Magnetoresistance of coherently strained La2/3Ba1/3MnO3/SrTiO3 superlattices

A series of coherently strained multilayer thin films of SrTiO3/La2/3Ba1/3MnO3 have been fabricated on (100) SrTiO3 and (100) NdGaO3 substrates by laser molecular-beam epitaxy. By the in-plane coherency strain the out-of-plane lattice constant could be continuously adjusted from 3.916 to 3.975 Angstrom by varying the relative thickness of the SrTiO3 and La2/3Ba1/3MnO3 layers. The strain results in a biaxial distortion epsilon (bi) of La2/3Ba1/3MnO3 that strongly affects the electrical transport properties and the magnetoresistance. Our measurements show that there is a clear correlation between epsilon (bi) and the temperature T-p corresponding to the maximum in the resistivity versus temperature curves as well as the measured magnetoresistance. By varying the strain we could derive the quantity Delta = (T-p/T-p(bulk))(d(2)T(p)/d epsilon (2)(bi)) giving the sensitivity of the materials properties to biaxial strain. Our data provide evidence for the relevance of the Jahn-Teller electron-phonon coupling in the doped manganites. Our analysis further shows that biaxial strain is an important variable that has to be taken into account in the design of thin-film structures used for magnetoelectronic devices based on doped manganites.