5 / 15
Page 53
S e p t e m b e r 2 4 - 2 6 , 2 0 1 8 | B u d a p e s t , H u n g a r y
OF EXCELLENCE
IN INTERNATIONAL
MEETINGS
alliedacademies.comYEARS
Magnetic Materials 2018
Materials Science and Nanotechnology
|
Volume 2
MAGNETISM AND
MAGNETIC MATERIALS
2
nd
International Conference on
Mater Sci Nanotechnol 2018, Volume 2
CALCULATION OF ANISOTROPIC EXCHANGE COUPLING CONSTANTS IN
IRIDATES
Alexander Yaresko
Max Planck Institute for Solid State Research, Germany
B
ecause of strong spin-orbit coupling within the Iridium 5d shell magnetic interaction in Ir4
+
oxides cannot be described by
an isotropic Heisenberg-like model and anisotropic exchange interactions become important. In α-Na
2
IrO
3
and α-Li
2
IrO
3
,
in which edge sharing IrO octahedra form a honeycomb lattice, magnetic interaction was suggested to be bond-dependent
and to be described by the Kitaev model. Recently, another complex Ir oxide β-Li
2
IrO
3
has been synthesized which is expected
to be close to forming a Kitaev spin liquid. Ir ions in this compound form a “hyper-honeycomb” lattice, a three-dimensional
analogue of the honeycomb lattice of α-Na
2
IrO
3
. In Sr
2
IrO
4
, Sr
3
Ir
2
O
7
and in R
2
Ir
2
O
7
compounds, where
R
is a rare-earth ion, with
the pyrochlore structure, on the other hand, the dominant anisotropic exchange is the anti-symmetric Dzyaloshinskii–Moriya
interaction. We present results of LSDA+U band structure calculations for Na
2
IrO
3
, Sr
2
IrO
4
, and some R
2
Ir
2
O
7
iridates. The strength
of the Coulomb repulsion U is adjusted by comparing the calculated optical conductivity to experimental optical spectra. Then,
magnetic interactions in these compounds are estimated by mapping the total energy calculated for various non-collinear
magnetic configurations constrained by magnetic symmetry onto an effective model which includes isotropic Heisenberg-like as
well as bond-dependent anisotropic magnetic interactions. It is shown that the variation of the total energy cannot be described
by the isotropic Heisenberg-like model and anisotropic terms may be as strong as the isotropic ones.