2D Heisenberg antiferromagnetism in spin-orbit Mott insulator Sr2IrO4
A. Matsumoto1, T. Takayama1 and H. Takagi2
1
Department of Advanced Materials, University of Tokyo, Chiba 277-8561, Japan
2
Department of Physics, University of Tokyo, Tokyo 133-8654, Japan
In 5d transition metal (TM) oxides, the interplay between electron correlation
and spin-orbit coupling gives rise to novel electric phases. Recently Sr2IrO4 was found
to be a Jeff = 1/2 Mott insulator where spin and orbital degrees of freedom are entangled
[1]. The magnetic coupling in such spin-orbit Mott insulator might be critically different
from that in 3d-based Mott insulators. For example, in the limit of strong spin-orbit
coupling, the magnetic coupling is theoretically proposed to be governed by a nearly
Heisenberg model likewise in the case of small spin-orbit coupling, when TM-O-TM
bond angle is 180°as seen in corner-shared octahedra network [2]. We focused on
Sr2IrO4 to reveal the magnetism of spin-orbit Mott insulator.
Sr2IrO4 crystallizes in a K2NiF4-type layered perovskite structure, and
magnetically orders at 240 K. We investigated the detailed magnetic susceptibilities on
single crystals. The ground state was found to be antiferromagnetism, and only the
0.20
 (emu / mol )
in-plane susceptibility steeply increases just
above the transition temperature, likely due
to Dzyaloshinsky-Moriya interaction within
ab-planes. Meanwhile, at higher temperature,
the susceptibilities are almost isotropic. By
analyzing the susceptibilities at the high
temperature region, we found that they can
be well described by the 2D Heisenberg
antigerromagnetism. This indicates that
even in the limit of strong spin-orbit
H = 0.1 T
0.15
0.10
0.05
0.00
a H ∥( 1 0 0 )
c
H ∥( 0 0 1 )
0
100
200
300
coupling, Sr2IrO4 displays the isotropic
T (K)
Heisenberg magnetism. This situation
Fig. 1 Magnetic susceptibilities
of Sr2IrO4 single crystal.
contrasts with the 3d transition metal oxides,
where spin-orbit coupling is responsible for magnetic anisotropy.
[1] B. J. Kim et al., Science 323, 1329(2009)
[2] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009)