Lucian Diamandescu

The crucial role of particle morphology in the magnetic properties of haematite

Haematite particles of four different morphologies (polyhedral, platelike, needlelike and disk shaped) were synthesized by the hydrothermal method. The morphology and average particle diameter (1.4, 7.4, 0.2, and 0.12 μm, respectively) were determined by transmission electron microscopy combined with electron diffraction. The haematite samples were studied by transmission Mossbauer spectroscopy in the temperature range 4.2–300 K. In all cases, a weak ferromagnetic (WF) phase was present above the Morin temperature of 230 K and found to coexist with an antiferromagnetic (AF) phase below this temperature. However, the populations of the two phases at 230 K were demonstrated to depend on the morphology of the particles. Moreover, the WF and AF phases exhibit a different dependence of the magnetic texture on temperature and particle morphology.

From Magnetite to Cobalt Ferrite

We synthesized Fe3−xCoxO4 (x = 0−1) using the hydrothermal method in order to demonstrate the compositional modulation of magnetite to cobalt ferrite. Our Mössbauer spectroscopy results provided direct evidence for the presence of the Co substitution in the B sublattice, which was found to be accompanied by a systematic increase of the hyperfine magnetic field at these sites. The mechanism we propose relies on the substitution of Fe2+ by Co2+ in the B sublattice and is supported by the observed dependence of the populations of the (A) and (B) sites on content x of cobalt substitution. The X-ray diffraction (XRD) determinations demonstrated a linear increase in the lattice parameter when going from magnetite to cobalt ferrite. For the particular value x = 0.1, we report that the two sublattices of magnetite become equally populated with Fe. For this particular value of the cobalt content, we obtained a thin film sample by laser ablation deposition and characterized its properties by XRD and conversion electron Mössbauer spectroscopy (CEMS).

Structural and magnetic properties of NiZn and Zn ferrite thin films obtained by laser ablation deposition

Laser ablation deposition has been used to synthesize nanoscale ferrite structures. Our investigations were performed on NiZn and Zn ferrite films deposited on silicon(100) substrates. Films produced by laser ablation at room temperature were annealed at 550°C for 1h. Other films were deposited directly at a 550°C substrate temperature without subsequent annealing. Complementary x-ray diffraction and superconducting quantum interference device magnetometry measurements helped identify the optimum laser ablation deposition conditions for obtaining the desired nanoferrite structures. From the hysteresis loops at 300 and 10K we identified the paramagnetic or ferromagnetic behavior of the films. The zero field cooled–field cooled (ZFC–FC) magnetization, M(T), curves yielded the value of the blocking temperature in both NiZn and Zn ferrite systems.

Influence of cobalt and nickel substitutions on populations, hyperfine fields, and hysteresis phenomenon in magnetite

In this work the magnetic properties of magnetite powders doped with Co and Ni are investigated as a function of dopant concentration. Two sets of Fe3−xTxO4 powders with T=Co and Ni, x=0–1 were prepared using a hydrothermal method, with particle sizes of about 1 μm. The Mossbauer measurements revealed that both Co2+ and Ni2+ ions are located mostly on the octahedral sites, affecting the hyperfine fields and relative populations of both sites. In the case of Co-doped magnetite, the hyperfine magnetic fields increase almost linearly with increasing cobalt content. In the case of Ni-doped magnetite, the influence of annealing temperature during preparation was studied. For both subcritical and critical temperatures, the hyperfine fields of the tetrahedral and octahedral sites are larger than those corresponding to the magnetite powder. Bulk magnetic properties of these powders were studied by means of hysteresis loops recorded at 4.2 K in an applied field of 1.5 T. The results are compared with the pure magn...

Synthesis and magnetic properties of haematite with different particle morphologies

Abstract Haematite particles of four different morphologies (polyhedral, platelike, needlelike and diskshape) were synthesized by the hydrothermal method. The morphology and average particle diameter (1.4; 7.4; 0.2 and 0.12 μm, respectively) were determined by transmission electron microscopy (TEM) combined with electron diffraction. The haematite samples were studied by transmission Mossbauer spectroscopy in the temperature range 4.2–300 K. In all cases, a weak ferromagnetic phase (WF) was present above the Morin temperature of 230 K and found to coexist with an antiferromagnetic phase (AF) below this temperature. However, the populations of the two phases at 230 K were demonstrated to depend on the morphology of the particles. Moreover, the WF and AF phases exhibit a different dependence of the magnetic texture on temperature and particle morphology.

