The paper reveals the structure formation and magnetic properties of amorphous alloys based on the Fe-Co-Cr-B system with varying proportions of Fe to Co. These materials were obtained in the form of metal ribbons through the melt spinning technique in an inert atmosphere. In the initial as-spun state, the ribbons exhibited an amorphous structure characterized by their ferromagnetic properties. As the content of cobalt in the alloy composition decreased, the thermal stability of the amorphous phase matrix increased, leading to a shift in the crystallization mechanism from primary crystallization of the α solid solution phase to eutectic type crystallization of the initial amorphous phase. The phase composition of alloys during crystallization of the amorphous matrix phase is investigated. Alloys with a reduced cobalt content during the heating process undergo crystallization driven by the eutectic mechanism. This results in the formation of a mixture of α and Me3B phases. During this process, a significant increase in the magnetic moment of the alloys was detected. The α phase, which was formed by eutectic crystallization, was found to be enriched in chromium. It has been demonstrated that achieving a highly coercive state, it is contingent upon maintaining a Fe / Co ratio greater than 3, while simultaneously ensuring that the chromium content exceeds 16 at.%. The obtained data provides guidance for the development of functional materials with controlled magnetic properties.