A study is reported on synthetic ferrimagnetic media, which is made of an initial or stabilization magnetic layer (L1) closer to the substrate and a thicker top magnetic layer (L2) separated by a Ru spacer layer. The effects of the magnetic anisotropy (KU-L1) and the thickness (tL1) of the stabilization layer on the thermal stability of synthetic ferrimagnetic media are systematically studied. The magnetic anisotropy KU-L1 is varied by changing the Pt content of CoCrPtB alloy while a constant thickness and the same composition are retained for the L2. Media coercivity, stabilization factor KUV/kBT, and thermal stability increase as a function of tL1. For a particular tL1 value, these factors are improved for higher KU-L1, though the interlayer antiferromagnetic coupling strength is decreased due to compositional changes. © 2002 American Institute of Physics.