Tailoring of the Perpendicular Magnetization Component in Ferromagnetic Films on a Vicinal Substrate

We have engineered the magnetic properties of 1–8 nm Co films epitaxially grown on an Au-buffered bifacial $\mathrm{W}(110)/\mathrm{W}(540)$ single crystal. The surface of $\mathrm{Au}/\mathrm{W}(110)$ was atomically flat, whereas the $\mathrm{Au}/\mathrm{W}(540)$ followed the morphology of the vicinal W surface, showing a regular array of monoatomic steps. For Co grown on $\mathrm{Au}/\mathrm{W}(540)$, the existence of the out-of-plane magnetization component extended strongly to a thickness $d$ of about 8 nm, which was accompanied by an anomalous increase of the out-of-plane switching field with increasing $d$. In addition, the process of up-down magnetization switching could be realized with both a perpendicular and in-plane external magnetic field.

Figure 1

Schematic configuration of the sample (a). LEED patterns on the vicinal surface at different preparation stages: (b) W(540) surface, (d) 8 nm Co film surface, and (c) STM images for 5 nm Au on W(540). LEED patterns were taken at electron energy of 120 eV.

Figure 2

Dependence of normalized remanent magnetization $M_r$ on the Co thickness for W(110) (open points) and W(540) (full points) substrate regions. Solid lines are calculated within the proposed model (Eq. (1)). Inset: the hysteresis loops for the 4.5 nm thick Co film on both the flat and vicinal region measured by $P$-MOKE. The loops linked with the arrows to the full points show a small field range for 1, 3.5, 4.5 and 8 nm thick Co on the vicinal surface.

Figure 3

Hysteresis loops measured as longitudinal Kerr ellipticity for the in-plane magnetic field applied along W[1–10] and W[001] directions for a Co thickness $d=4.5\mathrm{nm}$ (a),(b). Also, polar plots of the angular dependence of the coercive field (c),(d) and the polar component measured at $H_{\parallel }=0.14\mathrm{T}$ for the in-plane field magnetization reversal (e),(f) are shown (left column) flat W(110) and (right column) W(540) region.

Figure 4

Thickness dependence of $H_{\mathrm{sw}}$ for Co on the vicinal substrate. The solid line represents the $H_{\mathrm{sw}}^{\max }$ field calculated using Eq. (2). The insets show the $P$-MOKE loops for a Co thickness of 4.5 nm measured as a function of the perpendicular (lower curve) and in-plane (upper curve) magnetic field.