Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T
S.-H. Lee, C. Broholm, M. F. Collins, L. Heller, A. P. Ramirez, C. Kloc, E. Bucher, R. W. Erwin, N. Lacevic
Abstract
We have found weak long range antiferromagnetic order in the quasi-two-dimensional insulating oxide
KC
r
3
(OD
)
6
(S
O
4
)
2
which contains Cr
3+
S=3/2 ions on a kagomé lattice. In a sample with
≈
76% occupancy of the chromium sites the ordered moment is 1.1(3)
μ
B
per chromium ion which is only one third of the Néel value
g
μ
B
S=3
μ
B
. The magnetic unit cell equals the chemical unit cell, a situation which is favored by inter-plane interactions. Gapless quantum spin-fluctuations (
Δ/
k
B
<0.25
K) with a bandwidth of 60K >>
T
N
= 1.6K are the dominant contribution to the spin correlation function,
S(Q,ω)
in the ordered phase.