bluuebunny/crossref_metadata_2025 huggingface dataset:
A multilayer sigma‐coordinate thermodynamic sea ice model: Validation against Surface Heat Budget of the Arctic Ocean (SHEBA)/Sea Ice Model Intercomparison Project Part 2 (SIMIP2) data
Authors: Huwald H. , Tremblay L.‐B. , Blatter H.
Published: May 2005

A new multilayer sigma‐coordinate thermodynamic sea ice model is presented. The model employs a coordinate transformation which maps the thickness of the snow and ice slabs onto unity intervals and thus enables automatic relayering when the snow or ice thickness changes. This is done through an advection term which naturally appears in the transformed energy equation. Unlike previous approaches, the model conserves the total energy per layer (Jm−2 as opposed to Jm−3), which takes into account the changes in internal energy associated with thickness changes. This model was then tested against observational data from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment in the context of the Sea Ice Model Intercomparison Project, Part 2, Thermodynamics (SIMIP2). In general, the model reproduces the observed internal snow‐ice temperature and the ice thickness evolution very well. Results show that the ice thickness evolution is very sensitive to the ocean heat flux (Focn) and the thickness of the snow cover in winter. Given that the spatial variability in snow depth at small scale is large, the specification of the snow depth temporal evolution is crucial for an intercomparison project. Since Focn in SIMIP2 is calculated as a residual of the observed basal growth rates and heat conduction, the salinity of newly formed ice used in the simulations must be consistent with that used to derive Focn. Simulated and observed snow surface and snow‐ice interface temperatures suggest that not enough heat is conducted through the snow layer even when using a snow thermal conductivity as large as 0.50 Wm−1 K−1 (value derived from observed snow and ice internal temperature profiles). A surface energy budget of simulated and observed energy fluxes confirms this finding.
Climate variability at Marion Island, Southern Ocean, since 1960
Authors: Rouault Mathieu , Mélice Jean‐Luc , Reason Chris J. C. , Lutjeharms Johann R. E.
Published: May 2005

In recent decades, instrumental data recorded at the South African Weather Service station on Marion Island (46°54′S and 37°51′E) in the Southern Ocean shows that the local climate of this island has undergone significant changes since the 1960s, mostly in austral summer. These include a decrease in rainfall, an increase in nonrainy days, changes in wind speed and direction, and an increase in maximum and minimum local air temperature and in nearshore sea surface temperature. This study analyzes surface temperature, pressure, sea surface temperature, and rainfall recorded daily at Marion Island together with NCEP reanalyses to explore the mechanisms potentially associated with these changes. It is suggested that the changes to the local climate of Marion Island are linked to the well‐documented shift in phase of the semiannual oscillation in the Southern Hemisphere after about 1980.
Surface freshwater flux variability and recent freshening of the North Atlantic in the eastern subpolar gyre
Authors: Josey Simon A. , Marsh Robert
Published: May 2005

Variability in the air‐sea flux of freshwater (precipitation‐evaporation (P‐E)) and its connection to the observed freshening of the eastern half of the North Atlantic subpolar gyre over the period 1960 to present is investigated using atmospheric model reanalyses and observational data. Similar results are obtained from both the National Centers for Environmental Prediction/National Center for Atmospheric Research and ERA‐40 reanalyses, each of which shows a major increase in P‐E (primarily due to increased precipitation) in the gyre region in the mid‐1970s, from about 0.10 m yr−1 to 0.27 m yr−1. This increase is supported by independent rain gauge observations recorded in Iceland, the Faeroes, and Ireland. When integrated over a box centered on the eastern gyre, the atmosphere to ocean freshwater flux in the period 1975–1989 is 4 × 1012 m3 greater than that in the earlier period 1960–1974. This increase is about twice as large as the freshwater excess associated with major advective events such as the Great Salinity Anomaly. The link between the increase in P‐E and the two major modes of atmospheric variability in the region, the North Atlantic Oscillation (NAO) and the East Atlantic Pattern (EAP), is investigated. The EAP is found to be the dominant cause of the increase, with the NAO only playing a minor role. The impact of the surface freshwater flux trend on sea surface salinity is also examined through comparison with hydrographic measurements at 60°N, which show freshening since the mid‐1970s. The observed freshening can be largely explained as a direct response to changes in the air‐sea freshwater exchange.
Observed trends in extreme precipitation events in China during 1961–2001 and the associated changes in large‐scale circulation
Authors: Wang Yuqing , Zhou Li
Published: May 2005

The observed trends in extreme precipitation events, and those in annual and seasonal mean precipitation in China during 1961–2001 are analyzed. The results show that the annual mean precipitation increases significantly in southwest, northwest, and east China, and decreases significantly in central, north and northeast China. The increasing trends in east China occurred mainly in summer, while the decreasing trends in central, north, and northeast China occurred in both spring and autumn. The increasing trends in most of northwest China occurred in all seasons. Patterns of the trends in extreme daily precipitation events are similar to those in the annual and seasonal mean precipitation except in the northwest China where most areas show increasing trends in extreme events only in summer. The extreme precipitation events in the Yangtze River basin increased dramatically by 10%–20% every 10 years in summer, consistent with the increasing trends in summer mean precipitation in the region. The circulation over East Asia shows a weakening trend in the summer monsoon over central‐east China.
Springtime cloud condensation nuclei concentrations on the west coast of Korea
Authors: Yum Seong Soo , Hudson James G. , Song Keun Yong , Choi Byoung‐Cheol
Published: May 2005

