Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.

/pdf/monodisperse-fept-nanoparticles-and-ferromagnetic-fept-12j5xql32h.pdf

Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

4.1. Nanomachining with Scanning Probes 1831 4.2. Soft Lithography 1832 4.3. Embossing with Rigid Masters 1835 4.4. Near-Field Phase-Shifting Photolithography 1835 4.5. Topographically Directed Photolithography 1837 4.6. Topographically Directed Etching 1837 4.7. Lithography with Neutral Metastable Atoms 1838 4.8. Approaches to Size Reduction 1839 5. Techniques for Making Regular or Simple Patterns 1839

https://www.engr.colostate.edu/ECE581/fall07/xia%20chem%20rev%2099.pdf

Unconventional Methods for Fabricating and Patterning Nanostructures.

The ability to assemble nanoscopic components into larger structures and materials depends crucially on the ability to understand in quantitative detail and subsequently "engineer" the interparticle interactions. This Review provides a critical examination of the various interparticle forces (van der Waals, electrostatic, magnetic, molecular, and entropic) that can be used in nanoscale self-assembly. For each type of interaction, the magnitude and the length scale are discussed, as well as the scaling with particle size and interparticle distance. In all cases, the discussion emphasizes characteristics unique to the nanoscale. These theoretical considerations are accompanied by examples of recent experimental systems, in which specific interaction types were used to drive nanoscopic self-assembly. Overall, this Review aims to provide a comprehensive yet easily accessible resource of nanoscale-specific interparticle forces that can be implemented in models or simulations of self-assembly processes at this scale.

/pdf/nanoscale-forces-and-their-uses-in-self-assembly-3s798gq2hq.pdf

Nanoscale Forces and Their Uses in Self‐Assembly

High K/sub u/, uniaxial magnetocrystalline anisotropy, materials are generally attractive for ultrahigh density magnetic recording applications as they allow smaller, thermally stable media grains. Prominent candidates are rare-earth transition metals (Co/sub 5/Sm,...), and tetragonal intermetallic compounds (L1/sub 0/ phases FePt, CoPtY,...), which have 20-40 times higher K/sub u/ than today's hexagonal Co-alloy based media. This allows for about 3 times smaller grain diameters, D, and a potential 10-fold areal density increase (/spl prop/1/D/sup 2/), well beyond the currently projected 40-100 Gbits/in/sup 2/ mark, Realization of such densities will depend on a large number of factors, not all related to solving media microstructure problems, In particular it is at present not known how to record into such media, which may require write fields in the order of 10-100 kOe. Despite this unsolved problem, there is considerable interest in high Ku alternative media, both for longitudinal and perpendicular recording. Activities in this area will be reviewed and data on sputtered and evaporated thin FePt films, with coercivities exceeding 10000 Oe will be presented.

High K/sub u/ materials approach to 100 Gbits/in/sup 2/

▪ Abstract Areal density progress in magnetic recording is largely determined by the ability to fabricate low-noise, granular thin lm media with sufficient stability against thermal agitation to warrant long-term data storage. A key requirement is a medium microstructure with small, magnetically isolated grains to establish optimal macro- and micro-magnetic properties. A lower bound for the minimal average grain diameter, compatible with thermal stability, is imposed by the write field capability of the recording head. It is 10–12 nm assuming maximal writeable coercivities of 400 kA/m (5000 Oe). These are already achieved in today's state-of-the-art CoCr-based thin lm alloy media, leaving little room for further improvements and density gains based on continued grain size reduction. A threefold reduction in grain diameter, however, translating into a tenfold increase in areal density is theoretically possible if write field constraints can be overcome, allowing utilization of magnetically harder alloys. T...

Extremely High-Density Longitudinal Magnetic Recording Media

Thermally activated magnetization reversal processes become manifest in the dependence of the remanent coercivity on the time during which a magnetic field is applied opposite to the initial magnetization direction. They have important consequences for the long term stability and short time writeability of future high density recording media. In this paper, we report on a new experiment using a contact write/read tester to study the time dependence of the remanent coercivity over more than 10 orders of magnitude (from 6 ns to >60 s). Remanence coercivity and signal decay measurements of a CoPtCr recording medium with 5.5 nm thickness are presented.

