Structure magnetique du sulfure de fer FeS de type blende

Zinc blende type FeS, which is cubic at room temperature and becomes orthorhombic, pseudo-tetragonal ($\text{c}\text{a}\text{< 1}$) at the magnetic transition, has been studied by neutron diffraction. The magnetic space group is F_c 2 2' 2' : ferromagnetic (001) planes are coupled antiferromagnetically, and the moments lie along the a axis, in agreement with previous Mössbauer measurements. The exchange integral between nearest neighbours in the ab plane is thus weaker than those between nearest neighbours in the ac and bc planes.