Two magnetic-ordering temperatures in Fe/Al multilayered films

Abstract

We have prepared Fe/Al multilayers with individual layer thickness ranging from 5 to 200 \AA{}. For magnetic measurements, each sample was cooled in zero magnetic field from room temperature to 5 K. Then a magnetic field of 100 G was applied, and the magnetization was measured as the temperature was raised from 5 to 300 K. The magnetization initially rose as the temperature increased to a certain temperature ${\mathit{T}}_{\mathit{p}}$, beyond which the magnetization decreased with further increase in the temperature. The peak at ${\mathit{T}}_{\mathit{p}}$ was found in all of our samples of different layer thicknesses. We have also measured the Curie temperature ${\mathit{T}}_{\mathit{C}}$ and found it considerably higher than ${\mathit{T}}_{\mathit{p}}$. We show that ${\mathit{T}}_{\mathit{p}}$ represents a transition from one magnetic state to another, and it is suggested that it is probably due to an antiferromagnetic coupling between the Fe layers via the Al layers.