  Bimetallic Co/Au (core/shell) nanoparticle system exhibiting transition form
superparamagnetic (SPM) to superspin glass state (SSG) at low temperatures has
been investigated with respect to its magnetocaloric properties. Peaks of
magnetic entropy change vs. temperature dependences ($\Delta S_M(T)$) have been
observed at a temperature in the vicinity of SPM to SSG transition. Despite of
significant thermal hysteresis of magnetization at low applied fields a master
curve has been constructed from the $\Delta S_M(T)$ dependences employing
scaling analysis. That confirms the investigated transition is of the second
order type. Different values of critical exponents calculated from field
dependence of relevant magnetocaloric response parameters in the proximity of
critical temperature have been found for low and high applied fields. Moreover,
the exponents exhibited significant disagreement with theoretical values
characteristic of mean field theory as well as Ising models indicating distinct
behavior of the SSG system at critical temperature.
