and where l$_{i}$ = m$_{a,i}$ − m$_{b,i}$ and m$_{i}$ = m$_{a,i}$ + m$_{b,i}$ . The frequencies ω$_{a}$ = γKM$_{s}$ , ω$_{ex}$ = γλM$_{s}$ , ω$_{me}$ = γαP$_{o}$M$_{s}$ and ω$_{o}$ = γH$_{o}$ are associated with the magnetic anisotropy, exchange, magnetoelectric coupling and the external magnetic field respectively. The parameter P$_{o}$ represents the equilibrium spontaneous polarisation. It can be seen from Eqs.(13) to (16), that the dynamic magnetic and electric components are not coupled directly. Hence, the susceptibilities can be written as with magnetic components given by Here ω 2 afm = ω$_{a}$ ( ω$_{a}$ − 2 ω$_{ex}$ ) represents the antiferromagnet (AFM) resonance frequency. The frequency Ω$_{me}$ is defined as The frequency Ω$_{o}$ is the frequency shift due to an external magnetic field and is given by Even though there is no direct coupling between magnetic and electric parts represented by a ME susceptibility, the ME ω$_{me}$ still appears in the magnetic susceptibility, as seen in Eq. (18) to (20). This results from the fact that the canting condition involves the electric polarisation. Finally, the electric susceptibility for χ e xx is 6 χ e xx = ω 2 L − ω 2 ω 2 T ω 2 (23) Ω 2 o = ω$_{o}$ [ ω$_{o}$ − ω$_{a}$ sin θ + 4 ω$_{me}$ cos θ ] (22) Ω 2 me = 2 ω$_{me}$ ( 2 ω$_{me}$ + 1 2 ω$_{a}$ sin 2 θ − ω$_{ex}$ sin 2 θ ) (21) ⃗ m = χ m ⃗ h and ⃗ p = χ $^{e}$⃗ e, (17) − ω 2 f p$_{x}$ = − ( ζ$_{1}$ + ζ$_{2}$P 2 o ) p$_{x}$ + e$_{x}$ (16) − iωm$_{y}$ = 2 γM$_{s}$h$_{z}$ sin θ + ( ω$_{a}$ cos θ + 2 ω$_{me}$ sin θ ) l$_{x}$ + ( ω$_{a}$ sin θ − 2 ω$_{me}$ sin θ − ω$_{o}$ ) m$_{z}$, (14) − iωm$_{z}$ = 2 γM$_{s}$h$_{y}$ sin θ + ( ω$_{o}$ + 2 ω$_{me}$ cos θ ) m$_{y}$ (15) χ m y = 2 γM$_{s}$ ( ω$_{a}$ cos 2 θ + 2 ω$_{me}$ sin 2 θ + ω$_{o}$ sin θ ) ( ω 2 afm cos 2 θ + Ω 2 me + Ω 2 o − ω 2 ) (18) χ m z = 2 γM$_{s}$ ( ω$_{me}$ sin 2 θ + ω$_{o}$ sin θ ) ( ω 2 afm cos 2 θ + Ω 2 me + Ω 2 o − ω 2 ) (19) χ m yz = − χ m zy = i 2 γM$_{s}$ ( ω sin θ ) ( ω 2 afm cos 2 θ + Ω 2 me + Ω 2 o − ω 2 ) (20)