Structural characteristics and magnetic properties of chemically synthesized CoPt nanoparticles

Abstract

Co x Pt 100−x nanoparticles with dimensions from approximately 2 to 5 nm were synthesized using the reverse micelle method. High-resolution electron microscopy revealed single- and poly-crystalline nanoparticle structures. Twin boundary is a common feature in the polycrystals. As-grown nanoparticles did not show any coercivity at room temperature. However, the nanoparticles became ferromagnetic after annealing at 550 °C for 4 h. Face-centered-cubic to face-centered-tetragonal phase transformation of the nanoparticles that occurred at annealing temperatures above 550 °C was confirmed by electron diffraction patterns and x-ray diffractometry. Coercivity of the annealed nanoparticles were found depending on the nanoparticle chemical compositions. Composition atomic ratio of Co to Pt at around unity gives the highest coercivity of 5500 Oe at room temperature.

Magnetic properties of cobalt and cobalt–platinum nanocrystals investigated by magneto-optical Kerr effect

“…49 This change in the particle magnetic properties was essentially explained by the facecentered-cubic to face-centered-tetragonal phase transition occurring at annealing temperatures above 820 K. Nevertheless, the authors were not able to exclude particle coalescence as a main cause of the observed increase of the particle blocking temperature. Conversely, our MOKE measurements bear information, which can be used to exclude particle coalescence.…”

Bio-inspired Synthesis of Protein-Encapsulated CoPt Nanoparticles

“…[26±31] The synthesis of CoPt nanoparticles using surfactant-based templating has been successful in producing monodisperse particles that can be ordered into two-dimensional (2D) arrays. These synthetic approaches include reducing metal-organic precursors with reductants such as borohydride and diols, [26,32,33] redox transmetallation reactions [34] using reverse micelles, [35] and microemulsion techniques. [36] Another promising approach is to use biomacromolecules as templates for directed fabrication of metallic nanophases.…”

Formation of Fe3Pt phase in FePt-based nanocomposite magnets

“…Extensive studies on the chemical synthesis and postannealing of FePt nanoparticle systems have been reported during the past several years [4][5][6][7][8][9]. It is well known that as-synthesized FePt nanoparticles take a disordered facecentred cubic (fcc) structure which has low magnetocrystalline anisotropy.…”