Dipole interactions in crystals

Magnetic dipole interactions in crystals
David C. Johnston
Phys. Rev. B 93, 014421 (2016)

Eigenvalues (a) ${\lambda }_{(1/2,0,1/2)}$ for AFM wave vector k = (1/2,0,1/2)  r.l.u. and (b) ${\lambda }_{(1/2,1/2,1/2)}$ for AFM wave vector k = (1/2,1/2,1/2)  r.l.u. versus the $c/a$ ratio for a simple tetragonal lattice with the moments aligned along [010] ($b$ axis, solid red circles), [001] ($c$ axis, solid green diamonds), and [100] ($a$ axis, solid blue squares).