Tuning the Ferromagnetic Coupling of Fe Nanodots on Cu(111) via Dimensionality Variation of the Mediating Electrons

Using in situ magneto-optical Kerr effect measurements and phenomenological modeling, we study the tunability in both the magnetization anisotropy and magnetic coupling of Fe nanodots on a curved Cu(111) substrate with varying vicinity. We observe that, as the terrace width $w$ decreases, the magnetization anisotropy increases monotonically, faster when $w$ is smaller than the nanodot size $d$. In contrast, the magnetic coupling strength also increases until $w\ensuremath{\sim}d$, after which it decreases steeply. These striking observations can be rationalized by invoking the counterintuitive dimensionality variation of the surface electrons mediating the interdot coupling: the electrons are confined to be one dimensional (1D) when $w\ensuremath{\ge}d$, but become quasi-2D when $wld$ due to enhanced electron spillover across the steps bridged by the nanodots.