Magnetic Nanostructures Based on Nanoclusters of Iron Oxides

摘要

Using magnetization and M?ssbauer spectroscopy, investigations of the magnetic properties of α- Fe_2O_3–SiO_2 and γ-Fe_2O_3–SiO_2 nanostructures, including α-Fe_2O_3 nanoclusters 2 nm in size and γ-Fe_2O_3 nanoclusters 3–4 nm in size in silica gel pores, have been conducted. For α-Fe_2O_3–SiO_2 nanostructures, magnetic phase transitions of the first order are detected and examined with the transition temperature dependent on the nanocluster size and intercluster interactions. α-Fe_2O_3 nanoclusters up to 16 K remain in the noncompensated antiferromagnetic state (upper Morin point temperature). At low temperatures, α- Fe_2O_3 nanoclusters reveal quantum-size effects. For γ-Fe_2O_3–SiO_2 nanostructures, supermagnetic behavior with a blocking point dependent on intercluster interactions is typical. At low temperatures, intercluster interactions lead to the appearance of a coercive force of 0.03 T.