Magnetoelectric properties of BixCo2−xMnO4 (⩽x⩽0.3)

Abstract

We present the structural, dielectric and magnetization study of single phase polycrystalline Bi x Co 2−x MnO 4 ͑0 ഛ x ഛ 0.3͒, synthesized by a conventional solid state route. All the samples have the cubic spinel structure with Fd3m space group. Bi-substitution in Co 2 MnO 4 stabilizes the ferroelectric transition at a temperature of ϳ350 K and enhances the dielectric constant with a relaxor behavior. The capacitance-voltage ͑C-V͒ measurements confirm the ferroelectric nature at room temperature. Ferrimagnetic nature of the Co 2 MnO 4 is preserved in the Bi-substituted samples. Magnetocapacitive coupling proves candidature of these materials from an application point of view. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2894518͔In multiferroic materials, magnetism and ferroelectricity ͑FE͒ coexist. These materials have attracted considerable attention in recent years. [1][2][3][4][5][6][7] The simultaneous occurrence of ferromagnetism/ferrimagnetism ͑FM͒ and FE and the coupling between these two order parameters could lead to the emergence of new storage media, which enable electrically reading/writing of the magnetic memories and vice versa, yielding more degrees of freedom from device application point of view. Multiferroics with coupled electrical and magnetic properties are termed as magnetoelectric multiferroics. However, there are only very few multiferroic materials with a sufficient amount of magnetoelectric coupling because of the contrasting origins of these properties. Among recently established magnetoelectric multiferroic materials, 8 frustrated magnets and geometrical frustration of lattice degrees of freedom have been found to be the leading mechanisms for perovskite manganites and cubic spinel systems, respectively. In this context, for FE and FM to coexist in single phase, the atom which moves off the center to induce the electric dipole moment should be different from those that carry the magnetic moment ͑atoms with partially filled d orbitals, responsible for FM͒. Recent ab initio calculations for existing ferroelectrics suggest that atoms with d 0 configuration create more off center distortion. 2,4 In principle, coexistence of FE and FM can be achieved through either an alternative mechanism like a non-d electron for magnetism or through an alternative mechanism for FE. In practice, alternative mechanisms for FE are pursued. 7 One such alternative followed is the induction of nonmagnetic ions having stereochemically active lone pair of electrons that may introduce off centering in the structure containing transition metal ions. 9 Also, spin-phonon coupling that may lead to dielectric anomalies has been envisaged for geometrically frustrated ZnCr 2 O 4 spinel. 10 Multiferroicity in conventional spinel oxides has been predicted 11 and studied. However, the strength of magnetoelectric coupling was found to be weak. 12 One can think of a way to engineer a new class of materials, combining the mechanisms discussed in previous paragraph to achieve multiferroicity in spinel materials. Inc...

Electron spin resonance and resistivity studies of charge-ordered Bi(1−x)SrxMnO3

“…BiMnO 3 exhibits ferroelectric as well as ferromagnetic properties and hence can be used as a good multiferroic material [10,11]. The Bi doped manganites have been shown to be prospective materials for multiferroic and bolometric applications [12][13][14][15]. Bi 0.5 Sr 0.5 MnO 3 has been shown to be a promising candidate for use as a cathode material in solid oxide fuel cells because of its high electrochemical performance [16].…”

Structural and transport properties of Bi-substituted Co2MnO4

“…Details of the material synthesization are given elsewhere. 4 The crystal structure of the materials was studied at room temperature using a Bruker D8 x-ray diffractometer with Cu K␣ radiation in 2 range of 15°-75°. The dc-conductivity measurements were performed using the standard four-probe technique in a temperature range of 150-400 K. The temperature was controlled within Ϯ50 mK using a Lakeshore temperature controller.…”

“…11 We propose to engineer a class of materials by incorporation of Bi in the spinel structure of cobalt manganite spinels ͑Co 2 MnO 4 ͒. In our earlier work 4 we have shown that BixCo 2−x MnO 4 ͑Ͻ0x Ͻ 0.3͒ exhibit a strong magnetoelectric coupling up to ϳ180 K. We present here the detailed structural and electrical properties of the Bi x Co 2−x MnO 4 ͑0.0Յ x Յ 0.3͒ system.…”

“…2,3 Chemical and physical properties of ternary spinels can be tailored by changing the cation distribution at tetrahedral and octahedral sites. [4][5][6][7][8] In all spinel-like structures the oxygen parameter u has a value around 0.375 and is crucial for transport properties. For u = 0.375, the arrangement of O 2− ions are exactly a cubic close packing.…”

Magnetoelectric behavior of ferrimagnetic BixCo2−xMnO4 (x=0, 0.1 and 0.3) thin films

“…In practice, coexistence of FE and FM is achieved through induction of non-magnetic ions having stereochemically active lone pair of electrons, which can introduce off centering in the structure containing magnetic transition metal oxides [5,6]. Recently, we have reported that incorporation of Bi has introduced noncentrosymmetric charge ordering and consequently polarization in the Co 2 MnO 4 spinel structure along with non-collinear antiferromagnetic (AFM) ordering among the Co 2 + sublattices, which lead to FM and magnetoelectric effect [7,8]. It is important to mention here that the above work was reported for the bulk material, whereas these properties in the thin film form are required for device realization.…”