Magnetic properties of FePt nanoparticles

• Published in: Journal of magnetism and magnetic materials 2003-10, Vol.266 (1), p.142-154
• Main Authors: Rellinghaus, Bernd, Stappert, Sonja, Acet, Mehmed, Wassermann, Eberhard F
• Format: Article
• Language: English
• Subjects: Anisotropy; Coercivity; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Fine particles; Fine-particle systems; Intermetallic compounds; Magnetic anisotropy; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Nanoparticles; Physics; Small particles and nanoscale materials; Studies of specific magnetic materials
• ISSN: 0304-8853
• DOI: 10.1016/S0304-8853(03)00465-7

We have prepared FePt nanoparticles with concentrations in the vicinity of the stoichiometric Fe 50Pt 50 composition by means of a gas-phase-based process. The preparation technique employed allows to anneal (‘sinter’) the particles in the gas-phase prior to their deposition. Depending on the gas-pressure during preparation, the structure of the unsintered particles is icosahedral or polycrystalline face-centered cubic (FCC). Temperature-dependent magnetization measurements reveal that these particles are superparamagnetic at room temperature. Gas-phase sintering of polycrystalline FCC FePt nanoparticles results in the formation of predominantly single crystal particles which are face-centered tetragonal due to an increased degree of L1 0 order at elevated sintering temperatures T S. Concurrently, we observe an increase of both the blocking temperature T B and the coercivity H C with increasing T S. This enhancement of T B and H C is more pronounced in iron-rich off-stoichiometric samples, for which the concentrations are still within the L1 0 stability range of the FePt phase diagram. Fe 62Pt 38 particles, which are sintered at T S =1273 K , reach T B =530 K and H C0 =H C (T=0)=4.7 kOe . Whereas the elevated blocking temperature is mainly due a somewhat increased particle size at elevated sintering temperatures, the higher coercivity is attributed to the enhanced degree of L1 0 order in the gas-phase sintered particles.