Electronic configuration of Mn ions in the $\ddot{I}€$-d molecular ferromagnet ${\hat{I}}^2$-Mn phthalocyanine studied by soft x-ray magnetic circular dichroism

Abstract

We have studied the electronic structure of the molecular ferromagnet ${\hat{I}}^2$-Mn phthalocyanine (${\hat{I}}^2$-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 ${\hat{I}}^2$-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 $\ddot{I}€$ orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of ${\hat{I}}^2$-MnPc.

15 pages, 4 figures