Particle size effect on the magnetic properties of NiO nanoparticles prepared by a precipitation method

Nickel oxide (NiO) nanoparticles of nominal size range 16 nm and 25 nm were obtained by controlling the calcination temperature. These particles were prepared by the precipitation method. Structural, optical and morphological characterizations were done by X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy and scanning electron microscopy. Studies of magnetic measurements (up to 60 kOe) and temperature variations from 2 K to 300 K of the NiO nanoparticles were investigated. Particles of 16 nm exhibited a weak ferromagnetic component and hysteresis loop. There is a increase in coercivity Hc and the remanence Mr at 8 K accompanied by an exchange bias HE. HE monotonically tends to zero as the particles size varied from 16 nm to 25 nm. The hysteresis loop and the size dependent χ are interpreted with the uncompensated surface spins, whereas the transition at 30 K is suggested to be Néel temperature TN of the spins in the core of the 16 nm particles. In addition, the increasing temperature cannot showed an approach to saturation in the magnetization curve, it indicates the possibility of an asperomagnetism and/or spin glass behavior of the NiO nanoparticles.

Research highlights▶ Nanoscaled magnetism has become a very active area of research because of its unique properties and their technological applications. ▶ NiO nanoparticles were prepared by a novel precipitation method. ▶ The structural, morphological, optical and magnetic investigations were performed for two different particle size ranges. ▶ Detailed magnetic investigations in the temperature range of 2–300 K and in magnetic fields up to 60 kOe were reported. ▶ Significant exchange bias was observed and it depends greatly on the particle size.