B. Lengsfield

/spl Delta/H(M,/spl Delta/M) method for the determination of intrinsic switching field distributions in perpendicular media

We describe a method for the experimental characterization of intrinsic switching field distributions in perpendicular media. The method is based upon a comparison between the major loop and a set of recoil loops, which start at a certain distance /spl Delta/M away from saturation. In particular, we measure the applied field difference /spl Delta/H between the recoil loops and the major loop at identical M values, for which the average demagnetizing fields are the same. By analyzing complete /spl Delta/H(M,/spl Delta/M) data sets taken from multiple recoil loops, we gain a detailed measure of the intrinsic switching field distribution D(H/sub S/). Using polar-Kerr effect measurements of recording disk samples, we demonstrate the capabilities of our approach.

Energy Barriers in Composite Media Grains

Thermal stability is critical for magnetic grains in high density recording applications. Composite media grains consisting primarily of a hard and soft layer with intergrain exchange coupling are examined. Here it is shown, as in single domain particles, that power laws, to a good approximation, describe the field dependence of the energy barrier. In general, the power law exponent decreases with increasing relative moment and/or decreasing relative anisotropy of the soft/hard subgrain. Results for a variety of medium parameters as well as grain orientations are given

Head challenges for perpendicular recording at high areal density

To explore recording head challenges for perpendicular recording at 200 Gb/in/sup 2/ and beyond, the design, fabrication and performance of narrow track dual-element heads were studied using an ABS trailing shield writer design and a conventional CIP-GMR reader design. Parametric recording tests of these heads on low noise CoCrPt/SUL media show that, with the trailing shield design, good writability and low disk transition jitter around 2.5 nm were achieved at narrow write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes around 1 mV and T/sub 50/ widths around 28 nm were also achieved at read trackwidths around 60 nm. The areal density potential of these heads was studied using a PRML channel at /spl sim/50 MB/s data rate. Results show linear densities around 1000 Kbpi at ontrack byte error rates of 10/sup -4/, and track densities around 200-240 ktpi using a criterion of 15% offtrack to trackpitch ratio. In all, areal densities of 210-230 Gb/in/sup 2/ were achieved with these head and disk components.

Writeability Enhancement in Perpendicular Magnetic Multilayered Oxide Media for High Areal Density Recording

A systematic investigation of the switching behavior and writeability characteristics of perpendicular magnetic oxide media was performed by varying the number of oxide layers as well as the anisotropy Ku gradient in multilayered oxides. The media switching behavior highly depends on the magnetic volume of laterally exchange-coupled cap layer as well as the vertical exchange coupling between oxide and cap layers. The media switching field is significantly reduced with incoherent switching mode. The media writeability is further enhanced by employing the multilayered oxides whose anisotropy values vary. Higher Ku graded oxide media exhibits improved resolution, sharper transition, and higher signal-to-noise ratio. An analytical 9-spin model is used to study the impact of anisotropy grading, intergranular and interlayer exchange coupling on writeability and noise performance. The 9-spin model is found to qualitatively agree with the experimental results. Both model and experiment indicate that optimal tuning of the media anisotropy and exchange to the head design is critical in attaining good recording performance.

Incoherent Switching Amount Analysis of Exchange Spring Media by Using Initial Minor Loop Slope Measurement

We describe a newly developed initial minor loop slope (IMLS) experimental method capable of measuring reversal switching in exchange spring perpendicular media. The slope peak height is centered near the mediums coercivity Hc. The magnitude of the peak signal is correlated with the soft top (cap) layers moment, Mst, and the exchange coupling strength between the cap and hard magnetic oxide layers. The peak position was correlated to the media Hc for media that is thermally stable and migrates to smaller fields in less stable media. The IMLS results are compared with both remanent angular dependence coercivity, Hcr, measurements and micro-magnetic simulations. This technique provides a simple method of characterizing incoherent switching behavior in different types of exchange spring media.

Comparison of Experiment and Simulation Results of Interlayer Thickness Effect in Perpendicular Recording Media

The effect of interlayer thickness (tIL) on recording performance of the media showing relatively close to coherent switching behavior is investigated. The range of t IL was widely controlled from 20 to 45 nm by inserting an amorphous CrTa filling layer between NiW(6 nm)/Ru(14 nm) and amorphous FeCoTaZr soft underlayer (SUL). Minor heating effects at a thicker CrTa on a glass substrate are detected, but the change in magnetic properties and microstructure even at tIL= 45 nm is small enough to study the head-to-SUL spacing effect. A thinner IL clearly improves both reverse overwrite (ROW) and signal-to-noise (SoNR2T) at 2 T, but it reduces resolution (RES). Less dependence of magnetic core width (MCW) on t IL is shown due to compensation of wider magnetic write width (MWW) and narrower erasure band (EB) at a thinner IL. According to simulation results, a thinner IL enhances field strength underneath the center of the writer and more field penetration into the media but the maximum effective field located near the gap changes very little. These field profiles improve writeability at low frequencies, but they do not affect much at mid-to-high frequencies. This situation can explain better ROW, lower RES, and wider MWW at a thinner IL. Higher crosstrack field gradient at a thinner IL corresponds to narrower EB. The improvement of SoNR2T at a thinner IL is caused by the increase in signal at low frequency and the further decrease in dc noise. All the recording parameters with increasing t IL are qualitatively consistent with simulation results.

EBL thickness and transition parameter in perpendicular oxide media

This paper investigates the effect of varying the exchange-break-layer thicknesses (leading to a change in intergranular exchange) on spectral rolloff and the transition parameter (a-parameter). The rolloff curves are obtained by measuring the amplitude of the fundamental harmonic peak at each written density. A systematic increase of the low frequency amplitude is observed as the EBL thickness decrease.

Thermal decay in perpendicular media

Thermal decay is one of the main limitations in longitudinal recording. In depth understanding the decay processes in perpendicular recording allows understanding the effect of thermal decay on the error rate and improving the design of head, media and channel. In the present paper we investigate thermal decay processes in perpendicular recording media by means of experiments and modeling.

Demagnetization effects in coercivity measurements: a generalized Sharrock model for perpendicular media

In the present paper we develop a generalized form of the Sharrock equation which accounts for demagnetization effects in both remanence and time-dependent coercivity experiments. We show that the inclusion of a demagnetization field leads to an apparent time dependence and rescaling of the attempt frequency, f/sub 0/. In this paper we compare the predictions of this model to earlier forms of the Sharrock expression as the strength of the demagnetization interaction and the sweep rate is varied. The mean-field approximation leads to a solvable model where the inclusion of volume and anisotropy distributions can be included in a simple manner.

Generalized /spl Delta/H/sub C/-method for the determination of intrinsic switching field distributions in perpendicular media

A magnetometry method was developed for the experimental characterization of intrinsic switching field distributions in perpendicular media. The applied field difference /spl Delta/H between the various recoil loops and the major loop was measured for identical distance M-values away from saturation, i.e. the same average demagnetizing fields. Also, a more refined measurement of the entire switching field distribution D(H/sub S/) was gained by analyzing the complete /spl Delta/H(M,/spl Delta/M)-data set from multiple recoil loops. Using micromagnetic modeling, the reliability and precision of the described /spl Delta/H(M,/spl Delta/M) method was studied.