MnF₂ adopts a tetragonal crystal structure (a = b > c, all angles as 90°) as shown in Figure 6.03.

Only Mn carries a moment.

Magnetic structure: corner Mn shows up and body-centered Mn shows down moment, resulting an antiferromagnet (AFM).

Since AFM, T_N is 67 K, easy to study.

Mn moment is 5 μ_B so magnetic scattering is considerably strong and hence the magnetic signal is large.

If one considers a ferromagnetic form with the Mn moments along c, all of Mn moments point the same way, so they are equivalent, and the magnetic scattering comes from a bct arrangement of moments.

Kittel tells us that the structure factor for bcc (or bct) requires h+k+l = 2n and we see the same.

Figure 6.03: Crystal strcture and neutron diffraction of Mn₂.