Perpendicular Magnetic Storage Research Articles

Thickness Dependence of Magnetic Switching Dynamics of Barium-Ferrite as A High-Density Perpendicular Magnetic Storage Media

Micromagnetic study of material thickness dependence of Barium-ferrite nano-dot magnetization dynamics has been performed. The used materials characteristics in this research represent the properties of Barium-ferrite. Barium-ferrite was modeled as a nano-dot with a surface area of 50 50 nm2 and its thickness varies from 5 nm to 100 nm. This nano-dot was simulated using micromagnetic simulator software by solving Landau-Lifshitz-Gilbert equation. According to this study, obtained that the Barium-ferrite nano-dot has excellent thermal stability. Magnetization rate of this nano-dot decreases exponentially with the increase of thickness. The fastest magnetization rate observed in 5 nm of nano-dot thickness, meanwhile 45 nm for the slowest rate. Magnetization reversal mode of this Barium-ferrite nano-dot is dominated by domain wall nucleation and propagation. During the propagation of the domain wall, the exchange interaction becomes the main aspect compared to the other contributed energies.

LDPC product coding scheme with extrinsic information for bit patterned media recoding

Since the density limit of the current perpendicular magnetic storage system will soon be reached, bit patterned media recording (BPMR) is a promising candidate for the next generation storage system to achieve an areal density beyond 1 Tb/in2. Each recording bit is stored in a fabricated magnetic island and the space between the magnetic islands is nonmagnetic in BPMR. To approach recording densities of 1 Tb/in2, the spacing of the magnetic islands must be less than 25 nm. Consequently, severe inter-symbol interference (ISI) and inter-track interference (ITI) occur. ITI and ISI degrade the performance of BPMR. In this paper, we propose a low-density parity check (LDPC) product coding scheme that exploits extrinsic information for BPMR. This scheme shows an improved bit error rate performance compared to that in which one LDPC code is used.

Micro-structural origin of elongation in swift heavy ion irradiated Ni nanoparticles: A combined EXAFS and DFT study

Aiming for perpendicular magnetic storage usage, shape anisotropy is introduced in Ni nanoparticles (NPs) embedded inside a thin SiO2 matrix using swift heavy ion irradiation (SHI). Systematic increase in NPs' aspect ratio along the direction of incident SHI beam is observed up to 5 × 1013 ions/cm2 (5e13) fluence from grazing incidence small angle X-ray scattering measurements. Strikingly, at higher fluences the major dimension (along SHI beam) got reduced. This observation is totally intriguing as usually particle elongation increases with applied fluence. To understand this anomaly, as a first step, we have performed a combined near and far edge X-ray absorption spectroscopy (XANES and EXAFS) analysis. This shows irradiated Ni NPs sustain their metallic phase even with increased structural disorder and reduced atomic co-ordination. However an atypical reduction in local structural anisotropy beyond 5e13 fluence is observed from angle dependent EXAFS: following the same trend as NP elongation. To have a better insight, the role of the electronic spin of individual atoms in controlling particle shape is investigated. Using the lattice temperature profiles derived from thermal spike model, we have carried out ab initio molecular dynamics (MD) simulations to understand the structural distortion at higher temperatures. The experimentally observed structural and shape anisotropy in the irradiated NPs is only realized when spin polarization contributions were considered in our calculations. From the pair correlation function and atom-wise spin density plots, we conclude that presence of spin affects the second co-ordination shell and controls the atomic arrangements in such a manner that elongated structures are preferred in the irradiated system at intermediate fluence (i.e. 5e13). Further increase in MD temperature to 6000 K (corresponding to 1 × 1014 ions/cm2 fluence) results in disordered spin alignment and melting of moderately weak spin polarized Ni NPs: thus violating conventional trend of increasing particle elongation w.r.t SHI fluence.

Synthesis of FePt Nanocubes Using Mo(Co)<sub>6</sub> as a Reducing Agent and their Magnetic Properties

FePt thin films with perpendicularc-axis orientation have potential for application as magnetic media for data storage, In order to be used as perpendicular magnetic storage media,The chemically synthesized cubic FePt nanoparticles is easier to assembed oriented nanoarray, especially the cubic FePt nanoparticles with shape anisotropy is expected to trigger magnetic anisotropy.In this study we provide a simple method to synthesize single crystalline FePt nanoparticles with cubic shapes.The key factor to formation of cubic morphology is using Mo (Co)6as a reducing agent. As-synthesized FePt nanocubes with size that are close to 7-10nm The self-assembly FePt nanocubes are chemically disordered with face centre cubic (fcc) structure where as after annealing these particles changed to face centre tetragonal (fct) ordered structure. The phase analysis, structure, and magnetic properties were determined by X-ray diffraction (XRD), High resolution transmission electron microscope (HRTEM), Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) techniques.

