Influence of grain boundaries on the magnetization reorientation transition in ultrathin films

A magnetic reorientation transition is studied in situ in model experimental systems of Co grown on Au(111) and Au(788). Results from magneto-optic measurements and scanning tunneling microscopy, obtained on these two different self-ordered systems, demonstrate that grain boundaries formed during the film growth strongly influence the magnetic properties of the films. The nanometer scale of the magnetization reversal at the transition makes the temperature an essential parameter to predict experimental features observed in the magnetic reorientation transition.

Figure 1

STM images of $\mathrm{Co}∕\mathrm{Au}\left(111\right)$ (left) and $\mathrm{Co}∕\mathrm{Au}\left(788\right)$ (right) for 1 ML [(a) and (b)], 2 ML [(c) and (d)], and 4 ML [(e) and (f)]. The drawings represent the unit cells of the Co dot arrays delimited by herringbone on Au(111) and separated by step edges on Au(788).

Figure 2

Raw hysteresis loops stored during the reorientation transition for $\mathrm{Co}∕\mathrm{Au}\left(111\right)$ (a) and $\mathrm{Co}∕\mathrm{Au}\left(788\right)$ (b). Each 0.1 ML step are shown from 4 to 5 ML for Au(111) and from 2.5 to 3.5 ML for Au(788).

Figure 3

(a) Residual magnetization at zero field versus Co thickness for Au(788) surface (open circle) and Au(111) surface (dark triangle). The solid lines correspond to the model described in the text, the dotted line to the Stoner-Wohlfarth model. (b) Thickness variation of the effective anisotropy and linear fits for both samples.

Figure 4

Schematic of magnetic anisotropies. A schematic of the Co film structure highlights the periodic phase grain boundary.