Charge ordering and disordering transitions inPr1−xCaxMnO3 (x=0.4)as investigated by optical spectroscopy

The magnetic-field dependence of optical spectra and their anisotropy have been investigated for a single crystal of ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3\hspace{1em}(x=0.4\mathrm{})\mathrm{}$ at 30 K. The charge-ordered (CO) state is transformed into a ferromagnetic metallic state by a magnetic field of 6.5 T, which is manifested in a huge change of optical spectra over a wide photon-energy region (0.05 eV–3 eV). The observed change in magnitude and anisotropy of the optical spectra with the external magnetic field has been elucidated in terms of the spin- and orbital-ordering structures in the CO state.