Z-Site Substitution-Driven Transition From Semiconducting Antiferromagnetism to Half-Metallic Ferromagnetism in FeCrRuSi and FeCrRuP Heusler Alloys

We report a first-principles density functional theory study employing a modified Becke–Johnson potential of the quaternary Heusler alloys FeCrRuSi and FeCrRuP crystallizing in the Y-type (I) structure. At its equilibrium lattice parameters, FeCrRuSi is predicted to be a semiconducting antiferromagnet, exhibiting an indirect band gap of ≈ 0.69 eV in both spin channels, with the Fermi level located just above the valence-band maximum, indicative of weak n-type character. In sharp contrast, FeCrRuP displays robust half-metallic ferromagnetism, characterized by a metallic majority-spin channel and a minority-spin indirect gap of ≈ 0.72 eV, resulting in 100% spin polarization at the Fermi level. This pronounced change in electronic and magnetic behavior is attributed to a weakening of the d–p hybridization induced by the Z-site substitution. Replacing Si with P leads to a slight lattice expansion, reducing the covalent interactions between the main-group p states and the transition-metal d orbitals. Projected density-of-states analyses reveal that the minority-spin gap in FeCrRuP originates from strong hybridization between P-3p states and transition-metal d states, whereas FeCrRuSi shows a more balanced p–d contribution, consistent with antiferromagnetic order. These results demonstrate that Z-site substitution is an effective route to engineer magnetic order and half-metallicity, identifying FeCrRuP as a promising candidate for spintronic applications.