FePt and CoPt nanoparticles co-deposited on silicon dioxide—a comparative study

Abstract

We compare CoPt and FePt nanoparticles grown under identical conditions on oxidized Si substrates by electron beam co-evaporation. Growth was performed under high vacuum conditions at substrate temperatures of 1023 K and was immediately followed by an annealing step. This process forms CoPt and FePt nanoparticles with mean diameters between ∼17 and ∼22 nm. In particular, the annealing step results in grain size enlargement for all samples and in a progressive magnetic hardening of the nanoparticles which reach maximum perpendicular coercivities of ∼6.6 kOe (for the CoPt) and ∼10.2 kOe (for the FePt nanoparticles). We show that, during this annealing step, a progressive transition towards the hard magnetic L1(0) ordered phase takes place in both materials. In contrast to FePt, CoPt nanoparticles must be annealed in order to crystallize in this phase.

Synthesis of L10 ferromagnetic CoPt nanopowders using a single-source molecular precursor and water-soluble support

“…2 CoPt alloy nanoparticles are also known to function as chemical CO oxidation catalysts 4 and as electrochemical catalysts for CO or methanol oxidation. 5 CoPt nanoparticles of near 1 : 1 alloy stoichiometry have been prepared via hydrogen reduction, 6,7 borohydride reduction, [8][9][10][11][12] polyol reduction, [13][14][15][16][17][18] sol-gel methods, 19,20 reverse micelle methods, 21,22 galvanic displacement, 23 evaporation methods, [24][25][26][27] ion-beam depositiom, [28][29][30] pulse-laser-deposition/ ablation/sputtering methods, [31][32][33][34][35] or by bio-inspired or biomimetic methods. 36,37 Common to these methods is use of separate sources of Co and Pt and a two-step process entailing formation of CoPt nanoparticles with subsequent thermal annealing.…”

Effects of annealing temperature, atomic composition, film thickness on structure and magnetic properties of CoPt composite films

“…[39], and higher than that of the nanoparticles reported by other researchers [40,41]. The differences of H C between nanoparticles and films can be ascribed to the different kinetic and thermodynamic behavior of the ordering process [1,7,14,[42][43][44][45]. Since the coercivity is closely related to the magnetocrystalline anisotropy of an individual grain [25], the different Co compositions will result in different magnetocrystalline anisotropies and H C .…”

Effect of Thicknesses on the Microstructure and Magnetic Properties of CoPt Thin Films

“…The composition of the glass substrate was SiO 2 . The surface energy of amorphous SiO 2 (about 0.3 J/m 2 ) [12] is much smaller than that of ordered L1 0 CoPt crystal (about 12.4 J/m 2 ) [13]. The surface energy difference between the glass substrate and CoPt alloy would cause the CoPt films to form island-like shapes to reduce the surface energy of the samples during annealing [14].…”