Single-layer Perpendicular Media Research Articles

Performance analysis of a 0.3-Tb/in/sup 2/ low-power MFM-based scanning-probe device

In this paper, we present an analysis of the performance of a 0.3-Tb/in/sup 2/ ultralow-power magnetic-force-microscopy-based scanning-probe storage device actuated by microelectromechanical systems technology. The device is currently under development at Carnegie Mellon University, Pittsburgh, PA. The analysis shows that, with an optimized commercial single-layered Co-based perpendicular medium with an optimized tip trajectory, a signal-to-noise ratio of 20-25 dB is achievable. The analysis includes general design considerations as well as various aspects of performance such as recording dynamics, PW/sub 50/, intersymbol-interference limit, detection sensitivity, thermal degradation, intertrack interference, off-track errors, process variations, and surface fluctuation effect. Design/performance standards for the new device are suggested.

Hilbert filter for double-layer perpendicular recording media

Summary form only given. Readback waveforms from GMR heads in perpendicular magnetic recording are completely different from the regular longitudinal recording waveforms. Proper signal equalization is therefore critical. For this purpose a Hilbert filter is discussed. This filter is known to transform the dipulse response from a single layer perpendicular media into a longitudinal signal, however, for double layer perpendicular media with a soft magnetic underlayer its properties have not been reported yet. In this paper the authors discuss the performance of the Hilbert filter for double-layer perpendicular recording media.

Recording physics of perpendicular recording with single layered medium and ring head

In this article, the recording physics of a ring head with a single layered perpendicular medium (Ring/SL) is studied and the results are compared with a single pole head with a double layered perpendicular medium (SPT/DL) by using various simulations and experiments. The Ring/SL has much lower effective medium coercivity than the SPT/DL due to the substantial longitudinal field component of ring head and the incoherent rotation mode of medium magnetizations. Furthermore, switching time of the Ring/SL is estimated as only 10%∼30% of the SPT/DL. In the Ring/SL, the head field gradient of 40 Oe/nm is enough for maximizing SNR. The Ring/SL shows very low noise characteristics especially at high linear density. The signal output of the Ring/SL is smaller than the SPT/DL, but it is large enough to be detected. Therefore, it can be concluded that the combination of single layered perpendicular medium and ring head is highly promising for ultrahigh density recording.

Optimum design rule of hysteresis loop for ultrahigh density recording in single-layered perpendicular media

Micromagnetic studies have been performed to find optimum shape of hysteresis loop in a single-layered perpendicular medium for ultrahigh density recording. A good index that was inversely proportional to signal-to-noise ratio (SNR) was developed. By using this index, we found the optimum loop shape should have terms of the ratio of nucleation field to coercivity within -0.4 to -0.6, the loop slope within 2 to 4, and the ratio of grain thickness to grain diameter larger than 2.5.

Effects of magnetic layer thickness on negative nucleation field and Cr segregation behavior in CoCrPt/Ti perpendicular media

Based upon our previous study on the formation of a large negative “nucleation field” in CoCrPt/Ti single layered perpendicular media (I.S. Lee et al., J. Appl. Phys. 85 (1999) 6133), dependency of magnitude of negative nucleation field on CoCrPt/Ti with variation of Pt content and CoCrPt thickness was investigated. Difference in the degree of Cr segregation with the film thickness for a given film composition was also discussed. It was found that Cr segregation behavior might be closely associated with the nature of residual stress in the magnetic layer. When there was tensile stress in the film, Cr segregation was not significant. To understand the origin of the negative nucleation field, micromagnetic simulation was performed and it was found that a normalized nucleation field, H n/ K u, linearly depended upon K u/ M s 2 and weakly depended on exchange parameter among grains when uniform grain size was assumed. Read/write simulation results show that a high negative nucleation field is effective in increasing the signal output.

Low NLTS approach: Perpendicular/Longitudinal composite media

It is desirable to employ low NLTS media in high density magnetic recording. The perpendicular/longitudinal (P/L) composite media, consisting of a perpendicularly oriented top layer and a longitudinally oriented underlayer, tends to have lower NLTS value than the single layered perpendicular media due to the opposite shift direction of NLTS in the two recording layers. Experimental results show that the P/L composite media has a lower NLTS than a single layered perpendicular media, and its NLTS value is slightly less sensitive to flying height or switching speed variation when compared with single layered perpendicular media.

