Paramagnetic Anisotropy, Electronic Structure, and Ferromagnetism in Spin S = 32 Manganese(II) Phthalocyanine

Abstract

Measurements are reported of magnetization and the average magnetic susceptibility of manganese (II) phthalocyanine in the range 1.7–300°K, which confirm that the Mn(II) atom is in an $\text{S\hspace{0.17em}=\hspace{0.17em}3\hspace{0.17em}/\hspace{0.17em}2}$ spin state, and that weak ferromagnetic interactions are present in the crystal, presumably between adjacent molecules. Single crystals of MnPc are moderately anisotropic; the principal magnetic moment ${\mu }_{\Vert }{\text{\hspace{0.17em}=\hspace{0.17em}4.0 μ}}_B$ remains constant between 80–300°K while ${\mu }_{\perp }$ increases from 4.4 μ_B (300°K) to 5.0 μ_B (90°K). This magnetic anisotropy is consistent with a ${}^4{A}_{\text{2g}}$ ground state into which the excited term ${}^4{E}_g$ is mixed by spin–orbit coupling. Possible pathways for superexchange are considered.