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

摘要

The effect of long-time annealing on the exchange anisotropy of polycrystalline Mn_(75)Ir_(25) d_(AF)/Co_(70)Fe_(30) 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℃, 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.