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Title: Synthesis, structural characterization and magnetic properties of Fe/Pt core-shell nanoparticles

Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with D{sub o} = 3.0 nm and distribution width λ{sub D} = 0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size = 3.1 nm. Measurements of magnetization M vs. T (2 K–350 K) in magnetic fields up to 90 kOe show a blocking temperature T{sub B} = 13 K below which hysteresis loops are observed with coercivity H{sub C} increasing with decreasing T reaching H{sub C} = 750 Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies f{sub m} = 10 Hz–5 kHz is measured to determine the change in T{sub B} with f{sub m} using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency f{sub o} = 5.3 × 10{sup 10 }Hz and anisotropy constant K{sub a} = 3.6 × 10{sup 6 }ergs/cm{sup 3}. A fit of the M vs. H data up to H = 90 kOe for T > T{sub B} to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness.
Authors:
; ;  [1]
  1. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)
Publication Date:
OSTI Identifier:
22410095
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:
77 NANOSCIENCE AND NANOTECHNOLOGY; CHANNELING; COERCIVE FORCE; HYSTERESIS; IRON; KHZ RANGE; LINE WIDTHS; MAGNETIC FIELDS; MAGNETIC MOMENTS; MAGNETIC PROPERTIES; MAGNETIZATION; NANOPARTICLES; NANOSTRUCTURES; PARTICLE SIZE; PLATINUM; RELAXATION; SYNTHESIS; TEMPERATURE DEPENDENCE; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION