Sintering behavior of spin-coated FePt and FePtAu nanoparticles

Abstract

FePt and [FePt]95Au5 nanoparticles with an average size of about 4nm were chemically synthesized and spin coated onto silicon substrates. Samples were subsequently thermally annealed at temperatures ranging from 250to500°C for 30min. Three-dimensional structural characterization was carried out with small-angle neutron scattering (SANS) and small-angle x-ray diffraction (SAXRD) measurements. For both FePt and [FePt]95Au5 particles before annealing, SANS measurements gave an in-plane coherence length parameter a=7.3nm, while SAXRD measurements gave a perpendicular coherence length parameter c=12.0nm. The ratio of c∕a is about 1.64, indicating the as-made particle array has a hexagonal close-packed superstructure. For both FePt and FePtAu nanoparticles, the diffraction peaks shifted to higher angles and broadened with increasing annealing temperature. This effect corresponds to a shrinking of the nanoparticle array, followed by agglomeration and sintering of the nanoparticles, resulting in the eventual loss of positional order with increasing annealing temperature. The effect is more pronounced for FePtAu than for FePt. Dynamic coercivity measurements show that the FePtAu nanoparticles have both higher intrinsic coercivity and higher switching volume at the same annealing temperature. These results are consistent with previous studies that show that additive Au both lowers the chemical ordering temperature and promotes sintering.

Stable Ordered FePt Mesoporous Silica Catalysts with High Loadings

“…Highly active and stable catalysts may be designed by controlling the size and composition of supported metal nanoparticles. – For supported catalysts synthesized by precursor reduction, , chemical vapor/fluid deposition, or coprecipitation, , it is difficult to control the size and surface morphology of the metal clusters as well as the binding to the surface. An emerging concept in catalyst design is to presynthesize metal nanocrystals coated with stabilizing ligands to control the morphology and then infuse the particles onto high surface area ordered mesoporous supports. – The highly uniform and tunable size and curvature of 1D and 3D pores in ordered mesoporous substrates facilitates dispersion and stability of the nanoparticles. – …”

Electronic and magnetic properties of bimetallicL10cuboctahedral clusters by means of fully relativistic density-functional-based calculations

“…These results opened a route to understand and fabricate high density magnetic recording materials using deposited NPs on surfaces. There are several experimental [38,39] and theoretical [28][29][30][31][32][40][41][42][43][44][45] studies regarding isolated NPs aiming to obtain the best morphologies and magnetic behavior covering monometallic NPs [29][30][31], binary alloys [28,42,43,45] and even capped NPs [32,44]. Gruner et al have carried out a total energy study of a wide range of structures of various shapes and sizes for (Fe,Co)Pt NPs [28] as well as for Fe(Pd,Ni) [45].It was found that the most energetically favored structures obtained were those of ordered multiply twinned icosahedra and decahedra shapes.…”

First principles study of Ag, Au, and Cu surface segregation in FePt-L1

“…[7][8][9][10][11][12][13] One of the possible approaches to achieve high L1 0 order and a correspondingly high magnetic anisotropy is by doping FePt nanoparticles with a third element. 1,3 Atomic species such as Ag, [14][15][16][17][18][19][20] Au,17,[19][20][21][22][23][24][25] and Cu 25-27 have been previously tested. To follow this approach, it is imperative to determine whether dopants concentrate inside the particle cores or segregate at the surfaces.…”