JOANNA GONDRO STRUCTURE, CORE LOSSES, CURIE TEMPERATURE, DEFECTS IN THE STRUCTURE OF THE BULK AMORPHOUS ALLOY FE55CO15W2Y8B20 This paper presents studies relating to the structure and soft magnetic properties of the bulk amorphous alloys Fe55Co15W2Y8B20. Samples were made using the method of injecting a liquid alloy into a copper water-cooled mold in the form of plates. The structure and microstructure were examined using X-ray diffractometry. Magnetic properties were investigated from static and dynamic measurements. For the samples, the core losses were measured. The influence of structure defects on the magnetization process in strong magnetic fields was also investigated. For this purpose, the theory developed by H. Kronmüller was used. It was shown that the magnetization process in strong magnetic fields is associated with two-dimensional defects, so-called pseudo-location dipoles.