Nanocalorimetric analysis of the ferromagnetic transition in ultrathin films of nickel

We report on in situ heat capacity measurements (370-800 K) using quasiadiabatic ultrafast differential scanning nanocalorimetry in thin films (1-200 nm) of Ni grown by electron beam evaporation. The heat capacity shows a broad peak with a rounded maximum that is attributed to the decrease of long-range interactions in the ferromagnetic to paramagnetic phase transition of Ni. The calorimetric data exhibit a reduction of the Curie temperature as the thickness of the films (or the average grain size) decreases. The magnitude of the jump in specific heat at T-C scales with the number of surface or interface atoms. (C) 2008 American Institute of Physics.