Temperature-dependent magnetic second-harmonic generation from Fe nanostructures grown on vicinal W(110)

Temperature-dependent magnetic second-harmonic generation (MSHG) at normal incidence (NI) is used to determine magnetization curves from Au-capped ultrathin Fe nanostructures grown on a vicinal W(110) substrate. Aligned magnetic nanostructures grown on low-symmetry interfaces are generally inhomogeneous, with different magnetic species, such as terrace and step atoms, contributing to the overall magnetic response from the interfacial regions. A phenomenological model of NI MSHG intensity and contrast at magnetic interfaces of 1 m symmetry is used to extract the magnetization information. Two characteristic temperatures are identified for both 0.75 and 2.0 monolayers of Fe, and it is proposed that the increased sensitivity of SHG to step atoms, compared to linear optical techniques, allows the contribution of boundary atoms to the spin block response to be directly detected at lower temperatures. The behavior of boundary spins such as these is expected to be important for atomic-scale magnetic structures.

Figure 1

(a) NI MSHG $y$-polarized intensity difference, $\Delta I_y$, at 80 K and fits (solid lines), together with the resulting hysteresis curve (below), from Au-capped 0.25 ML Fe films grown on vicinal W(110): $\phi \approx$ 0${}^{°}$ (), $\phi \approx$ 90${}^{°}$ (). (b) Temperature variation of the MSHG contrast and simultaneous fit, together with extracted magnetization curve (below). Inset: schematic of 10-atom-wide Fe stripes grown out from the step edge (capping by Au not shown).

Figure 2

(a) NI MSHG $y$-polarized intensity difference, $\Delta I_y$, at 80 K and fits (solid lines), together with the resulting hysteresis curve (below), from Au-capped 0.75 ML Fe films grown on vicinal W(110): $\phi \approx$ 0${}^{°}$ (), $\phi \approx$ 90${}^{°}$ (). (b) Temperature variation of the MSHG contrast and simultaneous fit, together with extracted magnetization curves (below). Inset: schematic of 30-atom-wide Fe stripes grown out from the step edge (capping by Au not shown).

Figure 3

(a) NI MSHG $y$-polarized intensity difference, $\Delta I_y$, at 80 K and fits (solid lines), together with the resulting hysteresis curve (below), from Au-capped 2 ML Fe films grown on vicinal W(110): $\phi \approx$ 0${}^{°}$ (), $\phi \approx$ 90${}^{°}$ (). Inset: enlargement of normalized curves showing a small change in shape (b) Temperature variation of the MSHG contrast and simultaneous fit, together with extracted magnetization curves (below). Inset: schematic of 2 ML of Fe grown on the stepped W(110) substrate (capping by Au not shown).