リングヘッド／垂直単層磁気記録媒体系におけるトラック端部磁化状態の解析

The effect of magnetic pole shape on the remanent magnetization state at the track edge was studied for a ring-type head and a single-layered perpendicular medium system. An MIG head and a merged MR head were used for recording. These heads have symmetric and asymmetric magnetic pole structures, respectively. It was found that the remanent magnetization state at the track edge of a single-layered perpendicular medium was greatly influenced by the shapes of the magnetic poles. Thus it is necessary to improve the shape of magnetic poles in order to realize the higher track density for a single-layered perpendicular medium.

Low noise performance of CoCrPt single-layer perpendicular magnetic recording media

Magnetic and noise characteristics of CoCrPt single-layer perpendicular recording media prepared by high-rate deposition process have been investigated. The medium noise was reduced by high-rate deposition, however the inter-diffusion between the CoCr/sub 19/Pt/sub 10/ magnetic layer and a TiCr/sub 10/ underlayer was observed at the interface. The magnetic properties were improved by introducing a CoCrRu underlayer between the CoCrPt and the TiCr layers. Addition of 2-nm-thick MgO layer between the CoCrRu and the TiCr layers was found to be useful to increase the coercivity and to reduce the medium noise.

High performance CoPtCrO single layered perpendicular media with no recording demagnetization

High coercivity CoPtCrO single layered perpendicular medium has been newly developed in order to solve the recording demagnetization problem, and exhibited the excellent recording characteristics with ring type head; the areal recording density being higher than 11 Gbit/inch/sup 2/. The high Pt content and the segregation structure with thick oxygen-rich boundaries led this perpendicular medium to high coercivity, steep hysteresis slope at Hc, and high squareness at the same time. These features were found to be primary factors for both high SNR and suppressed recording demagnetization.

単層膜媒体による垂直磁気記録の誤り率特性

The bit-error rate (BER) performance of 16/17(0,6/6) coded PRML systems for a single-layered perpendicular medium was studied by conducting read/write experiments using a spinstand system. The results show that the E3PR4ML system exhibits the best performance among the PRML systems evaluated in this paper, and achieves a BER of less than 10-6 at a high linear density such as 375 kbpi.

Engineering issues study of ring-shaped head recording on single layered perpendicular media

This article presents results of experimental study on the engineering issues of using ring-shaped thin-film head and single layered perpendicularly orientated media for high density magnetic recording. Comparing with the experiment conducted with longitudinal media, this combination is of smaller sensitivity of its nonlinear transition shift to the variation of the head–disk spacing, smaller writing current for saturation recording even if the media coercivity is 25% higher than that of the longitudinal counterpart. Furthermore, the width of its erasure band is quite comparable to the case using longitudinal media, if the writing current is selected properly. On the other hand, the combination is of slightly larger asymmetry of its track profile and slightly more sensitive to the skew angle increment, if the anisotropic magnetoresistive head is used for reading.

Signal and noise characteristics of thin film media estimated by magnetic force microscopy

An analytical magnetic force microscopy has been applied to investigate the relationship between the media S/N and the microscopic magnetization irregularities of CoCr-alloy longitudinal and single-layer perpendicular media recorded at linear densities up to 450 kFCL. When the S/N is compared between longitudinal and perpendicular media, a 16-nm-thick CoCrPt longitudinal medium shows a little higher S/N than that of a heat-treated 25-nm-thick CoCrTa perpendicular medium. The medium S/N is found to deteriorate with increasing the size and the number of magnetization transition irregularity.

Microscopic magnetization structures and noise in single-layer perpendicular thin film media

A new method to evaluate microscopic magnetization intensities has been developed based on a magnetic force microscopy (MFM) observation. The MFM tip-to-sample distance is varied to get quantitative information at the magnetic layer surface. The method is applied to investigate the origin of medium noise in single-layer perpendicular media. The irregular magnetization in the DC erased state and the average size of magnetization irregularities are quantitatively evaluated for CoCr-alloy perpendicular media with different noise characteristics.

Noise Properties of an Electroless-deposited CoNiReP Perpendicular Magnetic Recording Medium and a Perpendicular / Longitudinal Composite Medium

Noise properties as well as read / write characteristics of a CoNiReP single-layer perpendicular magnetic recording medium and a perpendicular / longitudinal composite medium are investigated by using a merged ring-type write / MR read head. The reproduced voltage of the composite medium is higher than the single-layer perpendicular recording medium in the region of lower than 100kFRPI. The noise power of the CoNiReP single-layer perpendicular recording medium is almost independent of recording density, similar to a CoCr perpendicular recording medium prepared by sputtering method. The noise power of the composite medium was lower than the superposition of the noise power of the longitudinal magnetization underlayer alone taking account of spacing loss and the noise power of the perpendicular magnetization upperlayer alone. But no noise reduction was obtained in the case of using narrow gap recording head. In order to realize excellent noise properties as well as read / write characteristics, it is necessary still more to clarify the effect of head and medium parameters and to optimize these parameters.

