Abstract :
A neutron powder diffraction (NPD) study of a polycrystalline rare-earth deficient Pr1−xMnO3 allowed us to analyse the room temperature crystallographic structure, the low temperature magnetic structure and its thermal evolution. The refinement of the crystallographic structure leads to a crystallographic composition Pr0.90(1)MnO3, nominally containing 30% of Mn4+ ions. The distortion of the MnO6 octahedra is important, implying the presence of the Jahn–Teller effect. Low temperature NPD data show that Pr0.90(1)MnO3 becomes ordered below TN≈86 K. Firstly, only Mn atoms order with a canted spin arrangement given by a CxFy arrangement. The magnetic moments form an angle close to 45° with the a-axis that varies very little with temperature down to 1.5 K. Pr atoms order below 53 K with a ferromagnetic structure of the Fy type. The magnetic moment obtained for Mn atoms at T=1.5 K is μMn=2.72 μB, whereas for Pr atoms it is 0.32 μB. The magnetic moment for Mn atoms is smaller than expected from the corresponding amount of Mn3+ and Mn4+ ions, which suggests that not all of the Mn spins contribute to the long-range ordering, becoming partially trapped in a spin-glass-like state.
