Effect of Cr substitution on the crystal and magnetic structure of (Pr0.55Ca0.45)MnO3: A neutron powder diffraction investigation

he crystal and magnetic structures of (Pr0.55Ca0.45)(Mn1-yCry)O-3 (y=0.00,0.03,0.06) have been investigated between 5 and 300 K by neutron powder diffraction and dc magnetic measurements. An orthorhombic-to-monoclinic phase transition occurs on cooling in (Pr0.55Ca0.45)MnO3 at T approximate to 239 K; at lower temperature charge ordering in the Mn sublattice, coupled with orbital ordering, induces an AFM spin ordering within the monoclinic phase. Cr substitution at the Mn site hinders the structural phase transition, although for the y=0.03 sample small amounts of the monoclinic phase coexist at low temperature with the main phase characterized by an orthorhombic structure. Cr substitution prevents charge ordering, favoring double exchange and hence FM spin ordering within the Mn sublattice.