Coupling Single Molecule Magnets to Ferromagnetic Substrates

Double Decker Structure

Electronic config. of Tb: [Xe]4f96s2

Phthalocyanine C32H18N8

TbPc2 (Terbium-Phthalocyanino) SMM

Easy axis of Ni:Out of Plane (OP) of Ni filmand collinear with TbPc2 axis.

OP axis is created by adding 13 monolayers of Ni on Cu(100) surface.

Experimental Setup

Easy axis of Ni:In Plane (IP) of Ni film and perpendicular to TbPc2 axis.

IP axis is created by adding 6 monolayers of Ni on Ag(100) surface.

A magnetic field B was applied parallel to x-ray direction at normal (=0o ) and grazing (=70o ) incidence to measure OP and IP magnetization.

X-ray Magnetic Circular Dichcroism (XMCD):

Difference spectrum of two x-ray absorption spectra (XAS) taken in a magnetic field, one taken with left circularly polarized light, and one with right circularly polarized light.

Coupling between MTb and MNi is anti-ferromagnetic.

When easy axis of Tb is orthogonal to Ni, Tb XMCD reduced, signaling weakening of Tb magnetization.

X-ray Absorption spectra (XAS)

Addition of a oxygen layer between Pc and Ni film results in oxidation of Pc ligand.

Exchange field ~ 0.6 T

Doping of Ni film with Li leadsto reduction of Pc ligand.

Exchange field ~ 2.5 T

B(T)(=0o ) (=70o )

B(T)

Tuning Exchange Interaction

(=0o ) (=70o )

Conclusion

SMMs couple to ferromagnetic (FM) metal film.

The superexchange interaction mediating the coupling can be tuned by oxidizing or reducing the FM substrate.

The SMMs magnetization depends critically on the alignment of the molecule and substrate easy axis.

The enhanced thermal stability of the TbPc2 magnetic moment and possibility to orient it parallel or antiparallel to the substrate make TbPc2 very interesting for application as spin valve device.