Dynamic coercivity measurements in thin film recording media using a contact write/read tester

This article reports on the properties of the media prepared on glass substrates which were used in IBM’s 10 Gbit/in.2 demonstration. In order to support a linear density of 315 kbpi and a track density of 33 ktpi, the remanant coercivity Hcr and remanant moment thickness product Mrt of the magnetic layer were 3450 Oe and 0.37 memu/cm2, respectively. The media used a NiAl seed layer, a CrV underlayer, a Co alloy magnetic layer, and a carbon overcoat protection layer. The magnetic film had a grain size of 12 nm as observed by transmission electron microscopy. The preferred orientation (PO) of the magnetic layer was (1010). This PO enables one to sustain high coercivities at low values of Mrt. It is observed that the c-axis in-plane texture of the magnetic layer is critical to achieve a low noise medium. Using a focused-ion-beam (FIB) trimmed giant magnetoresistance head and conventional partial response maximum likelihood channel, the on-track-error rates were measured at the 10−10 level.

10 Gbit/in.2 longitudinal media on a glass substrate (invited)

Variations of in-plane magnetic properties are observed in most commercial thin-film media. Magnetic anisotropies of varied origins give rise to preferred orientations quantified by the term orientation ratio (OR). Several mechanisms for in-plane anisotropy have been proposed. Oblique angle of incidence effects from vacuum deposition can lead to the formation of tilted columnar or curved grains resulting in a strong shape anisotropy. The most effort has been involved in understanding 'scratch' anisotropy in textured media where OR develops along texture lines. Mechanisms involving stress, preferred orientation, circumferential alignment of grain c-axes, and radial out of plane c-axis effects have been proposed. Recent experiments and calculations suggest that isotropic media, (OR=1), are superior in signal to media noise, S/N/sub m/, at high recording densities. It is thus important to understand the origin of in-plane anisotropies in thin-film media so as to control them for possible recording property improvements or eliminate them altogether to achieve an isotropic media.

In-plane anisotropy in thin-film media: physical origins of orientation ratio

We have successfully demonstrated magnetic recording at an areal density of 5 Gb/in/sup 2/ and a data rate of 10 MB/s using narrow track dual element heads with conventional AMR sensors and low noise Co alloy thin film disks. In this work, the target densities of 240 K bpi/spl times/21 K tpi were achieved by a combination of narrow track and low-flying technologies. The write and read head trackwidths were reduced to submicron dimensions, with high moment pole-tips to maintain good writability. At the same time, magnetic spacing was substantially reduced by using low-flying airbearing surface designs. Finally, significant signal-to-noise improvements were attained with the development of high sensitivity AMR read heads and very low noise thin film media. Recording tests showed satisfactory writability in terms of overwrite and hard-transitions from the submicron width write heads. Readback yielded symmetrical signals close to 1 mV//spl mu/m and rolloff measurements yielded 50% densities as high as 7000 fc/mm. Track profile and microprofile measurements showed write and read trackwidths to be around 1.2 /spl mu/m and 0.7 /spl mu/m respectively, with tight side-writing and sidereading characteristics. An overall assessment of the parametric recording results suggested an areal density feasibility of around 5 Gb/in2. This projection was confirmed by error rate testing at 10 MB/s using a PRML channel with digital filter and write precompensation. At low ontrack errors of 10/sup -10/-10/sup -9/ without error correction codes, linear densities of /spl sim/240 K bpi and optimized track pitches of /spl sim/1.2 /spl mu/m were achieved, corresponding to areal densities of /spl ges/5 Gb/in/sup /2.

Mary Frances Doerner

Papers

Extremely High-Density Longitudinal Magnetic Recording Media

Dynamic coercivity measurements in thin film recording media using a contact write/read tester

10 Gbit/in.2 longitudinal media on a glass substrate (invited)

In-plane anisotropy in thin-film media: physical origins of orientation ratio

5 Gb/in/sup 2/ recording demonstration with conventional AMR dual element heads and thin film disks