Temperature and size dependence of magnetic and electron magnetic resonance parameters of Fe nanoparticles embedded in an amorphous SiO_2 matrix

摘要

Temperature dependence (5 K to 300 K) of the magnetic properties of two Fe/SiO_2 (15/85) nanocomposites with Fe particle size D (~-) 17 nm and 30 nm is reported using magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the samples, done by X-ray diffraction, TEM, and Mossbauer spectroscopy shows the presence of x-Fe, amorphous SiO_2, and some nanosize Fe~(3+) oxides. both samples are ferromagnets in the 5 K to 370 K range with coercivity H_c(30 nm)>H_c(17 nm). In EMR studies, a single resonance line near g = 2.2 characteristic of x-Fe is observed in both samples at 300 K, with linewidth △H(30 nm) > △H(17 nm). With decreasing temperature, the EMR line shifts to lower fields and broadens, which is similar to observations in other nanoparticle systems.