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The crystal structure, magnetic ordering, and dielectric characteristics of polycrystalline powder samples of La2NiMn1-xRuxO6 (x = 0.25-0.75) solid solutions have been studied. The X-ray diffraction results were analysed in detail, and reliably show that all compounds have a monoclinic (P2(1)/n) structure with Ni and Mn/Ru ions occupying the 2c and 2d sites, respectively. Magnetic susceptibility measurements reveal a ferromagnetic order for La2NiMn0.75Ru0.25O6 and La2NiMn0.5Ru0.5O6. The ferromagnetic transition temperature decreases from 200 K for La2NiMn0.75Ru0.25O6 to 175 K for La2NiMn0.5Ru0.5O6. Dielectric measurements show large dielectric constants (similar to 10(4)) at room temperature. In addition, the temperature-dependent loss-tangent Tan delta(T) curves reveal relaxation characteristics due to charge transfer between nearest cations.

The structural and magnetic properties of the Dy2CoMnO6, Dy2NiMnO6 and Gd2CoMnO6 double perovskites are investigated using X-ray powder diffraction and squid magnetometry. The materials adopt an orthorhombic structure (space ground Pnma) with disordered Co(Ni)/Mn cations, and exhibit ferrimagnetic transitions near T(C)85, 95, and 115K respectively. T-C was found to monotonously depend on the orthorhombic distortion (a-c)/(a+c) of the compounds. The crystal structure of the compounds was investigated as a function of temperature (16-1100K range), evidencing changes in the BO6 octahedron near T-C. The magnetic entropy changes are estimated for comparison of the magnetocaloric properties to those from literature.

Effects of Ru doping on the structure and magnetic properties of La2CoMn1-xRuxO6 ceramics with different compositions (x = 0, 0.1, 0.2, 0.3, 0.5, 0.75, 1.0) have been investigated using a variety of complementary techniques (X-ray powder diffraction and photoelectron spectroscopy, electron microscopy, and magnetometry). Phase-pure polycrystalline samples were prepared by the conventional solid-state reaction method including high pressure (3000 kg/cm(2) ) treatment of the original mixture of reagents. X-ray diffraction analyses of the samples accompanied with Rietveld refinement suggested a change in the crystal structure upon doping: for 0 <= x <= 0.3 the structure of the samples is predominantly disordered orthorhombic (s.g. Pnma) which transformed to ordered monoclinic (s.g. P2(1)/n) for 0.5 <= x <= 1. This suggests that Ru doping induces (partial) cation order in the B-sublattice. Magnetic measurements indicated a low temperature ferromagnetic phase, and a positive value of the Curie-Weiss temperature (theta cw) was derived for all samples of composition x <= 0.75. However, the Curie temperature (T-c) and theta cw decreased with increasing Ru doping. These changes in Tc upon doping can be correlated to the changes in the nearest neighbor and next nearest neighbor exchange interactions. The sample with x =1 orders antiferromagnetically at approximately 25 K.

Synthesis, crystal structure and magnetization measurements of phase pure polycrystalline RVO3 (R=Lu, Yb and Tm) are reported. The compounds were stabilized in the orthorhombic structure by thermal treatment of the respective precursors (RVO4) in a reducing atmosphere. Special pressure treatment was carried out during the synthesis to ensure phase pure samples without secondary phases. Magnetization measurements reveal the presence of two spin ordering temperatures in the samples. Interestingly, at the lower spin ordering temperature, TsO2, the uncompensated excess moment of the antiferromagnetic spin structure has different field dependences above and below TsO2, causing a jump in the thermal evolution of the magnetization that changes sign with increasing field strength. This jump is associated with the reported magnetic and orbital rearrangement in the samples, and the different spin configurations in the C- and G-type antiferromagnetic structures.