Magnetic field effects on the optical spectrum of FeCl2

The intensity of the ligand-field zero-phonon line of FeCl₂ at 4272 Å has been measured in magnetic fields up to 40 kOe at temperatures of 8 and 11°K. The intensity first rises and then falls with increasing field, as the crystal passes through a phase transition from an antiferromagnetic (metamagnetic) to a ferromagnetic state.