Item

Abstract

The magnetic structures of the triangular lattice antiferromagnet
CuFeO2 below 14 K are described by an Ising model despite the fact that
its high-spin Fe3+ (d(5)) ions (S = 5/2, L = 0) cannot have a uniaxial
magnetic moment. To resolve this puzzling picture of magnetism, we
estimated the relative strengths of various spin-exchange interactions
of CuFeO2 by performing a spin dimer analysis and then determined the
relative stabilities of a number of ordered spin states of CuFeO2, Our
calculations show that, in terms of a Heisenberg model, the
noncollinear 120 degrees spin arrangement predicted for a triangular
lattice antiferromagnet is more stable than the collinear
four-sublattice antiferromagnetic structure observed for CuFeO2 below
11 K. To find a probable cause for stabilizing the collinear spin
alignment along the c axis below 14 K, we considered the defect ions
Fe2+ and Cu2+ of the CuFeO2 lattice created by oxygen deficiency and
oxygen excess, respectively. Our electronic structure analysis suggests
that these defect ions generate uniaxial magnetic moments along the c
axis and hence induce the surrounding Fell ions to orient their moments
along the c axis.