  We have studied the magnetic properties of multilayers composed of
ferromagnetic metal Co and heavy metals with strong spin orbit coupling (Pt and
Ir). Multilayers with symmetric (ABA stacking) and asymmetric (ABC stacking)
structures are grown to study the effect of broken structural inversion
symmetry. We compare the perpendicular magnetic anisotropy (PMA) energy of
symmetric Pt/Co/Pt, Ir/Co/Ir multilayers and asymmetric Pt/Co/Ir, Ir/Co/Pt
multilayers. First, the interface contribution to the PMA is studied using the
Co layer thickness dependence of the effective PMA energy. Comparison of the
interfacial PMA between the Ir/Co/Pt, Pt/Co/Ir asymmetric structures and
Pt/Co/Pt, Ir/Co/Ir symmetric structures indicate that the broken structural
inversion symmetry induced PMA is small compared to the overall interfacial
PMA. Second, we find the magnetic anisotropy field is significantly increased
in multilayers when the ferromagnetic layers are antiferromagnetically coupled
via interlayer exchange coupling (IEC). Macrospin model calculations can
qualitatively account for the relation between the anisotropy field and the
IEC. Among the structures studied, IEC is the largest for the asymmetric
Ir/Co/Pt multilayers: the exchange coupling field exceeds 3 T and consequently,
the anisotropy field approaches 10 T. Third, comparing the asymmetric Ir/Co/Pt
and Pt/Co/Ir structures, we find the IEC and, to some extent, the interface PMA
are stronger for the former than the latter. X-ray magnetic circular dichroism
studies suggest that the proximity induced magnetization in Pt is larger for
the Ir/Co/Pt multilayers than the inverted structure, which may partly account
for the difference in the magnetic properties. These results show the intricate
relation between PMA, IEC and the proximity induced magnetization that can be
exploited to design artificial structures with unique magnetic characteristics.
