Temperature behaviour of iron nanograins in Nanoperm-type alloys

Abstract

The evolution of hyperfine interactions with temperature is studied for Fe 80 M 7 Cu 1 B 12 (M = Mo, Nb and Ti) nanocrystalline alloys with the help of 57 Fe Mössbauer spectrometry. The nanocrystalline structure features an amorphous residual matrix surrounding the crystalline nanograins of bcc-Fe. In addition, interfacial regions comprising atoms located on the surface of nanocrystals are considered. Special attention is paid to the temperature behaviour of hyperfine magnetic fields of the nanograins. The temperature dependence of hyperfine magnetic fields pointed out significant differences between bulk and nanosized bcc-Fe, suggesting a decrease in the corresponding magnetic ordering temperature. The higher the crystalline content is, the lower the difference between the hyperfine fields of bulk bcc-Fe and nanocrystalline Fe grains. This tendency is observed for M = Nb and Ti whereas it is completely opposite for M = Mo. The present results are explained in terms of mechanical stresses induced during the transformation from the amorphous to the nanocrystalline state, thus excluding a significant number of impurities diffused into the nanocrystalline grains.

Subsurface structure and magnetic parameters of Fe-Mo-Cu-B metallic glass

“…3 by light grey broadened spectral components. Possible superparamagnetic relaxation of the fi ne ferromagnetic particles would be demonstrated by their rather broad spectral lines [10], which is, however, not the present case.…”

“…The corresponding Mössbauer subspectra of magnetite are green (A-sites) and dark green (B-sites), whereas those of bcc-Fe nanocrystals are blue. Broad cyan components represent Fe atoms located at the surfaces of the nanograins, the so-called interface regions [10]. The relative contents of bcc-Fe (including the interface regions) and magnetite are of 12% and 16%, respectively.…”

Evolution of structure and local magnetic fields during crystallization of HITPERM glassy alloys studied by in situ diffraction and nuclear forward scattering of synchrotron radiation

“…Mössbauer spectroscopy (MS) is a method that directly correlates magnetic states of the studied materials with their structure through hyperfine interactions [7][8][9][10]23]. It is, however, quite time consuming and thus not suitable for observation of rapid dynamic processes.…”

“…In order to ensure consistency of the obtained hyperfine parameters we have checked their temperature evolution rather than to relay upon fitting of a single NFS interferogram. This approach is closely discussed in [8] for the case of conventional Mössbauer spectra. As demonstrated by Fig.…”

Mössbauer and MFM Investigations of Surface Magnetism in NANOPERM Nanocrystalline Alloys

“…Bulk magnetism is thoroughly studied also by Mössbauer spectrometry [1]. The latter was employed even at elevated temperatures of measurement [2,3] to follow temperature behaviour of iron nanograins. Their vibrational thermodynamics was recently studied by nuclear inelastic scattering of synchrotron radiation [4].…”