Rotational power losses in amorphous ferromagnets as a function of frequency

Rotational power losses per cycle W
r
have been measured as a function of rotational frequency f between about 0 and 50 Hz on the amorphous ferromagnet Metglas 2826 (Fe
40
Ni
40
P
14
B
6
) under various conditions of magnetization, up to saturation. The measurements were performed by monitoring the rate of change of the angular velocity of a top spinning in a magnetic field perpendicular to its axis, in which disk specimens (diameter 22 mm, thickness 0.06 mm) were mounted. At all frequencies losses are found to increase almost linearly with the relative magnetization M/M
s
up to a maximum for M/M
s
= 0.94, and then to drop very rapidly to zero for complete saturation. When the rotational losses W
r
are plotted vs. f, one finds that these curves are characterized by large excess losses and by a non linear dependence on rotational frequency, similar to the behavior observed in the alternating loss case.