Effect of bending stresses on the high-frequency magnetic properties and their time stability in a cobalt-based amorphous alloy with an extremely low magnetostriction

An unusual effect of the stresses of bending (toroidal sample diameter $D$) on the hysteretic magnetic properties ($H_c$, $\mu_5$) of an amorphous Со$_{69}$Fe$_{3.7}$Cr$_{3.8}$Si$_{12.5}$B$_{11}$ alloy with an extremely low magnetostriction ($|\lambda_s|\le$ 10$^{-7}$) is revealed. These properties are measured in a dynamic regime at a magnetic-field frequency $f$ = 0.1–20 kHz. The coercive force of the alloy $H_c$ weakly depends on $D$ at low frequencies ($f <$ 1 kHz), and permeability $\mu_5$ ($H$ = 5 mOe), in contrast, is independent of $D$ at high frequencies and is dependent on $D$ at low frequencies. The samples subjected to high-temperature (390$^\circ$C) annealing followed by water quenching exhibit “anomalous” dependences: permeability $\mu_5$ increases with decreasing toroidal sample radius, i.e., with increasing bending stresses. The detected dependences are related to the fact that magnetization reversal via the displacement of rigid domain walls is predominant at low frequencies and during static measurements and magnetization reversal via the displacement of flexible domain walls is predominant at high frequencies.