Observation of Kosterlitz-Thouless spin correlations in the colossally magnetoresistive layered manganite $L{a}_{1.2}S{r}_{1.8}M{n}_2{O}_7$

Abstract

The spin correlations of the bilayer manganite $L{a}_{1.2}S{r}_{1.8}M{n}_2{O}_7$ have been studied using neutron scattering. On cooling within the paramagnetic state, we observe purely two-dimensional behavior with a crossover to three-dimensional scaling close to the ferromagnetic transition. Below $T_C$, an effective finite size behavior is observed. The quantitative agreement of these observations with the conventional quasi two-dimensional Kosterlitz-Thouless model indicates that the phase transition is driven by the growth of magnetic correlations, which are only weakly coupled to polarons above $T_C$.

4 pages (RevTex), 3 embedded EPS figures