Cloud condensation nuclei (CCN) measurements were made with the Desert Research Institute (DRI) instantaneous CCN spectrometer at the Korea Global Atmosphere Watch (GAW) Observatory (KGAWO) (36°32′N, 126°19′E) on the west coast of the Korean Peninsula from May 1–22, 2004. A TSI CPC3010 counter simultaneously measured condensation nuclei (CN). For seven of these days, submicron aerosol size distributions were also measured with an SMPS. Data were classified maritime or continental according to air mass back trajectories. Average maritime and continental CCN concentrations at 1% supersaturation were 2406 cm−3 and 5292 cm−3, respectively, while CN concentrations were 3983 cm−3 and 8313 cm−3, respectively. The average ratios of CCN to CN concentrations were 0.64 for both maritime and continental. These results suggest ubiquitously high aerosol concentrations in this area regardless of air mass origin.
High percentage of positive lightning along the USA west coast
Authors: Ely Brandon L. , Orville Richard E.
Published: May 2005

Analyses of the cloud‐to‐ground (CG) lightning characteristics recorded by the US National Lightning Detection Network (NLDN) along the west coast reveal an average annual percentage of positive CG flashes around 40%, while the average value for the USA is approximately 10%. The primary goal of the study was to document and suggest reasons for this positive CG anomaly. Through seasonal and monthly storm analysis, it was determined that the high annual percent positive along the coast is the result of the low variability in total CG flashes throughout the year coupled with a high number of positive CG flashes during the winter season which can be directly attributed to the climate of the Pacific Coast. The topography of the region was determined to affect the areal distribution of the percent positive anomaly by restricting the inward extent of the coastal climate. The secondary goal of the study was to determine whether the following meteorological variables were related to the dominant CG polarity in a storm: 1) the variation of charge region heights using the −10°C level as a proxy and 2) the tilting of the charge regions by strong windshear. Statistical analysis showed that the height of the −10°C temperature level is related to the dominant CG polarity in a storm, while the windshear did not show a significant relationship. In addition, analyses showed that the thunderstorms that produced few CG flashes (<6 flashes) contributed most to the total number of positive CG flashes.
Assessing the effectiveness of direct injection for ocean carbon sequestration under the influence of climate change
Authors: Jain Atul K. , Cao Long
Published: May 2005

This paper studies the effect of climate change on simulated efficiency of carbon injection at different locations and ocean depths using an Earth system model of intermediate complexity, ISAM‐2.5D. Following the OCMIP carbon sequestration protocol, we carried out a series of carbon injection simulations. The ISAM results show that warming over the next 500 years under the IPCC S650 and WRE1000 stabilization scenarios could change the ocean circulation and thereby increases the residence time of CO2 disposed into the deep ocean, particularly for Atlantic injection. However, the warming does not have a significant effect on carbon injections into the Pacific and Indian Oceans, where circulation change is small. This new finding contrasts with previous OGCM results.
Shh directs cell‐cycle exit by activating p57Kip2 in the zebrafish retina
Authors: Shkumatava Alena , Neumann Carl J
Published: May 2005

The Hedgehog (Hh) family of signalling proteins control both differentiation and proliferation during animal development. Previous studies have shown that Hh signalling has a stimulatory effect on the cell cycle in several organs by controlling core cell‐cycle components. Here, we show that Sonic hedgehog (Shh) signalling has the opposite effect in the zebrafish retina, where it leads to cell‐cycle exit, and that this is mediated by transcriptional activation of the cyclin kinase inhibitor p57Kip2. The loss of p57Kip2 activity strongly resembles the Shh mutant eye phenotype, and overexpression of p57Kip2 rescues cell‐cycle exit in Shh mutants, indicating that p57Kip2 is both necessary and sufficient to mediate Shh‐induced cell‐cycle exit in the retina. These findings raise the possibility that stimulation of cell‐cycle exit through regulation of core cell‐cycle components may be part of a general mechanism required for Hh‐directed differentiation.
Functional regulation of oestrogen receptor pathway by the dynein light chain 1
Authors: Rayala Suresh K , den Hollander Petra , Balasenthil Seetharaman , Yang Zhibo , Broaddus Russell R , Kumar Rakesh
Published: May 2005

Overexpression and phosphorylation of dynein light chain 1 (DLC1) have been shown to promote the growth of breast cancer cells. However, the role of DLC1 in the action of the oestrogen receptor (ER) remains unknown. Here, we found that oestrogen induces the transcription and expression of DLC1. DLC1 facilitated oestrogen‐induced ER transactivation and anchorage‐independent growth of breast cancer cells. We show that DLC1 interacts with ER, and such interaction is required for the transactivation‐promoting activity of DLC1. Further, DLC1 expression led to enhanced recruitment of the DLC1–ER complex to the ER‐target gene chromatin. Conversely, DLC1 downregulation compromised the ER‐transactivation activity and also its nuclear accumulation, suggesting a potential chaperone‐like activity of DLC1 in the nuclear translocation of ER. Together, these data define an unexpected upregulation of DLC1 by oestrogen and a previously unrecognized DLC1–ER interaction in supporting and amplifying ER‐initiated cellular responses in breast cancer cells.
Mismatch repair participates in error‐free processing of DNA interstrand crosslinks in human cells
Authors: Wu Qi , Christensen Laura A , Legerski Randy J , Vasquez Karen M
Published: May 2005

