Abstract

The composition-dependent magnetic properties of B2-ordered Fe_1-x(Mn/Co)_xRh alloys with substitutional disorder on the Fe sublattice are investigated using first-principles calculations within the coherent potential approximation. By systematically substituting Mn and Co on the Fe sublattice, we establish d-band filling as the primary control parameter governing magnetic stability in this itinerant system. Mn substitution (hole doping) shifts the Fermi level into the minority-spin bonding states, driving a collapse of spin polarization (crossing zero at x≈0.5) and the emergence of competing antiferromagnetic interactions (ηMn<0). Even though the ferromagnetic configuration remains energetically well separated from the G-type AFM-II configuration across the studied range (ΔE up to ∼0.35 eV/atom), this exchange competition drives an “itinerant magnetic softness” that suppresses the Curie temperature by ∼450 K—a finite-temperature instability set by the near-cancellation of competing exchange interactions rather than by AFM–FM energy proximity. In contrast, Co substitution (electron doping) acts as a “magnetic hardener” by pinning the Fermi level within the majority-spin pseudogap, preserving high spin polarization (|P|≈0.75) and stabilizing ferromagnetic exchange across the full composition range. These results show that tuning the Fermi level relative to the pseudogap provides a systematic, microscopic framework for controlling magnetic stability in B2-ordered itinerant magnets, distinct from simple magneto-volume models.

Greeshma R

Research Scholar

My research interest includes the study of alloys, molecules and oxides.

Rudra Banerjee

Assistant Professor, Computational Condensed Matter

Designing next-generation magnetic, catalytic, and quantum materials from first principles — bridging atomic-scale disorder to device-relevant function.