On the Origin of Short-Range Order above T c in Fe, Co, Ni

Strong magnetic short-range order has been observed in Fe and Ni above the Curie temperature T c . The origin of this short-range order has always been somewhat of an enigma. We give here a simple theory to show that the ferromagnetic coupling J 1 between nearest neighbours is weaker in the ferromagnetic state than in the completely disordered local moment state. Thus it is relatively easy for the system to disorder on a coarse length scale, retaining locally a substantial degree of ferromagnetic order.