Mössbauer study of nanostructured iron fluoride powders

Abstract

Nanostructured iron fluoride powders were prepared using the grinding route for different times and different intensities. Their structural, microstructural and magnetic properties are investigated by means of both transmission Mössbauer spectrometry as a function of temperature and in-field 57 Fe Mössbauer spectrometry. We report a fitting procedure which successfully describes the zero-field Mössbauer spectra recorded at different temperatures. It allows us to describe the powders as crystalline grains and grain boundaries which behave as antiferromagnets and speromagnets, respectively. Such arrangements are confirmed by in-field Mössbauer spectrometry. According to x-ray diffraction data, the size of grains and the thickness of grain boundaries are found to be strongly dependent on the grinding conditions. The occurrence of superparamagnetic effects at high temperature gives clear evidence for the role of grain boundaries in the magnetic coupling of crystalline grains.

Effect of boron on structural and magnetic properties of the Fe60Al40 system prepared by mechanical alloying

“…Indeed, the topological disorder tends to strongly reduce the magnetic moments and so the hyperfine fields at 57 Fe nuclei, which in turn, affect the surface layer of adjacent crystalline grains. Such an effect has been clearly observed in the case of nanostructured fluoride powders milled for different durations and different energy milling conditions, for which a high hyperfine field is evidenced for the nanocrystalline grains, low values (rather broad distribution) being due to disordered grain boundaries and intermediate values being attributed to the surface layer of the grains [18]. Those aspects will be further detailed on the basis of a numerical modelling in a forthcoming paper [19].…”

Thermoinductive Decomposition of Hydrated Iron Trifluoride in a Stream of Argon

“…Цей факт може бути свідченням формування зародків фази FeF 2 [7], або фази -Fe 2 O 3 в суперпарамагнетному стані [14], причо-му другий варіянт є ймовірнішим, оскільки він узгоджується з ре-зультатами термогравіметричного аналізу. Для цього матеріялу зафіксовано перехід фази r-FeF 3 в магнетовпорядкований стан, що є наслідком росту розмірів частинок [13]. Середній розмір ОКР в да-ному випадку становить близько 25 нм.…”

“…На ДТА-кривій при даній темпера-турі присутній ендопік, що свідчить про завершення фазового пере-ходу -FeF 3 3H 2 O  HTB-FeF 3 0,33H 2 O. Результати Мессбауерівсь-кої спектроскопії підтверджують наявність  4% гідратованої фази HTB-FeF 3 0,33H 2 O. Фаза r-FeF 3 , сформована при температурі 425C, також знаходиться в суперпарамагнетному стані. Розмір частинок фази r-FeF 3 в цьому випадку не перевищує 16 нм [13], що узгоджу-ється з результатами розрахунку середнього розміру ОКР для цієї фази за формулою Дебая-Шеррера, який дає значення близько 17 нм.…”

Non-aqueous sol–gel synthesis of nano-structured metal fluorides

“…Physical methods are condensation of nano-materials from a suitable vapour phase, e.g., PbF 2 [2], mechanical milling, e.g., FeF 3 and GaF 3 [3], laser dispersion, e.g., NaF [4], and molecular-beam epitaxy for coatings, e.g. [5,6].…”

“…Samples of 15 mol% Fe 3+ in MgF 2 prepared from different sources of Fe 3+ (FeCl 3 , Fe 2 (SO 4 ) 3 , Fe(OMe) 3 ) were post-fluorinated with CCl 2 F 2 as well as with HF and the resulting catalysts compared with each other. All catalysts had high surface areas, the HF post-fluorinated were superior in this respect, most likely due to the lower fluorination temperature needed (120 8C versus 350 8C).…”