Abstract <p>The work is devoted to magnetic materials based on (Fe₆₂Cr₂₄Co₁₄)_81+<i>x</i>B_{18–<i>x</i>}Si₁ (at %) alloys, where <i>x</i> = 0, 2, and 4. The materials were prepared in the form of metallic ribbons by melt spinning, i.e. rapid quenching from the melt onto a rotating copper disk in an inert atmosphere. In the as-spun state, ribbons had an amorphous structure. The structure and phase transformations in the alloys upon heating were analyzed using X-ray diffraction methods. The dependences of the magnetic moment and heat flow of the alloys heated at the same heating rate were found. Variation in the phase composition during crystallization of the amorphous structure and its influence on the magnetic properties of the alloys were studied. It was found that, for a highly coercive state to form, the alloy structure should present a mixture of the α and Fe₃B phases, which is also characterized by high thermal stability and microhardness. The alloys demonstrate the coercive force 20.8–43.2 kA/m, saturation magnetization 0.70–1.15 T, residual magnetization 0.36–0.54 T, and microhardness 1350 ± 90 HV after crystallization heat treatment. The (Fe₆₂Cr₂₄Co₁₄)₈₁B₁₈Si₁ alloy has the best set of properties: high thermal stability, a decrease in the saturation magnetization (by 22%) and coercive force (by 13%) in the range from room temperature to 500°C.</p>