Speaker
Description
Metallophthalocyanines (MPcs), planar aromatic macrocycles with transition metals such as Fe and Cu at their core, exhibit versatile electronic and magnetic properties, making them ideal candidates for applications in molecular spintronic, magnetic storage, and quantum computing [1].
The previous magnetic study of CuPc and FePc grafted on high-density polyethylene (HDPE) was done using the EPR method [2], where the components of the spectra are preserved in a wide temperature range confirming the assumption of very small zero-field splitting, however, the question of temperature-dependent spin-state has remained open. In this study, we investigate the surface electronic and magnetic properties of parent FePc and CuPc in bulk form, as well as FePc deposited on thin HDPE foil, using X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) at temperature range $4$ K – $20$ K under varying magnetic fields ($2$ T – $6$ T). Our results reveal a strong XMCD signal evolution with temperature and magnetic field, providing insights into the spin states and ligand effects in both FePc and CuPc. The magnetic properties differ between bulk and foil materials, and a detailed analysis will be presented. For FePc deposited on HDPE foil, the XMCD measurements at $4$K show an increase in intensity with the applied magnetic field, and XAS and XMCD behaviour changes significantly with increasing of temperature up to $20$K at $2$T magnetic field, suggesting a possible field-induced spin crossover (HS $\rightarrow$ LS) [3]. The differentiation between tetrahedral (Td) and octahedral (Oh) Fe sites is also analysed, highlighting the impact of local coordination on the magnetic response.
The application of XMCD sum rules allows us to extract the spin (ms) and orbital (ml) moments using the procedure described in [4], further refining our understanding of the electronic structure and magnetic anisotropy in these systems.
References:
[1] M. Warner et al., “Potential for spin-based information processing in a thin-film molecular semiconductor,” Nature, vol. 503, no. 7477. Springer Science and Business Media LLC, pp. 504–508, Oct. 27, 2013. https://doi.org/10.1038/nature12597
[2] A. Reznickova et al., “Magnetic and Surface Properties of Metallophthalocyanines (M = Cu, Fe) Grafted Polyethylene,” The Journal of Physical Chemistry C, vol. 122, no. 2. American Chemical Society (ACS), pp. 1396–1403, Jan. 08, 2018. https://doi.org/10.1021/acs.jpcc.7b10984
[3] R. Pasquier and M. Alouani, “Calculated iron $L_{2,3}$ x-ray absorption and XMCD of spin-crossover Fe(phen)$_{2}$(NCS)$_{2}$ molecule adsorbed on Cu(001) surface,” 2023, arXiv. https://doi.org/10.48550/ARXIV.2309.02078
[4] P. V. B. Pinho et al., “Stoichiometry driven tuning of physical properties in epitaxial Fe3-Cr O4 thin films,” Applied Surface Science, vol. 615. Elsevier BV, p. 156354, Apr. 2023. https://doi.org/10.1016/j.apsusc.2023.156354
