Longitudinal Recording Media Research Articles

Surface chemistry of NiP plated substrates

Circumferential texture grooves polished into NiP plated AlMg substrates promote magnetic crystal anisotropy in longitudinal recording media. Freshly textured or washed NiP is a chemically reactive surface, and combines with atmospheric moisture and carbon dioxide to form Ni carbonates. These adventitious products alter the surface morphology and interfere with magnetic domain growth.

Modeling of long-time thermal magnetization decay in interacting granular magnetic materials

We present a general method to evaluate the long-time magnetization decay in granular magnetic systems. The method is based on Arrhenius-Neel kinetics with the evaluation of the energy barriers in a multidimensional space. To establish a possible reversal mode, we suggest the use of Metropolis Monte Carlo and for the mode statistical sampling-the kinetic Monte Carlo criteria. The examples considered include long-time magnetization decay in CoCrPt low-magnetization longitudinal recording media and in a collection of Co particles with different concentrations.

A study of orientation ratio in longitudinal magnetic thin-film media on plasma-treated textured substrates

The effects of plasma treatment of textured substrates on orientation ratio (OR) as well as in-plane Cr(200)/Co(11.0) preferred orientation (PO) and coercivity (Hc) in longitudinal magnetic recording media have been systematically investigated. OR is found to increase by ∼0.2–0.3 with enhanced PO and Hc for samples with slightly rf sputter etched substrates. Further Ar+ plasma dry etching (higher power/longer duration) leads to a slow decrease of OR to ≤1, then a worsened/vanishing PO and finally a drastic drop in Hc. The origin of OR is primarily attributed to stress effects (of most importance being the anisotropic stress induced preferential easy axis distribution), with anisotropic topography and PO as two necessary preconditions for OR >1. Ion beam bombardment induced chemical/structural modifications and residual stress in the substrate surface layer may play important roles in film growth/structures/properties and therefore in the mechanisms of the evolution of OR with plasma treatment.

Dynamic coercivity and adjacent track erasure in longitudinal magnetic recording media

Adjacent track erasure (ATE) is investigated for longitudinal recording media with different remanent magnetization and thickness product. The dynamic switching field Hcrp for moment fraction p is found to be a good indicator of signal erasure due to ATE. Given the head fringing field, Hcrp curves can be used to predict ATE for long exposures. Conversely, from the signal degradation of neighboring tracks due to ATE, the average fringing fields at a particular distance from the write head can be estimated.

Understanding and optimizing laminated recording media (invited)

We find subnanometer spacer layers are sufficient to decorrelate the transition noise of the layers in laminated longitudinal recording media, thus improving the media signal-to-noise ratio. These results are surprising given that the layers remain structurally correlated due to their epitaxial growth, and therefore the noise in the layers may be expected to be correlated as well. Experimental results suggest that the reduced transition noise is produced by a slight shift between the transition locations in the layers. This shift is created by the recording head and allows the transitions to sample a different microstructure, thus decorrelating the transition noise.

Thermal stability improvement for longitudinal magnetic recording media

This paper reports and discusses the effects of M/sub r/t cancellation and bottom/top magnetic layer thickness ratio on thermal stability and recording characteristics of low-noise synthetic antiferromagnetic (SAF) longitudinal recording media. It is shown that by proper design and process, SAF media with low M/sub r/t cancellation can deliver excellent overall recording performance with acceptable thermal stability. We present a unique approach to significantly improve the thermal stability of SAF media with low M/sub r/t cancellation by adjusting the bottom/top magnetic layer thickness ratio. Increasing the bottom/top magnetic layer thickness ratio significantly improves amplitude decay rate and media coercivity temperature dependence with little sacrifice in recording performance.

The spatial structure of media noise

The spatial structure of dc and transition noise in perpendicular and longitudinal recording media is studied. Experimental techniques for local dc noise and transition noise analysis are described. It is demonstrated that the dc and transition noise is deterministic and repeatable at given medium location. The transition noise is correlated with the dc noise; the local fluctuations of the dc saturated magnetization are becoming enhanced when a transition is written at this location. This enhanced local dc noise is explained by local medium demagnetization which is strongest at the transition, it determines the transition noise magnitude.

