  N\'eel-type magnetic skyrmions in multilayer films have attracted significant
amount of attention recently for their stability at room temperature and
capability of motion driven by a low-density electrical current, which can be
potentially applied to spintronic devices. However, the thermal effect on the
formation of the skyrmions and their behavior has rarely been studied. Here, we
report a study on the creation of skyrmions in [Pt/Co/Ta]10 multilayer samples
at different temperatures using an in-situ Lorentz transmission electron
microscopy. By imaging the magnetization reversal process from positive
(negative) saturation to negative (positive) saturation, we found that the
skyrmions can be created by nucleation from ferromagnetic saturation state and
by breaking the labyrinth domains under certain external fields. By tuning the
external fields, a maximum density of skyrmions was reached at different
temperatures. The key finding is that the creation of the skyrmions in the
multilayers depends critically on the temperature and thermal history.
