Effects of nanocrystallization upon the soft magnetic properties of Co-based amorphous alloys

Abstract

Amorphous samples of Vitrovac(R) 6025 metallic alloys were nanocrystallized by thermal annealing at temperatures in the range 576–716 K, well below the crystallization temperature (831 K, as obtained by differential scanning calorimetry at 20 K/min) and times in the range 10–90 min. Initial magnetic permeability exhibited a maximum of ∼109 000 (from ∼20 000 for the as-quenched state) for annealing times of ∼15 min, and then a decrease toward a plateau value (30 000–40 000) for longer times. Domain wall relaxation frequency showed the opposite behavior, a minimum of ∼9 kHz (from 40 kHz for the as-quenched value) for the permeability maximum, and then a stabilization at ∼15 kHz. Transmission electron microscopy observations confirmed that for annealing times up to 60 min., crystallite size is smaller than 30 nm. Permeability and relaxation frequency results are interpreted in terms of the dependence of wall bulging on anisotropy and free-wall surface area between pinning sites.

Joule Heating Preannealing Effect in the Coercivity Field and Magnetostriction Constant of Co66Fe4Mo2Si16B12Alloy

“…This reduction of the coercive field values (in the sample treated at 1.2 A 30 min) could be ascribed to the internal stress relaxation such as has been widely reported in metallic glasses [3]. The increase in the coercive field in the sample treated at 1.55 A 5 min could be related to the hardening connected to a nucleation process before the nanocrystallization process is completed as it has been reported by other authors [4]. Sample treated at 1.20 + 1.55 A was nanocrystalline with softening magnetic character owing the magnetic coupling between the small crystallites.…”

Influence of the dipolar interactions in the magnetization reversal asymmetry of hard–soft magnetic ribbons

“…8 Previous works have reported about the effects of thermal treatments on this alloy in the range of 250-480°C and times between 10 and 90 min. 9,10 These treatments were directed to obtain the nanocrystallization of the samples, which results in an enhancement of their soft magnetic properties. In the present work the samples were annealed at higher temperatures, in the range of 500-540°C, still below the crystallization temperature (T crys = 558°C) and during short times of 10-20 min.…”

The effect of surface etching and dation on the permeability spectrum of nanocrystalline Fe85-x Co x Nb7B8 ribbon

“…Practices of oxidation on nanocrystalline ribbons have been carried out on ribbon's surface by some researchers [4] . A tiny shift of relaxation frequency is found on slightly oxidized Nanoperm ribbons [5] . Some researchers also performed etching on nanocrystalline ribbons.…”