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 d(AF)/Co70Fe30 4 nm bilayers was investigated to induce large unidirectional anisotropy constant, J(K), with very thin antiferromagnetic layer. As a notable result, extra large value of J(K)=0.87 erg/cm(2) was obtained in the bilayer with d(AF)=5 nm after 200 h annealing at 250 degreesC, 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 J(K) by the long-time annealing is explained as a result of the change of the distribution of antiferromagnetic spin directions. (C) 2004 American Institute of Physics.