Structural, Magnetic, and Mössbauer Investigation of Ordered Iron Nitride with Martensitic Structure Obtained from Amorphous Hematite Synthesized via the Microwave Route

Abstract

Amorphous hematite synthesized by a simple and fast microwave route was used to obtain Fe16N2 fine particles by reducing in 5% H2/Ar gas flow, followed by long time nitridation in ammonia gas flow at temperatures below 200 °C. Depending on nitridation temperature, various amounts of metallic iron were present along with the α″-Fe16N2 main phase. A small amount of iron oxide was observed by Mössbauer spectroscopy, but it was undetected by X-ray diffraction due to its high degree of amorphization. Increased amounts of Fe3N and Fe4N phases were observed at a nitridation temperature above 150 °C, which had a detrimental effect on the magnetic properties. Structural information and phase composition were extracted from Rietveld refinement of the XRD data. Values of the magnetization at saturation measured at 40 kOe and 25 °C of 222 emu/g for α″-Fe16N2 and 192 emu/g for metallic iron were obtained via magnetic measurements, Rietveld, and Mössbauer analysis.

Tuning structural and magnetic properties of Fe oxide nanoparticles by specific hydrogenation treatments

“…As for example, the saturation magnetization of the newly formed metallic phase is more than 50% higher than in bulk metallic Fe. Therefore, hydrogenation treatments seem to be even more effective in this respect as compared to more expensive and time consuming nitriding treatments leading to ordered iron nitride with martensite structure of high saturation magnetization 43 . Specific aspects related to the unidirectional anisotropy of nanoparticles with core-shell magnetic structures assigned to the as prepared sample and the partially reduced sample are also discussed in detail.…”

Structure and Thermal Stability of (H2O)4 Tetrahedron and (H2O)6 Hexagon Adsorbed on NaY Zeolite Studied by Synchrotron-Based Time-Resolved X-ray Diffraction

“…Commonly, such studies are made at room temperature from predehydrated and sealed samples. However, with this method only a limited set of snapshots is obtained, and cooling the samples to room temperature may obscure the true dehydration process . In order to fully understand physical properties of the material, it is necessary to determine both the framework structure and the cation positions under actual working conditions (i.e., in situ measurement) of thermal dehydration.…”