  Atomistic spin model simulations are immensely useful in determining
temperature dependent magnetic prop- erties, but are known to give the
incorrect dependence of the magnetization on temperature compared to exper-
iment owing to their classical origin. We find a single parameter rescaling of
thermal fluctuations which gives quantitative agreement of the temperature
dependent magnetization between atomistic simulations and experi- ment for the
elemental ferromagnets Ni, Fe, Co and Gd. Simulating the sub-picosecond
magnetization dynam- ics of Ni under the action of a laser pulse we also find
quantitative agreement with experiment in the ultrafast regime. This enables
the quantitative determination of temperature dependent magnetic properties
allowing for accurate simulations of magnetic materials at all temperatures.
