Electron paramagnetic resonance spectra near the spin-glass transition in iron oxide nanoparticles - art. no. 012407

Electron paramagnetic resonance (EPR) in iron-oxide nanoparticles (similar to2.5 nm) embedded in a polyethylene matrix reveals the sharp lien broadeni ng and the resonance field shift on sample cooling below T(F)approximate to 40 K. At the same temperature a distinct anomaly in the field-cooled magne tization is detected. The temperature dependences of EPR parameters below T -F are definitely different than those found for various nanoparticles in t he superparamagnetic regime. In contrast to canonical bulk spin glasses, a linear fall-off of the EPR linewidth is observed. Such behavior can be expl ained in terms of the random-field model of exchange anisotropy.