On the solid phase transformation goethite → hematite

Abstract Mossbauer spectroscopy has been used to investigate the solid phase transformation of goethite into hematite at 250°C. An Avrami-Erofeyev-type relation was found to describe the thermal conversion of alpha oxihydroxide to the alpha iron oxide. No intermediate phase was observed in the analyzed samples. The reaction constant was determined. A possible nucleation mechanism is also discussed.

A Mössbauer study of manganese-doped magnetite

Abstract A series of Fe 3− x Mn x O 4 samples with x =0–0.6 was prepared using the hydrothermal method. The system was characterized using transmission Mossbauer spectroscopy. The dependence of the site hyperfine magnetic fields and populations on the content x of Mn substitution was derived from the spectra. The results are consistent with Mn 2+ ions substituting for Fe 2+ ions in the octahedral B sublattice. In particular, the site-specific substitution of Mn ions for the B2 sites was evidenced.

Interaction of New-Developed TiO2-Based Photocatalytic Nanoparticles with Pathogenic Microorganisms and Human Dermal and Pulmonary Fibroblasts

TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe–N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe–N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

Innovative Self-Cleaning and Biocompatible Polyester Textiles Nano-Decorated with Fe–N-Doped Titanium Dioxide

The development of innovative technologies to modify natural textiles holds an important impact for medical applications, including the prevention of contamination with microorganisms, particularly in the hospital environment. In our study, Fe and N co-doped TiO2 nanoparticles have been obtained via the hydrothermal route, at moderate temperature, followed by short thermal annealing at 400 °C. These particles were used to impregnate polyester (PES) materials which have been evaluated for their morphology, photocatalytic performance, antimicrobial activity against bacterial reference strains, and in vitro biocompatibility on human skin fibroblasts. Microscopic examination and quantitative assays have been used to evaluate the cellular morphology and viability, cell membrane integrity, and inflammatory response. All treated PES materials specifically inhibited the growth of Gram-negative bacilli strains after 15 min of contact, being particularly active against Pseudomonas aeruginosa. PES fabrics treated with photocatalysts did not affect cell membrane integrity nor induce inflammatory processes, proving good biocompatibility. These results demonstrate that the treatment of PES materials with TiO2-1% Fe–N particles could provide novel biocompatible fabrics with short term protection against microbial colonization, demonstrating their potential for the development of innovative textiles that could be used in biomedical applications for preventing patients’ accidental contamination with microorganisms from the hospital environment.

Low Power Resistive Oxygen Sensor Based on Sonochemical SrTi0.6Fe0.4O2.8 (STFO40)

The current paper reports on a sonochemical synthesis method for manufacturing nanostructured (typical grain size of 50 nm) SrTi0.6Fe0.4O2.8 (Sono-STFO40) powder. This powder is characterized using X ray-diffraction (XRD), Mössbauer spectroscopy and Scanning Electron Microscopy (SEM), and results are compared with commercially available SrTi0.4Fe0.6O2.8 (STFO60) powder. In order to manufacture resistive oxygen sensors, both Sono-STFO40 and STFO60 are deposited, by dip-pen nanolithography (DPN) method, on an SOI (Silicon-on-Insulator) micro-hotplate, employing a tungsten heater embedded within a dielectric membrane. Oxygen detection tests are performed in both dry (RH = 0%) and humid (RH = 60%) nitrogen atmosphere, varying oxygen concentrations between 1% and 16% (v/v), at a constant heater temperature of 650 °C. The oxygen sensor, based on the Sono-STFO40 sensing layer, shows good sensitivity, low power consumption (80 mW), and short response time (25 s). These performance are comparable to those exhibited by state-of-the-art O2 sensors based on STFO60, thus proving Sono-STFO40 to be a material suitable for oxygen detection in harsh environments.