A. Hoser

Magnetic structures and physical properties of Tm3Cu4Ge4 and Tm3Cu4Sn4.

Tm(3)Cu(4)Ge(4) crystallizes in the orthorhombic Gd(3)Cu(4)Ge(4)-type crystal structure (space group Immm) whereas Tm(3)Cu(4)Sn(4) crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm(3)Cu(4)Ge(4) the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector k = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm(3)Cu(4)Sn(4), given by a propagation vector k = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector k = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm(3)Cu(4)Ge(4) and Tm(3)Cu(4)Sn(4), respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.

Magnetic and Neutron Diffraction Studies of Magnetic Properties of the Nanoparticle RMnO3 (R = Tb, Dy) Manganites

We report the X-ray and neutron diffraction and magnetic measurements of the polycrystalline bulk and nanosize RMnO3 (R = Tb, Dy) compounds synthesized at temperatures of 800 and 850 °C. Diffraction data indicate that all the samples crystallize in the orthorhombic crystal structure (space group Pnma). The crystal structure parameters change slightly with preparation. All the samples are shown to be antiferromagnets. The Mn magnetic moments order near 40 K while the rare earth ones order below 10 K. Macroscopic magnetic and neutron diffraction data indicate the small difference of properties of bulk and nanosamples in the case of DyMnO3 and significant difference in TbMnO3. For nano-TbMnO3, the observed broadening of magnetic peaks suggests the cluster-like character of magnetic ordering.