  The Stoner-Wohlfarth (SW) model is a classical model for magnetic hysteresis
of single-domain particles. For two-dimensional magnets at finite temperature,
the SW model must be extended to include intrinsic strong spin fluctuations. We
predict several fundamentally different hysteresis properties between 2D and 3D
magnets. The magnetization switching diagram known as the Asteroid figure in
the conventional SW model becomes highly temperature dependent and asymmetric
with respect to the transverse and longitudinal magnetic fields. Our results
provide new insights for 2D magnetic materials based spintronics applications.
