Recording characteristics of electroless-plated perpendicularrecording flexible disks with a perpendicular head

Perpendicular magnetic recording using a main-pole-driven perpendicular head was tested using electroless-plated flexible disks. Soft magnetic NiFeP films, also produced by electroless plating, were used as an underlayer of a perpendicular recording medium in this test. Two types of flexible double-layer media, composed of an electrodeless-plated CoNiReP film with two types of NiFeP underlayers with a coercivity of 2 and 5.5 Oe, were fabricated, and their recording characteristics were measured. A recording density value of 75 kFRPI was obtained for the medium with the softer magnetic 2-Oe underlayer, about twice as high a value as that for the medium with the 5.5-Oe underlayer     

Recording performance characteristics of granular perpendicular media

The recording performance of CoCrPtO granular-type perpendicular media was examined with two types of perpendicular heads to demonstrate the importance of matching head and media designs in perpendicular recording. Shielded-pole heads with high write field gradients, field angles, and sufficient write field magnitude yielded superior writability and signal-to-noise ratio as compared to mono-pole heads. The recording performance dependences on head-to-medium spacing, interlayer thickness, and soft-underlayer (SUL) thickness were also weaker with the shielded-pole heads. In addition, the effect of stray fields on the SUL domain noise was investigated for a synthetic antiferromagnetically-coupled (SAF) SUL. A radial field close to the exchange field of the SAF SUL was found to induce domain noises that could potentially cause errors in recording systems.     

Recording on perpendicular anisotropy media with ring heads

This paper reports experimental studies directed at the application of ring head structures to a perpendicular recording system. The media tested were sputter deposited films of CoCrTa alloys. Ferrite heads were studied, but the thin film head was chosen for evaluating roll-off, overwrite, and superposition. The data presented in the paper demonstrates the potential of high density recording with a single layer medium with perpendicular magnetic anistropy and a thin film head separated by 0.20 micrometers.     

Recording characteristics of coated disks having high coercivity powder

The recording characteristics of coated disks having high coercivity powder, in particular metal powder, are given. We manufactured various disks containing γ-Fe2O3(coercivity: 350 Oe), iron-cobalt metal powder (400 - 800 Oe) and iron metal powder (650 Oe), respectively. The recording characteristics of these disks were measured by using a Mn-Zn ferrite head whose saturation magnetization was 5,000 gauss. It was found that disks with higher coercivity showed a capacity for increased bit density, but at the same time, poor overwrite characteristics. The optimum coercivity proved to be about 650 Oe. The typical values for metal powder coated disks (650 Oe) were: critical bit density: 19,000 BPI reproduced output: 1 mV at 19,000 BPI overwrite: -30 dB.     

Transitions on perpendicular rigid disks in quasi-contact

Results of quasi-contact recording on rigid perpendicular disks are presented in this paper. Footprints of Various recording heads on different recording media, obtained at quasi-static contact conditions using a high resolution magnetoresistive transducer, provide useful information such as sharpness of the magnetization transition and the effect of the demagnetizing field. Very high density magnetization transitions, up to 12500 fc/mm, on single-layer perpendicular rigid disks were recorded and read back by thin film ring heads at a velocity of 5-8 m/s under quasi-contact conditions. At high linear densities the amplitudes on the experimental density response curve are higher than those obtained by the linear superposition of experimental isolated pulses.     

Composite media for perpendicular magnetic recording

A composite perpendicular recording media consisting of magnetically hard and soft regions within each grain is proposed. Application of applied field initially causes the magnetization of the soft region to rotate and, thus, change the angle of the effective field applied to the hard region. This important change in the effective field is enabled by an exchange layer that moderates the interaction between the two regions. Energy arguments show that the resulting performance (as measured by the ratio of energy barrier to switching field) is similar to the previously proposed tilted media, while avoiding some of the difficulties. In particular, fabrication of the proposed composite media appears to be significantly easier than that of tilted media.     

