Magnetoresistance of coherently strainedLa2/3Ba1/3MnO3/SrTiO3superlattices

Abstract

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 \AA{} 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 ${\ensuremath{\varepsilon}}_{\mathrm{bi}}$ 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 ${\ensuremath{\varepsilon}}_{\mathrm{bi}}$ 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 $\ensuremath{\Delta}{=(T}_{p}{/T}_{p}^{\mathrm{bulk}}{)(d}^{2}{T}_{p}/d{\ensuremath{\varepsilon}}_{\mathrm{bi}}^{2})$ 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.