Magnetic Structures of the Polymorphic Forms of Manganous Sulfide

Manganous sulfide exists in three polymorphic forms. There are two cubic modifications, $\alpha$-MnS having the rock salt structure and $\beta$-MnS with the zinc blende structure. The third form is hexagonal $\beta$-MnS with the wurtzite structure. The magnetic susceptibilities of all three forms and the antiferromagnetic structures, as determined by neutron diffraction, are reported. $\alpha$-MnS exhibits ordering of the second kind, in agreement with earlier work. The spin direction, however, is found to be in the ferromagnetic (111) sheets rather than along cube edges. In the cubic $\beta$-MnS case, the magnetic structure is the hitherto unobserved "improved ordering of the first kind" proposed by Anderson. The spin direction is normal to the unique cubic axis. The hexagonal $\beta$-MnS antiferromagnetic structure can be derived from the cubic $\beta$-MnS by stacking the close-packed (111) sheets of the zinc blende form according to the scheme $\mathrm{ABA}$—appropriate to hexagonal close-packing. The magnetic unit cell is orthohexagonal with ${a_0}^{\prime }=a_0\sqrt{3}$, ${b_0}^{\prime }=2\mathrm{}{a}_0$, ${c_0}^{\prime }=c_0$, where the unprimed symbols refer to the original hexagonal cell. The spin direction is normal to the (011) plane. These magnetic structures are discussed on the basis of an indirect exchange coupling mechanism.