Silicon nitro carbide, SiCN, exhibits excellent high-temperature properties.
It can withstand temperatures of up to 1800° C, which is superior to those of Si, SiC
and Si3N4. Magnetic composites, as well as electrically conductive ceramics on the
basis of SiCN, can be developed. Therefore, SiCN constitutes a new class of materials
for high-temperature electronics. SiCN ceramics, doped with the transition metal ions
exhibiting superparamagnetic features are promising in building high-temperature
magnetic and pressure sensors. EPR (electron paramagnetic resonance) and FMR
(ferromagnetic resonance) techniques can provide important information on the
properties of SiCN and its magnetic derivatives, in conjunction with structural,
magnetic and electric measurements. In the present work, EPR signals due to
sp2–hybridized carbon-related dangling bonds were recorded over the 4 - 300 K range.
SiCN ceramics consist of nanoparticles of SiCN and a free carbon phase. The two EPR
signals, which were only resolved at the higher frequencies of W (95 GHz) and G (170
GHz) bands are due to carbon-related dangling bonds present as (i) defects on the freecarbon
phase and (ii) within the bulk of SiCN ceramic network. SiCN magnetic
ceramics, doped with the Fe ions were synthesized at different pyrolysis temperatures
in the range 600° - 1600°C. Several magnetic phases in SiCN/Fe composite are
detected by EPR/FMR technique. The main sources of magnetism in these samples are:
(i) superparamagnetic nanoparticles of Fe3Si, (TC = 800°C), (ii) nanoparticles of Fe5Si3
(TC = 393°C), which appear above 1000°C in single-domain state and (iii) nanoparticles
of Fe70SixC30-x (620°C).
Keywords: Antiferromagnetic interaction, Curie law, Curie temperature,
Dangling bonds, EPR, EPR linewidth, Ferromagnetic nanoparticles, FMR,
Fluctuations of the magnetization, High-frequency EPR, Multi-frequency EPR,
Nanoparticles, Phase-transition, Silicon nitro carbide (SiCN) ceramics, SiCN/Fe
ceramics, SiCN/Mn ceramics, Superparamagnetic nanoparticles,
Superparamagnetism, Temperature dependence.
