Abstract <p>Using scanning electron, optical, and scanning probe microscopy, the surface structure of unannealed amorphous electrical engineering alloys—foils with the composition Fe₇₃(SiBNb)₂₇ and alloys of the same composition with the addition of 1% Cu, obtained by ultrafast cooling via melt spinning onto a rotating copper drum—was studied. On the free surfaces of the foils not in contact with the rotating drum, microformations and irregularities in the form of “micropoints” with characteristic sizes below 0.5 μm were found; these may, during the operation of electrical products, initiate electric field gradients on the foil surface. Exposure to underwater plasma did not lead to any change in the magnetic properties of the studied materials. In the Fe₇₃(SiBNb)₂₇ foil with the addition of 1% Cu, treated with 10 and 40 pulses of a low-frequency (10–20 Hz), weak magnetic field (10–100 kA/m), magnetic contrast was observed: in phase contrast mode, exposure to 40 magnetic field pulses produced triangular features associated with the formation of closing prismatic domains, whose domain wall width is approximately 1–2 μm; after exposure to 10 magnetic field pulses, a specific magnetic contrast pattern was observed over the entire studied foil area. A weak dependence of specific magnetization on the number of magnetic pulses was also observed for the Fe₇₃(SiBNb)₂₇ foil with 1% Cu: increasing the number of pulses led to a slight decrease in specific magnetization.</p>