Intralayer coupling in self-organized Fe nanoclusters grown on vicinal Si(111)

This paper reports on the magnetic properties of Fe thin film grown on vicinal Si(111). The surface analysis, performed via scanning tunneling microscopy, showed that the iron grows in a form of two distinct types of elongated nanosized grains, aligned parallel and perpendicular to the substrate steps, respectively. A phenomenological model was used to interpret the experimental magnetization data which considers the two types of Fe nanoclusters with both cubic and uniaxial anisotropies, where those of each type are all identical and aligned. Every particle of the first type is coupled to the adjacent particle of the other type only via direct exchange coupling through the corresponding surface atoms. The experimental hysteresis loops as well as the coercivity and remanent magnetization angular variations are very well reproduced by the model, demonstrating that the magnetic behavior of this system is mainly determined by the ferromagnetic intralayer exchange coupling.

Figure 1

Left panel: $1\mu \mathrm{m}\times 1\mu \mathrm{m}$ STM image of the $3\mathrm{nm}$ thick Fe film as well as a schematic perspective view of the grains oriented in-plane parallelly and perpendicularly to the steps. Right panel: $0.35\mu \mathrm{m}\times 0.35\mu \mathrm{m}$ STM images of six different areas of the film’s surface.

Figure 2

(a) XANES spectra recorded at the Fe $K$ edge; (b) Fourier transform of Fe $K$ edge EXAFS signal.

Figure 3

In-plane hysteresis loop data (symbols) and the corresponding calculated curves (lines) for six representative magnetic field angles; the parameters used are $V_B∕V_A=1.5$, $H_1^i=170\mathrm{Oe}$, $H_2^i=36\mathrm{Oe}$, $H_u^A=9\mathrm{Oe}$, $H_u^B=13.5\mathrm{Oe}$, $H_{d,i}^{\mathrm{eff}}=18.7\mathrm{kOe}$, and $H_E=3.8\mathrm{Oe}$, whose definitions are given in the text.

Figure 4

Angular dependences of the experimentally measured coercivity, normalized remanent magnetization (symbols), and the corresponding calculated variations (lines). The fitting parameters used in the calculations are the same as those given in Fig. 3. The insets show the polar plots of the same variations, where the gray lines correspond to model hysteresis loops calculated using $H_E=1.9\mathrm{Oe}$ instead of $3.8\mathrm{Oe}$.