Magnetic and structural properties of ferrihydrite/hematite nanocomposites

Nano-Sized Fe(III) Oxide Particles Starting from an Innovative and Eco-Friendly Synthesis Method

“…In Figure 5, the magnetization response at room temperature for all the ferrihydrite samples is showed. The linear magnetic field dependence is consistent with the paramagnetic behavior found by most of the authors at ambient temperature, where also a contribution from antiferromagnetic susceptibility must be taken into account [23,55,56]. On the contrary, Pannalal et al [57] found a small hysteresis and departures from linearity in the initial part of the M(H) curve.…”

“…From FESEM image the pseudo-spherical clusters are clearly visible (Figure 8f), and they are characterized by two distinct morphologies of the assembled particles: A spherical morphology, attributed to the residual ferrihydrite, and a rhombohedral one, that can be related to the hematite particles emerging on the surface of the aggregate as well. These observations confirm the hypothesis that the phase transformation from ferrihydrite to hematite is due to an oriented attachment growth, where the ferrihydrite NPs form aggregates, already visible after two weeks of aging, and becoming larger with time until they define a typical crystalline morphology of hematite [55]. TEM images of the sample calcined at 500 °C (Figure 8g,h), show that the hematite NPs formed by calcination in dry conditions seem to have plate-like morphologies, almost hexagonal, with dimensions between 25 and 35 nm.…”

“…Assuming Curie-like temperature dependence, these values correspond to about 2.5 µ B for Fh 0.1M and 3.0 µ B for the other three samples: In all cases less than the theoretical value (5.9 µ B ) for isolated Fe 3+ ions. susceptibility must be taken into account [23,55,56]. On the contrary, Pannalal et al [57] found a small hysteresis and departures from linearity in the initial part of the M(H) curve.…”

Effect of Initial Salt Composition on Physicochemical and Structural Characteristics of Zero-Valent Iron Nanopowders Obtained by Borohydride Reduction

“…The core-shell structured chains of the nZVI aggregates are The results of the morphology study of the nZVI samples obtained in this work are well correlated with their composition and the results obtained by other authors. The 2D structures produced using the iron nitrate salt are characteristic of ferrihydrite being a poorly crystalline iron compound with the crystallites' size of 2-6 nm [52][53][54]. The structures similar to the obtained ones via the reduction of iron sulphate in this work were also observed by different researchers [55,56].…”

Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy

“…Figure b with | K U / K H | = 17 is closest to the “kidney bean” shape often associated with hematite FORC diagrams (Brownlee et al, ; Carvallo et al, ; Carvallo & Muxworthy, ; Church et al, ; Jovane et al, ; Liu et al, ; Martín‐Hernández & Guerrero‐Suárez, ; Muxworthy et al, ), especially considering that we simulated populations of identical particles, rather than for coercivity distributions, which would further smear the signal. Examples of dominantly uniaxial central ridge behavior have also been documented for hematite (e.g., Jiang et al, ; Pariona et al, ; Roberts et al, ). A transition to uniaxial switching behavior is predicted here for samples with low | K U / K H | (Figures d, h, l, p).…”