In $5d$ Ir oxides with an interplay of spin-orbit coupling and electron correlations, we have tailored a spin-orbital magnetic insulator out of a semimetal ${\mathrm{SrIrO}}_3$ by tuning the structure through superlattices [$({\mathrm{SrIrO}}_3{)}_m$, ${\mathrm{SrTiO}}_3$] ($m=1,2,3,4$, and $\infty$). We observed the systematic decrease of the magnetic ordering temperature and the resistivity as a function of $m$. The transition from the semimetal to the insulator is found to be closely linked to the appearance of magnetism at $m\simeq 3$. Long range magnetic ordering was realized even in the $m=1$ single layer superlattice, implying that the design and realization of novel electronic phases is feasible at the level of a single atomic layer in complex Ir oxides.

The evolution of electronic (spin and charge) excitations upon carrier doping is an extremely important issue in superconducting layered cuprates and the knowledge of its asymmetry between electron- and hole-dopings is still fragmentary. Here we combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper L₃ resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone centre and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the Γ-point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin excitations (paramagnons) recently observed in hole-doped compounds even at high doping levels.

Single-crystal synchrotron x-ray diffraction measurements in strong magnetic fields have been performed for magnetoelectric compounds $\mathrm{Gd}\mathrm{Mn}{\mathrm{O}}_3$ and $\mathrm{Tb}\mathrm{Mn}{\mathrm{O}}_3$. It has been found that the $\mathit{P}\Vert a$ ferroelectric phase induced by the application of a magnetic field at low temperatures is characterized by commensurate lattice modulation along the orthorhombic $b$ axis with $q=1∕2$ and $q=1∕4$. The lattice modulation is ascribed to antiferromagnetic spin alignment with a modulation vector of $(01∕41)$. The change of the spin structure is directly correlated with the magnetic-field-induced electric phase transition, because any commensurate spin modulation with $(01∕41)$ should break glide planes normal to the $a$ axis of the distorted perovskite with the $Pbnm$ space group.