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 A\(Co 2 A\Pd 9 A) n \Co 2 A\FeMn x A\Pd 20A, where n is the number of bilayers from 1 to 20 and x ranges from 10 A to 250 A. The (Co/Pd) multilayer begins to be exchange biased with FeMn thicker than 30 A 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.