Design of Bifunctional Oxide Multilayers

Bifunctional materials, capable of serving as ferroelectric/ferromagnetic actuators, sensors, and memory devices, can be designed from first principles using a combination of Density Functional Theory, atomistic simulations, and thermodynamic modeling. A relaxed multilayer structure, consisting of magnetite Fe₃O₄ upon the doped perovskite Pb(Zr_0.5Pd_0.5)O₃ is shown in the Figure below. Here, a chemically and structurally optimized material will be able to couple electric-field response of the perovskite slabs to the magnetic-field response of the magnetite slabs. The multidimensional space of chemical composition, slab thickness, and interface geometry can be explored by computer simulation more completely and more rapidly than by experiment. Collaboration with experimentalists is essential to choose models which can potentially be realized in the laboratory and finally commericialized.

Bifunctionality can be achieved by stacking two different crystalline materials if they are chemically and structurally compatible. Here the well-known ABO₃ perovskite phase which shows ferroelectric behavior is coupled to the equally well known M₃O₄ spinel phases which show a variety of magnetic properties. By chemically doping each phase, and using chemical vapor deposition as a tool, one can conceptually (and sometimes actually) grow bifunctional multilayers. The key variables are chemical composition; e.g. (A,A´)(B,B´)O_3-x and (M,M´)₃O_4-y and repeating layer thickness; the limits of stability and functionality can be explored by computer modeling both as an analysis tool and as a predictor to guide experimental growth regimes.