  We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes
using thermal pyrolysis method and the effect of shape anisotropy on the static
and dynamic magnetic properties were studied. Shape anisotropy of approximately
10 % was introduced in nanocubes by making nanodiscs using a linear chain amine
surfactant during synthesis process. It has been observed that, ferromagnetism
persisted above room temperature and a sharp drop in magnetic moment at low
temperatures in zero-field cooled magnetization may be associated with the spin
disorder due to the effective anisotropy present in the system. Dynamic
magnetic properties were studied using RF transverse susceptibility
measurements at different temperatures and the singularities due to anisotropy
fields were probed at low temperatures. Symmetrically located broad peaks are
observed in the frozen state at the effective anisotropy fields and the peak
structure is strongly affected by shape anisotropy and temperature.
Irrespective of size the shape anisotropy gave rise to higher coercive fields
and larger transverse susceptibility ratio at all temperatures. The role of
shape anisotropy and the size of the particles on the observed magnetic
behaviour were discussed.
