NiO core-shell nanostructure with ferromagnetic-like behavior at room temperature

We report on ferromagnetic-like magnetic properties, at room temperature, of spherical nickel oxide core-shell nanoparticles synthesized by sol-gel combustion method. The sample is characterized by using transmission electron microscopy (TEM), selected electron area diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS) and superconducting quantum interference device (SQUID) magnetometer. The SAED, EDX and RS show high quality and purity of the sample. The TEM images point to core-shell NiO nanostructure with a well crystallized NiO core and surface disorder shell. The size of the nanoparticles of about 5 nm and thickness of the surface shell below 1 nm are estimated from the TEM and HRTEM measurements. The measurements of the magnetization reveals ferromagnetic-like behavior of the sample at room temperature with remanent magnetization M-r = 0.0087 emu/g and coercive field H-C = 115 Oe. These magnetic properties are quite different than in NiO bulk materials and uncommon for nanosized NiO materials. These results also indicate that the synthesized NiO core-shell nanostructure is suitable for spin-valve applications. (C) 2012 Elsevier B. V. All rights reserved.