Evidence for superparamagnetism in ultrathin Fe and FexMn1−x films on Cu(1 0 0)

Abstract

We re-examine the onset of ferromagnetism of Fe/Cu(100) grown at 300K. We find evidence of superparamagnetism in the thickness interval ∼1.5–1.8ML since in this regime a description via Ising superparamagnetism works well. The results on Fe/Cu(100) are being used for a further analysis on our recent data on FCC FexMn1−x films with x∼60%. We observed in this concentration regime non-zero M–H loops yet no hysteresis. We made the additional observation of significant Fe surface segregation. With this in mind, we analyzed these loops in the same fashion and found again a superparamagnetic behavior.