Grain size effect on magnetic properties of REMnO₃ (RE = Pr, Nd)

X-ray diffraction and magnetic using dc and ac methods measurements of the polycrystalline and nanosize REMnO₃ (RE = Pr, Nd) powdered samples have been performed. The nanosize manganites were synthesized with a sol-gel method at different (800, 850 and 900 °C) temperatures. The average size of synthesized nanoparticles (from 56 to 89 nm) and polycrystalline powders (above 200 nm) was estimated using the x-ray diffraction data. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature with smaller values of the lattice parameters in the nanosamples. The temperature-dependent ac magnetic susceptibilities show a sharp high-temperature peak connected with Mn magnetic moments ordering. The low-temperature maximum of magnetic susceptibility is proposed to be due to the polarization of the rareearth sublattice by an effective exchange field of the Mn ordered sublattice. The antiferromagnetic ordering of Mn sublattice and paramagnetic Curie temperatures as well as the magnetic moment values for the nanosize samples were found to be smaller than those for polycrystalline sample

Phase transitions in TbMnO₃ manganites

X-ray diffraction and magnetic measurements of polycrystalline and nanosize TbMnO₃ manganites have been performed. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature. The nanosize manganites were synthesized with a sol-gel method at different (800 and 900°C) temperatures. The average size of synthesized nanoparticles (from 45 to 70 nm) was estimated by using the x-ray diffraction and low-temperature adsorption of argon methods. An information on the evolution of properties of TbMnO₃ with changing grain size, temperature and magnetic field was obtained. The crystal structure parameters of nanospecimens change slightly with changing the nanoparticle size. The peculiarities of magnetic ordering in polycrystalline and nanosize TbMnO₃ were compared. Magnetization and the Nèel temperature corresponding to antiferromagnetic ordering of the Tb³⁺ sublattice decrease as the particle size is reduced. The inverse magnetic susceptibility of the nanoparticle samples deviates from the Curie–Weiss law below 50 K, that is connected with the magnetic ordering of the Mn³⁺ moments. Specific heat of the nanosize samples exhibits anomalies related to the magnetic ordering of the Tb³⁺ and Mn³⁺ sublattices

Magnetic Properties of the RCoSn (R=Tb-Er) and RRhGe (R=Ce, Nd) Compounds

Magnetic properties of orthorhombic RCoSn (R = Tb-Er) and RRhGe (R = Ce,Nd) (of the TiNiSi-type of crystal structure), were studied by magnetometric and neutron diffraction methods. All RTX compounds order antiferromagnetically at low temperatures. The magnetic structure of TbCoSn and HoCoSn is sine-wave-modulated with the wave vectors k$\text{}_{1}$ = (0, 0.25, 0.11) and k$\text{}_{2}$ = (0, 0.333, 0), respectively. The magnetic structures of CeRhGe and NdRhGe compounds are collinear (C mode). Magnetic moments of 1.4(2) and 2.0(2) μ$\text{}_{B}$ localized respectively on Ce and Nd ions, are aligned along the a-axis

Magnetic Properties of RRhGe (R = Dy and Tm) Compounds

The magnetic properties of the ternary intermetallic RRhGe (R = Dy and Tm) were investigated by magnetic and neutron diffraction measurements. These compounds crystallize in a TiNiSi-type orthorhombic structure and are antiferromagnets with the Néel temperature 20 K (R = Dy) and 6.2 K (R = Tm). The neutron diffraction data reveal that the magnetic order in TmRhGe is collinear with the magnetic unit doubled along the b-axis respective to the crystal one