Magnetic Bubble Domain Phase at the Spin Reorientation Transition of Ultrathin $\mathrm{Fe}/\mathrm{Ni}/\mathrm{Cu}(001)$ Film

Magnetic domain phases of ultrathin $\mathrm{Fe}/\mathrm{Ni}/\mathrm{Cu}(001)$ are studied using photoemission electron microscopy at the spin reorientation transition (SRT). We observe a new magnetic phase of bubble domains within a narrow SRT region after applying a nearly in-plane magnetic field pulse to the sample. By applying the magnetic field pulse along different directions, we find that the bubble domain phase exists only if the magnetic field direction is less than $\sim 10$ degrees relative to the sample surface. A temperature dependent measurement shows that the bubble domain phase becomes unstable above 370 K.

Figure 1

Magnetic domain images of $\mathrm{Fe}(\mathrm{\text{wedge}})/\mathrm{Ni}(10.6\mathrm{ML})/\mathrm{Cu}(001)$ for (a) as grown sample and (b) after applying a nearly in-plane magnetic field pulse. (c) Zoom-in image of the bubble domains in the SRT region. (d) Domain width as a function of the Fe film thickness, before and after in-plane magnetization. The solid line is a guide to the eye.

Figure 2

(a) SRT position in the Fe-Ni thickness plane. Magnetic bubble domain images of (b) $d_{\mathrm{Fe}}=2.9\mathrm{ML}$, $d_{\mathrm{Ni}}=5.5\mathrm{ML}$; (c) $d_{\mathrm{Fe}}=3.1\mathrm{ML}$, $d_{\mathrm{Ni}}=8.0\mathrm{ML}$; (d) $d_{\mathrm{Fe}}=3.6\mathrm{ML}$, $d_{\mathrm{Ni}}=10.8\mathrm{ML}$; (e) $d_{\mathrm{Fe}}=4.1\mathrm{ML}$, $d_{\mathrm{Ni}}=13.6\mathrm{ML}$.

Figure 3

Bubble domain phase of $\mathrm{Fe}(3.55\mathrm{ML})/\mathrm{Ni}(10.6\mathrm{ML})/\mathrm{Cu}(001)$ (a) after applying a nearly in-plane magnetic field pulse and (b) after applying a magnetic field pulse in the opposite direction. The reversal of the domain contrast shows that there exists a small normal component of the magnetic field pulse.

Figure 4

Magnetic domain images of $\mathrm{Fe}(3.3\mathrm{ML})/\mathrm{Ni}(9\mathrm{ML})/\mathrm{Cu}(001)$ after applying a magnetic field pulse (a) less than $\sim 5°$ from the sample surface, (b) $\sim 10°$ from the sample surface, (c) $\sim 20°$ from the sample surface, and (d) perpendicular to the sample surface.

Figure 5

Bubble domains near $\mathrm{Fe}(3.5\mathrm{ML})/\mathrm{Ni}(10.6\mathrm{ML})/\mathrm{Cu}(001)$. The bubble domains change to the stripe domains after increasing the temperature to 370 K. The stripe domains remain after cooling to room temperature.