Magnetic and Electrical Characteristics of Nd 3+ and Mn 2+ -Co-doped Calcium Molybdato-Tungstates Single Crystals.

Single crystals of Ca 1-3 x - y Mn y □ x Nd 2 x (MoO 4 ) 1-3 x (WO 4 ) 3 x molybdato-tungstates (□ denotes vacant sites) with a scheelite-type structure have been successfully grown by the Czochralski technique in an inert atmosphere. This paper presents the results of structural, optical, magnetic, and electrical properties, as well as the broadband dielectric spectroscopy measurements of single crystals with different Nd 3+ ion concentrations, i.e. , when x = 0.0050 or x = 0.0098, and with constant content of Mn 2+ ions, i.e. , when y = 0.0050. Our magnetic studies have shown that substitution of diamagnetic Ca 2+ ions in the CaMoO 4 matrix with paramagnetic Nd 3+ ones with a content not exceeding 0.02 and having a screened 4f-shell revealed a significant effect of orbital diamagnetism and Van Vleck's paramagnetism. Both single crystals have revealed residual electrical conductivity without an intrinsic region and a change of sign of the Seebeck coefficient at ca. 230 K. Dielectric spectroscopy measurements have shown constant values of relative permittivity (ε r ∼ 8) and loss tangent (tan δ ∼ 0.01) both up to 400 K and up to 1 MHz, as well as the Fermi energy (∼0.04 eV) and the Fermi temperature (∼500 K) determined for both crystals from the diffusion component of thermopower. These results suggest the presence of shallow acceptor and donor levels in the studied crystals.