Writers: Maria Elenice dos Santos, Rafael Aparecido Ferreira, Paulo Noronha Lisboa-Filho, Octavio Peña
Keywords: Multiferroic materials; Magnetic properties; Ferrimagnetism; Valence fluctuations
Abstract: 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 Bi3þ ions entering into the CoIII octahedral sites do not alter the effective moment, meff 8.2 mB, whereas both the magnetization M50 kOe at the highest field (50 kOe) and the field-cooled MFC magnetizations increased when increasing the Bi content. The ferrimagnetic character of the parent compound, Co2MnO4, is maintained for all materials although the antiferromagnetic interactions Co2þ–Co2þ 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 Bi3þ ion is responsible of non-centrosymmetric charge ordering and should lead to multiferroı¨sme conditions for the BixCo2xMnO4 material.
DOI: 10.1016/j.jmmm.2012.09.070
