Exchange anisotropy of L1₂-Mn₃X (X = Ir, Rh, Ru)/Co-Fe bilayers

The L1₂ -phase formation and resultant exchange anisotropy were examined in Mn-Rh/Co-Fe and Mn-Ru/Co-Fe bilayers, varying the substrate temperature, T_sub, during the deposition of Mn-Rh or Mn-Ru layer. The superlattice diffractions from the Mn₃Rh were detected. The unidirectional anisotropy constant, J_K, was enhanced more than double with increasing T_sub from room temperature to 130°C ∼ 170°C, similarly to Mn-Ir/Co-Fe bilayers. The maximum J_K value obtained was 0.77 erg/cm² for the Mn-Rh/Co-Fe bilayer and 0.56 erg/cm² for the Mn-Ru/Co-Fe bilayer. The blocking temperature, T _B, was increased about 80°C to 100°C, in accordance with enhancing J_K. Variations of J_K and T_B as a function of antiferromagnetic layer thickness, d_AF, were also studied. The critical thickness of d_AF was less than 5 nm for both the bilayers.