EPR Evidence of Jahn-Teller Polaron Formation in La 1-x Ca x MnO 3+y

摘要: The electron paramagnetic resonance (EPR) signal in the mixed valence perovskite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3+y}$ was investigated regime for ${}^{16}$O and ${}^{18}$O isotope substituted compounds. characteristic differences observed EPR intensity linewidth two samples can be explained by a model which bottlenecked spin relaxation takes place from exchange-coupled constituent ${\mathrm{Mn}}^{4+}$ ions via ${\mathrm{Mn}}^{3+}$ Jahn-Teller to lattice. For $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2$ ferromagnetic exchange energy $J$ exhibits ${}^{16}\mathrm{O}{/}^{18}\mathrm{O}$ oxygen effect of $\ensuremath{\sim}\ensuremath{-}10%$. effects suggest presence polarons these materials.