Christian Wäckerlin, Paul Scherrer Institute
Spin-bearing metal-organic complexes on ferromagnetic surfaces provide novel and exciting systems to control and switch spins by chemical ligands. For their experimental investigation in comparison with DFT+U calculations we combine element specific X-ray Magnetic Circular Dichroism (XMCD) and Scanning Tunneling Microscopy (STM). The paramagnetic ad-molecules can undergo a significant exchange coupling with magnetic substrates leading to magnetic order even up to room temperature. [1]A ferromagnetic and antiferromagnetic alignment can be obtained by the choice of the substrate and possible inter-layers. We investigate the influence of an optional, external ligand binding to the open site of square-planar molecular complexes opposite to the substrate. Thereby, we can “switch-off”, [2]tune and even “switch-on” [3]the spin in the adsorbed complex. We show that, on surface, the exact outcome of those chemical reactions is not identical to the case of a free molecule. By exploiting this interaction with the substrate we can go beyond “conventional” magnetochemistry and we can also modify the strength and the sign of the exchange-interaction with the substrate. [4]The observation of these effects provides a rapidly growing understanding of the fundamental processes at the organic-inorganic interface. This knowledge can serve as a basis to develop applications in organic spintronics or magnetochemical sensors.
Furthermore, by using synthetically directed molecular self-assembly, we fabricate ordered two-dimensional layers of Fe and Mn complexes in a chessboard-like lattice (cf. image). [5]The selective response towards axial ligation with ammonia allows to reversibly control the magnetic moments in this Fe-Mn-Fe spin-array.
[1] A. Scheybal et al, Chem. Phys. Lett. 411, 214 (2005)
[2] C. Wäckerlin et al, Nat. Commun. 1, 61 (2010)
[3] C. Wäckerlin et al, Angew. Chem. Int. Ed. DOI:10.1002/anie.201208028 (2013)
[4] C. Wäckerlin et al, Chem. Sci. 3, 3154 (2012)
[5] C. Wäckerlin et al, Adv. Mater. DOI:10.1002/adma.201204274 (2013)
