Fig. 3.

Blocking temperatures for small cubic (green) and spherical (blue) grains of iron. The small peak observed at the start of the cubic blocking temperature curve corresponds to a narrow unstable zone of hard-axis aligned single vortices (HSV) that mark the transition between stable SD and stable SV domain states (24, 30). The dotted lines are extrapolations of blocking temperature beyond the size range for which full micromagnetic computations were performed.