Heat‐treatment methods for obtaining low core loss in Fe rich amorphous alloys with high magnetic induction and the physical mechanism concerned will be discussed. Field annealing is necessary to avoid inducing local magnetic anisotropies or magnetic domain wall fixing, and then to make stress relieving effective. Consequently, field annealing can reduce hysteresis energy loss. However, core loss at high frequencies involves a fairly large anomalous eddy current loss. This is due to a large size of 180° magnetic domains resulting from field annealing. Oblique field annealing is, on the other hand, effective to reduce anomalous eddy current loss, because of increase in the number of 180° domain walls. The experimental relation between core loss and domain structure obtained on Fe(72)Co(8)Si(5)B(15) has satisfactorily been explained by the simple model on the basis of bar‐like 180° wall motion. Magnetic properties of Fe(81)‐(B, C, Si) (19) amorphous alloys suitable for transformer materials will also be rep...

Anomalous eddy current loss and amorphous magnetic materials with low core loss (invited)

Static and dynamic observations of magnetic domains in amorphous Fe-B-Si and Fe-B-Si-C ribbons have been made employing a 200 kV scanning electron microscope (SEM) and a special stage allowing in situ application of mechanical stresses and dc and ac magnatic fields. Average domain width in the demagnetized state is found to decrease with increasing demagnetizing frequency, and to be relatively insensitive to tensile stress. Under ac conditions, a great range in the mobility of individual walls is often observed. Some domain walls are strongly pinned, in many cases by obvious surface defects. The implications of these and other observations on hysteresis and eddy-current losses, coercivity, and permeability are discussed.

SEM studies of magnetic domains in amorphous ribbons

SEM techniques are used to study domain structures in amorphous ribbons with transverse or oblique magnetic anisotropy. Domain widths are much finer than in ribbons with longitudinal anisotropy, and vary with ribbon dimensions and anisotropy constant. The effects of applied magnetic fields and applied stresses are also discussed.

Domain studies on amorphous ribbons with transverse or oblique magnetic anisotropy

Magnetic measurements of hysteresis loops and transverse susceptibilities have been done on as‐cast iron based amorphous alloys on the surface and in the bulk of the ribbons Bitter technique has been used to obtain the domain patterns a‐Fe78B13Si9 shows an anisotropy perpendicular to the ribbon plane with maze domain ‘‘island’’ structures The surface measurements do not detect any difference in behavior compared to the observed bulk properties a‐Fe815B145Si4 shows different behavior in the surface and in the bulk of the ribbon with a perminvar‐type hysteresis loop from the surface and magnetization perpendicular to the ribbon plane with well‐aligned closure domains The analysis of the different magnetic experimental data and selective changes in the internal stresses produced by different treatments support a model of the layered character of the anisotropies in this sample with tensile stresses and in‐plane anisotropy in the surface and compressive stresses and anisotropy perpendicular to the ribbon’s surface in the bulk Finally, a rough calculation shows that the thickness of the surface in‐plane anisotropy region is of the order of the surface roughness

Surface and bulk magnetic anisotropy in amorphous alloys

Annealing amorphous ribbons in a field in the plane at an angle to the long axis induces an easy axis also at an angle to the long axis and decreases the domain width. These effects result in a decrease in the 60-Hz losses and for domain rotations of less than approximately 5°, there is no increase in exciting voltamperes or decrease in remanence. For domain rotations of greater than about 5° the losses continue to decrease, but the exciting voltamperes increase and the remanance decreases. These effects are consistent with the domain rotation induced by the annealing.

Effect of field annealing angle on the magnetic properties of an amorphous Fe-B-Si-C alloy

Soft magnetic properties of amorphous metals are interesting for application in transformers and other devices. So far, annealing in a field applied parallel to the amorphous ribbon axis was necessary to obtain the desirable magnetic properties. However, the amorphous cores made by this annealing method exhibit large eddy current losses. In order to reduce such large anomalous losses, we have improved the field annealing method, by applying the field oblique to the ribbon axis. In Fe-rich amorphous alloys, the core losses have been reduced by about 30-40 % by this method. Relation between the core losses and the magnetic domain structure has been investigated by comparing with the theory of Pry and Bean.

H. Fujimori

Papers

Anomalous eddy current loss in amorphous magnetic thin sheets and its improvement