中央研究院 原子與分子科學研究所

Using x-ray photoemission electron microscopy and the magneto-optical Kerr effect, we have demonstrated a perpendicular magnetic anisotropy that could be due to exchange coupling between the ferromagnetic and antiferromagnetic layers. The results of magnetic imaging and hysteresis loops show that the magnetization of Fe and permalloy (Py) films orients from the in-plane to perpendicular direction, as an Mn underlayer is above a threshold value that depends on the Fe or Py layer thickness. Their thickness-dependent behaviors can be quantitatively described by a phenomenological model that takes into account the finite-size effect of the antiferromagnet on exchange coupling. The anisotropy energy extracted from the model and the thermal stability of perpendicular magnetization enhanced with the increase of the Mn underlayer further demonstrate the exchange coupling nature.FIG 1. (a)-(c) Magnetic domain images of a 6 ML Fe/wedged-Mn bilayer measured with different relative orientations between the polarization of incoming x-ray and samples at 220 K. The magnetization direction of the Fe domains switches from in-plane to perpendicular direction while the thickness of Mn layer is increased.FIG 2.Magnetic easy axis phase diagram for (a) Fe/Mn biayers and (b) Py/Mn bilayes, measured by MOKE at 220 K. The solid lines are the SRT boundaries fitted with theoretical model