Spin-glass like behaviour in the nanoporous Fe2O3 with amorphous structure

The porous Fe2O3 was synthesized chemically. The average size of the particle was similar to 85.0 nm, which was observed by scanning electron microscopy. The signature of porous structure was confirmed by a N-2 adsorption/desorption isotherm and intense x-ray powder diffraction peak at low angle. The x-ray diffraction pattern at high angle indicates the amorphous structure. Mossbauer investigations show that the value of the hyperfine field is similar to 498.0 kOe at 4.2 K which is much smaller than that of the hyperfine field of crystalline alpha/gamma-Fe2O3 and consistent with the values of amorphous Fe2O3. The temperature dependence of zero-field cooled magnetization exhibits a peak at 18.0 K (T-f), where T-f follows the Almeida-Thouless relation as T-f alpha H-2/3. The ageing phenomenon of the magnetic relaxation below T-f and the memory effect in the field-cooled magnetization indicate the typical features of the classical spin-glass compounds below the spin freezing temperature at T-f.