Protein- and peptide-directed syntheses of inorganic materials.

The aim of this article is to provide a comprehensive review of current research activities that center on superparamagnetic colloids. We begin with an overview of synthetic strategies that have been developed for generating both nanoscale and mesoscale superparamagnetic colloids, with a focus on those systems that can be prepared as monodisperse samples and in relatively large quantities. We then discuss a variety of techniques that have been exploited for modifying surface properties, as well as for controlling the assembly and patterning of these magnetically active colloids. Towards the end, we highlight a range of innovative applications enabled by the unique combination of superparamagnetism and colloidal suspension. We conclude this review article with personal remarks and perspectives on the directions toward which future research in this area might be directed.

Superparamagnetic Colloids: Controlled Synthesis and Niche Applications**

Nanofabrication of magnetic storage media, where servo marks, discrete tracks or individual islands are defined, offer the prospect for improved performance and increased areal density. However, this increase in performance will require that new and additional processes be introduced into disk manufacturing. We review here the fundamental patterning and fabrication processes that have been proposed, along with their respective strengths and weaknesses and the potential advantages they may offer for magnetic recording. The increase in data density afforded by nanofabrication may have added significance as more conventional approaches to ever increasing density will encounter physical limitations set by the thermal stability of the recorded bits.

https://iopscience.iop.org/article/10.1088/0022-3727/38/12/R01/pdf

Nanofabricated and self-assembled magnetic structures as data storage media

Control of the formation of nanostructures during their synthesis can be achieved using either equilibrium conditions, such as in nanostructure templating, or non-equilibrium conditions, such as in reaction–diffusion systems. This review analyses the different method types with the aim of producing guidelines for the rational design of hybrid organic–inorganic nanostructures. Understanding how chemically derived processes control the construction and organization of matter across extended and multiple length scales is of growing interest in many areas of materials research. Here we review present equilibrium and non-equilibrium self-assembly approaches to the synthetic construction of discrete hybrid (inorganic–organic) nano-objects and higher-level nanostructured networks. We examine a range of synthetic modalities under equilibrium conditions that give rise to integrative self-assembly (supramolecular wrapping, nanoscale incarceration and nanostructure templating) or higher-order self-assembly (programmed/directed aggregation). We contrast these strategies with processes of transformative self-assembly that use self-organizing media, reaction–diffusion systems and coupled mesophases to produce higher-level hybrid structures under non-equilibrium conditions. Key elements of the constructional codes associated with these processes are identified with regard to existing theoretical knowledge, and presented as a heuristic guideline for the rational design of hybrid nano-objects and nanomaterials.

Self-assembly and transformation of hybrid nano-objects and nanostructures under equilibrium and non-equilibrium conditions

In recent years, the stability of recorded data against thermal decay has become an important criterion for judging the performance of magnetic recording systems. Continued growth of storage densities in the presence of thermally activated behaviour, often called the `superparamagnetic effect', requires new innovations in the recording system in general, and the recording media, in particular. This paper reviews some of the recent advances in recording media (e.g. oriented and antiferromagnetically coupled media) that have helped magnetic recording to maintain the areal density growth rate. However, more innovations and novel architectures are needed for the solutions of tomorrow. Among the more promising media approaches, which are discussed in this paper, are perpendicular, patterned and self-assembled nanoparticle media. Additionally, thermally assisted recording is also reviewed as it combines good writeability with high thermal stability.

http://iopscience.iop.org/article/10.1088/0022-3727/35/19/201/pdf

Magnetic recording: advancing into the future

Nanoscale CoPt grains were prepared within protein shells from aqueous reactants. A series of particles with varying Co:Pt ratios was used to explore the transition from superparamagnetic to ferromagnetic behavior at room temperature. TEM and electron diffraction confirmed ordered fct CoPt phases with an average grain size of 4.1 nm. Magnetic characterization was performed at room temperature using VSM. The use of this system to prepare high-density recording media is discussed.

Self assembled nanoparticulate CO:PT for data storage applications

Chemically synthesized high-anisotropy magnetic nanoparticles have demonstrated thermal stability and extremely narrow size distributions that are critical for reducing noise in future media applications. Due to their monodispersity, they also exhibit emergent self-patterning that could potentially support bit-per-particle densities up to 2 to 8 Tb/cm/sup 2/ (10 to 50 Tb/in/sup 2/). The authors report on the challenges and progress in developing self-organized nanoparticle arrays for magnetic recording at densities up to and beyond 30 Gb/cm/sup 2/ (200 Gb/in /sup 2/), and in particular describe the beneficial use of biological templates in developing such media. CoPt grains are prepared within monodisperse protein spheres from aqueous reactants, with synthesis conditions controlling grain size, structure, and composition. Dispersions of these protein-encapsulated grains can be induced to form patterned precursor films that retain long range order irrespective of a distribution in grain size. Assemblies are annealed to form films of L1/sub 0/ phase nanomagnets within carbonized shells that can support stable transitions up to 1 Gb/cm/sup 2/ (6 Gb/in/sup 2/).

Biologically derived nanomagnets in self-organized patterned media

A novel system has been used to manufacture nanoparticulate Cu:Pt with an average diameter of 8nm and very small standard deviation. The system uses a protein called ferritin that normally stores iron in viva, but this iron can be chemically removed. The hollow protein can then be used to grow Co:Pt nanopmicles which are subsequently heat treated to promote a particular crystalline phase. The femtin can be deposited onto a substrate where it naturally self assembles into an HCP monolayer under appropriate conditions. If the protein is then carbonised or otherwise removed, a regular HCP close packed array of 8nm Co:Pt particles is left. The theoretical storage densit of a thin film exploiting the patterned qualities of the HCP arrangement is 4.5 Tbitshu , Work is presented regarding the development of a magnetic thin film media based on these processes.

K.K.W. Wong

Papers

Self assembled nanoparticulate CO:PT for data storage applications

Biologically derived nanomagnets in self-organized patterned media

Self assembled nanoparticulate copt for data storage applications