We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO 3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO 3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO 3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO 3 ceramic synthesized at 880°C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current.

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Raman spectra of ZnO and Co substituted Zn 1−x Co x O ͑ZCO͒ were carried out using the Raman microprobe system with an Ar + ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E 2 low mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization ͑1.2 B /Co͒ for 10% Co substitution, which decreased with at further increase in Co concentrations. The intensities of E 1 ͑LO͒ at 584 cm −1 and multiphonon modes at 540 cm −1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution ͑x =15%-20%͒ were identified to be due to the spinel ZnCo 2 O 4 secondary phase.

The multi phonon Raman scattering in Mn doped (1%–10%) ZnO was observed at room temperature using 514.5nm Ar+ laser. The additional optical modes at 327, 332, 482, 532, and 680cm−1 in Zn1−xMnxO targets were identified as the second order Raman modes in the disordered lattice and the precipitation of the secondary phase ZnMn2O4. The crystalline grain sizes of 1%, 3%, 5%, and 10% Mn doped ZnO samples were calculated by phonon confinement model as 31.8, 18.3, 15.9, and 14.1nm, respectively. The optical band gap was found to be increased (3.27–3.41eV) due to the Mn doping.

The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1−xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400K) and frequency (1kHz–1MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300K and 9.28GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the multiferroic properties of BiFeO3.

The magnetic and structural properties of InAs:Mn self-organized diluted magnetic quantum dots grown by low-temperature ͑ϳ270°C͒, solid-source molecular-beam epitaxy using a very low InAs growth rate ͑Ͻ0.1 ML/ s͒ are investigated. A Curie temperature ͑T C ͒ of ϳ350 K is measured in a sample grown with a Mn/ In flux ratio of 0.15. Electron energy-loss spectroscopy confirms that most of the Mn remains within the InAs quantum dots. We propose as a possible explanation for this high T C the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms amongst the InAs quantum dots.

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