A5113223502- Magnetic properties of thin films
- Magnetic Properties and Applications
- Physics of Superconductivity and Magnetism
- Magnetic Field Sensors Techniques
- Magnetic and transport properties of perovskites and related materials
- Non-Destructive Testing Techniques
- Theoretical and Computational Physics
- Advanced Memory and Neural Computing
- Quantum and electron transport phenomena
- Magnetic Properties of Alloys
- Advanced Condensed Matter Physics
- Adhesion, Friction, and Surface Interactions
- Copper Interconnects and Reliability
- Neural Networks and Applications
- Characterization and Applications of Magnetic Nanoparticles
- ZnO doping and properties
- Advanced Data Storage Technologies
- Atomic and Subatomic Physics Research
- Semiconductor materials and devices
- Cellular Automata and Applications
- Solidification and crystal growth phenomena
- Advanced Optical Imaging Technologies
- Advanced Electrical Measurement Techniques
- Neural Networks and Reservoir Computing
- Magneto-Optical Properties and Applications
West Virginia University
2025
Western Digital (United States)
2016-2021
University of Kentucky
2014-2016
Hitachi Global Storage Technologies (United States)
2003-2009
Hitachi (Japan)
2005-2007
Kodak (Japan)
1986-2005
IBM Research - Almaden
1998-2003
IBM (United States)
2002
Kodak (United States)
1985-1997
Eastman Chemical Company (United States)
1988-1993
The voltage V(t) induced by a sinusoidal drive current traversing 125-μm-diameter BeCu wire plated with 1 μm NiFe is observed to be very strong function of axial dc magnetic field. basic physics this phenomenon explained classically in terms Faraday’s law induction and Stoner–Wohlfarth magnetization reversal, which yield theoretical predictions that are good agreement experiment. For amplitudes the order 100 mA, frequencies 5 MHz, field sensitivity dV/dH can as large V/Oe (per cm wire),...
Read heads using current-perpendicular-to-plane (CPP) giant magnetoresistance sensors have been fabricated and tested under high-density recording conditions. A of 5.5% shield-to-shield spacing 45 nm achieved by an all-metal single-spin-valve with Heusler-alloy-based free reference magnetic layers. read widths ~45 were on perpendicular media, resulting in signals above 1 mV signal-to-noise ratio ~30 dB. Linear densities excess 1050 kbpi thermal fly-height control, compatible areal ~400 Gb/in...
We have developed a self-aligned, high-yield process to fabricate current-perpendicular-to-plane giant magnetoresistance (GMR) spin-valve sensors of sub-100-nm dimensions. A pinned synthetic antiferromagnet is used as the reference layer which minimizes dipole coupling free and field-induced rotation layer. find that critical currents for spin-transfer-induced magnetization reversal vary dramatically with relatively small changes in in-plane magnetic field, contrast theoretical predictions...
A theoretical micromagnetic study of the basic magnetic and performance characteristics an unshielded dual coupled thin-film self-biased magnetoresistive sensor is presented. The usual sense current flowing in Permalloy magnetoresistor (MR) provides a magnetizing field for strongly magnetically soft adjacent layer (SAL) whose resulting demagnetization acts as bias source MR. analysis methods presented provide quick, accurate, numerically well-conditioned solutions relevant equations. Results...
We have used scanning electron microscopy with polarization analysis and photoemission to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay exchange interactions in asymmetrically coordinated vertices short-range dipole among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist frustrated at room temperature. Numerical simulations include long-range between agree images as-grown P2T...
We report on an experimental study of current-induced switching in perpendicular magnetic random-access memory (MRAM) cells with variable resistance-area products (RAs). Our results show that addition to spin-transfer torque (STT), self-heating and voltage-controlled anisotropy also contribute can explain the RA dependencies switching-current density STT efficiency. findings suggest thermal optimization MRAM result significant reduction currents.
This paper considers magnetization fluctuations (mag-noise) in current-perpendicular-to-plane (CPP) read sensors, due to either thermal or spin-torque induced instability. The former are relevant both tunneling (TMR) and giant-magnetoresistance (GMR) devices, the latter a potentially more serious limitation most all-metal GMR sensors. Discussion of mag-noise is here treated by micromagnetic simulation. instability includes analytical modeling combined with experimental measurements.
This paper derives expressions for the critical current at onset of spin-transfer-torque (STT) instability in CPP-GMR read heads, as a function relative angle (theta) between free and reference layer magnetizations. Including general angular dependent STT coefficient B(q=cos(theta)) exclusive momentum conserving sin(theta) factor, is found to depend on both B(q) dB/dq non-collinear case |q| < 1. The also details experimental measurement currents 50-nm sized devices with synthetic...
We introduce a differential planar Hall effect method that enables the experimental study of spin orbit torque switching in-plane magnetized free layers in simple bar device geometry. Using this method, we Pt thickness dependence currents and show they decrease monotonically down to minimum ∼5 nm, while critical current power densities are very weakly dependent, exhibiting values Jc0 = 1.1 × 108 A/cm2 ρJc02=0.6×1012 W/cm3 at thickness. Our results suggest significant reduction parameters...
This paper describes materials development, device modeling, and initial test results for a novel GMR reproduce head ultrahigh density recoding (/spl sim/ 10 Gbit/in/sup 2/). It consists simply of 20-bilayer multilayer, self-stabilized by intrinsic antiferromagnetic interlayer coupling, self-biased sense current into bipolar, field-gradient-sensing bias state. Analogous to dual magnetoresistive (DMR) such GMR-DMR is capable achieving very high linear resolution without shields. Tape-test...
