| Bimetallic oxalates are a class of layered, molecular-based or organic magnets with transition metals M(II) and M'(III) coupled by oxalate molecules C2O4 in an open honeycomb structure. The Fe(II)Fe(III) bimetallic oxalates exhibit an unusual negative magnetization in small magnetic fields. Energy, structure, and symmetry considerations are used to construct a reduced Hamiltonian that includes the antiferromagnetic exchange JcS·S’ between the Fe(II) and Fe(III) spins and the spin-orbit interaction -λS·L on the Fe(II) sites. By shifting the Fe(II) ions with respect to the oxalate molecules, the organic cation between the bimetallic layers alters the C3-symmetric crystal field and the orbital angular momentum Lzcf of the ground-state doublet at the Fe(II) sites. Magnetic compensation (cancellation of the moment on the Fe(II) and Fe(III) sublattices) occurs for a range of Lzcf. We predict that the giant negative magnetization can be controlled by using light to flip the orbital angular momentum L or by appling uni-axial strain to quench the orbital angular momentum Lzcf of the doublet. This work was done by Randy S. Fishman in collaboration with Fernando Reboredo at MTG, ORNL. Phys. Rev. B 77, 174433 (2008) |
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