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We proposed 3D architectures of complex oxides as a way to derive novel properties: various 3D shapes were formed by self-shaped free-standing membranes, and curvature-induced polarization in an otherwise nonpolar material was observed.

We investigate the origin of insulating weak-ferromagnetic phase in ultra-thin epitaxial La0.67Sr0.33MnO3 (LSMO) films on SrTiO3 substrate using density functional theory calculation together with X-ray linear dichroism (XLD). The calculations show that symmetry breaking of the crystal field at the LSMO surface largely lowers the energy level of Mn d3z2 orbital at the surface and leads to full occupancy of the d3z2 orbital in majority spin channel, and XLD spectra clearly show the preferential occupation of Mn d3z2 orbital at the surface. Such an orbital reconstruction and charge redistribution in the ultra-thin films largely suppresses double-exchange interaction and favors super-exchange interaction, resulting in G-type antiferromagnetic spin ordering and insulating state. The anisotropic exchange interaction due to spin-orbital interaction leads to spin canting, and thus the films show weak ferromagnetism.

Oxide interfaces such as LaAlO 3 /SrTiO 3 (LAO/STO) are interesting platforms for the investigation of 'spin-orbitronics' because of their strongly coupled spin and orbital degrees of freedom due to the inversion asymmetry of the structure. In this investigation, we demonstrate a tunable Rashba spin-orbit field at the LAO/STO interface via the application of an external gate electric field. The strength of the Rashba field was indirectly estimated by measuring the planar angle dependence of the anisotropic magnetoresistance (AMR). The asymmetry of the planar AMR between h = 0 and p indicates the existence of Rashba spin-orbit fields, which are tunable by adjusting the current density and gate electric field. From the AMR measurements, the effective Rashba field exhibits up to 4 T for the application of an external back-gate voltage of 30 V. This controllable and relatively high Rashba field suggests that the LAO/STO is an attractive 2-D interface for potential spin-orbitronic applications, such as spin-charge converters, spin-FETs, and spin-orbit torque devices.

We performed capacitance–voltage analysis of 5-nm-thick LaAlO3/SrTiO3 heterostructure containing two-dimensional-electron-gas (2DEG) at the interface. The complex impedance of the heterostructure was measured as a function of frequency for a wide range of gate biases. The impedance spectra showed a different behavior above and below an applied voltage of −1.8 V. The capacitance determined from the impedance was approximately 1.2 nF above −1.8 V and was drastically reduced to ∼0.01 nF below this voltage, owing to depletion of 2DEG and the insulating SrTiO3 underneath it. This suggests that devices utilizing LaAlO3/SrTiO3 can facilitate switching operations in a very small voltage range.

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