Magnetic properties of DyFe5−xCoxAl7: Suppression of exchange interactions and magnetocrystalline anisotropy by Co substitution

In 3d−4f intermetallic compounds, a Co substitution for Fe usually strengthens the exchange interactions due to a shift of the Fermi energy to a region of the 3d band with higher density of states. Here, we study the influence of Co on the magnetism of ferrimagnetic DyFe5Al7 using magnetization measurements in static (up to 14 T) and pulsed (up to 58 T) magnetic fields. We find that the homogeneity range of DyFe5−xCoxAl7 is limited to x≤2.5. The Co substitution for Fe produces a strong detrimental effect on the 3d−3d intrasublattice exchange interactions, which leads to a pronounced decrease of the Curie temperature and of the 3d−4f intersublattice exchange field. A reduction of the density of states at the Fermi level might occur due to a broadening of the 3d band. A decrease of the rare-earth contribution to the magnetic anisotropy energy is also observed with increasing Co content. This is attributed to a competition between the Fe and Co contributions to the crystal electric field at the Dy site.