Magnetic properties of nanosized γ-Fe2O3 and α-(Fe2/3Cr1/3)2O3, prepared by thermal decomposition of heterometallic single-molecular precursor

Thermal decomposition of the trinuclear complex [Fe2CrO(CH 3COO)6(H2O)3]NO3 at 300, 400 and 500 °C gave γ-Fe2O3 nanoparticles along with amorphous chromium oxide, while decomposition of the same starting compound at 600 and 700 °C led to the formation of α-(Fe2/3Cr 1/3)2O3 nanoparticles. Size of γ-Fe 2O3 nanoparticles, determined by X-ray diffraction, was in the range from 9 to 11 nm and increased with formation temperature growth. Average size of α-(Fe2/3Cr1/3)2O 3 nanoparticles was about 40 nm and almost did not depend on the temperature of its formation. γ-Fe2O3 nanoparticles possessed superparamagnetic behavior with blocking temperature 180250 K, saturation magnetization 2935 emu/g at 5 K, 4449 emu/g at 300 K and coercivity 400600 Oe at 5 K. α-(Fe2/3Cr1/3)2O 3 nanoparticles were characterized by low magnetization values (2.7 emu/g at 70 kOe). Such magnetic properties can be caused by non-compensated spins and defects present on the surface of these nanoparticles. The increase of α-(Fe2/3Cr1/3)2O3 formation temperature led to decrease of magnetization (being compared for the same fields), which may be caused by decrease of the quantity of defects or non-compensated spins (due to decrease of particles surface). © 2011 Elsevier B.V.