title: Determination of the magnetic contribution to the heat capacity of cobalt oxide nanoparticles and the thermodynamic properties of the hydration layers.
abstract: We present low temperature (11 K) inelastic neutron scattering (INS) data on four hydrated nanoparticle systems: 10 nm CoO·0.10H(2)O (1), 16 nm Co(3)O(4)·0.40H(2)O (2), 25 nm Co(3)O(4)·0.30H(2)O (3) and 40 nm Co(3)O(4)·0.026H(2)O (4). The vibrational densities of states were obtained for all samples and from these the isochoric heat capacity and vibrational energy for the hydration layers confined to the surfaces of these nanoparticle systems have been elucidated. The results show that water on the surface of CoO nanoparticles is more tightly bound than water confined to the surface of Co(3)O(4), and this is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to water on Co(3)O(4) nanoparticles. This supports the trend, seen previously, for water to be more tightly bound in materials with higher surface energies. The INS spectra for the antiferromagnetic Co(3)O(4) particles (2-4) also show sharp and intense magnetic excitation peaks at 5 meV, and from this the magnetic contribution to the heat capacity of Co(3)O(4) nanoparticles has been calculated; this represents the first example of use of INS data for determining the magnetic contribution to the heat capacity of any magnetic nanoparticle system.
authors.affiliation: Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Spencer
authors.forename: N L
authors.initials: NL
authors.lastname: Ross
authors.forename: S F
authors.initials: SF
authors.lastname: Parker
authors.forename: B F
authors.initials: BF
authors.lastname: Woodfield
authors.forename: J
authors.initials: J
authors.lastname: Boerio-Goates
authors.forename: S J
authors.initials: SJ
authors.lastname: Smith
authors.forename: R E
authors.initials: RE
authors.lastname: Olsen
authors.forename: A I
authors.initials: AI
authors.lastname: Kolesnikov
authors.forename: A
authors.initials: A
authors.lastname: Navrotsky
authors.forename: C
authors.initials: C
authors.lastname: Ma
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D008280:Magnetics; D053758:Nanoparticles / Q000737:chemistry*; D033363:Neutron Diffraction; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D053838:Scattering, Small Angle; D013816:Thermodynamics; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D010087:Oxides; D014867:Water; D003035:Cobalt; C060728:cobalt oxide