Interface structures in FePt/Fe3Pt hard-soft exchange-coupled magnetic nanocomposites

Abstract

Self-assembly of FePt and Fe3O4 nanoparticles of different sizes led to various FePt–Fe3O4 nanocomposites. Annealing the composite under reducing atmosphere at 650 and 700 °C induced magnetically hard FePt phase and magnetically soft Fe3Pt phase. The FePt and Fe3Pt phases were either linked by a common interface or coexisted within one grain as domains with sizes <10 nm. This ensures the effective exchange coupling of magnetically hard and soft phases. High-resolution transmission electron microscopy studies provide detailed structural characterization for the FePt based nanocomposites.

Prospects for nanoparticle-based permanent magnets

“…Figure 9a is similar to the chemically prepared FePt-F 3 Pt and compacted SmCo 5 :Fe 65 Co 35 nanocomposites discussed earlier [10,47,48,17]. If the dimension of the soft phase is too large, magnetic reversal initiates in the soft magnetic phase, owing to its lower anisotropy.…”

“…Nanocomposite magnets have been prepared using wet-chemical [10,17], cluster-deposition and ball-milling methods [47-49, 54, 55]. For example, a TEM image of self-assembled FePt-Fe 3 Pt nanocomposites prepared by a simple mixing of FePt and Fe 2 O 3 nanoparticles and subsequent thermal annealing is shown in Figure 7a [47,48].…”

“…In particular, the desired crystalline ordering in permanent-magnet nanoparticles, e.g., the hexagonal CaCu 5 -type in RCo 5 alloys and face-centered tetragonal structure (L1 0 -chemical ordering) in FePt, is important to obtain the high anisotropies in these materials to realize their permanent-magnet properties [17][18][19].…”

Microstructures and magnetic alignment of L10 FePt nanoparticles

“…13,14 For FePt nanoparticles with a few nanometers in diameter, they prefer to form as a single crystal to minimize their total energy. This was confirmed by the high resolution TEM ͑HRTEM͒ images for as-made FePt nanoparticles.…”

In-cluster-structured exchange-coupled magnets with high energy densities

“…Because of the similarities in the crystal structures and the scale of the structure, it is difficult to distinguish between the ordered Fe 3 Pt and FePt phases. Li et al 14 used high resolution electron microscopy to distinguish Fe 3 Pt and FePt. Also notable in their study was that the contrast between the two phases was not sharp.…”