Time: 16:15 – 17:00

We welcome Marco Marino, Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano

Magnetic coupling between Fe phthalocyanine molecules and antiferromagnetic oxides by first principles

Abstract

In organic spintronics, the problem of understanding the interfaces of organic-inorganic heterostructures is acquiring major interest, so to coin the term spinterface [1]. We attempt to understand how the spinterfaces can be used in antiferromagnetic spintronics devices. In particular, the adsorption of organic molecules on antiferromagnetic substrates offers a channel to modify the magnetic properties of the substrates through light, without the need of a strong spin-orbit coupling and hence with beneficial effects on the spin transport properties.

We focus on transition-Metal (TM) oxides with an antiferromagnetic ground-state and low spin-orbit coupling, such as NiO and Cr2O3, and organic molecules with metallic centers, such as metal-phthalocyanines

(Pc) [2]. We employ ab-initio methods based on Density Functional Theory

(DFT) to describe the electronic, structural and magnetic properties of these interface systems.

A mapping of our DFT results into an Heisenberg model allows us to gain further understanding of the coupling between the parts of the spinterface. Two methods to obtain such mapping are used: the energy method and the Green’s function method. It emerges that the substrate Heisenberg structure changes due to adsorption-related charge-transfer mechanisms, suggesting the use of optical excitations to tune these changes.

Through optical spectra simulations, we deduce that photon absorption can induce similar charge-transfer mechanisms, hence suggesting the possibility to produce modifications of the substrate magnetic properties through light.

Fig. Side-view of FePc molecule adsorbed on Cr2O3. (a) minimum energy adsorption configuration, (b)  its spin density and (c) charge density variations with respect to the isolated system (isovalues in the range of 0.001Å-3). Cr atoms of different magnetization are colored in light blue and purple.

[1] M. Cinchetti, V. Alek Dediu and Luis E. Hueso Activating the molecular spinterface, Nature Materials 16, 507 (2017).

[2] M. Marino, E. Molteni, S. Achilli and G. Fratesi Ab-initio electronic, magnetic, and optical properties of Fe-phthalocyanine on NiO(001), Inorganica Chimica Acta 561, 121877 (2024).