Influence of strain on the magnetization and magnetoelectric effect in La0.7A0.3MnO3/PMN-PT(001) (A=Sr,Ca)

We investigate the influence of a well-defined reversible biaxial strain <= 0.12% on the magnetization (M) of epitaxial ferromagnetic manganite films. M has been recorded depending on temperature, strain and magnetic field in 20-50 nm thick films. This is accomplished by reversibly compressing the isotropic in-plane lattice parameter of the rhombohedral piezoelectric 0.72PMN-0.28PT (001) substrates by application of an electric field E <= 12 kV cm(-1). The magnitude of the total variable in-plane strain has been derived. Strain-induced shifts of the ferromagnetic Curie temperature (T-C) of up to 19 K were found in La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 films and are quantitatively analyzed for LSMO within a cubic model. The effective magnetoelectric coupling coefficient alpha=mu(0)dM/dE <= 6x10(-8) s m(-1) at ambient temperature in the magnetic-film-ferroelectric-substrate system results from the strain-induced M change. It corresponds to an enhancement of mu(0)Delta M <= 19 mT upon biaxial compression of 0.1%. The extraordinary large alpha originates from the combination of three crucial properties: (i) the strong strain dependence of M in the ferromagnetic manganites, (ii) large piezo-strain of the PMN-PT substrates, and (iii) effective elastic coupling at the film-substrate interface.