Non-Heisenberg covalent magnetism in iron oxide clusters

Abstract

The sensitivity of material properties to the atomic and nanoscale morphology is most clearly demonstrated in small gas-phase clusters. In particular, magnetism serves as an extremely sensitive probe of the smallest modifications of atomic environment. This Rapid Communication demonstrates the drastic changes in both the exchange mechanism and the atomic moments in iron oxide clusters as compared to the bulk. In particular, the exchange is essentially non-Heisenberg and the exchange interactions are increased by an order of magnitude compared to bulk hematite. In addition, very large atomic magnetic moments are observed on oxygen sites due to strong spin polarization. As Fe 3 O + 4 and Fe 5 O + 7 are pure trivalent, double exchange is excluded and super exchange is the dominant exchange mechanism in these iron oxide clusters. Therefore, the non-Heisenberg behavior is attributed to covalent magnetism as the hybridization between Fe 3d and O 2p orbitals for clusters is strongly enhanced compared to bulk hematite and becomes magnetic state dependent.

Magnetic exchange interactions in SrMnO$_3$

“…Nevertheless, this raises the question of whether the apparent non-Heisenberg behavior of the Mn spins can be reduced by considering the spin-polarization of the O atoms in an appropriate way. Several authors have discussed spin polarization on oxygen atoms as a potential source for non-Heisenberg behavior in transition metal oxides 11,[31][32][33] . Considering a spin polarization energy of the O atoms, as discussed, e.g., in Ref.…”

Comment on “Proper and improper chiral magnetic interactions”

“…It is also important to note that the spin-configuration dependence of the parameters is not exclusively a noncollinear issue. In fact, the calculated exchange parameters in general depend on the underlying magnetic configuration [28][29][30]. A simple example of this is a diatomic molecule with a ferromagnetic ground state, where a calculation of the exchange parameters of the ground state configuration and the antiferromagnetic configuration is expected to yield exchange parameters of opposite sign, but with equal strength.…”