Electronic configuration of Mn ions in the $\pi$-d molecular ferromagnet $\beta$-Mn phthalocyanine studied by soft x-ray magnetic circular dichroism

TL;DR

This study investigates the electronic structure of the ferromagnetic $eta$-Mn phthalocyanine using XAS and XMCD, revealing the Mn ions' ground state and proposing a key exchange mechanism responsible for its ferromagnetism.

Contribution

The paper provides detailed electronic configuration analysis of Mn ions in $eta$-MnPc and identifies the $^4E_g$ ground state, highlighting the role of $a_{1g}$-$a_{1g}$ exchange coupling in ferromagnetism.

Findings

Mn ions are in a $^4E_g$ ground state with a specific electron configuration.

The ferromagnetism is linked to $a_{1g}$-$a_{1g}$ exchange coupling via the phthalocyanine ring.

The study combines experimental XAS/XMCD data with cluster-model calculations.

Abstract

We have studied the electronic structure of the molecular ferromagnet $\beta$-Mn phthalocyanine ($\beta$-MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T$<$8.6 K, by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the experimental results and subsequent cluster-model calculation, we find that the ferromagnetic Mn ion in $\beta$-MnPc is largely in the $^4$$E$$_g$ ground state arising from the ($e$$_{g}$)$^3$($b$$_{2g}$)$^1$($a$$_{1g}$)$^1$ [($d_{xz,yz}$)$^3$($d_{xy}$)$^1$($d_{z^{2}}$)$^1$] configuration of the Mn$^{2+}$ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the $^4$$E$$_g$ ground state originates from the $a$$_{1g}$ orbital of the Mn$^{2+}$ ion, it is proposed that $a$$_{1g}$-$a$$_{1g}$ exchange coupling via the $\pi$ orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of $\beta$-MnPc.