  In the spirit of multi-scale modelling magnetization dynamics at elevated
temperature is often simulated in terms of a spin model where the model
parameters are derived from first principles. While these parameters are mostly
assumed temperature-independent and thermal properties arise from spin
fluctuations only, other scenarios are also possible. Choosing bcc Fe as an
example, we investigate the influence of different kinds of model assumptions
on ultra-fast spin dynamics, where following a femtosecond laser pulse a sample
is demagnetized due to a sudden rise of the electron temperature. While
different model assumptions do not affect the simulational results
qualitatively, their details do depend on the nature of the modelling.
