The interplay between magnetism, structure, and strong electron-phonon coupling in binary FeAs under pressure

Unlike the ferropnictide superconductors, which crystallize in a tetragonal crystal structure, binary FeAs forms in an orthorhombic crystal structure, where the local atomic environment resembles a highly distorted variant of the FeAs4 tetrahdedral building block of the ferropnictide superconductors. However, like the parent compounds of the ferropnictide superconductors, FeAs undergoes magnetic ordering at low temperatures, with no evidence favoring a superconducting ground state at ambient pressure. We employ pressure-dependent electrical transport and x-ray diffraction measurements using diamond anvil cells to characterize the magnetic state and the structure as a function of pressure. While the MnP-type structure of FeAs persists up to 25 GPa, compressing continuously with no evidence of structural transformations under pressure, features in the magnetotransport measurements associated with magnetism are not observed for pressures in excess of 11 GPa. Where observable, the features associated with magnetic order at ambient pressure show remarkably little pressure dependence, and transport measurements suggest that a dynamical structural instability coupled to the Fermi surface via a strong electron-phonon interaction may play an important role in enabling magnetism in FeAs.