Mössbauer spectra of superparamagnetic Fe3O4

Magnetic fluids for synthesis of the stable adduct -Fe2O3/CTAB/Clay

“…5, which is not characteristic of bulk stoichiometric magnetic g-Fe 2 O 3 [26], owing to the fact that such nanosized maghemite immobilized on carriers (i.e. surfactant) [27] would give a spectrum possessing the Mo¨ssbauer parameters different from those of bulk stoichiometric maghemite.…”

Dendrite‐Like Self‐Assembly of Magnetite Nanoparticles on Porous Silicon

“…The line broadening and asymmetry is a striking feature of the MS of magnetite particles with distributions of particle size in the range of a few tenths of nanometers 24–28. However, the lack of a contribution from a temperature‐independent paramagnetic component in the MS of Figure 4 indicates that the particle sizes exceed the limit to produce superparamagnetic behavior.…”

“…The reduction of the B hf values compared with the corresponding values of bulk magnetite is attributed to particle size effects. Thermal fluctuation influences the shape of Mössbauer spectra more profoundly for smaller particles as their B hf values reduce significantly 24–28. At 77 K three out of the four components have very similar IS values with a weighted average of around 0.45 mm s −1 and both samples have increased B hf values between 49.0 and 53.2 T. The fourth component in each spectrum, which has a lower absorption area (6–8 %), possesses a higher IS value around 0.63 mm s −1 , while its B hf value remains at 45.0 T for both samples.…”

“…However, the lack of a contribution from a temperature‐independent paramagnetic component in the MS of Figure 4 indicates that the particle sizes exceed the limit to produce superparamagnetic behavior. The upper size limit of magnetite nanoparticles for the appearance of superparamagnetism, monitored as a contribution from a paramagnetic component to the MS at RT, is about 6 to 10 nm 24–28. Thus, the major contribution to the MS arises from particles with sizes of a few tenths of nanometers.…”

Characterisation of oxidation products of modified Nd–Fe–B type magnets

“…Having in mind these options for the interpretation of the paramagnetic components we see that component P2 has MP that correspond to those of superparamagnetic ␣-Fe 2 O 3 particles [17], and component P4 to superparamagnetic Fe 3−x O 4 (or Fe 3−x−y Co y O 4 ) particles [12,18], respectively. Another fact that adds to this interpretation is the appearance of the 'broadened bases' of the corresponding diffraction peaks of ␣-Fe 2 O 3 and spinel (Fe 3−x O 4 or Fe 3−x−y Co y O 4 ) phases on the XRD diagrams shown in Fig.…”