Nanocrystallization and magnetic anisotropy in

Time dependence of hysteresis loop displacement in hard–soft magnetic systems

“…The relaxation time of such an aftereffect can be estimated as t ¼ t 0 expðDE=k B TÞ with t 0 $10 À10 s, k B the Boltzmann constant and DE the energy barrier that can be approximated in this case by the anisotropy energy. An anisotropy constant of about 5 Â 10 4 Jm À3 has been deduced for these particles [6]. This results in relaxation times of 0.5 min-30 days for particles with sizes between 16 and 18 nm, which is comparable to the duration of our measurements.…”

“…Previous investigations proved that these thermal treatments give rise to low volume fractions ðf $15 Â 10 À3 Þ of crystallites sized about 16-70 nm that could be Co 3 B or HCP Co whose crystallographic easy axes are randomly oriented [2,6]. When these samples are submitted to a relatively high magnetic field previous to the measurement of the hysteresis loop, the result is an asymmetrical magnetization reversal characterized by different slopes of both branches of the hysteresis loop that cut the horizontal axis at fields H 1 surrounding matrix: as the crystallites are much harder than the amorphous, their magnetization and so their dipolar field remains practically unvarying while the applied field H sweeps to trace the loop, so producing an internal field H i ¼ H AE H d (sign ''þ'' corresponding to the particles magnetized parallel to the positive applied field what will result in a loop shifted towards negative fields and sign ''À'' corresponding to the opposite).…”

Temperature dependence of biased hysteresis loops in hard-soft nanocrystalline Co-based ribbons

“…Nevertheless, both the reflections observed in the electron pattern and the peaks standing out from the halo of the amorphous phase in the XRD pattern, point to Co 3 B and hcp Co as the most plausible candidates. These findings agree well with previous studies on samples of the same composition with similar thermal treatments [8,6,11].…”

“…In a previous work it was already reported that annealing Co 66 Fe 4 Mo 2 Si 16 B 12 amorphous ribbons at temperatures slightly below the crystallization temperature, T cr = 558°C (see the differential scanning calorimetry diagrams in [8]), give rise to samples with biased magnetic HL [6]. For the present work samples of this amorphous precursor, 40 mm long, 5 mm wide, and 25 μm thick, were annealed in Argon atmosphere in a preheated furnace at temperatures ranging from 500°C and 530°C and for times between 10 min and 360 min.…”

Nanocrystallization and fracture characteristics in Co-based ribbons

“…The nanocrystallization process of Co-rich amorphous alloys has been extensively studied [14][15][16][17] and it can be observed that depending on the temperature and time of the thermal treatment different nanocrystalline characteristics can be obtained. If the amorphous Co-based material is submitted to a thermal treatment at a temperature slightly below the crystallization one (500°C) during a short time, the material obtained is formed by crystallites of about 50 nm embedded in a remnant amorphous matrix.…”