The exchange field decays when spin valves are subjected to a that rotates the pinned layer towards reverse direction. decay results from competition between torque on interfacial AF spins layer, which lowers barrier for thermal switching, and KuV product of grains, provide stability. Typical values rates at 125 °C vary 5–35%/decade, depending upon AF. A comparison decay-rates many AF’s important valve heads shows IrMn (blocking temperature, Tb∼250 °C) is most stable, followed by NiMn (350...
To explore recording head challenges for perpendicular at 200 Gb/in/sup 2/ and beyond, the design, fabrication performance of narrow track dual-element heads were studied using an ABS trailing shield writer design a conventional CIP-GMR reader design. Parametric tests these on low noise CoCrPt/SUL media show that, with good writability disk transition jitter around 2.5 nm achieved write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes 1 mV T/sub 50/ widths 28 also read...
Magnetic recording read heads have been fabricated and tested using a dual-spin-valve (dual-SV) current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) sensor stack. Thin IrMn antiferromagnetic layers are used for top- bottom-pinned layers, resulting in total stack height of 50 nm. Operational with physical trackwidths ranging from 60 to 30 nm achieved. Successful readback testing is obtained perpendicular media, observed magnetic widths as low 46
We demonstrate that the addition of Dy capping layers in current perpendicular to plane giant magnetoresistive spin-valves can increase critical density beyond which spin-torque induced instabilities are observed by about a factor three. While capped samples exhibit nonmagnetic 1/f noise, it is sufficiently small be unimportant for read head operation at practical data rates.
Simple IrMn spin-valves are investigated for use in high density recording head sensors. Top-IrMn of the form NiFeCr(40 /spl Aring/)/NiFe(32 Aring/)/CoFe(5)/Cu(25 Aring/)/CoFe(30 Aring/)/IrMn(80 Aring/)/Ta(50 Aring/) were deposited by magnetron sputtering. By tailoring pinned layer composition at CoFe/IrMn interface to Co/sub 60/Fe/sub 40/, exchange bias can be increased above 400 Oe with a GMR amplitude about 12%. Recording heads fabricated total gap thicknesses down 900 Aring/, magnetic...
A dual magnetoresistive (DMR) reproduce head consisting of two nominally identical, adjacent stripes separated by a conductive spacer is demonstrated. This two-terminal device relatively simple to fabricate, does not require magnetic shields for high linear resolution, self-biased, and immune electrical shorting between MR elements. The measured output voltage vs. recorded density agrees well with theoretical predictions. For large record densities >100 kFCI, more advanced DMR designs are...
Various biasing techniques have been proposed for vertical magnetoresistive stripe detectors to improve their linearity. In the soft-adjacent- layer design, a high-permeability film (SAL) is located close (MR). The sense current in MR magnetizes SAL, which turn generates magnetostatic bias field at MR. Thin-film heads based on SAL concept fabricated sapphire, using conventional methods, and tested. A theoretical description are treated as coupled Stoner-Wohlfarth particles has generalized...
The frequency dependence of the transverse biased permeability μ′t(f ) has been measured up to 250 MHz in thin (0.044 μm) and thick (2.1 unpatterned sputtered permalloy films with uniaxial anisotropy. In these films, initial along hard axis can be described by classical eddy current damping model assuming uniform rotation. For both μ′t at low agrees reasonably well Hoffman’s ripple appropriate values for structure factor. film, is independent within experimental error least MHz. However,...
A NiFe/Co/Cu GMR spin-valve magnetometer is designed, built, and tested. Thin-film flux-concentrators provide 50/spl times/ gain, yielding hysteresis-free sensitivity 1/R dR/dH=11%/0e in a 1 mm/sup 2/, internally temperature compensated device. Detection levels of 2 /spl mu/Oe/(Hz)/sup 1/2/ (at Hz) are limited by 1/f resistance noise the films, which examined detail. Improvement 10/spl possible via increased device size, as well lower MR films.
Dual IrMn-pinned current-perpendicular-to-plane giant magnetoresistive sensor structures have been investigated, and their signal noise characteristics are compared to similar standard single sensors, using test with sizes down 50nm. The intrinsic ΔRA product is found be increased by a factor of nearly 2 between dual spin valves, although the parasitic resistance due second 80-nm-thick layer stack limits net increase in ΔR∕R 1.5. For valve antiparallel free reference layers, power spectral...
We present an analytical model for calculating the energy barrier magnetic field-driven domain wall-mediated magnetization reversal of a magneto-resistive random access memory cell and apply it to study thermal stability factor Δ various thicknesses W layers inserted into free layer (FL) as function size temperature. find that, by increasing thickness, effective perpendicular anisotropy (PMA) density FL film monotonically increases, but at same time, mainly decreases. Our analysis shows in...
Thermal magnetization fluctuations (mag-noise) in giant magnetoresistive (GMR) spin valve (or any MR) heads will serve as a fundamental limit on their signal-to-noise-ratio (SNR). Measured mag-noise several varied spin-valve read sensors is shown to be good quantitative agreement with predictions based the fluctuation-dissipation theorem. The dependence of and head-SNR sensor geometry other device parametrics discussed.
Adjacent-track interference (ATI) in a dual-layer perpendicular recording system arises during both writing and reading. During writing, the stray fields from write head can cause side erasure. A dc-erase method using media with low nucleation field is used to identify extent polarity of these fields. In strong anisotropy soft underlayer (SUL), experimental results reveal that causing ATI have cross-track asymmetry due interactions between flux magnetization SUL. On readback, amplitude...
The calculation of the reproduce signal from a magnetoresistive (MR) sensor is complicated by spatial non-uniformities in sensor's magnetization <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{M}</tex> and large variations fields over height sensor. In general, accurate performance calculations require nonlinear self-consistent computations, which must be repeated at numerous head-medium positions. However, if one interested first-harmonic...