Exchange anisotropy of polycrystalline Mn–Ir∕Co–Fe bilayers enlarged by long-time annealing

The effect of long-time annealing on the exchange anisotropy of polycrystalline Mn75Ir25 dAF∕Co70Fe304nm bilayers was investigated to induce large unidirectional anisotropy constant, JK, with very thin antiferromagnetic layer. As a notable result, extra large value of JK=0.87erg∕cm2 was obtained in the bilayer with dAF=5nm after 200h annealing at 250°C, which is larger than twice the maximum value of PtMn∕Co–Fe system usually used in spin valves of hard disk drives. According to the single spin ensemble model, the enlargement of JK by the long-time annealing is explained as a result of the change of the distribution of antiferromagnetic spin directions.