Magnetic permeability enhancement effect in the Fe_86–xNb_xB₁₄ (x = 5, 6) amorphous alloys

Abstract

The magnetic permeability enhancement effect in the Fe 86-x Nb x B 14 (x = 5, 6) amorphous alloys was studied by making use of magnetic measurements (permeability, coercive field, magnetization) and Mössbauer spectroscopy. It was shown that annealing for 1 h at elevated temperatures causes a significant increase of magnetic permeability and a reduction of material instabilities. The observed effect takes place in the so-called relaxed amorphous phase without forming any nanocrystallites and may be attributed to annealing out of free volume leading to formation of small iron clusters with different magnetic structures. . (a) 202, No. 13 (2005) / www.pss-a.com 2575

Soft magnetic properties of the Fe72Co10Nb6B12 amorphous alloy

“…Therefore, we conclude that the optimization effect should be attributed to coagulation and a partial annealing out of free volume (relaxed amorphous phase). This process leads to formation of small iron clusters (about a hundred atoms or less) which are magnetically coupled and act as randomly oriented sub-nanograins [5]. In such a system, according to the random anisotropy model [1,11], the magnetic anisotropy averages out when the clusters or sub-nanograins dimensions are much smaller than the ferromagnetic exchange length.…”

“…The observed effect was attributed to annealing out of free volume leading to formation of small iron clusters [5]. Niobium as an alloying addition causes a slowing down of diffusion processes, i.e.…”

“…Recently, in a series of papers [2][3][4][5] it was shown that the optimization effect in the Fe 86−x Nb x B 14 (x = 2-8) group of amorphous alloys takes place in the so-called relaxed amorphous phase free of ␣-Fe nanograins. The observed effect was attributed to annealing out of free volume leading to formation of small iron clusters [5].…”

Structural Relaxation in Fe78Nb2B20Amorphous Alloy Studied by Mössbauer Spectroscopy

“…2 allow concluding that the observed optimization effect cannot be attributed to iron nanostructure. The significant increase of permeability is due to annealing out of free volume and a reduction of internal stresses, as it was discussed in [6][7][8][9][10][11][12].…”

“…Such a microstructure averages out magnetic anisotropy and gives an enhancement of magnetic permeability. However, as it was shown at first time in [6] in some alloys the optimization effect can be observed without formation of iron nanograins and can be attributed to annealing out of free volume (frozen into material during fabrication) and a reduction of internal stresses [6][7][8][9][10][11][12]. This effect is especially interesting because it allows obtaining very good soft magnets free of embrittlement -the main disadvantage -of nanostructured magnets.…”