Influence of the grain size on the magnetic properties of TbMnO_{3}

The magnetic properties including magnetic structure of poly and nano samples of TbMnO_{3} are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form: modulated magnetic structure described by the propagation vector k=(k_{x},0,0) with different value of k_{x} for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the k_{x} component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the k_{x} values are larger for nano samples

Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle TbMnO3

This paper reports on investigations of magnetic properties, crystal and magnetic structures on $TbMnO_{3}$ prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol-gel method at temperatures of 800 and 850$^{\circ}$C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector $k = (0, k_{x}, 0)$ in between 41-5 K. Below T = 21 K, a change from a collinear ($A_{y}$ mode) into non-collinear ($A_{y}G_{z}$ mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated $G_{x}A_{y}F_{z}$ mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector $k = (0, k_{y}, 0)$, with ky components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear Ay mode down to 1.6 K where the Tb moment becomes ordered ($G_{x}A_{y}$ mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure