Structure-dependent exchange in the organic magnets Cu(II)Pc and Mn(II)Pc

Abstract

We study exchange couplings in the organic magnets copper͑II͒ phthalocyanine ͓Cu͑II͒Pc͔ and manganese͑II͒ phthalocyanine ͓Mn͑II͒Pc͔ by a combination of Green's function perturbation theory and ab initio density-functional theory ͑DFT͒. Based on the indirect exchange model, our perturbation-theory calculation of Cu͑II͒Pc qualitatively agrees with the experimental observations. DFT calculations performed on Cu͑II͒Pc dimer show a very good quantitative agreement with exchange couplings that our theoretical group extracts by using a global fitting for the magnetization measurements to a spin-1 2 Bonner-Fisher model. These two methods give us remarkably consistent trends for the exchange couplings in Cu͑II͒Pc when changing the stacking angles. The situation is more complex for Mn͑II͒Pc owing to the competition between superexchange and indirect exchange.

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

“…These functionals listed in Fig.1 and Fig.2 have predicted a ferromagnetic interaction except for HSE06 giving an anti-ferromagnetic one. However, these calculated exchange interactions is much larger than the nearest-neighbouring exchange interaction in CuPc crystal (typically ∼ 0.1 meV) [2,4] and the hyperfine interaction on CuPc (typically ∼ 10 −5 meV) [11].…”

“…In sharp contrast to the LDA and GGA, the hybrid-exchange functionals including O3LYP, B3LYP, and HSE06 can eliminate the self-interaction error and balance the tendencies to delocalize and localize Kohn-Sham orbitals by mixing Fock exchange with that from a generalized gradient approximation (GGA) exchange functional [37]. The hybrid-exchange functionals have previously been shown to provide a good description of the localised spins and magnetic properties [4,5,7,40,41]. Especially for CuPc (spin -1 2 ), it is crucial to treat the localised d-electron and delocalized pelectron wave functions on the same foot.…”

“…Copper-phthalocyanine (CuPc) [2][3][4][5] has received the most extensive experimental and theoretical studies as compared to other MPcs. Nevertheless, the recent experimental and theoretical studies have demonstrated that the α-phase cobalt-phthalocyanine (CoPc) has much stronger exchange interaction than CuPc and raises its transition temperature above the boiling point of liquid nitrogen [7,8].…”

“…The metal-phthalocyanine (MPc), in which a metallic ion is centred at a conjugated Pc ring, has attracted much attention recently due to its fascinating physical properties [1][2][3][4][5][6][7][8][9][10][11]. Especially, the spin-bearing MPcs are of great interest.…”

Subspace Representations in Ab Initio Methods for Strongly Correlated Systems

“…The accepted understanding 51,54,55 of the spectroscopic nature of the gap in the copper phthalocyanine monomer is that the HOMO level is dominated by a doubly-occupied a 1u orbital which consists of a superposition of Carbon p z orbitals delocalized on the pyrrole rings of both monomer units, while the spectroscopically correct LUMO level is also a delocalized doublydegenerate orbital, of e g symmetry composed of a superposition of π orbitals on pairs of macrocycle Carbon atoms. We may expect some minor differences in the spectroscopic properties in the dimer system with respect to the monomer, due to σ-bonding between moieties, but for the main features to be preserved.…”