Abstract
We present low temperature (11 K) inelastic neutron scattering(INS) data on four hydrated nanoparticle systems: 10 nmCoO·0.10H2O (1), 16 nmCo3O4·0.40H2O (2), 25 nmCo3O4·0.30H2O (3) and40 nm Co3O4·0.026H2O (4). The vibrational densities of states were obtained for all samples and from these theisochoric heat capacity and vibrational energy for the hydration layers confined to the surfacesof these nanoparticle systems have been elucidated. The results show that water on thesurface of CoO nanoparticles is more tightly bound than water confined to the surface ofCo3O4, andthis is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to wateron Co3O4 nanoparticles. This supports the trend, seen previously, for water to be more tightly boundin materials with higher surface energies. The INS spectra for the antiferromagneticCo3O4 particles (2–4) also show sharp and intense magnetic excitation peaks at5 meV, and from this the magnetic contribution to the heat capacity ofCo3O4 nanoparticles has been calculated; this represents the first example of use of INS data fordetermining the magnetic contribution to the heat capacity of any magnetic nanoparticlesystem.
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