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The technological appeal of multiferroics is the ability to control magnetism with electric field. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii-Moriya (DM) interaction. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics.

A reversal of magnetization requiring only the application of an electric field can lead to low-power spintronic devices by eliminating conventional magnetic switching methods. Here we show a nonvolatile, room temperature magnetization reversal determined by an electric field in a ferromagnet-multiferroic system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a magnetoelectric device demonstrates an avenue for next-generation, low-energy consumption spintronics.

We report direct experimental evidence for a room-temperature, ∼130  μC/cm(2) ferroelectric polarization from the tetragonal-like BiFeO(3) phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.

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...