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Title: Mesoporous Co{sub 3}O{sub 4} nanostructured material synthesized by one-step soft-templating: A magnetic study

A combined magnetization and zero-field {sup 59}Co spin-echo nuclear magnetic resonance (NMR) study has been carried out on one member of a recently developed class of highly ordered mesoporous nanostructured materials, mesoporous Co{sub 3}O{sub 4} (designated UCT-8, University of Connecticut, mesoporous materials). The material was synthesized using one-step soft-templating by an inverse micelles packing approach. Characterization of UCT-8 by powder x-ray diffraction and electron microscopy reveals that the mesostructure consists of random close-packed Co{sub 3}O{sub 4} nanoparticles ≈ 12 nm in diameter. The N{sub 2} sorption isotherm for UCT-8, which is type IV with a type H1 hysteresis loop, yields a 134 m{sup 2}/g BET surface area and a 7.7 nm BJH desorption pore diameter. The effect of heat treatment on the structure is discussed. The antiferromagnetic Co{sub 3}O{sub 4} nanoparticles have a Néel temperature T{sub N} = 27 K, somewhat lower than the bulk. A fit to the Curie-Weiss law over the temperature range 75 K ≤ T ≤ 300 K yields an effective magnetic moment of μ{sub eff} = 4.36 μ{sub B} for the Co{sup 2+} ions, indicative of some orbital contribution, and a Curie-Weiss temperature Θ = −93.5 K, consistent with antiferromagnetic ordering. The inter-sublattice and intra-sublattice exchange constants for the Co{sup 2+} ions are J{sub 1}/k{sub B} = (−)4.75 K and J{sub 2}/k{sub B} = (−)0.87 K, respectively, both correspondingmore » to antiferromagnetic coupling. The presence of uncompensated surface spins is observed below T{sub N} with shifts in the hysteresis loops, i.e., an exchange-bias effect. The {sup 59}Co NMR spectrum for UCT-8, which is attributed to Co{sup 2+} ions at the tetrahedral A sites, is asymmetrically broadened with a peak at ≈55 MHz (T = 4.2 K). Since there is cubic symmetry at the A-sites, the broadening is indicative of a magnetic field distribution due to the uncompensated surface spins. The spectrum is consistent with antiferromagnetically ordered particles that are nanometer in size and single domain.« less
Authors:
; ;  [1] ; ;  [2] ;  [1] ;  [3]
  1. Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060 (United States)
  2. Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)
  3. (United States)
Publication Date:
OSTI Identifier:
22271204
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 11; Other Information: (c) 2014 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; ANTIFERROMAGNETISM; COBALT 59; COBALT IONS; COBALT OXIDES; CURIE-WEISS LAW; DESORPTION; ELECTRON MICROSCOPY; HYSTERESIS; ISOTHERMS; MAGNETIC FIELDS; MAGNETIC MOMENTS; MAGNETIZATION; NANOSTRUCTURES; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; SPIN ECHO; TEMPERATURE DEPENDENCE; X-RAY DIFFRACTION