99th Nanostructured Materials Seminar
FePt nanoparticle assemblies
- magnetic and physical properties and the potential for ultra-high density
recording
Professor R.W. Chantrell
Seagate Research, Pittsburgh, and York University, UK
Date: Wednesday, October 6, 2004
Time: 10:00 - 11:30
Place: Sengen 7th Floor Small Seminar Room, NIMS
FePt nanoparticle assemblies have considerable potential as ultra-high
density magnetic storage media. Their importance arises from the high anisotropy
of the L10 phase which is necessary to ensure thermal stability of written
information for the small grain sizes required because of noise limitations
imposed on the medium by ultra-high density recording systems. As prepared
by chemical techniques the particles are close to monodisperse with average
sizes around 3 nm, and deposited monolayer films readily form Self Assembled
Magnetic Array (SOMA) structures. However, as prepared the particles exist
in the (low coercivity) chemically disordered cubic phase. The subsequent
high temperature annealing required to produce the ordered high anisotropy
phase generally leads to sintering and a strong exchange coupling between
the particles. I will review some current models of FePt SOMA, including
a model of the self-organisation process and a Monte-Carlo model of the
macroscopic magnetic properties. This gives excellent agreement with experimental
data, but requires assumptions about the intrinsic magnetic properties
of the particles. I will review some recent atomistic calculations of the
properties of single FePt particles which provide an important basis for
the understanding of experimental data.