DNA interstrand crosslinks (ICLs) present formidable blocks to DNA metabolic processes and must be repaired for cell survival. ICLs are induced in DNA by intercalating compounds such as the widely used therapeutic agent psoralen. In bacteria, both nucleotide excision repair (NER) and homologous recombination are required for the repair of ICLs. The processing of ICLs in mammalian cells is not clearly understood. However, it is known that processing can occur by NER, which for psoralen ICLs can be an error‐generating process conducive to mutagenesis. We show here that another repair pathway, mismatch repair (MMR), is also involved in eliminating psoralen ICLs in human cells. MMR deficiency renders cells hypersensitive to psoralen ICLs without diminishing their mutagenic potential, suggesting that MMR does not contribute to error‐generating repair, and that MMR may represent a relatively error‐free mechanism for processing these lesions in human cells. Thus, enhancement of MMR relative to NER may reduce the mutagenesis caused by DNA ICLs in humans.
Roles for replichores and macrodomains in segregation of the Escherichia coli chromosome
Authors: Lesterlin Christian , Mercier Romain , Boccard Frédéric , Barre François‐Xavier , Cornet François
Published: May 2005

Recent work has highlighted two main levels of global organization of the Escherichia coli chromosome. Macrodomains are large domains inferred from structural data consisting of loci showing the same intracellular positioning. Replichores, defined by base composition skews, coincide with the replication arms in normal cells. We used chromosome inversions to show that the dif site, which resolves chromosome dimers, only functions when located at the junction of the replichores, whatever their size. This is the first evidence that replichore polarization has a role in chromosome segregation. We also show that disruption of the Ter macrodomain provokes a cell‐cycle defect independent from dimer resolution. This confirms the existence of the Ter macrodomain and suggests a role in chromosome dynamics.
Write current optimization for single-pole and trailing-shield heads in perpendicular recording
Authors: Xiao M. , Lengsfield B. , Takano K. , Ikeda Y. , Do H. , Rosen H.
Published: May 2005

Recording performance as a function of write current is studied for single-pole and trailing-shield heads. Optimal write current is not obvious from saturation curves. Media noise, jitter, and error rate give better guidance. For a single-pole head, there is an optimal write current, beyond which, the field strength may continue to increase, but field gradient degrades leading to higher noise. For trailing shield achieved by reverse-flying longitudinal heads, the field magnitude and gradient from the main pole continue to improve with increasing write current. However, the return pole erasure also increases. There is a critical current, above which, partial erasure from the return pole leads to excessive noise. Finite-element modeling of these two types of write poles has been performed to confirm and understand the experimental findings.
A thin wire array and magnetic host structure with n<
Authors: Dewar G.
Published: May 2005

Construction of artificial media possessing a negative index of refraction can be simplified by using a nonconducting ferrimagnetic host medium to provide a negative permeability and an array of conducting wires to provide a negative permittivity. The interaction between the ferrimagnet and the wire array, which destroys the negative permittivity of the wire array, can be overcome by cladding the wires with an insulating, nonmagnetic jacket. Calculations of the propagation constants and transmission coefficients for a square array of cladded wires in a ferrimagnetic host are presented. The calculations are near exact for wavelengths significantly greater than the lattice parameter of the wire array. For wires a few microns in diameter, a lattice constant of 0.8mm, and an appropriate ferrimagnetic host in a biasing magnetic field, a transmission band 0.5GHz wide centered near 16GHz exhibits a negative index of refraction. Losses in the ferrimagnet and impedance mismatch to vacuum limit the peak transmission amplitude ratio through a slab 3.0cm thick to ≈3%.
A concept of exchange-coupled recording medium for heat-assisted magnetic recording
Authors: Kikitsu Akira , Kai Tadashi , Nagase Toshiyuki , Akiyama Jun-Ichi
Published: May 2005

A concept of exchange-coupled magnetic layer is presented for the heat-assisted magnetic recording medium. Magnetic layers with different Curie point (TC) and similar coercivity (Hc) are stacked via exchange coupling. Hc of the double layer changes abruptly at near TC of one of the layers. This means that the recording temperature can be reduced with little reduction in the thermal stability. A medium consisting of two Co∕Pd multilayers was fabricated as this medium. The temperature dependence of Hc of the double layer was similar to that of the expected one by a numerical calculation.
Prediction of spike noise based on soft underlayer energy minimization
Authors: Khan M. U. , Victora R. H.
Published: May 2005

An energy minimization and balancing approach was adopted to predict the occurrence of spike noise by obtaining estimates of the magnetostatic and total wall energy of a soft underlayer (SUL) for a given configuration of domain walls. We find that single-layer SULs (thicknesses of 100–200 nm) are usually sources of spike noise unless their saturation magnetization is below 70–100emu∕cc. However, the use of such low-moment SULs is unacceptable in perpendicular recording. One solution that has been advocated is a multilayer SUL structure with C, Ta, etc., interlayers. Our predictions show that the ground state of a 200-nm double-layer FeCo∕C SUL is completely spike-free.
Magnetic and recording characteristics of perpendicular magnetic media with different anisotropy orientation dispersions
Authors: Choe G. , Zheng M. , Abarra E. N. , Acharya B. R. , Lee K. J.
Published: May 2005

