Superparamagnetism versus superspin glass behavior in dilute magnetic nanoparticle systems

The magnetization of diluted nanoparticle systems [Co80Fe20(t(n))/Al2O3(3 nm)](10) with t(n)=0.7 and 0.5 nm reveals strong paramagnetic contributions at low temperatures. They are due to atomically small magnetic clusters, which are undetectable in transmission electron microscopy and surround nanoparticles with saturating field-cooled magnetization. Zero field memory effects unequivocally discriminate between superspin glass and superparamagnetic behavior for t(n)=0.7 and 0.5 nm, respectively.