Itinerant nature of magnetism in iron pnictides: A first-principles study

Abstract

Within the framework of density-functional theory, we investigate the nature of magnetism in various families of Fe-based superconductors. (i) We show that magnetization of stripe-type antiferromagnetic order always becomes stronger when As is substituted by Sb in LaOFeAs, ${\text{BaFe}}_{2}{\text{As}}_{2}$, and LiFeAs. By calculating Pauli susceptibilities, we attribute the magnetization increase obtained after replacing As by Sb to the enhancement of an instability at $(\ensuremath{\pi},\ensuremath{\pi})$. This points to a strong connection between Fermi-surface nesting and magnetism, which supports the theory of the itinerant nature of magnetism in various families of Fe-based superconductors. (ii) We find that within the family $\text{LaOFe}Pn$ ($Pn=\text{P}$, As, Sb, and Bi), the absence of an antiferromagnetic phase in LaOFeP and its presence in LaOFeAs can be attributed to the competition of instabilities in the Pauli susceptibility at $(\ensuremath{\pi},\ensuremath{\pi})$ and (0,0), which further strengthens the close relation between Fermi-surface nesting and experimentally observed magnetization. (iii) Finally, based on our relaxed structures and Pauli susceptibility results, we predict that LaOFeSb upon doping or application of pressure should be a candidate for a superconductor with the highest transition temperature among the hypothetical compounds LaOFeSb, LaOFeBi, ScOFeP, and ScOFeAs while the parent compounds LaOFeSb and LaOFeBi should show, at ambient pressure, a stripe-type antiferromagnetic metallic state.