A systematic investigation of the magnetic and recording characteristics of CoPtCrO media with different Co grain magnetic anisotropy orientation dispersion (AOD) is performed. AOD is characterized by Δθ50 of the x-ray diffraction Co peak. AOD was systematically varied between 3.3° and 10.5° by varying the growth condition of Ru layer. With increasing AOD, more grain-boundary segregation occurs, resulting in reduced exchange coupling. Micromagnetic simulation and experimentally measured time dependence of coercivity indicate that magnetic switching of well-isolated Co particles is affected by exchange coupling strength as well as Co AOD. Higher coercivity, narrower switching field distribution, and good thermal stability are achieved with lower Co AOD. Reduced Co AOD leads to a substantial decrease of both transition jitter and dc noise.
Reduction of field through read element using shorter read shield
Authors: Mochizuki Masafumi , Suzuki Kaori , Ishikawa Chiaki , Etoh Kimitoshi , Katada Hiroyuki , Nishida Yasutaka , Okada Tomohiro
Published: May 2005

Values for field through the read element (Hread) in longitudinal and perpendicular magnetic recording are compared with the aid of three-dimensional (3d) finite element models. We show that the Hread of the single-pole-type head used in perpendicular magnetic recording (PMR) was larger than that of the inductive ring head used in longitudinal magnetic recording (LMR). This is because that the medium for a PMR system includes a soft under layer (SUL). The Hread of PMR is affected by the permeability and thickness of SUL. The characteristic length of the upper and lower shield layers at which the Hread starts to decrease is found to be roughly equal to the length of the return pole. Decreasing the length of the upper and lower shield is shown to be the most practicable and effective way to realize the reduction of Hread.
Stability analysis of ultrathin lubricant films via surface energy measurements and molecular dynamics simulations
Authors: Guo Qian , Li Lei , Hsia Yiao-Tee , Jhon Myung S.
Published: May 2005

The stability of nanoscale lubricant films was analyzed via both surface energy measurements and molecular dynamics (MD) simulations. Using the sessile method, the contact angles of deionized water and n-dodecane on Zdol lubricant films were measured to examine the dispersive and polar surface energy as well as the nanofilm stability. By calculating the free energy from MD simulations, we investigated surface energy of the lubricant film. Furthermore, the film disjoining pressure and the stability diagram were constructed from MD simulations to examine the layering structures in spreading phenomena. Our analysis exclusively focuses on the effects of the end-functionality and molecular weight.
Influence of control strategy on stator and rotor losses in high-speed permanent magnet brushless motors
Authors: Zhu Z. Q. , Chen Y. , Howe D.
Published: May 2005

The stator iron loss and rotor eddy current loss which results in a high-speed permanent magnet brushless motor when operated in brushless dc and ac modes, on both open-circuit and at rated load, with four different current control strategies, is investigated by finite element analysis. It has highlighted the significant influence of the phase current wave form. It has also shown that, on load, the rotor eddy current loss can be the dominant loss component, particularly in brushless dc mode.
Time-domain study of microtrack structure and artifacts
Authors: Taratorin Alexander M. , Klaassen Klaas B.
Published: May 2005

To study the microtrack signal, noise and track “skirts” a time-domain technique [A. Taratorin, M. Xiao, and K. Klaassen, IEEE Trans. Mag. 40, 129 (2004)] was used. It shows that the standard microtrack preparation (two-sided dc erasure) suffers from demagnetization caused by the write head fringe fields. Low density micro-track tail signals were studied by analyzing read-back wave forms at different offset locations from the microtrack center. It was established that the tail-related signal is generated by cross-track medium magnetization. The dependence of this tail signal on the medium orientation ratio (OR) is studied; the tail signal amplitude decreases for higher OR media. An improved microtrack preparation procedure is presented, using two-sided multiple-pass repetitive dc erasure. It is demonstrated that the procedure reduces the tail artifacts due to the smaller cross-track component of the far-away write head field
Dynamic heating in submicron size magnetic tunnel junctions with exchange biased storage layer
Authors: Kerekes M. , Sousa R. C. , Prejbeanu I. L. , Redon O. , Ebels U. , Baraduc C. , Dieny B. , Nozières J-P , Freitas P. P. , Xavier P.
Published: May 2005

The dynamic heating of submicron size junctions developed for the thermomagnetic write scheme was investigated. The dependency of the heating power density with the voltage pulse width (Δt) was measured and shows a [1−exp(−Δt∕t0)] phenomenological variation in the investigated range of pulse widths (5ns–1s). For submicron junction areas and constant pulse width, the heating power required for writing decreases as the junction area is reduced. The thermomagnetic write scheme was demonstrated through cycling of the cell between the two low and high resistance levels. This scheme was also shown to be insensitive to stray magnetic fields even in absence of any magnetic shielding of the memory.
Stability of GMR heads biased utilizing patterned exchange tabs
Authors: Zhang Wei , Chen Yingjian , Hiner Craig
Published: May 2005

