Cation distribution and magnetic characterization of the multiferroic cobalt manganese Co2MnO4 spinel doped with bismuth

The structural and magnetic properties of the cubic spinel oxide Co2MnO4 (Fd3m space group) doped with different concentrations of bismuth, were investigated by X-ray diffraction and SQUID magnetometry. The Bi3+ ions entering into the Co-III octahedral sites do not alter the effective moment, mu(eff) similar to 8.2 mu(B), whereas both the magnetization M-50 kOe at the highest field (50 kOe) and the field-cooled M-FC magnetizations increased when increasing the Bi content. The ferrimagnetic character of the parent compound, Co2MnO4, is maintained for all materials although the antiferromagnetic interactions Co2+-Co2+ are affected, resulting in higher values of the Curie-Weiss temperature. Due to the large ionic radius of Bi, octahedra distortions occur as well as valence fluctuations of the Mn ions, giving rise to Jahn-Teller effects and enhancing the exchange interactions. The off-center Bi3+ ion is responsible of non-centrosymmetric charge ordering and should lead to multiferroisme conditions for the BixCo2-xMnO4 material. (C) 2012 Elsevier B.V. All rights reserved.