The results of investigation of the nonuniformity of magnetization processes in an as-quenched ribbon of soft magnetic cobalt-based amorphous alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) are reported. The studies show that the prime cause for the nonuniformity of magnetic characteristics and magnetization processes is the nonuniformity of internal quenching stresses. The indirect characteristic of such stresses is the volume of domains with an orthogonal magnetization component. In the region of 180° domain wall motion, a bimodal field dependence of magnetic permeability and a bias field of hysteresis loops are found, which result from the ribbon nonuniformity across the thickness. The bias field and asymmetry of hysteresis loops are explained in terms of the formation unidirectional exchange anisotropy at the interface of ferromagnetic and antiferromagnetic phases of planar magnetization components oriented along the ribbon axis. The disappearance of bias field and hysteresis loop asymmetry across the ribbon width can be explained by decreasing the thickness of antiferromagnetic CoO oxide layer because of the different concentrations and depth of penetration of oxygen and hydrogen atoms introduced into the ribbon surface, which result from the interaction with atmosphere vapor in the course of ribbon preparation. © 2023, Pleiades Publishing, Ltd.