Magnetic anisotropy of antiferromagnet in exchange coupled Ni-Fe/Mn-Ni epitaxial bilayers

To investigate the magnetic anisotropy of the antiferromagnet, pseudo-single crystalline Ni-Fe/Mn₈₂Ni₁₈ bilayers were fabricated on MgO single crystal substrate by changing the crystallographic orientation, such as (110), (001), and (111) parallel to the film plane. According to the simple exchange anisotropy model proposed by Meiklejohn and Bean, the magnetic torque curves were analyzed for the bilayer whose antiferromagnetic layer thickness is less than the critical value to induce the exchange bias field. As results, we found that the magnetic anisotropy of the antiferromagnetic layer has strong correlation with the crystallographic symmetry in the film plane, i.e. the two-, four-, and six-fold symmetry in a (110), (001), and (111) oriented bilayer, respectively. The anisotropy energy of Mn₈₂Ni₁₈ determined from the saturation torque amplitude was 3.2 × 10⁵ erg/cm³ in (110), 1.4 × 10⁴ erg/cm³ in (001), and 7 × 10³ erg/cm³ in (111) orientation, respectively.