  The tunability of Ar+ ion irradiation of Co/Pd multilayers has been employed
to create depth-dependent perpendicular anisotropy gradients. By adjusting the
Ar+ kinetic energy and fluence, the depth and lateral density of the local
structural modification are controlled. First-order reversal curve analysis
through X-ray magnetic circular dichroism and conventional magnetometry studies
show that the local structural damage weakens the perpendicular anisotropy near
the surface, leading to a magnetization tilting towards the in-plane direction.
The ion irradiation method is complementary to, and may be used in conjunction
with, other synthesis approaches to maximize the anisotropy gradient.