Investigations on annealed Ni–P in Al–Mg/Ni–P substrates as soft underlayer for perpendicular recording media

The amorphous Ni–P layer in the Al–Mg substrates of longitudinal recording media have been annealed to form soft magnetic underlayer for perpendicular recording media. After annealing at about 300°C for 10min, the Ni–P layer crystallized and was found to have Ni3P and Ni phases. The annealed samples were found to have soft magnetic properties. As the annealing temperature was increased, the samples showed a larger coercivity. The optical surface analyzer (OSA) results indicated that crystallized Ni–P could show lower noise than sputtered Ni-Fe thin films.

Thermal stability of magnetic properties in ternary and quaternary Co-based alloy thin-film media

Co-based alloy thin films for longitudinal recording media are analysed. The magnetic stability of such media is studied with measurements of magnetization decay and of coercivity variation with the applied field sweep rate. The analysed films have different composition (ternary and quaternary Co alloy) and different thickness. Consequently they show different stabilities. Besides, the magnetization switching of the various films is diversified, as indicated by the rotational hysteresis analysis. The impact of such evolution on the thermal stability of the magnetic properties of the thin-film media is underlined.

Temperature Dependence of the Magnetization Reversal of Thin-Film Longitudinal Magnetic Recording Media

As longitudinal magnetic recording media approach the superparamagnetic limit, temperature-dependent effects are becoming ever more important. This work reports an unexpected temperature dependence for the Sharrock stability parameter S typically given as K/sub u/V/k/sub B/T, where K/sub u/ is the uniaxial anisotropy, V the switching volume, k/sub B/ is Boltzmann's constant, and T the temperature. Temperature-dependent vibrating sample magnetometer measurements were made of the saturation and remanent magnetization M/sub s/ and M/sub r/, remanent coercivity H/sub cr/, and K/sub u/. The Sharrock equation was used to calculate S, and the time-independent switching field H/sub o/ of representative longitudinal recording media. Instead of the product Sk/sub B/T decreasing proportionally to K/sub u/ or H/sub o/ with increasing temperature as initially expected, we find Sk/sub B/T decreases at approximately half this rate.

Influence of Magnetic Cluster-Size Distribution on Signal-to-Noise Ratio in Perpendicular Magnetic Recording Media

Perpendicular recording media noise is investigated with a microstructure model based upon magnetic clustering for irregular magnetization transitions. This model uses cylinders to account for the distribution of cluster diameters. Quantitative comparisons between experiments and calculations indicate that the cluster-size distribution of media can be estimated from the read/write properties. Estimates show that the cluster-size deviation of perpendicular recording media is somewhat larger than that of longitudinal recording media. Because calculations show that transition jitter depends strongly on the cluster-size distribution, reduction of the cluster-size deviation, as well as reducing the average cluster size, can significantly improve the signal-to-noise ratio of perpendicular recording media.

The Role of Dipolar Interactions in AFC-Media

We have experimentally studied the role of dipolar interactions in antiferromagnetically coupled (AFC) recording media. In addition to the antiferromagnetic interlayer exchange coupling, recorded transitions lead to dipolar interactions between the two magnetic layers, which also favor an antiparallel alignment of the magnetization for longitudinal recording media. For low recording densities, we find a strong increase of the bias field that is acting upon the lower layer with increasing transition density. At an intermediate density, this bias field exhibits a maximum, gaining about 300 Oe over the DC case and slowly decreases upon further increase of the recording density. Our experimental results are in good agreement with model calculations that take both, the dipolar inter- as well as intralayer contributions into account.

Micromagnetic modelling of SANS in longitudinal recording media

A micromagnetic calculation of the magnetic structure factor is performed for a model sample of longitudinal medium to investigate the dependence of the scattering intensity profile I m( q) on the intrinsic parameters of the magnetocrystalline anisotropy and intergranular exchange coupling. It is demonstrated that changes in the ratio of the external to the anisotropy field H/ H k lead to significant differences in the profile. The formation of domains, owing to increased coupling, can also change the period and the amplitude of the profile oscillations.

