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

A series of coherently strained multilayer thin films of SrTiO3/La2/3Ba1/3M nO3 have been fabricated on (100) SrTiO3 and (100) NdGaO3 substrates by las er molecular-beam epitaxy. By the in-plane coherency strain the out-of-plan e lattice constant could be continuously adjusted from 3.916 to 3.975 Angst rom by varying the relative thickness of the SrTiO3 and La2/3Ba1/3MnO3 laye rs. The strain results in a biaxial distortion epsilon (bi) of La2/3Ba1/3Mn O3 that strongly affects the electrical transport properties and the magnet oresistance. Our measurements show that there is a clear correlation betwee n epsilon (bi) and the temperature T-p corresponding to the maximum in the resistivity versus temperature curves as well as the measured magnetoresist ance. By varying the strain we could derive the quantity Delta = (T-p/T-p(b ulk))(d(2)T(p)/d epsilon (2)(bi)) giving the sensitivity of the materials p roperties to biaxial strain. Our data provide evidence for the relevance of the Jahn-Teller electron-phonon coupling in the doped manganites. Our anal ysis 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 magne toelectronic devices based on doped manganites.