Interparticle magnetic correlations in a nanosized g-Fe2O3 system

Small angle neutron scattering experiments performed on a powder of gamma-Fe2O3 nanoparticles reveal the existence of a temperature-dependent magnetic signal, increasing with decreasing temperature. The extra scattering appearing below 275 K is fitted to the sum of a Lorentzian and a Lorentzian squared. The first contribution is attributed to the spin correlations in the particle core, with a correlation length of 2.6 nm at T = 4 K. The second contribution indicates the presence of frozen clusters of coupled particles, with a correlation length that increases with decreasing temperature, up to 60 nm.