Ultrahigh-density storage media prepared by artificially assisted self-assembling methods

Two types of recording media possessing nanodot structures were investigated. The media were prepared by an artificially assisted self-assembling (AASA) method, which includes simple nanopatterning using a nanoimprint and fine nanopatterning using self-assembling organic molecules. One type of recording media is circumferential magnetic patterned media prepared on a 2.5-in.-diam glass plate. A Ni master disk possessing spiral patterns with 60-250 nm width lands and a 400 nm width groove was pressed to a resist film on a CoCrPt film to transfer the spiral patterns. A diblock copolymer solution was cast into the obtained grooves, and then annealed to prepare self-assembling dot structures aligned along the grooves. According to the dot patterns, the lower magnetic films were patterned by ion milling to yield patterned media with 40 nm diameter. We have also prepared FePt dot media with high magnetic anisotropy for near-field and magnetic-field hybrid recording aiming at more than 1 Tbin.2 density. A Ni stamp disk with aligned dot structures was also prepared by the AASA method to produce patterned media at the lowest cost. The other type of media was organic patterned media for X-Y type near-field optical storage. Bulky dye molecules were evaporated in vacuum to produce self-assembling amorphous nanodots. The dots were arranged by the AASA method, i.e., according to the polymethylmethacrylate film hole arrays or chemically patterned surface.     

Micro magnetic structure of magnetic clusters in CoCrTaPtB recording media

Micro magnetic structure in CoCrTaPtB recording media with H_c>3 kOe was studied by magnetic force microscope and LLG simulation. Two types of the characteristic magnetic structure were observed. One is the convergent-type magnetic structure, which is observed as localized magnetic cluster on bit. The other is the vortex structure, which is responsible for the recording bit peroration. These micro magnetic structures cause the medium noise in high-density recording and must be suppressed by adjusting coercive force H_c and inter-granular interaction to explore high density recording media.     

Small-angle polarized neutron scattering study of spherical Fe16N2 nano-particles for magnetic recording tape

We have performed small-angle polarized neutron scattering experiments of spherical Fe₁₆N₂ nano-particles, which are potential candidate materials for high density magnetic recording tape. The results were analyzed based on a core-shell model, and we evaluated the magnetic structure of the particles. The correlation between the magnetic structure and magnetic stability of the particles were discussed in terms of high density recordings.     

Influence of the crystal lattice modifications with doping ions on the reptation of magnetic recording particles

Magnetic recording particles are frequently subjected to ionic substitutions in order to improve their magnetic properties for use in recording media. In fine particle systems, the reptation of the magnetization cycles originates in the interaction between the magnetic moments of each particle and the microscopic configuration of the magnetization in the assembly. Therefore, it should be related to the magnetic order in the crystal structure of the particles. In this work the effect of the aforesaid ionic substitutions on the reptation is investigated, which, in general, is increased by the doping as a consequence of the modification of the magnetic order induced by the presence of the substituting ions.     

Heat Assisted Magnetic Recording with Matching Media and Recording Head Field

The dynamic performance of heat assisted magnetic recording （HAMR） on different media is investigated. Signal and signal-to-noise ratio enhancement are achieved in high coereivity perpendicular media with the aid of laser heating. Linear recording density is increased while saturation write current is lowered. Trailing field partial erasure is observed in lower coercivity media with a ring head, which causes signal reduction with increasing write current or application of a laser. Precautions should be taken against partial erasure in overall recording system optimization of HAMR in order to achieve ultrahigh recording density.     

Thermally assisted magnetic recording with bit-patterned media to achieve areal recording density beyond 5 Tb/in

Thermally assisted magnetic recording (TAR) with bit-patterned media was investigated by micromagnetic simulation. The media were assumed to be FePt layers. The effective head-field margin as well as the increase in temperature margin and down-track shift margin was investigated. Conditions of the head and medium that lead to a recording density beyond 5 Tb/in² were proposed.     

Theory of longitudinal digital magnetic recording on thick media

A theory of the digital magnetic recording process has been produced which facilitates the prediction of the recording properties of thick particulate and other media. It allows studies to be made of recorded patterns through the depths of media and the influence of these on overall recording properties. The theory is capable of dealing with particulate, thin-film and multilayer media.     

