No abstract

Pure CoO nanoparticles in the 4.5-18 nm range have been prepared by the decomposition of Co(ΙΙ) cupferronate in Decalin at 270 °C under solvothermal conditions. The particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The particles are stable because of the organic coating that occurs in situ. The organic coating is readily removed by heating the particles to 260 °C without loss of the nanoparticulate nature. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the small CoO nanoparticles (<16 nm). The small nanoparticles do not exhibit a distinct antiferromagnetic transition around 300 K as the bulk sample but instead show hysteresis below a blocking temperature of ∼10 K.

Observation of ferroelectricity among non-d0 systems, which was believed for a long time an unrealistic concept, led to various proposals for the mechanisms to explain the same (i.e. magnetically induced ferroelectricity) during last decade. Here, we provide support for ferroelectricity of a displacive-type possibly involving magnetic ions due to short-range magnetic correlations within a spin-chain, through the demonstration of magnetoelectric coupling in a Haldane spin-chain compound Er2BaNiO5 well above its Néel temperature of (TN = ) 32 K. There is a distinct evidence for electric polarization setting in near 60 K around which there is an evidence for short-range magnetic correlations from other experimental methods. Raman studies also establish a softening of phonon modes in the same temperature (T) range and T-dependent x-ray diffraction (XRD) patterns also reveal lattice parameters anomalies. Density-functional theory based calculations establish a displacive component (similar to d0-ness) as the root-cause of ferroelectricity from (magnetic) NiO6 chain, thereby offering a new route to search for similar materials near room temperature to enable applications.