Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Abstract

PACS 75.50. Kj, 75.75+a, 76.80.+y, 81.07.Wx Monodispersed amorphous Fe 2 O 3 nanoparticles with the size ranging from 1 to 4 nm have been prepared by thermally induced oxidative decomposition of Prussian Blue, Fe 4 [Fe(CN) 6 ] 3 , in air. Amorphous nanopowders exhibit specific magnetic behaviour strongly affected by interparticle interactions and extremely low particle size with a high contribution of the surface anisotropy as illustrated by temperature dependent and external field Mössbauer spectroscopy and magnetization measurements (4-300 K). Some of the properties are in close similarity to those of spin glasses including the fast thermal variation of superparamagnetic fraction in the Mössbauer spectra, or the particle size independence of the blocking temperature, and non-saturation of magnetization even at 5 K and magnetic field of 10 T. The reduced value of internal magnetic hyperfine field (∼49 T at 5 K) and no indications of the tetrahedral Fe 3+ sites in the 5T/5K external field Mössbauer spectra are the principal found differences in comparison with the magnetic behaviour of nanocrystalline γ-Fe 2 O 3 .

Investigations on Bi25FeO40 powders synthesized by hydrothermal and combustion-like processes

“…Field−dependent measurements below the blocking temperature reveal the formation of pronounced hysteresis loops (inset in Fig. 11b) in agreement with earlier reports on amorphous iron−oxides [55,56,57,58].…”

Carbon Electrodes Modified by Nanoscopic Iron(III) Oxides to Assemble Chemical Sensors for the Hydrogen Peroxide Amperometric Detection

“…Nanocrystalline magnetite (30 -40 nm) was prepared by thermal reduction of amorphous Fe 2 O 3 under hydrogen atmosphere at 300 8C [24]. Amorphous iron(III)-oxide nanopowder (2 -4 nm) was synthesized according to the procedure described in [25]. Prussian blue nanoparticles (15 -30 nm) were obtained by controlled solid-state oxidative decomposition of ammonium ferrocyanide at 160 8C [26].…”

Amorphous Iron(III) OxideA Review

“…The value of the magnetic ordering temperature, the interval of the coexistence of magnetically nonequivalent components (i.e., the transition range), or the saturation value of the hyperfine magnetic field are strongly affected by the local structure, size, and morphology of particles, and their interactions. Although temperature-dependent Mo ¨ssbauer spectra were recorded by several authors, 34,36,46,47,49,50,73 their interpretations differ depending on the investigated form of the amorphous iron(III) oxide.…”

“…The in-field Mo ¨ssbauer spectra were measured for amorphous Fe 2 O 3 in the form of pure nanopowder, 73 and also for the nanoparticles hosted in a silica aerogel matrix, 78 both in an external field applied parallel to the γ-ray direction. Independently of the different degrees of interparticle interaction, the spectra display negligible changes in comparison with those recorded in a zero-applied field at the same temperature.…”