An 57Fe Mössbauer effect study of poorly crystalline γ-FeOOH

57Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

“…The high-AEQ satellite component resolved from the calculated p(AEQ) profiles was tentatively ascribed by De Grave et al (1986) to iron species near the surface of the non-substituted lepidocrocite particles, a suggestion which emerged from the observation of a clear negative correlation between the specific surface area, and the area contribution of the satellite component to the total profile. Due to strong deformations of their coordinations, these surface irons are indeed expected to exhibit larger quadrupole splittings as compared to species located inside the particle.…”

Structure and composition of Fe–OM co-precipitates that form in soil-derived solutions

“…Although the distribution of ∆E Q contains the most crystal chemical information, which can be extracted from a Mössbauer spectrum (Rancourt et al, 2001), any changes in the crystallinity of the Fe-OM co-precipitates of our study may not be reflected by according shifts in the ∆E Q -distributions. Such difficulties arise in the evaluation of Mössbauer spectra, if low-crystalline phases are compared with even lower crystalline phases (De Grave et al, 1986). This is the particular difference of our study compared to other studies, in which pure Fe oxides were treated with stepwise increased concentrations of additives (e.g.…”

“…The broad distribution of ∆E Q indicates the coexistence of different Fe(III) environments in the Fe-OM co-precipitates, each with a characteristic degree of lattice distortion. Beside Fe oxide composition-induced shifts in ∆E Q , positively skewed distributions of ∆E Q were also explained with surface effects, in which surface-near Fe(III) polyhedra exhibit a more deformed coordination than the inner Fe(III) polyhedra (De Grave et al, 1986;Rea et al, 1994). A high proportion of surface-near Fe sites would also contribute to the pronounced tailing at higher ∆E Q as observed in our study (Figure 2A,C), provided that the crystallite sizes of the Fe-OM co-precipitates are comparably small.…”

Constraining the Origins of the Magnetism of Lepidocrocite (γ-FeOOH): A Mössbauer and Magnetization Study

“…Natural and synthetic samples occur as needle shaped crystallites or platelets with one of their dimensions that can reach a few nanometers, the other two being much larger. Lepidocrocite is an antiferromagnet with a Néel temperature, T N , ranging from 50 to 70 K depending on crystallinity and possibly water content (Johnson, 1969;De Grave et al, 1986). Although the Mössbauer spectra resemble those of an ensemble of superparamagnetic nanoparticles, it is clearly established, in particular through in-field Mössbauer spectra (De Grave et al, 1986), that lepidocrocite is paramagnetic above T N and that the shape of the Mössbauer spectra reflects an unusually broad distribution of Néel temperatures.…”

“…Lepidocrocite is an antiferromagnet with a Néel temperature, T N , ranging from 50 to 70 K depending on crystallinity and possibly water content (Johnson, 1969;De Grave et al, 1986). Although the Mössbauer spectra resemble those of an ensemble of superparamagnetic nanoparticles, it is clearly established, in particular through in-field Mössbauer spectra (De Grave et al, 1986), that lepidocrocite is paramagnetic above T N and that the shape of the Mössbauer spectra reflects an unusually broad distribution of Néel temperatures. Another puzzling feature of lepidocrocite is that the Field Cooled (FC) and Zero Field Cooled (ZFC) branches of the low field direct current (dc) susceptibility (Lee et al, 2004) are also akin to those encountered in ensembles of superparamagnetic nanoparticles (Tronc et al, 1995), although lepidocrocite laths or needles cannot be considered, from a magnetism point of view, as nanometric particles.…”