PAWEL PIETRUSIEWICZ MAGNETIC PROPERTIES OF FECOWYB-BASED FERROMAGNETIC ALLOYS WITH A SMALL ADDITION OF PT The paper presents the results of research on the effect of Pt addition in the amount of 2 to 3% at. in to bulk Fe61Co10B20Y8-xW1Ptx alloy on its structure and magnetic properties. Alloys in the form of tiles were made by pressing a liquid alloy into a copper liquid-cooled mold. Structural examinations were carried out using X-ray diffraction (XRD). The magnetic properties were examined using a vibration magnetometer (VSM). Based on structural investigations, the occurrence of crystalline phases, i.e.: a-Fe, Fe2B, FePt, Fe3Pt, FePt3, was found. The results of VSM tests showed that both saturation magnetization (m0Ms) and coercive field (Hc) significantly increased. The study showed that even a small change in the Pt content in the alloy affects its structure and thus significantly affects the magnetic properties.