Loss of the magnetism in FeS
  It is argued that the formation of the non-magnetic state of FeS in external pressures above 6.5 GPa is in agreement with the prediction of the quantum atomistic solid-state theory, an extension of the crystal-field theory with the spin-orbit coupling incorporated, and is related with the change of sign of the off-cubic trigonal distortion marked by the change of the c/a ratio from >1.63 (magnetic) to <1.63 (non-magnetic). Keywords: highly-correlated electron system, crystal field, low-spin state, Fe2+ ion, spin-orbit coupling 
Z.Ropka, R.J. Radwanski