We have grown epitaxial thin films of multiferroic BiMnO 3 using pulsed laser deposition. The films were grown on SrTiO 3 (001) substrates by ablating a Bi-rich target. Using x-ray diffraction we confirmed that the films were epitaxial and the stoichiometry of the films was confirmed using Auger electron spectroscopy. The films have a ferromagnetic Curie temperature (T C ) of 85±5 K and a saturation magnetization of 1 µ B /Mn. The electric polarization as a function of electric field (P − E) was measured using an interdigital capacitance geometry. The P − E plot shows a clear hysteresis that confirms the multiferroic nature of the thin films.PACS numbers: Valid pacs appear here Multiferroic materials are unique in that they exhibit both ferromagnetism and ferroelectricity simultaneously. 1 Such materials may be used to fabricate devices such as magnetic tunnel junctions with electrically tunable tunneling magnetoresistance and multiple state memory elements. 2 The recent interest in multiferroics is fueled both by the potential device applications and questions about the underlying physical principles leading to multiferroism. 3-7 Bulk multiferroic materials are rare, possibly due to conflicting requirements for ferromagnetism (FM) and ferroelectricity (FE). BiMnO 3 is perhaps the most fundamental multiferroic and has been referred to as the "hydrogen atom" of multiferroics. 8 In BiMnO 3 (BMO), as in BiFeO 3 , the 6s 2 lone pair on the Bi-ion leads to the displacement of that ion from the centrosymmetric position at the A-site of a perovskite unit cell. The resultant distortion leads to an FM interaction between the Mn-ions at the B-site in BMO. 9,10 In bulk form BMO has been observed to be both FM and FE. 11 Polycrystalline BMO can be grown under high pressure and within a very narrow range of growth conditions. While thin films of BMO have been grown by various groups, few such films have shown magnetic properties similar to bulk BMO and high enough resistivities i.e. low leakage currents to allow clear measurement of FE properties. 12-14 A possible reason for the low resistivities of BMO thin films is the substrate induced strain which exacerbates the growth of a highly distorted perovskite structure. Additionally, recent electron and neutron diffraction data have cast doubt over the purported non-centrosymmetry of the BMO crystal structure 15 and centrosymmetric structures have also been predicted using density functional theory calculations 16 . Since a non-centrosymmetric crystal a) Presently at: Department of Physics, University of California, Berkeley, California 94720, USA and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA b) Also at: Nanoscience Institute of Medical and Engineering Technology, University of Florida, 32611 c) Electronic mail: amlan@phys.ufl.edu structure is essential for ferroelectricity, the observed ferroelectric behavior of BMO may be due to strain and/or ordered oxygen vacancies. 17,18 BMO has a distorted perovskite-type structure ...

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The steady-state solution of filamentary memristive switching may be derived directly from the heat equation, modelling vertical and radial heat flow. This solution is shown to provide a continuous and accurate description of the evolution of the filament radius, composition, heat flow, and temperature during switching, and is shown to apply to a large range of switching materials and experimental time-scales.

We present resistive switching model for TaOx memristors, which demonstrates that the radius of a tantalum rich conducting filament is the state variable controlling resistance. The model tracks the flux of individual oxygen ions and permits the derivation and solving of dynamical and static state equations. Model predictions for ON/OFF switching were tested experimentally with TaOx devices and shown to be in close quantitative agreement, including the experimentally observed transition from linear to non-linear conduction between RON and ROFF. This work presents a quantitative model of state variable dynamics in TaOx memristors, with direct comparison to high-speed resistive switching data.

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