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Aging was characterized through measurement of core loss in small toroidal cores of metallic glass ribbons at various temperatures. The increase in core loss follows log‐time kinetics. It is shown that the activation energy spectrum model fits the data very well. Estimates of time for serious degradation of the properties of a commercial Fe‐B‐Si glass at device temperatures will be provided. In contrast to silicon steels, the addition of carbon to Fe‐B‐Si glasses is shown to have no adverse effects on aging behavior. The effects of surface crystallinity on the aging behavior are also discussed.

The electrical resistivity of cobalt single crystals of high purity has been measured for current densities j up to 400 A/mm2, at 4.2 K. Large deviations from Ohm’s law are observed when j exceeds ≃12 A/mm2, in agreement with theoretical predictions. The electron gas in translation exerts hydromagnetic forces on the domain walls. The deviations from Ohm’s law happen when these forces are large enough to overcome the pinning forces and to set the walls in motion, in a direction parallel to the drift speed of the charge carriers. The dragging forces also tend to reorient the walls in a direction parallel to the current. Magnetic fields parallel to the current are used to minimize this reorientation.

Glassy Fe77B23 when annealed at 623 K, in vacuum and in the absence of external magnetic fields, shows a deterioration of its soft magnetic properties. The coercive field Hc is found to increase sharply with time of anneal. (Hc = 220 A/m after 60 minutes of anneal, compared to the ’as cast’ value of 9 A/m). X‐ray diffraction (Mo‐Kα) is unable to detect crystallinity in samples annealed for up to 60 min. However, TEM studies show the emergence of small crystallites occupying less than 1% of the total volume. The size and number of these crystallites increase with time till 90 min. X‐rays then show the presence only of Fe3B. The TEM results indicate that the increase in Hc is the result of eutectic crystalliztion. At this same temperature, Fe76B24 also shows a similar effect with anneal time, but to a lesser extent.

Effects of crystalline precipitates, nucleating at temperatures slightly below the crystallization temperatures, on the soft magnetic properties are reported for some selected metallic glasses. Emphasis is placed on the effects due to the difference of the crystalline symmetry of the precipitates. The glassy alloys selected for the present study are Fe85B15, Fe77B23, and Fe60Ni25B15, which tend to precipitate bcc‐Fe, bct‐Fe3B, and fcc Fe‐Ni crystalline particles, respectively. It is concluded that the differences in structure of the precipitates are more important than their morphology in determining the ac properties of the materials at frequencies greater than 50 kHz.

In uniaxial ferromagnets such as Co, the presence of domains leads to an increase of the electrical resistivity. This ’’excess resistivity’’ δρ is proportional to β2, where β is the tangent of the Hall angle at saturation. We have investigated the dependence of δρ on wall orientation relative to the current, in pure Co crystals at 4 K. The current is always normal to the easy axis. Larger electrical currents and basal fields are used to reorient the stripe domains at will. Wall orientation is checked by Bitter powder patterns at 300 K. Largest δρ is for walls normal to the current. Its value agrees with theory, and is as high as 62% of the total resistivity of the sample. We have also measured the decrease of δρ as the samples are magnetized by a field parallel to the easy axis. It does not quite follow the parabolic law predicted by theory. The discrepancy may be caused by a spatial inhomogeneity of the demagnetizing coefficient in samples having a rectangular cross section. Finally, we have studied the ...

Excess core losses, attributable to mechanical resonances, are observed in tape‐wound toroidal cores of two Fe‐rich metallic glasses. In the absence of these resonances, the behavior of core loss as a function of frequency follows traditional models. The damping of the mechanical resonances is described in this paper. The reduction of the resonance losses is identified as due to externally supplied viscous damping forces.

Crystallization kinetics of Fe‐B‐Si metallic glasses, as characterized by the effective activation energy Ec and the Avrami exponent n have been studied using Differential Scanning Calorimetry. The data show that in the hypoeutectic (Fe‐rich) region, the glasses crystallize into α‐(Fe,Si) and Fe3B in that order. The growth of crystallites is diffusion controlled, and Ec falls off rapidly away from the eutectic trough. In the hypereutectic region, both crystalline phases are obtained simultaneously. Thermal stability is greatly enhanced by addition of Si(∼3 at. %) and the growth process is no longer purely diffusion controlled. The behavior of Ec and n versus composition is discussed. Effects on Ec and n of additions of small amounts of Ni and Mo are also reported. Such additions have direct relevance to the design of new glasses for applications at high frequencies.

Magnetization and nuclear magnetic resonance spin‐echo studies were carried out on an amorphous Co‐Fe‐Mn‐B‐Si alloy ribbon. The high‐field susceptibility is negligible and saturation is attained at H ∼1.6 MA/m. This would indicate that the alloy is a strong ferromagnet. At 4.2 K, the magnetic moment of the alloy corresponds to 1.13 μ B per atom. From the usual values of Co and Fe moments, and based on the charge transfer model, the Mn moment is estimated to be 3.7 μ B . Nuclear magnetic resonance studies also give a hyperfine field for Mn corresponding to a moment of about 3.5μ B , in agreement with the magnetization values. Such a moment for Mn is indeed high and is reported for the first time in amorphous alloys. The effects of annealing and crystallization on the nuclear magnetic resonance spectra are also reported. For instance, the crystalline phase Co3B contains Mn as an impurity, a fact which is indicated by the still high value of the Mn moment. Finally, the Co‐Mn coupling is shown to be ferromagnetic in both the amorphous and crystalline states.

The soft magnetic properties of a series of metallic glasses in the Co–Fe–Ni–Mn–B–Si system are described. These glasses have very low values for saturation magnetostriction (+5 to −1 ppm) and some of the highest values for saturation induction (1.1 to 1.3 T) reported for such glasses. Most importantly, the Curie temperture is lower than the crystallization temperature, thus allowing the use of easy, conventional annealing procedures for the optimization of the soft magnetic properties. Initial permeabilities in excess of 17 000 at 1 kHz may thus be achieved for optimal compositions within the system. These metallic glasses offer great promise for applications such as recording heads to be used in conjunction with high coercivity metal tapes.