Electronic configuration of Mn ions in the ππ-dd molecular ferromagnet ββ-Mn phthalocyanine studied by soft X-ray magnetic circular dichroism

We have studied the electronic structure of the molecular ferromagnet ββ-Mn phthalocyanine (ββ-MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T<8.6K, 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 ββ-MnPc is largely in the 4Eg4Eg ground state arising from the (eg)3(b2g)1(a1g)1(eg)3(b2g)1(a1g)1[(dxz,yz)3(dxy)1(dz2)1][(dxz,yz)3(dxy)1(dz2)1] configuration of the Mn2+ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the 4Eg4Eg ground state originates from the a1ga1g orbital of the Mn2+ ion, it is proposed that a1ga1g–a1ga1g exchange coupling via the ππ orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of ββ-MnPc.

► Mn phthalocyanine (MnPc) molecule is the molecular ferromagnet.
► An issue is whether the ground state of Mn ions in MnPc is 4Eg4Eg or 4A2g4A2g.
► X-ray magnetic circular dichroism reveals that the ground state is mainly in 4Eg4Eg.