Magnetic structure and perpendicular magnetic anisotropy of rare-earth (Nd,Pr,Gd)/Fe multilayers

The structural phase and the magnetic anisotropy of Nd/Fe, Pr/Fe, and Gd/Fe multilayers have been examined using magnetization measurements and conversion electron Mössbauer spectrometry. With decreasing Fe layer thickness dFe, the structural phase of the Fe layer changes from bcc crystalline to amorphous at the critical thickness dFec of 17–20 Å via an intermediate phase, which contains a paramagnetic phase in the Nd/Fe and Pr/Fe systems, but not in Gd/Fe. At just above dFec, Nd/Fe and Pr/Fe multilayers exhibit perpendicular anisotropy, which originates from the interface anisotropy due to the one ion anisotropy of Nd and Pr. However, Gd/Fe multilayers show in-plane magnetization because of the S-ionic Gd. Below dFec, the magnetization increases from nearly zero with decreasing dFe because of the exchange interaction between Fe and the rare earth (Nd,Pr,Gd).