M. Lederman

Advanced heads for perpendicular recording at high areal densities and high data rates

Perpendicular magnetic recording at high areal densities and high data rates has been studied. Using ring heads and perpendicular media with soft underlayer, we have successfully demonstrated the areal density of 60 Gb/in/sup 2/ at the corresponding ultrahigh-linear density of 750 kbpi, a bit-aspect ratio (BAR) of 9.4, and a data rate of 300 Mb/s. Comparing the BAR of 5.7 in our recent 63.2 Gb/in/sup 2/ demonstration on longitudinal media, a larger BAR has been demonstrated with present perpendicular recording system. We have also demonstrated the data rate capability of 1 Gb/s by using both ring heads and modified-single-pole heads on perpendicular media with soft underlayer. Finally, a comparison of high-data-rate recording between ring heads and single pole heads has shown that neither magnetic viscosity nor gyromagnetic switching in perpendicular media is the limiting mechanism for magnetic recording at data rates as high as 1 Gb/s.

Demonstration and characterization of 130 Gb/in2 magnetic recording systems

We have successfully demonstrated longitudinal recording at areal density of 130 Gb/in2 at a data rate as high as 170 Mbps (21 MB/s) and at a bit-aspect-ratio (BAR) of 2.9, using merged inductive-write/spin-valve-read heads on low noise thin film disks. The heads were fabricated with the standard photolithography and wafer pole trimming used in our currently available commercial products. The reader is a bottom synthetic spin valve (BSSV) with a 0.09 μm gap, and the writer has a conventionally trimmed pole with 0.09 μm gap. The reader magnetic read width (MRW) was measured at 0.10 μm. At read bias of ∼4 mA we measured reader sensitivity as high as 20 mV/μm. The write head was also optimized for tracks as narrow as 0.14 μm operating at overwrite (OW) of 36 dB and nonlinear transition shift (NLTS) better than −25 dB at 610 kBPI, without precomp. Using conventional media we measured total spectral SNR∼18 dB. The media to electronics noise ratio was 4.8, showing that we are still operating in a media noise li...

Advanced probe head for perpendicular recording

Basic design and recording performance of the advanced probe heads are described. Excellent writability of the advanced probe heads is demonstrated by a series of overwrite (OW) and nonlinear transition shift (NLTS) saturation measurements. Write currents as low as 5 mA/sub o-p/ are required for recording. Excellent OW can be obtained with both high and low OW ratios. Media with vibrating sample magnetometry coercivities as high as 7000 Oe can be recorded with OW of 30 dB. Better than -14 dB of NLTS was measured at a linear density of 600 kfci. Minimal side-writing has been observed using the advanced probe heads with square pole shape. External field sensitivity of the advanced probe heads has also been shown to be excellent as larger than 58 Oe of external field is required to erase a low density signal on a 3380-Oe disk. Modeling results also show that the basic architecture of advanced probe head is extendible to 0.1 /spl mu/m square pole.

Analysis of random telegraph noise in spin valve heads with ultra-thin free layers

Random telegraph noise (RTN) in spin valve heads with ultra-thin free layers is analyzed in both time and frequency domain. RTN is characterized by random fluctuation between two meta-stable states and is attributed to thermally activated domain instability. Lifetime of each meta-stable state is changes with bias current, with both being equal when RTN amplitude peaks while asymmetry is near zero. The lifetime at equilibrium can be quantified by the flatness of RTN spectra and is correlated with the normalized peak area under RTN amplitude versus bias current curve. This area scales with the energy barrier associated with RTN. With the same RTN peak area, lifetime at equilibrium is shorter for heads with thinner free layers but otherwise the same structure. Impact on reader instability for ultra-high areal density recording is discussed.

High linear density study of advanced single pole head

In this work, we present the general head design and magnetic recording performance of our second-generation advanced probe heads. These heads require as low as 5-mAo-p write currents for optimal recording. We demonstrate superior writeability via a series of overwrite (OW) and nonlinear transition shift (NLTS) saturation measurements. Excellent OW can be obtained with both high and low OW ratios. Media with VSM coercivities as high as 5500 Oe can be recorded with OW of 32 dB. We measured better than -12 dB of NLTS at a linear density of 1500 kfci. In this work, we present data where the magnetic read width (MRW) for the same read head is smaller when measured on perpendicular media compared to longitudinal media. We also show that the external field sensitivity of the advanced probe heads is excellent as larger than 32 and 23 Oe of external fields are required to erase a low-density signal on 3380- and 2200-Oe disks, respectively. Overall, the basic architecture of this advanced probe head is extendable to 0.12-/spl mu/m write track-width, while we discover no remanence in the pole.

Analysis of magnetic noise in lead overlaid giant magnetoresistive read heads

Thermally induced magnetic noise in giant magnetoresistive (GMR) read heads was characterized with both contiguous junction and lead overlaid design using an integrated spectral method. At 0.25 μm magnetic read width and 4 mA bias current, magnetic noise is twice as large as Johnson noise for lead overlaid design, while it is comparable with Johnson noise for contiguous junction design. The head signal-to-noise ratio gain of 2–3 dB with lead overlaid design is less than an amplitude gain of 50%–100% since it is limited by increased magnetic noise, which roughly scales with amplitude. Magnetic noise increases with bias current at a much faster rate than Johnson noise. Higher magnetic noise is attributed to weaker longitudinal bias field associated with the lead overlaid design. Fortunately, magnetic noise does not limit system level signal to noise ratio since media transition noise is dominant. However, it is projected that magnetic noise will account for an increased portion of total noise power at highe...

Inductive write heads using high moment pole materials for ultrahigh areal density demonstrations

In this paper, the high moment materials and their applications in the write heads for these areal density demonstrations will be discussed. Due to high intrinsic magnetic anisotropy and magnetostriction, which is typically about 4.5x10/sup 5/, FeCoN films exhibit typical coercivity in excess of 50 Oe, and isotropic in-plane magnetic properties, under un-optimised process conditions. A typical hysteresis loop of the film is shown.

Effect of CoPtCr/Cr on the magnetic properties of Permalloy

The effect of a hard bias material, CoCrPt, on the magnetic properties of Permalloy has been studied as a function of spacer layer thickness. In particular, a large increase in the coercivity without reduction in squareness of NiFe is observed. This increase may have relevant implications in the design of magnetoresistive heads. The results are explained qualitatively using a Random Field approach in the Imry-Ma.

Advanced spin-valve read-sensors for magnetic recording

Summary form only given. Giant magnetoresistive (GMR) read heads can certainly be cited as one of the major reasons for the phenomenal increase in hard-disk drive areal density, performance and value to the customer. Since the introduction of GMR heads into commercial products in 1997, the pace of the areal density race has increased to doubling on a yearly basis. The fast pace of GMR technology has been evident since its discovery. The GMR effect was first discovered in the laboratory in 1988 and in less than a decade had found its way into products. One reason for the speed of introduction of the head was that it shared many common process steps and equipment with the anisotropic magnetoresistive head technology that proceeded the GMR heads.

Current distribution effect on micro-track profiles in spin valve devices

The methodology of the micromagnetic theory for modeling micro-track profiles is discussed. Consistent results are obtained from modeling and experiments. Then, this theory is used to investigate the micro-track profile behavior in different current distributions at sensor junctions with different permanent magnet (PM) Mrt (remanent magnetization/spl times/thickness). It is found that a lower Mrt can lead to different microtrack profiles in different current distributions. With the PM Mrt there is less current distribution effect. Thus, ones could use this approach indirectly to estimate the PM field in sensors, which is of importance in spin valve head design.