There are lattice-matching ferromagnetic and ferroelectric perovskites like manganites (La,A)MnO3 (A = Sr, Ca, Ce) and titanates Pb(Zr,Ti)O3 which are favourable for the growth of epitaxial multilayers and offer interesting perspectives for the investigation of magnetoelectric coupling phenomena (mainly mediated elastically). Magnetoelectric coupling means the magnetization of the studied system depends on electric field, or electric polarization can be induced by magnetic field. Perovskite manganites have been investigated for two general reasons during the last decade: The very high spin polarization of conduction electrons might be useful in spintronics devices. Further, the correlation of several electronic and lattice degrees of freedom creates various ground states being particularly sensitive to external parameters like magnetic or electric fields, light, but also hydrostatic pressure or biaxial lattice strain. The latter is present in films and offers interesting ways to control their properties.

In our work, epitaxial film systems of manganites and titanates (PbZr0.48Ti0.52O3 (PZT)) have been prepared by off-axis pulsed laser deposition (PLD). In bilayers of a manganite and a PZT layer both, (i) biaxial strain induced by the PZT inverse piezoelectric effect and (ii) charge density modulation in the manganite induced by electric field effect from surface charges at the interface have been investigated. Both effects can be studied in a field effect device structure where they induce hysteretical resistance modulations of distinguishable type. Larger and more uniform strain has been obtained using piezoelectric substrates which allow electrical control of the strain state of films deposited on top. This approach provides access to the modulation of magnetization behavior by electric field, i. e. a primary magnetoelectric response in a composite multiferroic.

[1] C. Thiele, K. Dorr et al., Sensors and Actuators A (in press); Appl. Phys. Lett. (subm.)

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1. Reversible strain tuning of magnetism and electrical conductivity