Magneto-optics of single-molecule magnets with optical nanoantennas

Introduction Magnetoplasmonics, the interaction of surface plasmons with magnetism, can provide exciting prospects in non-reciprocal nanophotonics, optically-controlled nanomagnetism and highly-efficient chemical... [ view full abstract ]

Introduction

Magnetoplasmonics, the interaction of surface plasmons with magnetism, can provide exciting prospects in non-reciprocal nanophotonics, optically-controlled nanomagnetism and highly-efficient chemical sensing.[1,2] To gain these functionalities, one typically combines localized plasmon nanoantennas and ferromagnetic nanostructures.[3,4] Here we investigate the so far unexplored combination of molecular magnets with plasmonic nanostructures to reveal how the magneto-optical response of the former is modified in such hybrids.

Methods

Thin films (2 nm) of the TbPc2 single molecule magnet were prepared by thermal evaporation. Gold nanodisks were prepared by hole-mask colloidal lithography. Low temperature Magnetic Circular Dichroism experiments were carried out on a home-made spectroscopic setup capable of working between 250-2500 nm, 1.4-300 K and ±11.5 T.

Results

We tuned the geometrical parameters of the nanodisks so that their plasmon resonance would match the main absorption line of TbPc2. We observed a moderate (5x) but clear amplification of the optical and magneto-optical signals.

Discussion

To accurately interpret the magneto-optical response of the molecular-plasmonic hybrid structure, the magnetoplasmonic behavior of the gold nanodisks was modelled and taken into account.[5,6] We found that such contribution is far from being negligible, and it is mandatory to understand the optical and magneto-optical processes taking place in the hybrid nanostructure. This is, to the best of our knowledge, the first report of plasmon-assisted amplification of the magneto-optical signal of a molecular nanomagnet. These results indicate that plasmon-boosted magneto-optics can detect the magnetic properties of single-molecule magnet sub-monolayers, which are currently only accessible through x-ray magnetic circular dichroism at synchrotron radiation facilities.[7,8]

This work has been financed by the EC through grant 737093 — FEMTOTERABYTE — H2020-FETOPEN-2016-2017.

References

[1] Armelles et al. Adv. Opt. Mater. 1 (2013) 10.

[2] Pellegrini et al. ‘Magnetoplasmonics’ in Encyclopedia of Nanotechnology, Springer 2016.

[3] Armelles et al. Nano Lett. 15 (2015) 2045.

[4] Lodewijks et al. Nano Lett. 14 (2014) 7207.

[5] Pineider, F. et al. Nano Lett. 13 (2013) 4785.

[6] Sepulveda, B. et al. Phys. Rev. Lett. 104 (2010) 147401.

[7] Mannini, M. et al. Nature Mater. 8 (2009) 194.

[8] Mannini, M. et al. Nature Mater. 468 (2010) 417.