Investigation of Lattice Effects in Rare Earth Manganites by 18O-isotope Exchange

Abstract

The strong coupling between the electron spin and lattice arising from the Jahn-Teller effect of manganese ions plays an important role in the mechanism of colossal magnetoresistance and related properties of the rare earth manganites. The lattice effects in this class of oxides have been extensively studied through the application of hydrostatic as well as chemical pressures and magnetic fields. The recently observed giant ¹⁸O isotope effect provides direct evidence for the formation of lattice polarons in manganites. Here we report the preliminary results of our investigations on a variety of normal as well as ¹⁸O isotope-exchanged perovskite manganites exhibiting colossal magnetoresistance and charge ordering. The observed isotope shift of T_c as well as that of T_co is correlated with the key parameters controlling the lattice such as the Mn ³⁺ content, the average ionic radius of the A-site cation ⟨r_A⟩ , and the A-site ionic size disorder σ² .