Strain

An external stress σij applied to a sample introduces a strain termin the energy:
(1)
where ∈_ij = ˆm_{ij kl}H_kH_l is the magnetoelastic strain tensor. For an isotropic material with uniaxial stress σ along Oz, the contribution depending on M is −1/2λsσ(3 cos² θ − 1), where λ_s is the spontaneous magnetostriction. This is equivalent to a uniaxial anisotropy with K_u = (3/2)λ_sσ.