Giant magnetic anisotropy in tetragonal FeCo alloys

In order to further increase the recording density in hard disk drives, new media materials are required. Two essential parameters of future recording media are a large uniaxial magnetic anisotropy energy (MAE) K(u) and a large saturation magnetization M(s). Based on first-principles theory, we predict that very specific structural distortions of FeCo alloys possess these desired properties. The discovered alloy has a saturation magnetization that is about 50% larger than that of FePt--a compound that has received considerable attention lately-with a uniaxial MAE that can easily be tailored reaching a maximum value that is 50% larger than that of FePt.     

Correlations between the orientation of magnetic recording media determined by Mössbauer Spectroscopy and magnetic methods

The orientation of the easy magnetization axis of magnetic particles is a key parameter of the recording performance of magnetic recording media. Usually the orientation is measured by magnetic methods, but the applicability of the Mössbauer Spectroscopy has also been shown in the past. We show up and discuss the correlations between the results obtained by magnetic and Mössbauer measurements for the example of several magnetic tapes. We demonstrate that by a combination of both methods we are even able to estimate the mean canting angles distribution width of the easy axis of magnetization.     

Extensions of perpendicular recording

Gains in storage density in magnetic recording have fundamentally been achieved by scaling—reduced geometrical dimensions under the assumption that the recording physics does not change if all dimensions are scaled appropriately. It is becoming clear that evidence of the breakdown of scaling is now seen. We will here discuss ways to break the constraints on magnetic recording set by scaling. In particular, we will discuss energy-assisted recording, domain-wall-assisted recording, and bit-patterned media, with some emphasis on recording system considerations.     

Optical and Thermal Simulator for Laser-assisted Magnetic Recording

“Laser-assisted magnetic recording”, in which a recording media is heated by a laser beam while writing data, is attracting attention as a technology that enables a recording density of 1 Tb/in.². There exists another technology for media in which the recording layer is constructed with many small projections that enable high magnetic coercivity. This is called “patterned media”. For developing hard disk drives using these methods, we developed a simulator that analyzes the optical intensity distribution from the optical head for laser-assisted recording and the temperature profile on the patterned media. The simulator calculates the optical model using the finite-difference time-domain (FDTD) method. The thermal analysis of the three-dimensional model allows fast calculations using the alternating direction implicit (ADI) method. The heat source distribution data for thermal analysis is calculated in order to use the results of optical analysis. The optical and thermal analyses of the laser-assisted recording model were investigated with the simulator.     

Magnetic properties of Fe nanoparticles trapped at the tips of the aligned carbon nanotubes

The magnetic properties of iron nanoparticles partially encapsulated at the tips of aligned carbon nanotubes have been studied. The carbon nanotube wall not only protects the metallic particles from oxidization, but also reduces the inter-particle dipolar interaction by non-magnetic separation. Magnetic characterizations performed in the temperature range of 5–350 K with magnetic field up to 3 T show that these carbon-nanotube-supported iron particles are good candidates for high-density magnetic recording media.     

Atomic physics at the planned new RIKEN facility

Combining Mössbauer spectroscopy with magnetic property measurement, we have studied Fe-N and (Fe, Ni)-N powders for magnetic recording. The typical particles of the core (α-Fe)/shell (γ′-Fe₄N) structure have been successfully prepared. All the products are stabilized in a multi-organic solution. It has been found that the coercivity can be changed from 300 to 800 Oe by adjusting the shape of the particles. The special saturation magnetization of the particles can be adjusted from 120 to 180emu/g and their chemical stability is improved by substituting nickel for iron in γ′-Fe₄N. Following experiments for corrosion resistance, it is expected that (Fe, Ni)-N and the core/shell particles will be applied as recording media in the near future.     

Excellent magnetic properties of fullerene encapsulated ferromagnetic nanoclusters

Ferromagnetic nanoclusters are very useful for a magnetic recording. However, application of ferromagnetic nanoclusters is limited due to air-oxidation. One way to solve air-oxidation is to encapsulate ferromagnetic nanoclusters with inert materials such as carbon when they are produced. This allows us to keep excellent magnetic properties for a long time. In this work, we report a very simple synthetic method of fullerene (i.e., onions and nanotubes) encapsulated ferromagnetic nickel and cobalt nanoclusters by thermally decomposing metallocene vapors with a resistive heater. Protection from air-oxidation was tested by annealing encapsulated ferromagnetic nanoclusters in air up to ∼180°C for half a day and then, recording XRD patterns. No oxide peaks were observed in the XRD patterns, indicating that oxidation protection via fullerene encapsulation is very good. Magnetic property measurement showed that both fullerene encapsulated nickel and cobalt nanoclusters possessed excellent magnetic properties.     

