Magnetic states and spin-glass properties in Bi 0.67 Ca 0.33 Mn O 3 : Macroscopic ac measurements and neutron scattering

We report on the magnetic properties of the manganite ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(x=0.33)$ at low temperature. The analysis of the field expansion of the ac susceptibility and the observation of aging properties make clear that a spin-glass phase appears below $T=39\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the presence of magnetic order. Neutron scattering shows both magnetic Bragg scattering and magnetic diffusion at small angles and confirms this coexistence. In contrast to ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(x=0.3--0.33)$, which exhibits a mesoscopic phase separation responsible for a field driven percolation, the glassy and short range ferromagnetic order observed here does not cause a colossal magnetoresistance.