Abstract <p>The quasi-binary intermetallic compounds Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇ and Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇H_<i>y</i> exhibit easy-axis magnetocrystalline anisotropy in the iron concentration range 0.05&#xa0;&lt;&#xa0;<i>x</i>&#xa0;&lt;&#xa0;0.50. For compounds close to the edges of this range, at <i>x</i> = 0.03, 0.05, 0.41, 0.50, and 0.53, spin-reorientation transitions are realized. This paper presents a detailed study of these transitions based on the analysis of magnetocrystalline anisotropy energy function and micromagnetic analysis. Using the example of Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇ and Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇H_<i>y</i> compounds with spin-reorientation transitions, it is shown that, during the transition, the misorientation angles of the easy and hard magnetization axes, the magnetocrystalline anisotropy energy, and the domain wall energy reach their minimum values. The results of micromagnetic analysis of Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇ and Y₂(Fe_<i>x</i>Co_{1 –} _<i>x</i>)₁₇H_<i>y</i> indicate the existence of a domain structure in these compounds over the entire temperature range 0 &lt; <i>T</i> &lt; <i>T</i>_C, including the phase transition point. The analytical temperature dependences of the surface energy density of the domain walls of the compounds exhibit a characteristic minimum in the phase transition region. The type of this minimum is determined by the second magnetocrystalline anisotropy constant.</p>