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Doping ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ with Ti stabilizes the corundum paramagnetic metallic phase and restricts the transition to the monoclinic antiferromagnetic insulating phase at lower temperatures. In this study, we investigated the dependence of phase stability on Ti concentration for ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ nanocrystals as small as 20 nm. Ti doping of several percent induces a high-temperature insulating phase preserving the magnetic transition without the crystal symmetry change. The emergence of the insulating phases, which are peculiar to this crystal size, can be attributed to the enhancement of the on-site Coulomb interaction $U$ and increased mixing between ${a}_{1g}$ and ${e}_{g}^{\ensuremath{\pi}}$ states accompanied by characteristic lattice parameter changes in the high Ti doping region.

A two-dimensional electron gas interacting with an external periodic potential attracts attention as a designable artificial material to explore topological phases. Here, to introduce a periodic potential into a Shockley state, superstructures of CO molecules have been fabricated on a Cu(111) surface by atom manipulation with a low-temperature scanning tunneling microscope. Local electronic states have been investigated in relation to specific locations on the CO triangular lattice. All tunneling spectra of the lattice exhibit a reduction at the bottom energy of the surface-state band, which reflects absorption of surface-state electrons into the bulk. For an ($8\ifmmode\times\else\texttimes\fi{}8$) CO structure, spectra measured at positions corresponding to two equivalent triangular sublattices of artificial graphene have different features near the Fermi level. This sublattice site dependence is not observed for a ($6\ifmmode\times\else\texttimes\fi{}6$) structure. First-principles calculations for a ($4\ifmmode\times\else\texttimes\fi{}4$) structure have reproduced the local density of states that depend on the sublattice sites. These results can be understood that coupling between the surface state and the bulk is strengthened via scattering by the adsorbates, and that the external periodic potential is perturbed by the second layer of the Cu(111) substrate. The periodicity of the external potential appears to be the key parameter which dominates the equivalence of pseudospin states in the artificial graphene.

We study the magnetic structure of perpendicularly magnetized Fe nanowires grown on Au(788) by means of x-ray magnetic circular dichroism. The average size of ferromagnetic domains in the nanowires exponentially decreases with temperature, leading to a steeper decay in magnetization compared to nanoislands of Fe. The temperature dependence of magnetization and domain structures can be well described in terms of local atomic geometry, the number of atomic chains in nanowires, exchange coupling between adjacent spins, and magnetic anisotropy. The nonlinear coverage dependence of the activation energy for the creation of magnetic domains can be explained by overall shape of nanowires, which also implies that the magnetic switching processes are strongly shape dependent at the nanoscale.

In this study of fabricated one-dimensional (1D) monatomic Fe wires on a Au(788) substrate, electronic and magnetic features are investigated by angle-resolved photoemission spectroscopy (ARPES) and x-ray magnetic circular dichroism (XMCD). The ARPES spectra show little dispersion both in the parallel and perpendicular directions to the wires revealing a strongly localized nature of the $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ electrons. Finite intensity of the XMCD signals has angular dependence reflecting an anisotropic feature of the localized magnetic moments with an easy axis perpendicular to the substrate. Temperature and field dependence of the XMCD signals shows superparamagnetic behavior well described by the 1D Ising model exhibiting large hysteresis below the blocking temperature, which is ruled by the anisotropy energy. Increase of the average size of the spin blocks with reduced temperature enhances the dramatic change of the magnetic properties of the 1D spin system from soft to hard within a narrow temperature range.