Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulatorPr1−xCaxMnO3

The high temperature paramagnetic state in an antiferromagnetic insulator ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ is characterized by the ferromagnetic spin fluctuations with an anomalously small energy scale. The ferromagnetic fluctuations show a precipitous decrease of the intensity at the charge ordering temperature $T_{\mathrm{CO}},$ but persist below $T_{\mathrm{CO}},$ and vanish at the antiferromagnetic transition temperature $T_{\mathrm{N}}.$ These results demonstrate the importance of the spin ordering for the complete switching of the ferromagnetic fluctuation in doped manganites.