Structure, magnetization, and resistivity of La 1 − x M x CoO 3 ( M = Ca , Sr, and Ba)

We present an investigation of the influence of structural distortions in charge-carrier doped ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{CoO}}_{3}$ by substituting ${\mathrm{La}}^{3+}$ with alkaline-earth metals of strongly different ionic sizes, that is, $M={\mathrm{Ca}}^{2+},$ ${\mathrm{Sr}}^{2+},$ and ${\mathrm{Ba}}^{2+},$ respectively. We find that both the magnetic properties and the resistivity change nonmonotonically as a function of the ionic size of M. Doping ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{CoO}}_{3}$ with $M={\mathrm{Sr}}^{2+}$ yields higher transition temperatures to the ferromagnetically ordered states and lower resistivities than doping with either ${\mathrm{Ca}}^{2+}$ or ${\mathrm{Ba}}^{2+}$ having a smaller or larger ionic size than ${\mathrm{Sr}}^{2+},$ respectively. From this observation we conclude that the different transition temperatures and resistivities of ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{CoO}}_{3}$ for different M (of the same concentration $x)$ do not only depend on the varying chemical pressures. The local disorder due to the different ionic sizes of ${\mathrm{La}}^{3+}$ and ${M}^{2+}$ plays an important role, too.