Dielectric and magnetic characteristics of Ca1-x Mn x MoO4 (0 ≤ x ≤ 0.15) nanomaterials.

Scheelite-type Ca1-x Mn x MoO4 (x = 0.0, 0.01, 0.05, 0.10 and 0.15) nanomaterials were successfully synthesized via a combustion route. Dielectric studies showed a weak n-type electrical conductivity characteristic for insulators and low relative permittivity (ε r < 15) decreasing with increasing Mn2+ content. CaMoO4 and Mn2+-doped nanomaterials are chemically compatible with Al and Ag electrodes and promising for low-temperature co-fired ceramic applications. Magnetic studies showed, at room-temperature diamagnetism for pure CaMoO4, the balance between diamagnetism and paramagnetism for Ca1-x Mn x MoO4 (x = 0.01) and paramagnetic behaviour when 0.05 ≤ x ≤ 0.15 as well as the short-range antiferromagnetic interactions growing in strength as Mn2+ content increases. The Landé factor fitting procedure showed a spin-only contribution to the magnetic moment. CaMoO4 matrix unexpectedly revealed the residual paramagnetism at low temperatures derived probably from the molybdenum ions having unpaired 4d electrons as well as a paramagnetic-diamagnetic transition at 70 K.

Percolation limit and stability conditions for the spin glass state in the spinel families based on the two matrices CuCr(2)S(4) and CuCr(2)Se(4) doped by Sb ions.

The percolation limit of the appearance of the spin glass state in the compounds under study has been obtained experimentally. The conditions of stability of the spin glass state have been analyzed here on the basis of the de Almeida-Thouless theory for two spinels differing in the magnetic coupling constants. It turned out that for the higher value of the coupling constant the magnetic field influences the freezing temperature more strongly. Moreover, the greater the coupling constant the broader the range of the possible values of freezing temperatures, in other words the greater the temperature range of the appearance of the spin glass states. It was proved that for the stability of the spin glass state the existence of a small magnetic field is necessary. In our case the value of this field is equal to 3.46 × 10(-23)T(G). For the compounds under study the value of the magnetic coupling constant J cannot exceed 130 K for the spin glass state to appear.