We have demonstrated the fabrication of a spin-valve head with a CoFe∕PtMn antiferromagnetic (AFM) exchange-biasing layer for longitudinal stabilization. The application of Golden field annealing means the two AFM layers can be made of the same material with the same TB. The AFM layers may then be chosen to optimize pinning strength, corrosion resistance, etc. The transfer curve based on a pattered head structure with PtMn AFM stabilized free layer is smooth and free of any hysteresis. The head also has good linearity and bias point, and the performance is comparable with the standard abutted permanent magnet junction stabilization. Further optimization is expected to improve the performance, enabling an areal density of >120Gb∕in.2
Robust design of head interconnect for hard disk drive
Authors: Gao X. K. , Liu Q. H. , Liu Z. J.
Published: May 2005

Design of head interconnect is one of the important issues for hard disk drives with higher data rate and storage capacity. The impedance of interconnect and electromagnetic coupling influence the quality level of data communication. Thus an insightful study on how the trace configuration affects the impedance and crosstalk is necessary. An effective design approach based on Taguchi’s robust design method is employed therefore in an attempt to realize impedance matching and crosstalk minimization with the effects of uncontrollable sources taken into consideration.
Transient-free commutation of a resonant-mode array of inductors
Authors: Plotkin Anton , Paperno Eugene
Published: May 2005

A method and system are proposed for a transient-free commutation of a resonant-mode array of inductors. A single capacitor is used to tune the entire array, and triacs are used to commutate the inductors. To avoid the transients, the tuning capacitor is electrically locked when it stores the whole energy of the excited circuit. This prevents the capacitor from discharge during the fast, 0.1ms delays, where a triac disconnects the previously excited inductor and another triac connects the next inductor in series with the capacitor. The 0.1ms delays are defined by the triacs' recovery time. After completing the commutation, the fully charged tuning capacitor is unlocked, and the next excitation cycle begins with no transient. We neglect the short recovery delays and regard the commutation process as transient free. We also show that the recovery delays can further be reduced if the triacs are replaced with faster switching devices. Our experiments with an array of 64 inductors prove the efficiency and simplicity of the commutation method and system. The approach suggested can be useful in instrumentation, power and control magnetics, where a large number of resonant-mode inductors should be quickly commutated.
Write performance of shielded pole heads on media with thin soft underlayers
Authors: Benakli Mourad , Mallary Michael L. , Marshall Steven B. , Torabi Adam F.
Published: May 2005

Nonlinear finite element calculations show that the soft underlayer thickness in perpendicular media can be greatly reduced without significant loss of effective switching field strength by using a shielded pole writer in place of the more conventional monopole geometry. In addition, use of a thin soft underlayer (SUL) with a shielded pole writer with a thin SUL results in a higher gradient and a narrower magnetic write width. These results have been qualitatively confirmed experimentally.
Angular dispersion of the anisotropy in perpendicular media
Authors: Voznyuk V. G. , Misra A. , Doyle W. D. , Visscher P. B. , Chantrell R. W.
Published: May 2005

The angular dependence of the easy axis saturation remanence characterized by the parameter α50, traditionally associated with angular dispersion in soft films, was used to explore the anisotropy dispersion ΔθK in several perpendicular media samples. The crystalline grain angular dispersion Δθ50, obtained from the analysis of x-ray rocking curves, had similar values in the spacer layer and recording layer, consistent with the expected epitaxy, and varied from 5.2° to 8.4°. However, the values of α50 ranged from 15° to 29° and were not correlated with Δθ50. A micromagnetic simulation, using the Landau–Lifshitz–Gilbert formulation without thermal relaxation, required an angular dispersion ΔθK>19° compared to Δθ50=6.1°. A Monte Carlo simulation assuming thermal relaxation produced the observed value of α50 with a smaller ΔθK=12°. The results suggest that the actual angular anisotropy dispersion is significantly larger than the crystalline grain angular dispersion in typical perpendicular media.
Self-differential detection using laminated magnetic tunnel junctions
Authors: Saito Y. , Sugiyama H. , Inomata K.
Published: May 2005

We report on self-differential detection using laminated magnetic tunnel junctions. The self-differential elements using laminated magnetic tunnel junctions (MTJs) with 400-nm width were fabricated using photolithography. A chemical mechanical polishing technique was used before preparing the top MTJs. The differential resistance shows the signal output of plus and minus at the zero magnetic field, which indicates the potential for applications realizing high-density magnetic random access memories with very fast access time.
Pinholes and spin transfer effect in magnetic tunnel junction heads
Authors: Zhu Jian-Gang
Published: May 2005

Spin-transfer-induced microwave excitations in magnetic tunnel junction (MTJ) read heads have been investigated via spin-torque-modified micromagnetic modeling. This study focuses on the effect of possible pinholes in the barrier layer for a MTJ read head with permanent magnet stabilization. It is found that the critical current threshold for the spin-transfer-excited microwaves is significantly reduced if small pinholes exist in the tunnel barrier layer. The smaller effective conductive area, the smaller the current threshold. For a single small pinhole in the center of the barrier surface, the resulted spin-transfer-excited microwaves are chaotic in nature, yielding a significant 1∕f noise below 1GHz. The microwave excitation also strongly depends on the exact location of the pinhole(s). The study suggests that by studying the spin-transfer-excited microwaves, one can obtain a good knowledge about the possible existence of pinholes as well as their spatial distributions for the magnetic tunnel junction read heads.
Pole tip protrusion of giant magnetic recording heads: Simulation and experimental verification
Authors: Song Suping , Stoev Kroum , Fang Dori , Gan Wuxing , Rudman Victor , Wang James
Published: May 2005

