Magnetic Properties of Nanoparticle RMnO₃ (R=Pr, Nd, and Tb) Compounds

Abstract

The effect of particle size on the magnetic properties of RMnO₃ (R = Pr, Nd, and Tb) has been investigated by magnetometric and X-ray and neutron diffraction methods. The samples were obtained by a sol–gel method. The investigated compounds with a grain size < 100 nm crystallize in the orthorhombic crystal structure described by the Pnma space group. The crystal parameters for the nanoparticle compounds are slightly smaller than those for bulk materials Low temperature magnetic and neutron diffraction data indicate the difference in their magnetic properties. For the nanoparticle PrMnO₃ (annealed at 900 °C) and NdMnO₃ samples, the magnetic ordering of CxFy-type exists in Mn sublattice while in PrMnO₃ annealed at 800 °C it is missing. The Nd moments order below T ≈ 13 K according to a ferromagnetic arrangement of Fy-type.

For the nanoparticle TbMnO₃ compounds, the magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (k_x, 0, 0) with the different values of the k_x component for respective sublattices. The magnetic ordering in the Mn sublattice is described by a collinear C_x mode down to 1.6 K. Decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (FyAz mode). The observed broadening of Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.