Characteristics of perpendicular exchange bias in [Pt/Co]-IrMn multilayers

For [ Pt( 15)/ Co( t(Co))] (4) - IrMn( 50) ( in angstrom) multilayer ( ML) prepared by magnetron sputtering, the existence of an unusual peak in ferromagnetic ( FM) thickness dependence of exchange bias properties is observed. The exchange coupling field ( Hex) shows maximum value of 291 Oe for t(Co) = 3 angstrom(.) Such atypical behavior is ascribed to a reduction of the perpendicular effective magnetic anisotropy for either very thin or exceedingly thick t(Co). The hysteresis loops become asymmetric at intermediate angle with a shift not only along the field axis but also along the magnetization axis. H-ex and coercivity ( H-c) show a 1/ cos theta and 1/vertical bar cos theta vertical bar dependence on the angle (theta) between the applied measuring field ( H-a) and the perpendicular- plane cooling field, respectively. This 1/ cos theta dependence is caused by the strong out- of- plane magnetic anisotropy. (c) 2006 Elsevier B. V. All rights reserved.