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-d ispersive analysis (EDX) spectra indicate that these nanoparticles are stro ngly magnetic interacting order with chain-like features. Typical HREM imag es show that many planar defects (i.e., nanotwins and stacking faults) exis t 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 di ffraction (SAED) patterns show an indication of well-defined spots characte ristic of core-shell nanocomposite materials. Magnetization measurements as a function of magnetic fields and temperatures were performed in a SQUID m agnetometer. Superparamagnetic behavior above average blocking temperature (T-B) 170 K was exhibited, this superparamagnetic relaxation behavior was f ound to be modified by interparticle interactions, which depend on the appl ied field and size distribution. In addition, antiferromagnetic order occur red with a Neel temperature T-N of about 11 K. A spin-flop transition was a lso observed below T-N 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 microstr ucture, coupling with the strong interparticle interaction. (C) 2001 Elsevi er Science B.V. All rights reserved.