Nanocrystalline materials, which have been proposed to represent a new solid state structure, are investigated by Mössbauer spectroscopy. Nanocrystalline materials are polycrystals with a crystal size of typically 1–10 nm. These materials consist of two components of comparable volume fractions: a crystalline component and an interfacial component, formed by the atoms located either in the crystals or in the interfacial regions between them. As the atomic configurations of both components are different, two kinds of Mössbauer spectra are expected. Iron nanocrystalline material is found to exhibit a two-component Mössbauer spectrum, consisting of a crystalline component and a second one with different Mössbauer parameters. The Mössbauer parameters of the second subspectrum are consistent with the model of the interfacial component of a nanocrystalline material.

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Iron-based amorphous alloys have attracted technological and scientific interest due to their soft magnetic properties. Recently it was found that amorphous alloys like Fe73.5Cu1Nb3Si13.5B9 (FINEMETTM) have a transition to the nanocrystalline state after proper annealing, thus exhibiting excellent magnetic properties. An attempt was made to investigate the crystallization behaviour of this alloy, which is not yet fully known. The investigation was carried out by combining several methods, namely Mossbauer spectroscopy, X-ray diffraction, scanning and transmission electron microscopy as well as microprobe analysis. The alloy was studied after annealing at various temperatures for various times. The corresponding phase analyses are presented. Even after increasing the time of annealing at 950 degrees C from 1 h to 90 h significant changes in the phases were found. It became evident that the question of phase composition can be solved only by a combination of different methods.

Ferromagnetism and crystal lattice stability of bcc and fcc iron

Articles you may be interested inNonlinearities in composition dependence of structure parameters and magnetic properties of nanocrystalline fcc/bcc-mixed Co-Ni-Fe thin films Thin iron films (~18A thick and 90% enriched in Fe S7 ) were prepared on (001) Cu single-crystal substrates. The fcc structure was verified by electron microscopy. By Mossbauer spectroscopy it was found that antiferromagnetic ordering begins at around 80 ± 10K with hyperfine fields of about 16-20 kOe at 4.2 K. Additional proof for the existence of antiferromagnetism has been obtained by measuring the films in a longitudinal (parallel to the ')'-ray direction) external magnetic field. The apparent discrepancy in the literature of ferromagnetic and antiferromagnetic ordering in fcc films might be resolved by taking into account the differences concerning the film orientations.

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