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A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

We report an extraordinary coexistence of sign reversal of both magnetization and exchange bias field in the La0.2Ce0.8CrO3 nanoparticles. From the high resolution transmission electron microscopy image, and field dependence of thermoremanent and isothermoremanent magnetization measurements, the nanoparticles are found to be of core-shell nature. The core-shell configuration with an antiferromagnetic core of the Cr3+ and Ce3+ spins and a disordered shell with the uncompensated spins, explains the sign reversal of both magnetization and exchange bias field. The present study shows an excellent way of tuning the sign of both magnetization and exchange bias field in a single magnetic system.

In this paper we report the magnetic properties of nanosized CoO particles, prepared from sonochemically synthesized precursors and characterized using x-ray diffraction (XRD), conventional transmission electron microscopy (TEM) and scanning tunneling electron microscopy combined with energy dispersive x-ray analysis (STEM-EDX) techniques. The nanoparticles were faceted and the sizes varied between 30 and 60 nm depending on the time of annealing. They were stable even in the absence of any organic coating on them. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the CoO nanoparticles synthesized after 2 and 4 h of annealing of the sonochemically synthesized precursor under nitrogen. However, after 6 h of annealing, the nanoparticles show hysteresis not only at low temperatures (1.5 K) but also at higher temperatures (100 K and room temperature), indicating the presence of room temperature ferromagnetism.

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In this study, the ac magnetic hyperthermia responses of spinel CoFe 2 O 4 , MnFe 2 O 4 , and NiFe 2 O 4 nanoparticles of comparable sizes (∼20 nm) were investigated to evaluate their feasibility of use in magnetic hyperthermia. The heating ability of EDT-coated nanoparticles which were dispersed in two different carrier media, deionized water and ethylene glycol, at concentrations of 1 and 2 mg/mL, was evaluated by estimating the specific loss power (SLP) (which is a measure of magnetic energy transformed into heat) under magnetic fields of 15, 25, and 50 kA/m at a constant frequency of 195 kHz. The maximum value of SLP has been found to be ∼315 W/g for CoFe 2 O 4 and ∼295 W/g for MnFe 2 O 4 and NiFe 2 O 4 nanoparticles. We report very promising heating temperature rising characteristics of CoFe 2 O 4 , MnFe 2 O 4 , and NiFe 2 O 4 nanoparticles under different applied magnetic fields that indicate the effectiveness of these nanoparticles as hyperthermia agents.

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