Perpendicular exchange anisotropy in (Co/Pd)_n/FeMn multilayers

We report on the perpendicular exchange anisotropy in (Co/Pd) _n/FeMn multilayers. The thickness effects of antiferromagnetic and ferromagnetic layers on the exchange ansiotropy are investigated systematically. The sample consists of a stack of Si\Pd 70 Å\(Co 2 Å\Pd 9 Å)_n\Co 2 Å\FeMn x Å\Pd 20 Å, where n is the number of bilayers from 1 to 20 and x ranges from 10 Å to 250 Å. The (Co/Pd) multilayer begins to be exchange biased with FeMn thicker than 30 Å where the FeMn layer develops its antiferromagnetic nature. As the number of bilayers increases, the exchange bias is reduced while the coercivity increases as observed in systems with in-plane anisotropy.