Multilayer films of CoCrTa for perpendicular recording media

Multilayer structures of alternate magnetic and non-magnetic CoCrTa alloys have been prepared in which the magnetic properties can be widely varied by changing the magnetic layer and interlayer thicknesses, In this way, one example has shown that enhanced perpendicular anisotropy can be achieved as demonstrated by an increase in perpendicular coercivity Hc(perp) and a decrease in longitudinal coercivity Hc(&dlor.). This condition is desirable for application in perpendicular recording media. In addition, a second example has shown that by using much thinner layers (≃15 nm) it is possible to produce a structure in which the magnetization is longitudinal with a very low coereivity of 1.5 Oe. Such soft magnetic films with high Ms and low Hc(&dlor.) can be used as underlayers for perpendicular recording media in order to enhance the efficiency of pole heads.     

Ion-implantation studies on perpendicular media

Magnetic and structural properties of ion implanted perpendicular recording media have been investigated. Effects of 12C+ ion implantation with the doses of 2 x 10(11), 10(13), 10(14) and 10(16) ions/cm2 in the magnetic recording layer of conventional granular and continuous perpendicular media are reported in this paper. Implantation with the highest fluence of 10(16) ions/cm2 resulted in change of the magnetization reversal mechanism, thereby reducing coercivity. In continuous media the implanted ions cause increase in pinning defects, leading to an increase in coercivity. In contrast, high dose was found to cause similar change in the crystallographic properties of both the granular and continuous media.     

Nanocomposite magnetic films for high-density perpendicular magnetic recording media

Multi-layer nanocomposite structures of Ta/Ru/CoCr₁/FeCoTaCr(soft magnetic layer)/CoCr₂/CoCrPt-SiO₂(hard magnetic layer or recording layer)/C and Ta/Ru/CoCr₁/CoCrPt-SiO₂/CoCr₂/FeCoTaCr/C were proposed. This exchange coupled composite (ECC) media consisting of hard/soft stacked magnetic layers were promising in improving the writability of perpendicular magnetic recording media. A small CoCrPt c-axis orientation dispersion of about 3° was achieved with the optimized sputter conditions. The CoCrPt-SiO₂ grains were well segregated by SiO₂ at grain boundaries. The macro-magnetic properties showed that the stacked magnetic grains switched in a coherent mode and that switching field decreased with increasing the thickness of the soft magnetic layer.     

Wear properties of perpendicular magnetic recording media

Wear properties of sputtered Co-Cr/permalloy double layer on flexible substrate with and without an inorganic protective top layer were studied under simulated tribological conditions. A soft head slider (ex. glass) gave even severer damage to media than the hard one (ex. Al2O3-TiC), and a 200 Å thin inorganic protective top layer was effective enough to enhance resistance against wear. Read-write experiments were also done with use of the double layer flexible media with the protective top layer (200 Å in thickness) by running them on a specially designed driver unit with an Al2O3.TiC spherical SPT head. An out-put signal loss was no more than 3dB even after 10 million times of the head passes.     

Noise of low-coercivity single-layer perpendicular recording media

The noise of single layer CoCr media is investigated. A model is developed by treating the medium as a collection of columns. It appears that there is a strong correlation between magnetization direction of the columns. Neighbouring columns tend to have the same magnetization polarity, indicating exchange interaction. It is concluded that the media consist of domains. The domain width increases with the medium thickness. These domains can also result in a poor signal response at short wavelength.     

Magnetic anisotropy of perpendicular media on grooved structuresubstrate

Magnetic anisotropies were investigated for CoCr perpendicular magnetic films on grooved structure substrates (pitch length 2.1 μm) prepared by CF₄-reactive-ion etching. Perpendicular magnetic anisotropy decreases in the region where groove depth GD >650 A. The reduction is due to the inclination of the crystal growth axis on the groove surface. In-plane magnetic anisotropy, K_u∥, strongly depends on GD and saturation magnetization M_s. In a region of large GD and large M_s, Ku_∥ is mainly due to shape anisotropy. In a region of small GD and small M_s , K_u∥ is caused by perpendicular magnetic anisotropy, in addition to shape and magnetorestrictive anisotropy     