Nonlinear Distortions in Perpendicular Recording

Recording nonlinear transition shift (NLTS) and amplitude variation (NLAV) in perpendicular recording with thin-film media and a ring head were investigated. The NLTS in single layer perpendicular media was closely correlated to the medium parameters and recording conditions. A certain condition such as thinner medium with smaller residual magnetization can provide the NLTS smaller than that in longitudinal recording medium. Although direction of the NLTS was the same as that for longitudinal one, amplitude enhancement was observed at higher recording densities. Improvement in the nonlinear distortion has been made by introducing a small gap length recording head.

Nonlinear Transition Shift in the Combination of Single-layered Perpendicular Recording Medium and Ring Head

Nonlinear transition shifts (NLTS) in the combination of single-layered perpendicular recording media and ring head writing are investigated by read/write experiments employing the fifth harmonic elimination method. The NLTS of single-layered perpendicular recording medium can be kept at the low level at high linear recording density. The NLTS smaller than 10 % is observed at 300 kFCI for a 25 nm thick CoCrPt perpendicular recording medium. Decreasing the medium thickness improves the NLTS.

Low-Noise Co-Cr Perpendicular Medium with High Cr Content

We investigated the noise reduction mechanism of a Cr-rich Co72Cr28 perpendicular magnetic recording medium. By increasing the Cr content from 22 at% to 28 at%, the signal-to-noise ratio at a recording density of 70 kFCI was increased from 25 dB to 31 dB. The medium noise was reduced more than the magnetic parameters, such as MS and HC⊥. When the average crystalline diameter of the media increases, the medium noise of the Cr 28 at% medium does not increase, whereas that of a Cr 22 at% medium increases. Analysis of a medium with a Ti under-layer shows that the Δθ50 does not have any significant effect on the medium noise. To analyze the noise of these media, we introduced ΔM⊥ measurement method that takes account of the demagnetization field. The ΔM⊥ value is related to the medium noise. The relation is different from that of longitudinal medium. Analysis of the minor loops showed that the Cr 28 at% medium has low noise due to its highly stable dc-erased state. MFM observation for 4-μm-wide dc-erased tracks confirmed the mechanism for smaller reversed magnetic domains in a Cr 28 at% medium than in a Cr 22 at% medium. This mechanism contributes to the low noise of the Cr-rich Co-Cr single-layer perpendicular medium.

Characteristics of high-density recording using a single-layer perpendicular medium and a merged MR head

The combination of a merged MR head and a single-layer perpendicular medium is a promising technology for high-density recording. This paper describes a system that provides high-linear-density recording (over 150 kFCI) without requiring a contact recording method. Both-the large magnetic anisotropy and the large crystalline orientation of a Cr-rich Co/sub 72/Cr/sub 28/ medium hold out the promise of higher linear density. The large output signal also shows the possibility of increasing the track density. The baseline shift for narrow track widths is an issue that must be solved by equalization before this system can be used to realize future hard disk drive products.

Noise and ΔM⊥ analysis of a Cr-rich Co-Cr perpendicular medium for an MR head

The medium noise in a Cr-rich Co-Cr alloy perpendicular medium was investigated by using an MR head designed for longitudinal recording. Medium with a Cr content of 28 at.% showed a high crystalline orientation and a low write-demagnetization effect. The signal-to-noise ratio (S/N) of the medium was higher than that of conventional Co-Cr perpendicular media for inductive heads. The advantages of the medium derive from the large inter-particle perpendicular magnetic interaction (/spl Delta/M/spl perp/) of media, which increased linearly with the Cr content, reaching a maximum value at 28 at.%. This strong interaction in the medium results in a high S/N for a recording system using a single-layer perpendicular medium and an MR head.

High density magnetic recording on highly oriented CoCr-alloy perpendicular rigid disk media

High density magnetic recording is investigated for a combination of single-layered perpendicular media and ring-type heads. Medium magnetic properties (Hc and Mr/Ms) are improved by introducing a dual underlayer structure. Read/write experiments show that the linear recording resolution (D/sub 50/) increases drastically with decreasing magnetic spacing. D/sub 50/ values of 190-220 kFCI are observed using a flying MR head at an estimated magnetic spacing of 40 nm. Using contact recording, even higher resolution of D/sub 50/*=300 kFCI is confirmed. Side-writing and side-erasing can be reduced below 0.2 /spl mu/m by employing a narrow gap write head with trimmed sharp track edge, which demonstrates the possibility of track density greater than 25 kTPI. The recording areal density can be increased to the 10 Gb/in/sup 2/ level with the present recording system.