RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEAR

Investigation of the magnetic states in new spin-tetrahedral K4Cu4Cl10O†
X.G. Zheng,＊1 M. Fujihala,＊1 and I. Watanabe＊2
The spin-tetrahedral K4Cu4Cl10O showed a very broadsusceptibility maximum centered around 10 K and a rapid
increase below 5 K. SR measurements for the system wereperformed at RIKEN-RAL.
For K4Cu4Cl10O, no change appeared around 10 K, whichis consistent with a spin-singlet state theoretically predicted
for isolated spin tetrahedral system. Long-range order wasobserved below 4.4 K (Fig. 2), but with broad distribution
in the precession frequency, which is interpreted as
evidence for an incommensurate order.
25(G)

320

Asymmetry a(t) (%)

Geometrically frustrated magnets, in which localized
magnetic moments on triangular, kagome or pyrochlore
lattices interact through competing exchange interactions,have recently attracted a lot of interest owing to thediversity in the exotic ground states that they display.
Various reports on unconventional magnetic properties
provide a challenging and testing ground for theoreticalmodels. Among the several systems reported, the S-1/2
quantum systems have received particular attention.
While much of the kagome and pyrochlore
antiferromagnets, which are much more complicated totheoretically model than the triangular lattice, are still not
well understood, the isolated spin tetrahedral system withweak inter-tetrahedral couplings has recently attracted
attention because it can directly demonstrate the interplay ofinter-tetrahedral couplings with the built-in tetrahedral
frustration. Of more wide interest, they also represent aninteresting class of magnets consisting of weakly coupledmagnetic clusters. Till date, the Cu2Te2O5X2 (X = Cl, Br)
family and the related compound Cu4Te5O12Cl4 have been
considered the only real systems of such tetrahedra, but they
have remarkable structural anisotropies both inside andoutside the tetrahedra, leading to much controversy about
their anisotropic magnetic couplings and dimensionality[1-3]. There are several questions that prompt lot ofdiscussion. The most important one is the magnetic
dimensionality of the system due to the notable structuralanisotropies inside and between the tetrahedra.
Recently, we have synthesized new S-1/2 quantum
systems of spin-tetrahedral K4Cu4Cl10O, where themagnetic moments (Cu2+ spins) occupy a three-dimensional
tetrahedral lattice, as shown in Fig. 1.

2
100

10

203040T (K)

50

60

70

80

1510
5070 K
4.8 K
4.4 K

4.2 K
0.3 K

RIKEN-RAL

Time t ( s)Fig. 2. Zero-field μSR asymmetry spectra at typicaltemperatures for K4Cu4Cl10O obtained from theRIKEN-RAL beam line. The solid lines on the back of thehigh-temperature data are fitted curves as described in Phys.
Rev. B 87, 144425 (2013). The inset plot shows theestimated nuclear field distribution .
Here, our work shows that similar incommensurateordering also exists in a three-dimensional isolated spintetrahedral system.
References

Fig. 1. Tetrahedral lattice in K4Cu4Cl10O.
†Condensed from the article in Phys. Rev. B 87, 144425 (2013)
Department of Physics, Saga University＊2
RIKEN Nishina Center＊11) P. Lemmens, K.-Y. Choi, E. E. Kaul, C. Geibel, K. Becker, W.
Brenig, R. Valenti, C. Gros, M. Johnsson, P. Millet, and F. Mila,Phys. Rev. Lett. 87, 227201 (2001).
2) O. Zaharko, A. Daoud-Aladine, S. Streule, J. Mesot, P.-J.
Brown, and H. Berger, Phys. Rev. Lett. 93, 217206 (2004).
3) Z. Jagličić, S. El Shawish, A. Jeromen, A. Bilušić, A. Smontara,Z. Trontelj, J. Bonča, J. Dolinšek, and H. Berger, Phys. Rev. B73, 214408 (2006).

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