Structural, electrical and magnetic properties of Bi-substituted Co 2MnO 4

Abstract

Structural, electrical and magnetic properties of single phase Bi x Co 2− x MnO 4 (0 ≤ x ≤ 0.3) spinel materials synthesized by solid state reactions were studied. All the samples exhibit single phase with cubic spinel structure (space group Fd3 m) and the lattice parameter increases with the Bi-substitution. The grain size was also observed to increase with the Bi-substitution. All the samples exhibit the semiconducting behaviour and overall resistivity decreases with the increase in the Bi-substitution. The dc as well as ac conductivity data were analyzed in the light of various conductivity models. The dc conductivity data is explained using variable range hopping (VRH) model. All the samples show diffused ferroelectric (FE) transition and follow the Debye-type relaxation, whereas ferroelectric transition temperature ( T C ) increases with the Bi-substitution. The ac conductivity calculated from the dielectric data as a function of temperature and frequency demonstrate the cross-over from small polaron tunneling (SPT) to correlated barrier hopping (CBH) type conduction in these materials. The influence of cation composition on the magnetic properties of Bi x Co 2− x MnO 4 (0 ≤ x ≤ 0.3) mixed cubic spinel system has been studied by dc magnetization. Soft magnetic type behaviour was observed in the Bi-substituted samples, showing magnetic dilution and the increased value of saturation magnetization suggests the presence of canted spin structure due to the incorporation of Mn and Bi. Nevertheless, ferrimagnetic (FM) nature of the Co 2MnO 4 is preserved in the Bi-substituted samples. The coexistence of ferroelectricity and ferrimagnetism in these materials is attributed to the off centering of cations that result in non-centrosymmetric arrangement and canted spin structure. These materials are promising candidates for multiferroic applications.