Structural and electrical properties of oxide composite of two ferroic ternary Ba 0.6 Sr 0.4 TiO 3 and Ni 0.5 Zn 0.5 Fe 2 O 4 were investigated. Powder x-ray diffraction studies show that the end products, BST possess cubic perovskite structure and NZF possess cubic spinel structure. A very systematic phase transition between these two phases has been achieved for intermediate doping ranges. Surface morphology revealed a uniform grain distribution with very low porosity for entire composite series. Real and imaginary permittivity and loss tangents for all the composites up to 1 MHz frequency range show high dielectric constants and low losses, respectively. Exceptionally, high dielectric permittivity values were obtained for composite samples as compared to pristine end products. At lower frequencies, the values of dielectric permittivity were high, because the excitation of bound electrons, lattice vibration, dipole orientation and space charge polarization are active. At high frequencies, the dielectric permittivity exhibited frequency independence behavior for entire series. AC conductivities determined from the dielectric data exhibited strong frequency dependence with a non linear increase with increasing frequencies. The electrical conduction in the system may be modeled by hopping model.
Lead-free all oxide composite thin films comprising ferromagnetic (FM) and ferroelectric (FE) phases are observed as promising candidates for multifunctional device applications. A series of composites having systematic replacement of FM La0.67Sr0.33MnO3 (LSMO) by FE-Na0.5K0.5NbO3 (NKN), all oxide composite thin films were optimally grown by pulsed laser deposition. While x-ray diffraction confirmed a systematic phase change from a rhombohedral to an orthorhombic structure, almost monodispersed grain size distribution and smooth surface topography were revealed by atomic force microscopy. Two-probe dielectric spectroscopy indicated a pronounced enhancement of real permittivity for 0.4 sample as compared to the pure FM and FE parent compounds. Similarly, an enhancement in the magnetodielectric permittivity revealed high values for intermediate composites. The enhancement in the dielectric and magnetoelectric coupling is suggested to be due to the magnetostriction effect in FM (LSMO), which induces stress that is in turn transferred to the FE (NKN) phase, leading to strong FM–FE coupling. X-ray photoelectron spectroscopy reveals the presence of Mn in +3 and +4 states in the FE–FM composites. The presence of these mixed valence states can be ascribed to the magnetic properties within the composites.
Ca3CoMnO6, a quasi-1D Ising chain at low temperature offers rich fundamental physics and applications. We have studied the dielectric and magnetoelectric coupling in Fe doped Ca3CoMnO6 (CCMO) bulk ceramics prepared by co-precipitation technique. Single phase hexagonal crystal structure having R-3C space group was confirmed by x-ray diffraction. Extremely low currents were observed up to 20% Fe doping. Doping dependence of magnetoresistance (MR) revealed both positive and negative MR, with anomalously high MR values beyond 3000% in diluted Fe doped CCMO; whereas the higher doping of Fe was found to result in negative MR due to enhanced magnetostriction effects. The dielectric study was carried out for a range of 20 Hz to 10 MHz. The negative value of the colossal magnetodielectric induced in the Fe doped samples can be attributed to the magnetostriction effect along with interfacial Maxwell-Wagner polarization.
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