Indirect Magnetic Coupling of Manganese Porphyrin to a Ferromagnetic Cobalt Substrate

Abstract

The coupling mechanism of magnetic molecules to ferromagnetic surfaces is of scientific interest to design and tune molecular spintronic interfaces utilizing their molecular and surface architecture. Indirect magnetic coupling has been proposed earlier on the basis of density functional theory +U (DFT+U) calculations, for the magnetic coupling of manganese(II) porphyrin (MnP) molecules to thin Co films. Here we provide an experimental X-ray magnetic circular dichroism (XMCD) spectroscopy and scanning tunneling microscopy (STM) study of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) on rough (exhibiting a high density of monatomic steps) and smooth (exhibiting a low density of monatomic steps) thin Co films grown on a Cu(001) single crystal toward the assessment of the magnetic coupling mechanism. After deposition onto the surface, MnTPPCl molecules were found to couple ferromagnetically to both rough and smooth Co substrates. For high molecular coverage, we observed higher XMCD signals at the Mn L-edges on the smooth Co substrate than on the rough Co substrate, as expected for the proposed indirect magnetic coupling mechanism on the basis of its predominance on the flat surface areas. In particular, DFT+U calculations predict a weak ferromagnetic molecule-substrate coupling only if the chloride ion of the MnTPPCl molecule orients away (Co-Mn-Cl) from the Co surface.

Antiferromagnetic coupling of Cr-porphyrin to a bare Co substrate

“…2(b)]. This chemical shift confirms that chlorine is detached from CrTPPCl upon adsorption and directly adsorbed on the Co substrate [16]. As also evidenced by our data, Cl does not contribute to the AFM exchange coupling between CrTPP molecules and the bare cobalt.…”

“…In "on-surface" configurations novel properties can arise when the magnetic and electronic characteristics of the metal-organic species are subtly modified by the surface-molecule interaction. Accordingly, it was discovered that metallophthalocyanines and metalloporphyrins with 3d and 4f block metal centers exhibit remarkable electronic, optoelectronic, and magnetic properties when adsorbed on surfaces [1,2, [5][6][7][8][9][10][11][12][13][14][15][16]. Strikingly, the magnetic exchange coupling of the spin of metalloporphyrins or metallophthalocyanines with that of ferromagnetic (FM) substrates (Co and Ni) was found to induce stable magnetic order in the paramagnetic molecules at and above room temperature [1,2,11].…”

“…The magnetization of the substrate is reversed by applying an external magnetic field (| B| ∼ 120 mT). Due to the shape anisotropy the Co film saturates the magnetization along its [110] direction [16]. The XA/XMCD spectra are recorded in remanence at the Co and Cr L 3,2 edges using circularly polarized x-rays of opposite helicities, denoted as C + and C − (see Fig.…”

“…This is in agreement with Refs. [16,18], where it was found that similar molecules, manganese(III) tetraphenylporphyrin chloride (MnTPPCl), lose their chlorine ligand upon adsorption onto a bare Co substrate and thereby change their oxidation state from 3+ to 2+. monolayer on a Co substrate.…”

Interaction of Fe3+meso-tetrakis (2,6-dichloro-3-sulfonatophenyl) porphyrin with cationic bilayers: magnetic switching of the porphyrin and magnetic induction at the interface

“…As a result, the spin moment of the whole metalloporphyrin molecule decreases from 2.00 to 1.73 lB for the lipid-interacting molecule. It is noticeable that the net difference in the spin moment of the metalloporphyrin promoted by the association with the bilayer was higher than that described for in situ-sublimated Fe porphyrin molecules on ferromagnetic Ni and Co films on Cu(100) [64]. In this condition, the authors found a slight increase in the spin moment of the whole porphyrin molecule from 2.00 lB for the free molecule to 2.17 lB for the deposited molecule.…”