Influence of strain on 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 (Tc) of up to 19 K were found in La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 films and are quantitatively analysed for LSMO within a cubic model. The observed large magnetoelectric coupling coefficient alpha=mu0 dM/dE <= 6 10-8 s m-1 at ambient temperature results from the strain-induced M change in the magnetic-film-ferroelectric-substrate system. It corresponds to an enhancement of mu0 DeltaM <= 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.Comment: 15 pages, 6 figures, 1 tabl

A new species of Phrynobatrachus (Amphibia: Anura: Phrynobatrachidae) from north-western Guinea, West Africa

A new small Phrynobatrachus species from a gallery forest in north-western Guinea is described. Phrynobatrachus pintoi sp. nov. exhibits a combination of unique morphological characters and a distinctive color pattern, including: compact, oval body, short snout, warty dorsum and eyelid (although no eyelid cornicle is present), three pairs of large symmetric black spots on throat and breast, black spots on belly, more than one black bar on thighs and lower leg, finger and toe tips not expanded, and rudimentary web on foot. Furthermore, analysis of mitochondrial DNA from 16S rRNA reveals that this new species differs from other West African species of the genus by a minimum distance of 7%. Genetically the new species is closest to Phrynobatrachus fraterculus, P. cornutus, and P. gutturosus