Beyond the Heisenberg Model: Anisotropic Exchange Interaction between a Cu-Tetraazaporphyrin Monolayer andFe3O4(100)

Abstract

The exchange coupling of a single spin localized at the central ion of Cu-tetraazaporphyrin on a magnetite(100) surface has been studied using x-ray magnetic circular dichroism (XMCD). Sum rule analysis of the XMCD spectra results in Cu spin and orbital magnetic moments as a function of the applied external field at low temperatures (20 K). The exchange coupling is positive for magnetization direction perpendicular to the surface (ferromagnetic) while it is negative for in-plane magnetization direction (antiferromagnetic). We attribute the anisotropy of the Heisenberg exchange coupling to an orbitally dependent exchange Hamiltonian.

Strong antiferromagnetic exchange between manganese phthalocyanine and ferromagnetic europium oxide

“…This exchange energy is two orders of magnitude above the value found for Er(III) single-ion magnets on Ni, 5k one order of magnitude above the exchange coupling strength of Coporphyrin on graphene on Ni 5j and of TbPc 2 on Ni,15 but it is up to one order of magnitude below the exchange coupling strength of 3d transition metal complexes on Co and Ni.Remarkably, the Mn-Eu magnetic coupling reported here is nearly two orders of magnitude larger than that found for a Cu porphyrin derivative on magnetite 6. The Mn-Eu magnetic coupling is likely to be mediated via the Eu 5d bands which have been shown to be spin polarized.16a Because of an AFM coupling between Mn 3d and Eu 5d electrons 16b and the FM coupling between the Eu 4f and 5d orbitals, 8a,16b the net Mn-Eu coupling is AFM with an exchange coupling strength of = ex /(2 Eu Mn ) ≅ −0.82 meV taking into account Eu = 7/2.…”

Huge magnetically coupled orbital moments of Co porphyrin molecules and their control by CO adsorption

“…27 This has already been observed for single molecular spins on magnetic surfaces. 28,29 Referring to the line shape of the angle-dependent Co XAS and XMCD spectra, a comparison to results from CoPc bulk measurements 30 lets us conclude that the SOC mixes the ground state and the first excited state of the electronic structure of the Co ions. This results in a nonvanishing hole density at the e g orbital and a more than half filled a 1g orbital, and thus creates an IP m L .…”

Coupling of single, double, and triple-decker metal-phthalocyanine complexes to ferromagnetic and antiferromagnetic substrates

“…In such a case, a rotation of the 4f spin implies also a rotation of the electrons' orbit, thereby changing the electronic overlap with neighboring orbitals that is at the origin of superexchange. Anisotropic coupling, moreover, may be a general feature of hybrid metal-organic interfaces, as it has been reported recently also for Cu porphyrin molecules adsorbed on magnetite [32].…”

“…For TbPc 2 , instead, we find that the out-of-plane coupling remains AFM, whereas the in-plane coupling turns positive but with a large error bar. Competing FM and AFM interactions have been reported for Cu porphyrin molecules adsorbed on magnetite [32]. Here, because of the very large axial anisotropy of M Tb , the magnetic behavior of TbPc 2 is mostly sensitive to K ⊥ rather than K ∥ .…”