Addendum

The magnetic properties of ferrimagnetic fine particles in rocks have many parallels with those of spin glasses, magnetic recording media, ferrofluids and biomagnetic systems. The present brief review touches on some recent developments in rock magnetism that may be of interest to workers in these other fields.     

Uniform magnetic properties for an ultrahigh-density lattice of noninteracting co nanostructures

We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in2 (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.     

Drive-based recording analyses at >800 Gfc/in using shingled recording

Since the introduction of perpendicular recording, conventional perpendicular scaling has enabled the hard disk drive industry to deliver products ranging from ∼130 to well over 500 Gb/in² in a little over 4 years. The incredible areal density growth spurt enabled by perpendicular recording is now endangered by an inability to effectively balance writeability with erasure effects at the system level. Shingled magnetic recording (SMR) offers an effective means to continue perpendicular areal density growth using conventional heads and tuned media designs. The use of specially designed edge-write head structures (also known as ‘corner writers’) should further increase the AD gain potential for shingled recording. In this paper, we will demonstrate the drive-based recording performance characteristics of a shingled recording system at areal densities in excess of 800 Gb/in² using a conventional head.Using a production drive base, developmental heads/media and a number of sophisticated analytical routines, we have studied the recording performance of a shingled magnetic recording subsystem. Our observations confirm excellent writeability in excess of 400 ktpi and a perpendicular system with acceptable noise balance, especially at extreme ID and OD skews where the benefits of SMR are quite pronounced. We believe that this demonstration illustrates that SMR is not only capable of productization, but is likely the path of least resistance toward production drive areal density closer to 1 Tb/in² and beyond.     

Visible Infra-red Double Extinction Measurements in Densely Laden Media,New Progress

This paper describes new progress obtained with an optical technique called V.I.D.E. (Visible Infra-red Double Extinction) which simultaneously measures mean particle size in the range of 10–120 μm and mean number density in densely laden media (up to 0.1% volume fraction). The underlying theory, taking account of multiple light scattering, is recalled. Simultaneous size and concentration measurements are obtained by simultaneously recording transmittances of the medium at two well chosen wavelengths. Experimental results for suspensions of glass particles in air, are described and discussed. The size of particles given by the technique agrees with that given by optical microscopy and Malvern diffractometry. The V.I.D.E. technique is shown to be very suitable to investigate dense media whose optical thickness is up to nine and for which other techniques fail.     

Carbon-coated Non-magnetic Iron Oxide Particles for the Substrate of Multi-layered Magnetic Recording Media

Non-magnetic particles with finer size (less than 200 nm), higher dispersibility, higher blackness and lower electrical resistance are required to produce better multi-layered magnetic tape media which have non-magnetic substrate using non-magnetic sub-layer materials. A special method to prepare acicular hematite particles, whose cross-sectional diameter is about 150 nm, coated with carbon black using a surface modification agent is reported in this paper. Transmission electron microscopy photographs of carbon-coated hematite particles indicate that all of the carbon black is firmly bound to the surface in a distinct layer. The thickness of carbon-coating layer was about 1 to 2 nm if 15% by weight of carbon black is coated onto the particle surface.Non-magnetic substrates for multi-layered magnetic recording media prepared using the carbon-coated particles exhibit improvements in both light transparency and electrical resistance. A decrease in transparency of about 30% as well as a reduction in the electrical resistance of about 1.5 orders of magnitude relative to conventionally prepared substrates was achieved. The surface smoothness and the viscosity were also improved because the dispersibility of these particles in non-magnetic lacquer became better than that of the physical mixture of uncoated hematite particles and carbon black.     

Self-organisation,orientation and magnetic properties of FePt nanoparticle arrays

Self-organised magnetic arrays (SOMA) of high anisotropy particles are a promising candidate for ultra-high-density recording media. In principle SOMA media have the capability of storing 1 bit per particle, leading to possible reecording densities in excess of 10 Tbit/sq in. In this paper we consider two major aspects of SOMA media, namely the self-organisation process itself and the physics of the particle orientation process.