First-principles calculations of the magnetism of Fe$_2$O$_2$H$_2$

Abstract

By expanding the wave function in plane waves, we use the pseudopotential method of density functional theory within the generalized gradient approximation to calculate the effective magnetic coupling energies of the S=5/2 spins in the Fe2 dimer, approximated as Fe$_2$O$_2$H$_2$. Setting the Fe-O bond length at the value corresponding to the minimum total energy, we find the difference in antiferromagnetic and ferromagnetic exchange energies as a function of the Fe-O-Fe bond angle $θ$. The effective interaction is antiferromagnetic for 63$^{\circ}<θ<105^{\circ}$, and is ferromagnetic otherwise. Full potential augmented plane wave calculations were also performed at $θ=100,105^{\circ}$, confirming these results, and providing information relevant to the local anisotropy of the spin interactions.