Surface effects and magnetic ordering in few-nanometer-sized [variant_greek_epsilon]-Fe2O3 particles.

The magnetic properties of [variant_greek_epsilon]-Fe2O3 nanoparticles with an average size of 3.4 nm in a silica gel matrix are investigated using Mössbauer technique, electron spin resonance, and magnetic measurements. Two magnetic subsystems reveal in magnetic measurements. Paramagnetic subsystem is formed by the Fe(III) ions in the smallest (<3.5 nm) particles' shell, while ferrimagnetic ordering in the 'core' of the particles results in superparamagnetic behavior. The superparamagnetic behavior of the investigated samples is observed up to ∼800 K. The magnetic moment of the particles is formed by both the ferrimagnetic ordering characteristic of [variant_greek_epsilon]-Fe2O3 and the additional effect of uncompensated sublattices (planes). [ABSTRACT FROM AUTHOR]