Plasmon emission studies on nano-scale particulate recording materials

The optical field emitted by radiatively decaying plasmons is studied for the case when the surface supporting the plasma excitations is that of a ferromagnetic metal rather than that of one of the commonly studied noble metals. Comparison is made between the phenomenon observed for plasmons travelling freely on a continuous conducting surface and those localized around nano-scale particles on an insulating substrate or embedded in a dielectric host. In the first case, structure mediated optical excitation on a nickel grating produces plasmons that travel away from their source becoming subject to a variety of decay mechanisms including radiative emission. Similarly, localized plasmons created in a cobalt longitudinal recording medium composed of particles having near mono-disperse magnetic volumes ≈7 × 10−25 m3 are likewise observed to re-emit optical radiation in a narrow beam at high non-specular angles consistent with radiative plasmon decay. Moreover, the plasmon mode structure supported by the particles, and which is reflected in the angular structure of the emitted radiation, appears indicative of the physical shape of the particles. The possible significance of plasmon behaviour in the development of ultra-high density recording media is highlighted.

Micromagnetic torque studies of the intergranular exchange coupling and magnetocrystalline anisotropy in longitudinal recording media

Effects of the anisotropy and intergranular interaction in longitudinal media have been studied experimentally using micromagnetic simulation of torque. Two samples with different noise characteristics were compared in terms of the mean anisotropy field H k , H k distribution and exchange coupling stiffness C ∗ . Simulation results showed very good agreement with the results previously produced with other techniques, including TEM, FMR, Vector VSM, Delta-M and Delta-T.

Effect of transverse magnetic field on thin-film magneto impedance and application to magnetic recording

Abstract A potential of using the magnetoimpedance thin-film element as a read head in longitudinal recording medium is demonstrated. For this purpose, cross-anisotropy in magnetic layers plays an important role to achieve high sensitivity with respect to transverse external magnetic fields typical in longitudinal recording medium. A sputtered CoFeB/Cu/CoFeB film of 1.5 μm thick exhibits a sensitivity of about 10%/Oe for transverse fields in the frequency range of 30–40 MHz.

磁気クラスタ径分布を考慮した垂直磁気記録媒体の磁化モデル

This paper provides a microstructure model for perpendicular recording media based upon magnetic clustering, taking into account the size variation. We discussed comparisons between experiments and calculations based on the model for the saturation tendency of the experimental medium noise and confirmed validity of this model. With this model, both mean cluster size and standard deviation can be estimated from experimental read/write characteristics. The estimation shows that the cluster size deviation of current perpendicular recording media is somewhat larger than that of longitudinal recording media. The significance of the cluster size variation is pointed out.

Effects of magnetic states in recording media on moisture adsorption and surface hydrophobicity

In magnetic data recording, humidity is the most dangerous environmental factor that affects the stability of storage media carriers. It will lead to the magnetic media deterioration and also adversely affect the tribological performance at the head–disk interface. At every data bit of recording, the transition area in a longitudinal recording media has a near-perpendicular magnetic direction, either at north or south magnetic polarity. This investigation showed that a perpendicularly magnetized floppy disk at the south polarity was able to retain and adsorb water molecules into its coating media. The north polarity was found to have shown the exact opposite effect. As a result of this phenomenon, the physical surface condition and the surface hydrophobicity of a magnetized floppy disk has been affected. The interaction with moisture from the south-polarized disk could become ideal sites for fungus growth, which eventually affects the carrier's stability and its tribological performance.

High-density longitudinal recording media with CrMoB underlayer

The structural, magnetic, and recording properties of longitudinal recording media with CrMoB underlayer were studied and compared to those with CrMo underlayer. Media with CrMoB underlayer have smaller grain size, better grain segregation, lower coercivity, and better recording performance than media with CrMo underlayer.

Transition and DC noise characteristics of longitudinal oriented media

Transition and DC noise characteristics of longitudinal recording media were studied as a function of orientation ratio (OR). With increasing OR, a substantial decrease of DC noise is observed against the gradually increasing transition noise, resulting in the reduced media total noise. The increase in the media transition noise with OR is attributed to the increase in the cross-track correlation length s. The experimentally estimated s for the media with OR=1.8 is significantly larger than that of the media with OR=1.25, possibly resulting from the difference in magnetostatically coupled Co grains aligned to the track direction. For high-density low M/sub r/t designs, reducing DC noise by increasing OR, in spite of an increase in transition noise, becomes an effective means to increasing areal density.