Lattice distortion induced anomalous ferromagnetism and electronic structure in FCC Fe and Fe-TM (TM = Cr, Ni, Ta and Zr) alloys

Abstract Magnetic properties of BCC, FCC and HCP Fe and the effects of the Σ 3<01¯1>{111} grain boundary (GB) and the alloying elements of Cr, Ni, Ta and Zr are investigated by first-principles calculations. The FCC Fe changes continuously from the non-magnetic state at low volumes to the ferromagnetic state at high volumes. It is observed that Σ3{111} type GBs in FCC Fe have a negative formation energy since the formation of Σ3 GB is attributed to the local FCC-HCP transformation. Moreover, consistent with the variation of equilibrium volume caused by TM solute atoms, the magnetic moment of FCC Fe₇₀TM₂ is decreased with alloying Ni while increased with alloying Cr, Ta and Zr. Due to the difference in the valence electrons and atomic radius among those solute atoms, the chemical and mechanical effects on the bond structure of Σ3{111} GB in Fe and Fe₇₀TM₂ are respectively characterized by deformation electron density and plots of spin alignments. It is understood that the variation of the spin state of Fe₇₀TM₂₀ is dominated by the electron redistributions, as illustrated by the spin-flipping and the change of the bond structure.