The influence of oxygen vacancies on the dielectric relaxation behavior of pure and Eu-substituted BiFeO₃ nanoparticles synthesized by a sol–gel technique has been studied using impedance spectroscopy in the temperature range of 90 °C to 180 °C.

The authors fabricated Pb(Zr0.52Ti0.48)O3–NiFe2O4 composite films consisting of randomly dispersed NiFe2O4 nanoparticles in the Pb(Zr0.52Ti0.48)O3 matrix. The structural analysis revealed that the crystal axes of the NiFe2O4 nanoparticles are aligned with those of the ferroelectric matrix. The composite has good ferroelectric and magnetic properties. The authors measured the transverse and longitudinal components of the magnetoelectric voltage coefficient, which supports the postulate that the magnetoelectric effect comes from direct stress coupling between magnetostrictive NiFe2O4 and piezoelectric Pb(Zr0.52Ti0.48)O3 grains.

We investigated electronic structure of hexagonal multiferroic ${\mathrm{YMnO}}_3$ using the polarization dependent x-ray absorption spectroscopy (XAS) at O $K$ and Mn $L_{2,3}$ edges. The spectra exhibit strong polarization dependence at both edges, reflecting anisotropic Mn $3d$ orbital occupation. Moreover, the O $K$ edge spectra show that Y $4d$ states are strongly hybridized with O $2p$ ones, resulting in large anomalies in Born effective charges on off-centering Y and O ions. These results manifest that the Y $d^0$-ness with rehybridization is the driving force for the ferroelectricity, and suggest a new approach to understand the multiferroicity in the hexagonal manganites.

Polyethylene glycol (PEG) coated magnetic Fe₃O₄ nanoparticles with diameters of 12 nm, 15 nm, and 16 nm were synthesized by the usual co-precipitation method. The structure and morphology of the samples were characterized using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The ac magnetic susceptibility measurements were carried out using a vibrating sample magnetometer (VSM). The dc magnetic measurements were carried out using a commercial Quantum Design superconducting quantum interference device (SQUID). The XRD patterns indicated the sole existence of the inverse cubic spinel phase of Fe₃O₄ in all the samples. The histograms extracted from the TEM images show narrow size distributions with average sizes that are very similar to those obtained from the XRD images using the Scherrer’s formula. The temperature dependence of both coercivity and saturation magnetization, which were determined from the magnetic hysteresis loops, were found to have considerable deviations from the Bloch’s and Kneller’s laws. The size-dependent coercivity and saturation magnetization were found to be non-monotonic at nearly all temperatures. These results are discussed and attributed mainly to the finite size effects in addition to the existence of inter-particle interactions and of spin-glass structures that resulted from frozen canted surface spins at low temperatures.