Local perturbations in complex oxides such as domain walls 1,2 , strain 3,4 and defects 5,6 are of interest because they can modify the conduction or the dielectric and magnetic response and even promote phase transitions. Here we show that the interaction between different types of local perturbations in oxide thin films is an additional source of functionality. Taking SrMnO 3 as a model system, we use nonlinear optics to verify the theoretical prediction that strain induces a polar phase, and density functional theory to show that strain simultaneously increases the concentration of oxygen vacancies. These vacancies couple to the polar domain walls where they establish an electrostatic barrier to electron migration. The result 2 is a state with locally structured room-temperature conductivity consisting of conducting nanosized polar domains encased by insulating domain boundaries, which we resolve using scanning probe microscopy. Our "nanocapacitor" domains can be individually charged, suggesting stable capacitance nanobits with a potential for information storage technology.At first we verify the occurrence of strain-induced polar order in SrMnO 3 thin films.Motivated by the search for novel multiferroic materials, which combine magnetic and ferroelectric orders in the same phase, density functional theory (DFT) predicted the occurrence of ferroelectricity in the perovskite-structure alkaline-earth manganites at larger-than-equilibrium lattice parameters 7,8,9 . For bulk SrMnO 3 this prediction was confirmed by partial substitution of Sr by Ba which induces negative chemical pressure and leads to a polar state 10 . According to DFT, epitaxial SrMnO 3 films should develop a polarisation along one of the pseudocubic <110> axes under >1% epitaxial tensile strain 8 .20-nm films of single-phase SrMnO 3 were grown using pulsed laser deposition on (001)-oriented (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) with 1.7% tensile strain (see Methods). We characterised the strain state of the films using scanning transmission electron microscopy (STEM) and X-ray and electron diffraction. Figure 1a shows a cross-sectional STEM image evidencing the high quality of the films on the atomic scale with a sharp SrMnO 3 /LSAT (001) interface. The reciprocal space map in Fig. 1a verifies that the films are tetragonal and coherently strained. The electron diffraction In the anisotropy plot in Fig. 1c we present the optical polarisation analysis of the SHG signal obtained on a test area of 0.1 mm 2 . We fitted the angular dependence of the SHG signal by assuming a distribution of four polar domain states denoted as P 1+ , P 1− , P 2+ , P 2− . The indices refer to the orientation of the polar axis according to 1 ± ↔ ±[110] and 2 ± ↔ ±[1 10], see Fig. 1c. The coincidence of the measured data and the fit is excellent with a fitted ratio r = P 1 /P 2 = 0.53 in the population of P 1 -and P 2 -type domain states (r varied between different test areas). In contrast, fits assuming a polarisation along the[100] and [010] directions failed. We co...

Interest in manipulating the magnetic order by ultrashort laser pulses has thrived since it was observed that such pulses can be used to alter the magnetization on a sub-picosecond timescale. Usually this involves demagnetization by laser heating or, in rare cases, a transient increase of magnetization. Here we demonstrate a mechanism that allows the magnetic order of a material to be enhanced or attenuated at will. This is possible in systems simultaneously possessing a low, tunable density of conduction band carriers and a high density of magnetic moments. In such systems, the thermalization time can be set such that adiabatic processes dominate the photoinduced change of the magnetic order-the three-temperature model for interacting thermalized electron, spin and lattice reservoirs is bypassed. In ferromagnetic Eu 1 À x Gd x O, we thereby demonstrate the strengthening as well as the weakening of the magnetic order by B10% and within r3 ps by optically controlling the magnetic exchange interaction.

The relation between symmetry and functionality was pinpointed by Pierre Curie who stated that it is the symmetry breaking that creates physical properties. This fundamental principle is nowadays used for engineering heterostructures whose integral symmetry leads to exotic phenomena such as one-way transparency. For switching devices, however, such symmetry-related functionalities cannot be used because the symmetry in conventional heterostructures is immutable once the material has been synthesized. Here we demonstrate a concept for post-growth symmetry control in PbZr 0.2 Ti 0.8 O 3 and BiFeO 3 -based heterostructures. A conducting oxide is sandwiched between two ferroelectric layers, and inversion symmetry is reversibly switched on or off by layer-selective electric-field poling. The generalization of our approach to other materials and symmetries is discussed. We thus establish ferroic trilayer structures as device components with reversibly tunable symmetry and demonstrate their use as light emitters that can be activated and deactivated by applying moderate electric voltages.

We demonstrate spin-spiral-induced ferroelectricity in epitaxial TbMnO 3 films grown on YAlO 3 substrates down to a film thickness of 6nm. The ferroelectric polarization is identified by optical second-harmonic generation. Using x-ray resonant magnetic scattering we directly prove the existence of a noncollinear magnetic structure in the ferroelectric phase and thus bulk-like multiferroicity. The electric-field-induced reversal of the magnetic domains along with the reversal of the ferroelectric polarization evidences the rigid coupling of magnetic and ferroelectric order and hence a "giant" magnetoelectric effect in the films.

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