realize a medium with S=1 and α as small as possible, selection of material with 4πMs/Hkgrain=0.2 (for α=1.6) is promising. On the other hand, to realize a medium with Hc/Hkgrain as high as possible, selection of material with 4πMs/Hkgrain=0.70 (for α=1.3) is favorable.
Track edge effects in tilted and conventional perpendicular recording
Authors: Gao Kai-Zhong , Wang Xiaobin , Bertram H. Neal
Published: May 2003

Track edge effects in tilted and conventional perpendicular recording are analyzed. The write fields are calculated utilizing a three dimensional micromagnetic simulation that includes both the write pole and the soft underlayer. The dynamic reversal time and thermal stability of the recording layer are analyzed using a recent model involving mode analysis and the optimal collective reversal barrier. For conventional perpendicular recording, the effect of the write field angle at the track edge is to lower the medium energy barrier, which increases the guard-band width. For tilted perpendicular recording, the guard band is decreased due to an energy barrier increase caused by the write field angle.
Micromagnetic study of the intrinsic loop squareness S* in perpendicular media
Authors: Zhou Hong
Published: May 2003

Micromagnetic simulations have been performed to deshear the remanent hysteresis loops in perpendicular media. Results demonstrate that the intrinsic loop squareness S* increases with increasing the intergranular exchange couplings and with decreasing the intergranular magnetostatic interactions. However, within the range of parameters examined, changes of the magnetic film thickness and the medium-soft magnetic underlayer spacing exhibit negligible effect on S*. The applied field angle has also been found to exhibit insignificant effect on S* and Neff. Therefore, intergranular interactions are the major factors to determine S* and Neff. To deshear the loop, an effective demagnetization factor Neff was found applicable. Empirical formulas have been fitted to relate S* and Neff to media parameters.