Optimized Sol–Gel Chemical Route Using Vacuum Suction for Fabrication of Densely Packed NiFe2O4 Nanowires

Highly ordered nanowire arrays of NiFe2O4 spinel with a high aspect ratio were fabricated by sol–gel method associated with anodic aluminum oxide (AAO) templates. The preparation of nanowires was carried out by sol–gel method using nickel nitrate, ferric nitrate and citric acid. The molar proportion of nickel nitrate to ferric nitrate and citric acid was 1:2:3. The suction with 0.1 mbar vacuum was used to draw the gel into the AAO nanochannels. The results showed that the lowest annealing temperature is around 600 °C to obtain the single-phase nanostructured NiFe2O4. The NiFe2O4 nanowires were also uniform and parallel. TEM pictures determined the diameter size of the nanowires of about 100 nm. The magnetic results also showed that the wires have an easy axis of magnetization along their length and they are fully saturated in a field of 7 kOe. It seems that this material could be a good candidate for high perpendicular magnetic storage devices.

Looking back on Censtor and PMRC

Prehistory of Censtor Corporation was described. A ten-year study of Nature’s neurological ways and means of processing information led the author to the research of computer-based technology, in particular, perpendicular magnetic storage technology. With funding Censtor Corporation was founded with Dr. Robert Noyce as Chairman of the board. Censtor Corporation created novel technology on perpendicular magnetic recording with the unique head in contact with the medium.

Demonstration of ultra-high-resolution MFM images using Co 90Fe 10-coated CNT probes

We demonstrate ultra-high-resolution magnetic force microscopy images of perpendicular magnetic storage media using carbon nanotube probes coated by ferromagnetic Co 90Fe 10 films (20, 30, 40, and 50 nm). By optimizing ferromagnetic film thickness (effective tip diameter), we obtained best magnetic domain image with an 40 nm-Co 90Fe 10-coated tip (50 nm tip diameter) about a lateral detect density of 1200 k flux per inch on perpendicular magnetic storage medium, one of the highest resolutions in MFM imaging reported for this material system and structure. The observed dependence of tip dimension on signal contrast and image resolution was successfully explained by a theoretical analysis indicating that the signal contrast, along with the physical probe-tip dimension, should be taken into account to design magnetic probes tips for high-resolution magnetic force microscopy.

シリンダ状媒体対応傾斜パッドスライダの浮上安定性に関する検討

We studied a magnetic recording head for a cylindrical perpendicular magnetic storage system with regard to its stability when a slider is flying over a rotating 1-inch-diameter cylindrical medium. We also designed an inclined-pad-type slider for the cylindrical magnetic storage system. This slider has an inclined pad formed on its leading edge and a trailing pad formed on its trailing edge, to generate an air-bearing force. The inclined pad is protruded in the thickness direction of the slider relative to the trailing pad. A waveform of an acoustic-emission (AE) sensor and an envelope of a reproduced signal were obtained from the combination of the cylindrical perpendicular medium and fabricated this slider. These waveforms did not show any large pulse and thermal asperity associated with contact. These results confirm the flying stability of the inclined-pad-type slider.

A magnetic force microscope using CoFe-coated carbon nanotube probes

Ferromagnetic-film-coated carbon nanotube (CNT) probes were employed in a magneticforce microscope (MFM) observation. We succeeded in making a uniform ferromagneticfilm on the CNT probes by improving the coating process and selecting materials. Theperformance of the CoFe-coated CNT probe was evaluated in ultra-high-density perpendicularmagnetic storage media with densities from 600 to 1100 k flux changes per inch (FCI). Themagnetic domain structure of the magnetic storage media was clearly observed up to1100 kFCI. The ultimate lateral resolution of the newly developed MFM probes is down toabout 10 nm, which exceeds the bit length of a magnetic recording with a density ofTbit inch−2.

Switching behavior of single nanowires inside dense nickel nanowire arrays

Summary form only given. The suitability of nickel nanowire arrays for perpendicular magnetic storage media with areal densities beyond the superparamagnetic limit (>70 Gbit/in/sup 2/) is analyzed in this paper. Highly ordered alumina pore channel arrays are used as templates for the fabrication of magnetic nanowire arrays with a periodicity of 65 (180 Gbit/in/sup 2/) and 100 nm (75 Gbit/in/sup 2/) and pore diameters between 30 and 55 nm. A nearly perfect hexagonal arrangement for the magnetic columns occurs only inside very narrow process windows for periodic distances of 65, 100 and 500 nm, and - in contrast to most publications in this field - a degree of pore filling of almost 100% was achieved. Here, we will focus on nickel as a filling material due to its negligible magneto-crystalline anisotropy, so that the interactions between the anisotropy resulting from the nanowire shape and the stray field inside the magnetic arrays can be studied in detail. The small magnetic moment and the large exchange lengths (/spl lambda//sub ex/= (A/2K/sub 1/)/sup 05/ /spl ap/ 20 nm) of nickel leads to low dipole interactions between nanowires and a huge anisotropy along the column axis which enables nickel as a suitable material for pattern perpendicular magnetic media.