Structure Optimization of FePt Nanoparticles of Various Sizes for Magnetic Data Storage
- PDF / 863,517 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 63 Downloads / 161 Views
INTRODUCTION
CHEMICALLY synthesized self-assembled FePt nanoparticles have been proposed as magnetic recording media that could be thermally stable beyond 1 Tbit/in2 .[1] However, in order for the potential of this kind of media to be realized, many requirements must be addressed, such as long storage time, uniaxial crystallographic texture, self-assembly over large areas, and a narrow distribution of switching fields. The long storage time and high storage density can be achieved in high magnetocrystalline anisotropy materials such as the L10 phase of FePt. The chemical route typically produces FePt nanoparticles in the fcc disordered state, and subsequent annealing is needed to induce the chemical ordering transformation into the high magnetocrystalline anisotropy L10 phase.* While annealing is a route *For a list of methods of achieving the phase transformation fcc fi L10 other than thermal annealing, refer to Ref. 20 (Sections 1.3 and 4.2.3).
for the phase transformation fcc fi L10, it also promotes sintering and grain growth, which destroy
M. TANASE, formerly with the Data Storage Systems Center, Carnegie Mellon University, is with the Argonne National Laboratory, Lemont, IL, USA Contact e-mail: [email protected] J.-G. ZHU and D.E. LAUGHLIN are with the Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, PA 15213, USA C. LIU, formerly with Seagate Research, is with the Nanosys Inc., Palo Alto, CA 94304, USA N. SHUKLA, formerly with Seagate Research, is with the Institute for Complex Engineered Systems, Carnegie Mellon University, Pittsburgh, PA, USA T.J. KLEMMER and D. WELLER are with Seagate Research, Pittsburgh, PA, USA This article is based on a presentation made in the symposium entitled ‘‘Phase Transformations in Magnetic Materials’’, which occurred during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS-MPMD and ASMT-MSCTS Phase Transformations Committee. 798—VOLUME 38A, APRIL 2007
the self-assembly. Various methods aimed at avoiding sintering have been reported, such as rapid thermal annealing,[2] in-situ thermal annealing,[3] preannealing of surfactant,[4] inert coatings followed by annealing,[5] epitaxial growth at high temperatures (500 C[6]) or low temperatures (230 C[7]), metal additives for the reduction of the ordering temperature,[8] covalent bonding with the substrate,[9] salt matrix annealing,[10] and direct L10 production in high boiling point solvents.[11] Another problem associated with annealing is incomplete phase transformation due to the dependence of the transformation temperature on particle size. Several workers have suggested that FePt does not order below a critical size of 3 nm in nanoparticles and 4 nm in granular thin films.[12] More recent work on granular thin films[13] has succeeded in inhibiting grain growth of particles of 3.5-nm average size, but without the formation of the L10 phase in particles smaller than 4 nm. We report the phase transformation fcc fi L10 in particles of 3.2-nm diameter and also in sing
Data Loading...
