The magnetic properties of mesoscopic materials are modified by size and
surface effects. We present a sol-gel method used to tailor these effects,
and illustrate it on Co1+yAl2-yO4 spinel. Nanocomposites made of spinel oxide
Co1+yAl2-yO4 particles dispersed in an amorphous SiO2 matrix were
synthesized. Samples with various mass fractions -x of Co1+yAl2-yO4 in
composite, ranging from predominantly SiO2 (x = 10 wt%) to predominantly
spinel (x = 95 wt%), and with various Co concentrations in spinel y were
studied. The spinel grain sizes were below 100 nm with a large size
distribution, for samples with predominant spinel phase. Those samples showed
Curie-Weiss paramagnetic behavior with antiferromagnetically interacting Co
ions (? ? -100 K). The grain sizes of spinel stays confined in 100 nm range
even in the spinel samples diluted with as low as 5 wt% concentration of
amorphous SiO2. For the samples with predominant SiO2 the crystalline
nanoparticles are well separated and of size of around 100 nm, but with
presence of much smaller spinel nanoparticles of about 10 nm. The magnetic
properties of the samples with predominant silica phase showed complex
behavior, spin-glass magnetic freezing at the lowest temperatures and lower
absolute value of ? and consequently lower exchange constant.
Sol-gel as a method to tailor the magnetic properties of Co1+yAl2-yO4
