The aim of this work was to determine the nature of the structural defects that have a major influence on the magnetisation process within the investigated alloys. The structure of the alloys in the as-quenched state was investigated by means of X-ray diffractometry. It was confirmed that the samples were amorphous. The magnetisation was measured within magnetic fields ranging from 0 to 2T using a vibrating sample magnetometer (VSM). The investigation of the ‘magnetisation in the area close to ferromagnetic saturation’ showed that, for this class of alloys, the magnetisation process in strong magnetic fields is connected with the following two influences: 1) Firstly, the rotation of the magnetic moments in the vicinity of the defects, which are the sources of the short-range stresses, and, 2) The dumping of the thermally-induced spin waves by the magnetic field. In the case of the Fe63Co10Y7B20 alloy, the magnetisation process is connected with both point and linear defects, whereas for the Fe64Co10Y6B20 alloy, only with linear defects. This suggests that the size of the defects, determining the character of the magnetisation in the vicinity of ferromagnetic saturation, depends on the atomic packing density. On the basis of analysis of the magnetisation curves, the spin wave stiffness parameter (Dsp) was calculated.
 K. Błoch, M. Nabiałek, Acta Phys. Polon. A 127, 413 (2015). A. Lukiewska, J. Zbroszczyk, M. Nabialek, J. Olszewski, J. Swierczek, W. Ciurzynska, K. Sobczyk, M. Dospial, Arch. Metall. Mater. Sci. 53, 881 (2008).
 T. Holstein, H. Primakoff, Phys. Rev. 58, 1098 (1940).
 M. Nabialek, M. Szota, M. Dospial, P. Pietrusiewicz a, S. Walters, J. Magn. Magn. Mater. 322, 3377 (2010).
 T. Holstein, H. Primakoff, Phys. Rev. 59, 388 (1941).
 M. Nabiałek, M. Szota, M. Dośpiał, J. Alloys Compd., 526, 68 (2012).