Structure, Magnetization and Resistivity of La${}_{1-x}$M${}_x$CoO${}_3$ (M = Ca, Sr, and Ba)

Abstract

We present an investigation of the influence of structural distortions in charge-carrier doped \lmco by substituting La${}^{3+}$ with alkaline earth metals of strongly different ionic sizes, that is M = Ca${}^{2+}$, Sr${}^{2+}$, and Ba${}^{2+}$, respectively. We find that both, the magnetic properties and the resistivity change non-monotonously as a function of the ionic size of M. Doping \lmco with M = Sr${}^{2+}$ yields higher transition temperatures to the ferromagnetically ordered states and lower resistivities than doping with either Ca${}^{2+}$ or Ba${}^{2+}$ having a smaller or larger ionic size than Sr${}^{2+}$, respectively. From this observation we conclude that the different transition temperatures and resistivities of \lmco 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 La${}^{3+}$ and M${}^{2+}$ play an important role, too.

8 pages including 6 figures; accepted in Phys. Rev. B