Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 50 (2017)

Investigation of the magnetic ground state in a new one--dimensional quantum
spin system K2Cu3O(SO4)3
M. Fujihala,䠆1 S. Mitsuda,䠆1 I. Watanabe,䠆2 and R. Aish䠆2
The magnetic ground states of linear chain systems are
known to follow the Haldane’s conjecture 1) that thehalf-integer spin chains are gapless and integer spin chainsare gapped, which is supported by a vast amount oftheoretical and experimental results. On the other hand,competing interactions or inter-chain interactions can often
induce a spin gap, even in half-integer spin systems.2)
These exciting results indicate that exotic quantum states
will be discovered in one-dimensional spin systems withcompeting magnetic interactions based on the uniquearrangement of magnetic ions. In zero-dimensional S = 1/2
spin systems on an isolated spin cluster, the magnetic
ground state can be determined exactly. If a cluster contains
many spins, it is difficult to intuitively understand, andthere is a possibility of the presence of an exotic quantum
state. In the present study, we report the magnetism of theedge-sharing S = 1 tetrahedral cluster chain system
K2Cu3O(SO4)3. The unique competing interaction in a spinedge-sharing tetrahedron and the weak one-dimensional
inter-cluster couplings lead to the exotic quantum state.
Single-phase K2Cu3O(SO4)3 was verified to possess a
monoclinic crystal structure identical to the mineral (Fig. 1).
As illustrated in Figs. 1(b) and (c), magnetic ions of Cu2+
form the edge-sharing spin tetrahedral cluster that areconnected with each other by SO4í ions along the b-axis
direction. The inter-cluster magnetic interactions should be
weaker than intra-cluster magnetic interactions because they
are next-nearest-neighbor magnetic interactions through theCu-O-S-O-Cu exchange paths, hence we called this system
the “edge-sharing spin tetrahedral cluster chain.” Thenonmagnetic potassium ions are located as shown Fig. 1(b),thus resulting in a long inter-chain distance along the a-axis.
In this compound, Cu2+ ions have tetra-coordination, as
shown Fig. 1(d). Therefore, only the presence of very weakinter-chain magnetic interactions through the Cu-O-K-O-Cu
exchange paths is expected. Therefore, we conclude that
K2Cu3O(SO4)3 has good one dimensionally.
Wea Schottky-likeanomaly
at around
4 K,4andWeobserved
observeda Schottky-likeanomaly
at aroundK,
and anomaly
any anomaly
indicativeof long-rangeorderingisany
indicativeof long-rangeordering
is absent
absenttodown
to at
0.7 anomalies
K. The anomalies
down
at least
0.7least
K. Theat aroundat4 aroundK and
4 K and
100 K
were
in the temperaturedependence
100K wereseen
in seenthe temperaturedependenceof theof the magneticsusceptibility.
Moreover,clear spin-gap
magnetic
susceptibility.
Moreover,a clear aspin-gap
is seen3)
is seenin the inelastic
inthe inelastic
neutron neutron
scatteringscattering
spectrum.spectrum.
In order3) Intoorder to investigate
spin dynamics
CuO(SO)
investigate
the spinthedynamics
in K2in
CuK3O(SO)
,
we2
3 4 3
4 3,
we performed
muon
spinURWDWLRQ
rotationDQG
and UHOD[DWLRQ
relaxation (μSR)
performed
PXRQ
VSLQ
ȝ65 measurements atat thethe RIKEN-RAL
Muon facility
facility atat themeasurementsRIKEN-RAL Muon
Laboratory, UK.
UK.
Rutherford-Appleton Laboratory,
䠆1
䠆2

Department of Physics, Tokyo University of Science
RIKEN Nishina Center

Fig. 1. (a) The observed synchrotron x-ray diffraction
intensity pattern for K2Cu3O(SO4)3 and the result of thecalculated Rietveld structure refinements. (b), (c), (d) The
crystal structure of K2Cu3O(SO4)3. (e) An edge-sharing
tetrahedron with nearest-neighbor exchange couplings.

Fig. 2. (a) Temperature dependence of the internal field inK2Cu3O(SO4)3. (b) Temperature dependences of therelaxation rate.
Surprisingly,
thethe
ȝ65
UHVXOWVDUHareTXLWHGLIIHUHQW
IURP
WKH
Surprisingly,
μSR
resultsquitedifferent
fromresults
of ofthetheotheroscillation
theresults
otherexperiments.
experiments.AA clear
clear oscillation
indicative ofof thethelong-range
long-rangemagnetic
magneticorder
orderwaswasobserved
observed
atat(Fig.
2(a)).
addition,anomalyobserved
3.23.2
KK(Fig.
2(a)).
In In
addition,thetheanomaly
waswasobservedatataround(Fig. 2(b)).
2(b)). Further
Further detaileddetailed studies
studies arearound1515KK(Fig.
required.
At this point,that the sample wasrequired. At
point, we suspectsuspect that
deteriorated by moisture.
References
1) F. D. M. Haldane, Phys. Rev. Lett. 50, 1153 (1983).
2) M. Azuma, Z. Hiroi, M. Takano, K. Ishida, and Y. Kitaoka,
Phys. Rev. Lett. 73, 3463 (1994).
3) M. Fujihala et al.: unpublished.

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