High-density perpendicular recording media with large grain separation

The possibility of 300-500 Gbit/in/sup 2/ perpendicular recording using granular recording media has been investigated through micromagnetic simulation based on the Langevin equation. Writability and thermal stability in 10 years were obtained changing media parameters such as the grain size D, the grain separation d, and the thickness of the recording layer t/sub mag/ for proper combination of the grain saturation magnetization M/sub s-grain/ and the grain perpendicular anisotropy energy K/sub u-grain/. It was found that high-density recording is realized under the large grain separation, the large grain saturation magnetization, and the large grain anisotropy energy. The read/write calculation using ordered medium with D of 4.2 nm, d of 2.3 nm, t/sub mag/ of 12.0 nm, M/sub s-grain/ of 1313 emu/cm/sup 3/, and K/sub u-grain/ of 7.0 Merg/cm/sup 3/ confirmed the possibility of 1303 kFCI and 1954 kFCI perpendicular recording, leading to 325 and 488 Gbit/in/sup 2/ with 250 kTPI (track pitch of 102 nm).     

NiW/Ru underlayer for CoPt-SiO2 granular perpendicular recording media

This paper presented the usage of the NiW/Ru underlayer to replace the single Ru underlayer for promoting CoPt hcp (0002) texture. Fcc (111) textured NiW film was used to induce the Ru hcp (0002) texture. It was found that the utilization of the (111) textured NiW alloying layer promoted the formation of Ru(0002) texture, enhanced the magnetic grain isolation and generated the uniform grains with gain size less than 10 nm in CoPt-SiO2 recording layer. The out-of-plane coercivity was also enhanced with the growth of 10 nm NiW underlayer below the Ru layer.     

Processing of signals from media with perpendicular magnetic anisotropy

The readback signals from a ring (Karlqvist) head and recording medium with perpendicular magnetic anisotropy are analyzed using signal processing criteria. The self-consistent model developed by Beardsley and Potter is used to study the feasibility of detecting transitions at high densities. Simulated readback signals are discussed in terms of time and frequency domain characteristics. A simplified linear system model is proposed which includes the effects of media orientation. Filtering and detection methods for the "vertical" channel are discussed.     

CoCrPt/Ti perpendicular media onto nanostructured polymer templates

The fabrication and the study of the magnetic properties of CoCrPt/Ti nanostructures produced by sputtering onto ordered polymer templates are reported here. Samples exhibit a significant out-of-plane component of the magnetization higher than for planar films, and it is stronger for the thicker CoCrPt films, and for nanostructured films with the shorter period ordering. The shape of the polymeric templates plays an important role for the determination of magnetic easy-axis. Magnetic Force Microscopy images of the samples show a single magnetic domain structure with high out-of-plane anisotropy for the samples with longer ordering (480 nm period).     

Properties of one-sided probe heads on double-layer perpendicular recording media

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.     

Cobalt chromium perpendicular magnetic recording media: a corrosionstudy

An electrochemical and environmental chamber study of the effects of corrosion on the magnetic properties of various cobalt chromium thin-film compositions is reported. The propensity of these various materials towards corrosion is delineated, with suggestions for an optimum composition with respect to corrosion resistance. The effects of the presence of a titanium seed layer and those of a soft nickel/iron keeper layer on the corrosion resistance of the recording medium are studied     

The origins of defects in sputtered Co-Cr perpendicular magneticrecording media

The authors examine various causes of contamination and the defects they produce, and they typify some defects that originate at the metal/substrate interface, as nodules or extraordinary particles. They find that these are not caused by dirt or mishandling, but are induced by an exudate from the polymide substrates used. The nodules' characteristic acorn shape can be analyzed mathematically to suggest a possible exudate-induced mechanism for their formation and growth. The authors conclude that most of these defects can be eliminated     

Readback bit shift with finite pole-length heads on perpendicular media

Perpendicular writing fields are calculated for finite pole-length gapped heads, with and without a permeable layer beneath the magnetic medium. These head fields are used to compute readback waveforms from ideal perpendicular transitions, which are detected both by zero-crossings and by inflection points of the waveform. Linear readback bit shift, given by the difference between detected and written transitions, is normalized to half the minimum transition spacing. For detection by waveform zero-crossing, bit shifts are unacceptably large with an under layer. Without an underlayer, detection by inflection point is considerably better than by waveform zero-crossing. Surprisingly, bit shifts from inflection points are only marginally better without an underlayer than with one. A recording system with an underlayer may in fact give superior performance because of other contributions to the total bit shift.