A Micellar Approach to Magnetic Ultrahigh‐Density Data‐Storage Media: Extending the Limits of Current Colloidal Methods

Abstract

At the ultimate limit of magnetic recording, suitable storage media will consist of nanometer-sized entities, each of which will carry one bit of information. Materials with a high magnetocrystalline anisotropy energy are required to guarantee thermal stability of the ferromagnetic state at realistic operating temperatures. The face-centered tetragonal (fct) L1 0 FePt alloy belongs to the promising class of materials that offer the perspective of storing one magnetic bit per nanoparticle. [1][2][3] Widespread activities have therefore arisen worldwide, targeting novel strategies for both the synthesis [1,[4][5][6][7][8][9][10][11][12][13][14] of suitable magnetic nanostructures and their organization into superlattices [4,12,[15][16][17][18] by means of parallel processes. Here, we present a new approach for the synthesis of size-selected L1 0 FePt nanoparticles based on the self-organization of spherical micelles formed by diblock copolymers, thereby significantly extending a previous technique [19][20][21] to produce large-scale arrays of elemental nanoparticles. Our approach overcomes the typical drawbacks of the current colloidal routes towards densely packed arrays of ferromagnetic FePt nanoparticles while still guaranteeing areal densities exceeding 1 Tbits inch -2 (1 inch ≈ 2.54 cm).Since the first presentation of magnetic data-storage devices five decades ago, the areal density of digital information has increased by eight orders of magnitude to reach values of about 200 Gbits inch -2 , as found in present hard disk drives.[22]A few years ago, an efficient method was developed to synthesize FePt nanoparticles on the basis of wet-chemical synthesis (hereafter referred to "colloidal"), which involves particle stabilization by an organic-ligand shell.[1] The significant advantage of this approach, allowing a simple preparation of densely packed 2D nanoparticle arrays from corresponding particle solutions, is, however, compensated by some serious drawbacks related to the thin ligand shell (1-3 nm) which serves as a spacer between the nanoparticles. As a consequence of the resulting small interparticle distance, the nanoparticles exhibit a strong tendency to aggregate during heat treatments. [23,24] Thermal annealing at 500-600°C is, however, generally required in order to transform the assynthesized, chemically disordered (Fe and Pt atoms randomly distributed over the lattice sites) face-centered cubic (fcc) structure, which results in superparamagnetic behavior, into the magnetically attractive L1 0 phase. Furthermore, undesirable collective magnetic dynamics arise at such small interparticle distances through dipolar coupling; [24,25] collective modes, however, are clearly at odds with the idea of storing magnetic data in individual nanoparticles. Finally, the heat-treated colloidal FePt nanoparticles are found to be highly oxidized and contaminated by carbon because of the thermally induced decomposition of the organic shell.[26]Recent alternative routes for the synthesis of L1 0 FePt nanoparticles include...

Thermal Stability and Segregation Processes in Self-Assembled Size-Selected AuxFe1-x Nanoparticles Deposited on TiO2(110): Composition Effects

“…A H 2 plasma treatment has been successfully used by Wang et al 73 to reduce 25 nm-thick oxidized Fe-layers. Ethirajan et al 74 and Boyen et al 75 have also demonstrated that oxidized (O 2 -plasma treated) FePt and Co NPs, synthesized by the same inverse micelle encapsulation method used in the present work, can be completely reduced by atomic hydrogen exposure. In our samples, the first H 2 -plasma treatment at 300°C resulted in a reduction of the Fe 3+ signal, with 28% metallic Fe detected.…”

Magnetic Properties of Helicobacter Pylori Ferritins Genetically Prepared Under Different Biomineralization Conditions

“…Magnetic nanoparticle systems are an important research topic for various future applications including magnetic data storage [1], hyperthermia treatment agent [2], etc. Also, finite-size effect study and surface effect study can be performed with magnetic nanoparticle systems as model systems.…”

Fabrication of Magnetic Co/Pt Nanodots Utilizing Filled Diblock Copolymers

“…In accordance with their natural environment of fabrication (in solution) such nanoparticles are frequently and successfully used in biotechnology [24][25][26][27]. For the application in magnetic storage and spin devices a severe problem is to bring the particles on a supporting sample with the particles well aligned with regards to their crystal structure or magnetic axis [28][29][30]. The latter obstacle is circumvented by alternative methods that directly create the nanostructures on the supporting surface.…”

“…To tune the diameter as well as the spacing of the particles the organic spheres are shrunk in a plasma etching step before structure transfer [60][61][62]. A similar technique uses diblock copolymer micelles as selfassembling units which are filled with magnetic or nonmagnetic material [28][29][30][63][64][65]. Magnetic dot arrays can be directly created when magnetic core material is used and the organic shell is removed in oxygen plasma [28][29][30].…”

“…A similar technique uses diblock copolymer micelles as selfassembling units which are filled with magnetic or nonmagnetic material [28][29][30][63][64][65]. Magnetic dot arrays can be directly created when magnetic core material is used and the organic shell is removed in oxygen plasma [28][29][30]. Alternatively, non-magnetic cores can be brought onto a magnetic film in an identical procedure.…”