Large magnetic anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles

Abstract

Six-line ferrihydrite(FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes < d > ≈ 2 to 4 nm. The blocking temperatures T m B extracted from magnetization data increased from ≈ 10 to 20 K for increasing particle size. Lowtemperature Mössbauer measurements allowed to observe the onset of differentiated contributions from particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the ferrihydrite phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility χac(f, T ) measurements showed the dependence of the effective magnetic anisotropy energies Ea with particle volume, and yielded an effective anisotropy value of K ef f = 312 ± 10 kJ/m 3 .

Direct Evidence for Ferrous Ion Oxidation and Incorporation in the Absence of Oxidants by Dps from Marinobacter hydrocarbonoclasticus

“…Taken in combination with the observation that at 30 Konly adoublet species exists, this value points to core particles with sizes below 2.4 nm. [23][24][25] This is also in agreement with the amount of iron, 24 and 96 57 Fe II /Dps,w hich using as tructural model for ferrihydrite gives an estimation for core particle sizes with less than 2.2 nm. [26] However,for these small iron loads,particle density and spatial distribution on the inner cavity surface should be considered.…”

Effect of neutralized solid waste generated in lime neutralization on the ferrous ion bio-oxidation process during acid mine drainage treatment

“…Xiong et al [38] confirmed that 2-line ferrihydrite (Fe 5 HO 8 ·4H 2 O) was the only mineral phase that was present during the hydrolysis of ferric ions at pH ∼8 with a considerable amount of sulfates in the solution system. However, 2-line ferrihydrite is a poorly crystallized ferric hydroxide with two weak broad XRD peaks [39]. In the present study, poorly crystallized ferric hydroxide was indeed found in the SEM image of NSW (Fig.…”

ZnFe2O4 Nanocrystals: Synthesis and Magnetic Properties

“…The blocking temperature signals the range for which the time scale of magnetization measurements equals the relaxation time, and thus the anisotropy constant can be estimated from the T B value of the ZFC curve: 27 where K eff is the effective anisotropy constant, V is the particle volume, k B is the Boltzmann's constant, τ is the superparamagnetic relaxation time, and τ 0 is a factor of the order of 10 -9-10 -12 . [28][29][30] From eq 1 and with use of the T B value from 4 results in large magnetization values originated in the uncompensation of the antiferromagnetic B sublattice, which is known to be fully populated in normal configuration.…”