Pressure dependence of the electronic and magnetic properties of the layered antiferromagnetic insultaor FeI2

Nuclear hyperfine interaction parameters have been deduced from 57Fe Mössbauer spectra recorded in the range of 0–26 GPa and at temperatures of 10–296 K in anhydrous ferrous iodide. X‐ray diffraction data indicate that the compound is isostructral in the range 0–25 GPa. There is an abrupt change in the electronic state and spin dynamics of the transition‐metal (TM) atom, and in the magnetic behavior of the compound at 20 GPa. In the range 0–19 GPa, antiferromagnetic ordering occurs below well‐defined Néel temperatures TN. TN increases by more than ten‐fold and static internal fields of up to 12 Tesla are generated at the TM nuclear site. At pressures higher than 20 GPa hyperfine structure associated with atomic‐spin fluctuations are evident down to 10 K. An enhanced dynamic internal field of ∼30 Tesla — associated with the spin fluctuations — is sensed by the iron nucleus. No static magnetic ordering due to cooperative exchange interactions is observed above 20 GPa, in contrast to the magnetism that occurs in the low pressure regime.