Influence of Pressure on Electronic, Magnetic Behavior, and Fermi Surface Studies of SrFe2X2 (X = P, As, Sb) Iron-Based Superconductors

In ordered to understand the electronic structure, structural phase stability, magnetic properties, and Fermi surface studies of the 122 type of SrFe₂X₂, where (X = P, As, Sb) were investigated. For this purpose, the plane wave self-consistent method was used. Using the Brich–Murnaghan equation, their electronic structure and magnetic ordering were also investigated. It was understood that, under pressure, the compound SrFe₂As₂ undergoes a structural phase change from the tetragonal phase into the collapsed tetragonal phase. Further, due to their larger lattice constants, antimonides with larger local iron magnetic moment exhibit an enhanced Hund's rule coupling. Furthermore, smaller intra-atomic exchange coupling and significantly smaller lattice constants may be the cause of the extremely small local Fe moment for phosphates. The analysis of the valence charge density in the collapsed tetragonal phase demonstrates that the interactions between As atoms are more pronounced when compressed along the c-axis. The strength of this interaction is primarily governed by the Fe-As chemical bonding. The collapsed tetragonal phase of SrFe₂As₂ compounds, as observed in Fermi surface studies, indicates the absence of nesting of Fermi surfaces. It is clear that, from the studies, the tetragonal phase of Fermi surface nesting resulted in the long-range magnetic order, leading to the presence of superconductivity.