A series of coherently strained multilayer thin films of ${\mathrm{SrTiO}}_3{/\mathrm{L}\mathrm{a}}_{2/3}{\mathrm{Ba}}_{1/3}{\mathrm{MnO}}_3$ have been fabricated on (100) ${\mathrm{SrTiO}}_3$ and (100) ${\mathrm{NdGaO}}_3$ 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 Å by varying the relative thickness of the ${\mathrm{SrTiO}}_3$ and ${\mathrm{La}}_{2/3}{\mathrm{Ba}}_{1/3}{\mathrm{MnO}}_3$ layers. The strain results in a biaxial distortion ${\varepsilon }_{\mathrm{bi}}$ of ${\mathrm{La}}_{2/3}{\mathrm{Ba}}_{1/3}{\mathrm{MnO}}_3$ that strongly affects the electrical transport properties and the magnetoresistance. Our measurements show that there is a clear correlation between ${\varepsilon }_{\mathrm{bi}}$ 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 $\Delta {=(T}_p{/T}_p^{\mathrm{bulk}}{\left)\right(d}^2{T}_p/d{\varepsilon }_{\mathrm{bi}}^2)$ 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.

• Received 20 July 2000

DOI:https://doi.org/10.1103/PhysRevB.62.15806