Probing magnetic coupling between LnPc2 (Ln=Tb, Er) molecules and graphene / Ni(111) substrate with and without Au-intercalation: role of the dipolar field

Lanthanides (Ln) bis-phthalocyanine (Pc), the so called LnPc2 double decker, are promising
class of molecules, with well-defined magnetic anisotropy. In this work, we investigate the
magnetic properties of LnPc2 molecules UHV-deposited on the graphene/Ni(111) substrate, and
how they modify when an Au layer is intercalated between the Ni and graphene. X-ray
absorption spectroscopy (XAS), linear and magnetic circular dichroism (XLD and XMCD)
were used to characterize the systems and probe the magnetic coupling between LnPc2
molecules and the Ni substrate through graphene, both gold intercalated or not. Two types of
LnPc2 molecules (Ln=Tb, Er) with a different magnetic anisotropy (easy-axis for Tb, easyplane for Er) were considered. XMCD shows an antiferromagnetic coupling between Ln and Ni(111) even in the presence of the graphene interlayer. Au intercalation causes the vanishing
of the interaction between Tb and Ni(111). On the contrary, in the case of ErPc2, we found that
the gold intercalation does not perturb the magnetic coupling. These results, combined with the
magnetic anisotropy of the systems, suggests the possible importance of the magnetic dipolar
field contribution in determining the magnetic behaviour.