Mossbauer study of nanostructured iron fluoride powders

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 Mossbauer spectrometry as a function of temperature and in-held Fe-57 Mossbauer spectrometry. We report a fitting procedure which successfully describes the zero-field Mossbauer 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 Mossbauer 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.