This paper presents an integrated finite element modeling of the pole tip protrusion (PTP) of giant magnetic recording heads during writing operation. The convection heat transfer models are presented in detail and verified by Guzik measurements. Modeling results agree well with the measurements in terms of the protrusion and the temperature rise at reader. It is found that the second shield (S2) protrudes the most regardless of the presence or absence of the airflow such as induced by a spinning disk. It is also found that the viscous dissipation generated in air bearing gives a negligible impact on the PTP.
Texture and viscosity effects in particulate recording media
Authors: Gonzalez-Fernandez M. A. , Blocksidge G. , Bunce C. , O’Grady K. , el-Hilo M. , Sharrock M. P. , Seftick D.
Published: May 2005

This paper reports on a study of magnetic texture in a tape that has been fabricated with varying orientation of the long axes of the particles. The results have been correlated to measurements of the physical microstructure made using transmission electron microscopy. Studies of the switching field distribution of the particles in the tape and magnetic viscosity show a strong correlation to the texture with implications for thermal loss effects.
Whole-track imaging and diagnostics of hard disk data using the spin-stand imaging technique
Authors: Tse C. , Tseng C. , McAvoy P. , Mayergoyz I. , Krafft C.
Published: May 2005

The spin-stand imaging technique is further developed for the imaging and diagnostics of whole-track hard disk data from off-centered disks. It is shown that the hard disk tracks are nearly sinusoidally modulated in the radial direction due to eccentricity. Special centering algorithms have been devised that successfully demodulated the imaged tracks.
Analysis of thermal magnetic noise in spin-valve GMR heads by using micromagnetic simulation
Authors: Akimoto H. , Kanai H. , Uehara Y. , Ishizuka T. , Kameyama S.
Published: May 2005

The size of the sensor in spin-valve GMR heads has been reduced to increase the areal magnetic recording density. Thermal magnetic noise, which arises from thermal fluctuation, becomes the main source of head noise and a limitation on recording density. Insufficient abutted permanent magnetic biasing yields an asymmetrical waveform both for signal output and thermal magnetic noise. This is due to the same mechanism as that of Barkhausen noise. In contrast, it has been found that small Hex, which is the exchange coupling strength between the bottom pinned layer (Pin1) and the antiferromagnetic biasing layer, emphasizes thermal magnetic noise without affecting signal output. In a head with small Hex, the magnetization near the air bearing surface and the top of the Pin2 layer tilts in the direction of the track width and randomly flips in the opposite direction. In synthetic ferrimagnetic heads, thermal magnetic noise chiefly depends on Hex rather than unidirectional anisotropy, Hua. The value of Hua does not directly affect thermal magnetic noise. The results indicate that Hex must be considered for reducing thermal magnetic noise.
Stripe domain formation in antiferromagnetically coupled FeCoX layers
Authors: Girt Erol , Dobin A. Y. , Brucker C. , Richter H. J.
Published: May 2005

We demonstrate that antiferromagnetic coupling can be used to suppress the formation of stripe domains in FeCoX layers. Antiferromagnetic coupling forces the magnetization in FeCoX layers to align antiparallel, which increases the magnetostatic energy of the stripe domain state in FeCoX∕Ru∕FeCoX. This increases the minimum critical thickness for which stripe domains are observed in both FeCoX layers of the FeCoX∕Ru∕FeCoX structure. The critical thickness scales with the strength of antiferromagnetic coupling, Jex, and almost doubles for antiferromagnetic couplings larger than about 2mJ∕m2.
Direct print servo patterns for disk drives
Authors: Baker Bill R.
Published: May 2005

Printed compound phase patterns replace servowriters and provide absolute position information from local data. Higher-order phase bursts have the same downtrack frequency but different crosstrack pitches. Phase segments of higher-order bursts are encoded to identify each cycle of an array of fine position chevrons. Feature sizes are more uniform and better suited to printing methods and channel chips.
High-frequency magnetic-force microscopy characterization of magnetic recording writer poles
Authors: Nazarov Alexey V. , Plumer Martin L. , Pant Bharat B.
Published: May 2005

Measurements of longitudinal writer poles at the air bearing surface were performed using high-resolution magnetic-force microscopy (MFM) with low coercivity tips. Two-dimensional MFM maps were obtained for various write currents. The modeling results indicate that the MFM maps are related more to the field than to its second derivative. Two techniques were used, dc MFM and high-frequency (HF) MFM. The results show that the HF-MFM technique can distinguish between different writer designs. The writers with the best high-frequency performance showed gradual decrease of the maximum MFM signal with frequency up to 1.5GHz.
Magnetic interactions in FePt∕soft magnetic underlayer double-layered structure observed by anomalous Hall effect
Authors: Das Sarbanoo , Ito Sukefumi , Kitagawa Taku , Nakagawa Shigeki
Published: May 2005

