Mössbauer study of the magnetism and structure of amorphous and nanocrystalline Fe81−xNixZr7B12 (x=10–40) alloys

Abstract

Erratum: "Structure, hyperfine interactions, and magnetic behavior of amorphous and nanocrystalline Fe 80 M 7 Structure, hyperfine interactions, and magnetic behavior of amorphous and nanocrystalline Fe 80 M 7 B 12 Cu 1 ( M=Mo , Nb, Ti) alloys Soft magnetic amorphous and nanocrystalline Fe 81Ϫx Ni x Zr 7 B 12 (xϭ0 -40) alloys with very low coercivity and improved mechanical properties, as compared with the NANOPERM alloys, were prepared by a melt-quenching technique. The nanostructure was formed by annealing amorphous precursors in the temperature range T A ϭ440-620°C. Formation of the nanocrystalline phase was studied by Mössbauer spectroscopy, differential scanning calorimetry, and x-ray diffraction techniques. The composition of the nanocrystalline phase strongly depends on the Ni content in the alloy. For xϽ30 the dominating nanocrystalline phase is the bcc Fe, similarly to the NANOPERM alloys. However, the alloy with xϭ40 behaves in a clearly different way. Annealing of the Fe 41 Ni 40 Zr 7 B 12 alloy at T A ϭ520-620°C causes the formation of the nanograins of magnetically ordered cubic (FeNi) 23 B 6 and FeNi phases, as identified by the Mössbauer and x-ray diffraction measurements. Annealing at temperatures exceeding 590°C leads to the Mössbauer spectra at room temperature dominated by a single-line nonmagnetic component. Mössbauer measurements performed at low temperatures reveal a superparamagnetic origin of this spectral component. The superparamagnetic relaxation at the sample surfaces is restricted by the stress induced surface anisotropy related to the crystallization of the amorphous phase as revealed by the conversion electron Mössbauer results. The conversion electron Mössbauer measurements which allowed the comparison of the surface and bulk crystallization of Fe 81Ϫx Ni x Zr 7 B 12 alloys show clear differences between the surface and bulk crystallization for all alloy compositions. Unconventional Mössbauer studies utilizing radio frequency ͑rf͒ fields provide information on the soft magnetic nature of the alloys by observing the degree of rf-induced collapse of the hyperfine fields. The rf-Mössbauer technique, being particularly sensitive to magnetic anisotropy, provided information on the anisotropy fields in the alloys. It was found that the nanocrystalline FeNiB phase is magnetically very soft as revealed by the rf-Mössbauer technique. The complete rf collapse of the magnetic hyperfine structure was observed for the nanocrystalline Fe 41 Ni 40 Zr 7 B 12 alloy in clear distinction to the FeNiZrB alloys with xр30 and to similar earlier studies of NANOPERM alloys. An improved magnetic softness combined with much reduced brittleness of the Fe 41 Ni 40 Zr 7 B 12 samples offer attractive possibilities for technical applications of the nanocrystalline Ni-containing alloys.

Crystallization of amorphous FeNiZrB and FeNiCoZrB alloys

“…This spectral component may be attributed to the fcc-FeNi phase with high Ni-content. Similar single-line component was observed recently for FeNiZrB alloy annealed at T a > 700°C[1]. The magnetic behaviour of the fcc-FeNi system strongly depends on Ni content and the fcc phase becomes nonmagnetic for Ni content of about 30 at.%[4].…”

“…The search continues for soft magnetic nanocrystalline alloys with high saturation magnetization, combined with improved mechanical properties (reduced brittleness). Recently, the Fe 41 Ni 40 Zr 7 B 12 nanocrystalline alloy was studied [1], which revealed considerably reduced brittleness as compared with the nanocrystalline bcc-Fe phase observed in NANOPERM alloys.…”

The rf–Mössbauer study of the magnetic properties of nanocrystalline alloys

“…The examples of the applications of the rf-Mössbauer technique in the studies of magnetic properties of nanocrystalline alloys is presented below for the Fe 80 M 7 B 12 Cu 1 (M: Ti, Ta, Nb, Mo) [14,15] and Fe 81−x Ni x Zr 7 B 12 (x = 10-40) [16,17] alloys.…”

Magnetic properties of nanocrystalline FeNiCo x ZrB alloys (x=0, 10, 20)

“…The main disadvantage is their high brittleness. Recently, the Fe 41 Ni 40 Zr 7 B 12 nanocrystalline alloy revealed improved mechanical behaviour [2], however, that was associated with a significant decrease of saturation magnetization (hyperfine field) of nanograins. Here we discuss the experimental results obtained for FeNiZrB alloys to which the Co atoms were added in order to increase the saturation magnetization.…”

“…This technique, which combines the Mössbauer effect with the phenomena induced by the external radio-frequency (rf) magnetic field (the rf-collapse and rf-sideband effects), permits us to study changes of magnetic anisotropy and to follow the changes of magnetostriction associated with the formation of nanocrystalline grains. Recently, the rf-Mössbauer technique was applied successfully for studying nanocrystalline alloys [2,3] and is discussed in detail in ref. [4,5].…”