Ferromagnetic L1₀-Structured CoPt Nanoparticles for Permanent Magnets and Low Pt-Based Catalysts

Abstract

CoPt nanoparticles were successfully synthesized following a one-step liquid-phase chemical approach in the presence of a bismuth additive. The presence of bismuth enhanced the structural ordering, the particle morphology, and suppressed the sintering of nanoparticles during the postannealing. The effect of bismuth addition was studied extensively, and the synthesized nanoparticles were characterized by a plethora of techniques determining their crystal structure, particle size and morphology, while the magnetic properties were measured by vibrating sample magnetometry. The CoPt nanoparticles even in the as-made state reveal a relatively high room-temperature coercivity, up to 1.7 kOe, while after thermal annealing at 700 °C for 1 h, the coercivity reaches ∼14.6 kOe; these values are among the highest observed for CoPt nanoparticles. Furthermore, the excess bismuth phases could be removed by a simple acid treatment, leaving the structure and magnetic properties nearly unchanged for the annealed nanoparticles. These L1 0 -structured CoPt nanoparticles have potential applications in the fields of permanent magnets as well as low Pt-based catalysts.

Homogenization and short-range chemical ordering of Co–Pt alloys driven by the grain boundary migration mechanism

“…Typically, in binary intermetallic large coercive fields are achieved in chemically ordered phases of the alloy possessing a strong magnetic anisotropy [6][7][8][9]. Therefore, the formation of chemically ordered highly anisotropic CoPt phases is intensively investigated in both thin films and nanoparticles relying on doping of CoPt alloys with additional elements [10][11][12][13][14], growth at elevated temperatures [15][16][17][18][19][20][21], realization of composite materials [22] and ion beam irradiation [23,24]. Post-thermal treatment [25][26][27][28], e.g.…”

Low-Platinum-Content Exchange-Coupled CoPt Nanoalloys with Enhanced Magnetic Properties

“…The as-made nanoparticles, in a majority of the studies, pose the disordered face-centered cubic ( fcc ) crystal structure and show superparamagnetic behavior. Our group recently published the effect of bismuth addition on the equiatomic CoPt L1 0 ordering, in which the particles show partial ordering without any post-annealing exhibiting a 1.7 kOe room-temperature coercivity [ 42 ]. In general, thermal treatment at elevated temperatures is required to obtain the fully ordered, magnetically hard L1 0 crystalline phase.…”

Improvement of the Electrocatalytic Properties for the Methanol Oxidation Reaction (MOR) of the CoPt Alloy

“…The Co is also known as an oxophilic metal in the binary catalysts and has the advantage of being a cheap metal, leading to a decrease in the catalyst price. The CoPt alloys can be synthesized by several routes, among which we can mention the chemical reduction, electrochemical deposition or micellar technique [26][27][28][29][30][31].…”