The effect of magnetic interactions between an FePt recording layer with perpendicular magnetic anisotropy and a soft magnetic layer of FeCoB (or NiFe) was investigated using the anomalous Hall voltage measurement method. The nucleation field and the slope around the coercivity of the Hall hysteresis loop revealed by the recording layer were found to significantly decrease depending on the type of interface. The coercivity corresponding to the in-plane magnetization components of the soft magnetic layer was found to increase while coexisting with an FePt layer.
Magnetization reversal in interacting magnetic systems
Authors: Pham Huy Ngoc , Dumitru Ioan , Stancu Alexandru , Spinu Leonard
Published: May 2005

The effect of interparticle interactions on the precessional switching process of coupled ellipsoidally shaped particles subject to pulsed magnetic fields is analyzed by using the Landau–Lifshitz–Gilbert equation. The analysis of switching process is made using two different representations previously proposed in the case of isolated single domain particle. In one switching diagram the final configurational state of the magnetization vector is displayed as a function of the pulse strength and direction whereas in the other representation the final state of magnetization is correlated to the initial position of magnetization vector. It is found that the dynamics of the coupled system, reflected in both switching diagrams is strongly dependent of the interparticle distance and their bond angle.
Exchange-coupling-strength effect on the noise from soft magnetic underlayer
Authors: Zhou T. J. , Chen J. S. , Xu Y. J. , Zhang W. , Sun C. J. , Liu B.
Published: May 2005

The exchange-coupling-strength effect on the magnetic properties and noise of laminated [FeCo(tnm)∕Ru(0.9nm)]nC(5nm) films as a magnetic soft underlayer (SUL) for perpendicular recording was investigated. It is found that the remanent magnetization decreases significantly with increasing the exchange-coupling strength, whereas, the coercivity remains almost unchanged. The spike noise is clearly seen in the single layer films without exchange coupling and its peak value is as high as 250 mV. The spike noise is significantly suppressed by introducing antiferromagnetic coupling and even eliminated in the films with strongest antiferromagnetic coupling. The noise peak value can be as low as 25 mV for the films with strongest coupling. The average noise decreases with increasing exchange-coupling strength, but increases linearly with increasing the Mrt of SUL. The noise-reduction mechanism is also discussed.
Technique to obtain head-medium magnetic spacing in a disk drive
Authors: Fu Chengjiang , Takeo Akihiko , Bertram H. Neal
Published: May 2005

A technique is presented to determine the head-medium magnetic spacing utilizing square wave recording spectral measurements. Because spectral analysis does not give a unique separation of the spacing and the transition parameter, the transition parameter is first determined at low densities using time domain transition noise analysis. The total noise power versus density is utilized to determine the transition parameter variation with density due to record process nonlinearities. Spectral fitting gives both the spacing and the giant magnetoresistance gap length. It is shown this technique is robust by analysis of data on perpendicular media with both inductive and single pole heads.
Flying height stability and spindle motor vibration
Authors: Ng Ka Wei , Yuan Zhimin , Liu Bo
Published: May 2005

This paper reports the results of a study on the relationship between slider’s dynamic flying height stability and spindle motor vibration. The investigations were carried out with in situ flying height testing technology introduced by the authors. The unbalanced modes, which are the rocking motion of the spindle, were studied in the experiment. Results obtained show that the dynamic stability of slider is a function of the spindle vibration. It is interesting to notice that higher frequency vibration of spindle motor has a greater effect on slider dynamics. Investigations are also extended to characterize the dynamic behavior of the sliders with two types of air-bearing surface (ABS) designs. Results indicate that sliders with higher roll stiffness are of better dynamic performance and flying height stability under the unbalanced modes vibration of spindle motor.
Flying height adjustment by slider’s air bearing surface profile control
Authors: Zhang Mingsheng , Yu Shengkai , Liu Jin , Liu Bo
Published: May 2005

A new active slider structure is proposed for the flying height adjustment. A bulk PZT ceramic is bonded onto the backside of slider directly. The PZT actuator adjusts the flying height by control of air bearing surface profile. The total thickness of the active slider is same as a standard pico slider. This structure is easy to fabricate and compatible with standard product, it also keeps the air bearing surface intact. The thicknesses of the PZT and the glue are optimized with numerical simulations. This active slider has been demonstrated and the observed flying height adjustment is 2.3nm.
Novel multiscale modeling and its application to integrated head disk interface simulation
Authors: Guo Qian , Chen Haigang , Kim Woo Tae , Jhon Myung S.
Published: May 2005

We formulated a novel scaling rule, which can transform the information between two drastically different length scales. This formulation can be useful in the implementation of the periodic boundary conditions and is also suitable for the multiscale modeling for the integrated design of the head disk interface (HDI). To illustrate this scheme, the morphology of lubricant submonolayer films was simulated via molecular dynamics with a given cell periodicity (CP). By systematically tuning the CP by a factor of 2n (n, integer), we constructed the self-similar rule to link morphological parameters obtained from the moment/fractal analysis or wavelet transform as well as self-diffusion coefficients between different length scales. This scheme can be applied successively to obtain a macroscale surface and can systematically incorporate the lubricant dewetting into the air bearing design, which will be used as a full-scale integrated HDI simulator.
Reproduced waveform and bit error rate analysis of a patterned perpendicular medium R/W channel
Authors: Suzuki Y. , Saito H. , Aoi H. , Muraoka H. , Nakamura Y.
Published: May 2005

