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Band structure calculations are reported to describe the effects of Ta for Hf substitution on the electronic structure of the Laves phase of HfFe₂. According to experimental results emphasis is put on the investigation of the Hf_0.825Ta_0.175Fe₂ composition in comparison with the reference HfFe₂ and TaFe₂ compounds. By investigation of the theoretical interatomic exchange interactions constants, we showed the influence of the magnetovolume effect on the magnetic phase stability for one intermediate composition Hf_0.825Ta_0.175Fe₂, chosen in the most interesting part of the magnetic phase diagram with coexistence of ferromagnetic (FM) and antiferromagnetic (AF) behaviour. Evolution of the a lattice parameter is found to drive the change from FM to AF magnetic order. A detailed study of the interatomic Fe–Fe exchange coupling constants and their lattice dependence reveals that the ferromagnetic interaction with …