ACTA

Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle TbMnO₃

W. Bażela^a, M. Dul^a, V. Dyakonov^{b, c}, Ł. Gondek^d, A. Hoser^e, J.-U. Hoffmann^e, B. Penc^f, A. Szytuła^f, Z. Kravchenko^c, I. Nosalev^c and A. Zarzycki^g
^aInstitute of Physics, Technical University of Cracow, Podchorążych 1, 30-084 Kraków, Poland
^bInstitute of Physics, PAS, al. Lotników 32/46, 02-668 Warszawa, Poland
^cA.A. Gałkin Donetsk Physico-Technical Institute, NANU, R. Luxemburg 72, 83114 Donetsk, Ukraine
^dFaculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland
^eHelmholtz-Zentrum Berlin für Materialen and Energie GmbH, Hahn-Meitner-Platz 1, 14-109 Berlin, Germany
^fM. Smoluchowski Institute of Physics, Jagiellonian University, W.S. Reymonta 4, 30-059 Kraków, Poland
^gH. Niewodniczański Institute of Nuclear Physics, PAS, E. Radzikowskiego 152, 31-342 Kraków, Poland

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This paper reports on investigations of magnetic properties, crystal and magnetic structures on TbMnO₃ 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°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_yG_z mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated G_xA_yF_z mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, k_y, 0), with k_y components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear A_y mode down to 1.6 K where the Tb moment becomes ordered (G_xA_y mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.

DOI: 10.12693/APhysPolA.122.384
PACS numbers: 75.40.Cx, 75.47.Lx, 75.25.-j, 75.50.Ee