Patterned media were investigated as candidates for 1Tb∕in.2 recording. In the case of recording with a patterned medium, the noise due to the irregularity of the pattern has to be taken into account instead of the medium noise due to grains. The bit error rate was studied for both continuous and patterned media to evaluate the advantages of patterning. The bit aspect ratio (BPI/TPI) was set to two for the patterned media and four for the continuous medium. The bit error rate (BER), calculated with a PR(1,1) channel simulator, indicated that for both double layered and single layered patterned media an improvement of the BER over conventional continuous media is expected when the patterning jitter is controlled to within 8%. When the system noise is large the BER of single layered patterned media deteriorates more rapidly than that of double layered media, due to the higher boost in the PR(1,1) channel. It was found that making the land length to bit length ratio large was quite effective at improving BER.
New technique to determine the magnetic easy axis orientation in recording media
Authors: Berger A. , Marinero E. , Doerner M. , Bian X. , Tang K. , Polcyn A.
Published: May 2005

The degree of confinement of the magnetic easy axis parallel or perpendicular to the film plane plays a crucial role in both longitudinal and perpendicular recording media. In this paper, we demonstrate a versatile technique for the determination of such magnetic orientation based upon a distinct hysteresis anomaly that occurs near the hard magnetic axis. Here, one observes areas of energy gain in addition to the conventional hysteretic energy loss. The ratio of energy gain to loss increases with better definition of the easy axes and can therefore be utilized as its quantitative measure.
Structural characterization of nano-oxide layers in PtMn based specular spin valves
Authors: Zhou Min , Chen Lifan , Diao Zhitao , Park Chang-Man , Huai Yiming
Published: May 2005

A systematic structure characterization of nano-oxide layers (NOLs) and specular spin valves using x-ray diffraction and high-resolution transmission electron microscopy (HRTEM) has been studied. High-angle x-ray diffraction data show almost identical fcc textures for both natural and plasma NOL spin-valves. Low-angle x-ray reflectivity spectrum shows more deteriorated Kiessig fringes at high incident angles for natural oxide sample, indicating rougher interfaces in natural oxidation than in plasma oxidation. Oxygen exposure plays an important role in NOLs process. Fabricating NOLs without any crystal structure degradation is critical to obtain high MR ratio. HRTEM reveals that oxide clusters mixing with insufficiently oxidized CoFe layers prevailed in natural NOL, and the natural oxidation was inhomogeneous. In contrast, plasma NOL has a thinner, more homogeneously oxidized CoFe layers with sharp interfaces. In plasma NOLs, the structures still maintain CoFe crystal structure. The structures and magnetic correlation of the NOL specular spin valves are discussed.
Perpendicular write-head remanence characterization using a contact scanning recording tester
Authors: Zhou Yuchen , Zhu Jian-Gang , Tang Yaw-Shing , Guan Lijie
Published: May 2005

In this study, an experimental method for characterizing perpendicular write-head pole-tip remanence using a contact scanning recording tester is presented. The head remanence is characterized by imaging the written patterns generated by perpendicular write heads on dc-saturated perpendicular media. Write-head footprints are recorded with pulsed unidirectional currents while the head is stationary, followed by scanning the head in various directions at current-off state. Sufficient head remanent field yields written traces during the current-off scan. Projection of traces in multiple scanning directions enables pinpointing of the pole-tip remanence locations. It is found that the traces written by the remanent field appear only when pulse current amplitudes exceed a certain threshold value. The strength of remanent field also shows a dependence on current pulse polarity. The “stiffness” of the remanence is characterized by the amplitude of the opposite write current needed to eliminate the remanent field.
In situ measurement of surface stress evolution during sputter deposition of CoCrX∕Cr (X=Pt,Ta) thin film and its magnetic properties
Authors: Park J. K. , Ha G. W. , Oh D. Y.
Published: May 2005

The measurement of force per width of CoCrX∕Cr (X=Pt,Ta) bilayer showed that both the surface state and surface stress of CoCrX layer can be controlled by controlling the surface stress of Cr underlayer through the variation of its thickness and of the deposition conditions such as the deposition rate and temperature. The dynamic surface of CoCrX layer showing a compressive surface stress was a critical factor to determine its coercivity. This was because the phase decomposition of CoCrX alloy can be largely promoted at the compressive dynamic surface because of its high mobility.
Address line-assisted switching of vertical magnetoresistive random access memory cells
Authors: Anderson John M. , Brownell David J. , Prinz Gary A. , Huggins Harold , Van Luan V. , Christodoulides Joseph A. , Zhug Jian-Gang
Published: May 2005

Vertical magnetoresistive random access memory (VMRAM) is a high-density, nonvolatile memory that employs current perpendicular to the plane to switch soft (read) and hard (write) magnetic layers of a giant-magnetoresistive memory element. VMRAM cells consist of closed-flux toroid-shaped elements and intersecting address lines situated above and beneath the elements [J.-G. Zhu, Y. Zheng, and G. A. Prinz, J. Appl. Phys. 87, 6668 (2000)]. Experiments performed on 64-element strings show that the intersecting address lines effectively assist in VMRAM cell switching. With projected density scaling to 400Gbits∕in.2 [J.-G. Zhu, Y. Zheng, and G. A. Prinz, J. Appl. Phys. 87, 6668 (2000)], VMRAM has the potential to compete with both semiconductor memories and mechanical hard disks.