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

TL;DR

This study investigates exchange interactions in Cu(II)Pc and Mn(II)Pc organic magnets using perturbation theory and DFT, revealing insights into their magnetic coupling mechanisms and how structural variations affect these interactions.

Contribution

It combines Green's function perturbation theory and DFT to analyze exchange couplings in Cu(II)Pc and Mn(II)Pc, providing new quantitative and qualitative insights.

Findings

Perturbation theory agrees qualitatively with experiments for Cu(II)Pc.

DFT calculations match experimental exchange couplings for Cu(II)Pc.

Exchange interactions in Cu(II)Pc vary systematically with stacking angles.

Abstract

We study exchange couplings in the organic magnets copper(II) phthalocyanine (Cu(II)Pc) and manganese(II) phthalocyanine (Mn(II)Pc) by a combination of Green's function perturbation theory and \textsl{ab initio} density-functional theory (DFT). Based on the indirect exchange model our perturbation-theory calculation of Cu(II)Pc qualitatively agrees with the experimental observations. DFT calculations performed on Cu(II)Pc dimer show a very good quantitative agreement with exchange couplings that we extract 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 Cu(II)Pc when changing the stacking angles. The situation is more complex for Mn(II)Pc owing to the competition between super-exchange and indirect exchange.