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...

No abstract

No abstract

No abstract

No abstract

Gadolinium doped Zinc oxide (Zn1−xGdxO) nanocrystals with different percentage of Gd content (x = 0, 0.2, 0.4, 0.6, 0.8) have been prepared by the solid state reaction method. The structural, morphological and chemical studies of the samples were performed by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy dispersive X-ray (EDX) analysis. The XRD spectra confirm that all the samples have hexagonal wurtzite structure. Decrease in average crystallite size with an increase in Gd concentration is observed in XRD. SEM images show that the grain size of undoped ZnO is larger than the Gd doped ZnO, specifying the hindrance of grain growth upon Gd doping. The chemical composition of the samples was confirmed using Energy dispersive X-ray (EDX) analysis. The variation of dielectric constant (εr), dielectric loss (tan δ) and AC conductivity as a function of frequency is studied at room temperature in a frequency which ranges from 100 Hz -4.5 MHz by using LCR Hi TESTER. All the samples exhibit the normal dielectric behavior, i.e. decreases with increase in frequency which has been explained in the light of Maxwell-Wagner model. The dielectric constant and dielectric loss can be varied intensely by tuning Gd concentration in Zn1−xGdxO compounds.

The electrical characterization of bone is essential for the better understanding of the role of electrical stimulation in bone remodeling. Calcium Hydrogen Phosphate Dihydrate or brushite (CaHPO₄ 2H₂O) has been used in bone substitution owing to their fast resorption under physiological condition. Brushite is a suitable matrix for osteoconductive bone grafts. In this work, Calcium Hydrogen Phosphate single crystals have been grown by single diffusion gel growth technique. The powder XRD studies revealed the monoclinic structure of the grown crystals. The vibrational analysis of the crystals is done with FTIR spectroscopy and the major functional groups and their assigned vibrations are discussed. The frequency dependence of dielectric constant and ac conductivity at different temperatures have been studied in detail. This study shows decrease in the dielectric constant with the increase in frequency and temperature. The variation of ac conductivity is found to be increasing with frequency and decreasing with temperature.

We report the near-edge x-ray absorption spectroscopy (NEXAFS) at the Co/Mn L(3,2) edge and oxygen K edge of the well-characterized Bi-substituted Co(2)MnO(4) multiferroic samples. The evolution of peak features in NEXAFS spectra of the Co/Mn L(3,2) edge and O K edge show the Bi-induced redistribution of magnetic cations (Co/Mn). The variation in valence states of Co and Mn in all the substituted compositions is consistent with the observed ferrimagnetic behaviour of the samples. Magnetization data show the decrease in molecular field complementing the ferrimagnetism. The role of Bi in the enhancement of magnetic interactions as well as the appearance of ferroelectricity in Bi(x)Co(2-x)MnO(4) (0≤x≤0.3) is discussed.