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Title: Improvement of saturation magnetization of Fe nanoparticles by post-annealing in a hydrogen gas atmosphere

Fe nanoparticles (NPs) were synthesized by the thermal decomposition of Fe(CO){sub 5} and then post-annealing in a hydrogen gas atmosphere to produce highly monodisperse Fe NPs with high saturation magnetization (M{sub s}). The as-synthesized pre-anneal Fe NPs had an expanded α-Fe structure and M{sub s} was only 39% of that for bulk Fe because of the low crystallinity and the inclusion of a surfactant. Post-annealing of the Fe NPs in a hydrogen gas atmosphere at 200 °C improved the crystallinity of the Fe NPs from an amorphous-like structure to a body centered cubic (bcc) structure without any lattice expansion. This result indicates that hydrogen gas plays a significant role in improvement of the crystallinity of Fe NPs. Accompanying the improvement in crystallinity, M{sub s} for the Fe NPs increased from 86 to 190 emu/g{sub net} at 300 K, the values of which include the weight of surfactant. This enhanced M{sub s} is almost the same as that of bulk Fe (218 emu/{sub Fe}). It was concluded that the crystallinity has a significant influence on the M{sub s} of the Fe NPs because long-range ordering of the lattice can maintain strong direct exchange interactions between Fe atoms.
Authors:
; ; ;  [1] ; ;  [2]
  1. Research Laboratories, DENSO CORPORATION, 500-1, Minamiyama, Komenoki-cho, Nisshin, Aichi 470-0111 (Japan)
  2. Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan)
Publication Date:
OSTI Identifier:
22410167
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 17; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ANNEALING; BCC LATTICES; CARBON MONOXIDE; CRYSTALS; EXCHANGE INTERACTIONS; HYDROGEN; IRON; MAGNETIZATION; NANOPARTICLES; PYROLYSIS; SURFACTANTS