Abstract
Bimetallic oxalates are a class of layered organic magnets with transi-
tion metals M(II) and M'(III) coupled by oxalate molecules in an open
honeycomb structure. Of particular interest are the Fe(II)Fe(III) bimetal-
lic compounds, which are ferrimagnetically ordered below a transition
temperature that ranges from 30 to 48 K, depending on the cation that
separates the layers. In small magnetic fields, several of these compounds
exhibit giant negative magnetization below a compensation temperature
of roughly 2/3 Tc. By studying the behavior of the Kramer's doublet
ground state produced by the crystal-field splitting and constructing a
reduced Hamiltonian that includes both exchange and spin-orbit and in-
teractions, we can explain all of the important behavior of this class of
materials: the stability of magnetic order in two dimensions and the
existence of magnetic compensation in samples with high transition tem-
peratures. We also provide several new predictions for the spin-wave gap
and the optical flipping of the magnetic moment.
