Microstructural and magnetic properties of Ni–Ce nanocomposite particles

A new type of magnetic core–shell Ni–Ce nanocomposite particles (15–50 nm) are presented. Scanning electron microscope (SEM) images and X-ray energy-dispersive analysis (EDX) spectra indicate that these nanoparticles are strongly magnetic interacting order with chain-like features. Typical HREM images show that many planar defects (i.e., nanotwins and stacking faults) exist in large Ni core zone (10–45 nm); the shell layers (3–5 nm) are consisted of innermost NiCe alloy and outermost NiO oxide. Selected area electron diffraction (SAED) patterns show an indication of well-defined spots characteristic of core–shell nanocomposite materials. Magnetization measurements as a function of magnetic fields and temperatures were performed in a SQUID magnetometer. Superparamagnetic behavior above average blocking temperature (TB) 170 K was exhibited, this superparamagnetic relaxation behavior was found to be modified by interparticle interactions, which depend on the applied field and size distribution. In addition, antiferromagnetic order occurred with a Neél temperature TN of about 11 K. A spin-flop transition was also observed below TN at a certain applied filed. In particular, electron paramagnetic resonance (EPR) spectra at low and room temperature reflected this magnetic order nature associated with this type of core–shell microstructure, coupling with the strong interparticle interaction.