RIKEN Accel. Prog. Rep. 48 (2015)

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

Investigation of magnetic ground states in mixed kagome systems(Rb1−x Csx )2 Cu3 SnF12 by µSR
T. Suzuki,∗1,∗4 K. Katayama,∗2 H. Tanaka,∗2 T. Goto,∗3 and I. Watanabe∗4

∗1
∗2
∗3
∗4(a)

(c)

LF200G

0.27 KLF-µSR

1
Corrected Asymmetry

Corrected Asymmetry

119 K

0.8

5K

0.6

4K

0.4
3K
1K

0.2

0.8
3000 G

0.6
1500 G
1000 G

0.4
200 G

0.2

500 G

0.27 K36t (µs)

9001236t (µs)

9120.40.4(b)λ10.35(d)LF 200 gauss

T = 0.27 K
λ1
λ20.3

λ1 (µs-1)

λ20.2

430.22λ2 (µs-1)

00

λ1

100.1

0.1
50010T (K)020

1

λ2The Heisenberg kagome antiferromagnet (HKAF)
has attracted much attention in magnetism, because
several frustration and quantum eﬀects have been indicated by theories. For example, in√the classicalspin√model case for HKAF, the q = 0 or 3 × 3 magnetic
structure is stabilized when the next-nearest-neighborinteraction is considered. In the case of S = 1/2 kagome lattice, exotic magnetic ground states have beentheoretically predicted. For example, numerical calculations revealed that the ground state is a magnetically disordered spin liquid. In the ground state, triplet
excitations are gapped, and there exists the continuum of low-lying singlet states below the triplet gap1) .
Valence-bond crystal by a periodic arrangement of singlet dimers has also been proposed as the magnetic
ground state of S = 1/2 HKAF2) . Experimentally,
many kinds of HKAF have been investigated as thecandidate for the ideal kagome spin lattice material.
Another new candidate for the ideal kagome latticewith an exotic magnetic ground state was reported
by Ono et al. The cupric compound A2 Cu3 SnF12 (A= Cs, Rb), which is the subject of this study, is a
newly synthesized family of S = 1/2 HKAF3,4) . For
Cs2 Cu3 SnF12 , the weak-ferromagnetic behavior is observed below TN = 20 K, and it is suggested that theantiferromagnetic ordered state appears4) . On the other hand, for Rb2 Cu3 SnF12 , the ﬁrst realization of the”pinwheel” valence bond solid (VBS) ground state in
the S = 1/2 HKAF are conﬁrmed by inelastic neutron measurements5) . Quite recently, mixed kagomesystems (Rb1−x Csx )2 Cu3 SnF12 have been prepared6) .
By magnetic susceptibility and speciﬁc heat measurements on single crystals, they reported a phase diagram, which shows the existence of the quantum phasetransition from the VBS to the AF phase at xc = 0.53.
In this concentration, the spin gap vanishes and theordered state disappears from the view point of magnetization results.
We carried out LF-µSR measurements in x = 0.53
single crystal to investigate dynamical magnetic properties microscopically. Figure 1 (a) shows LF-µSR
time spectra in 200 gauss at various temperatures.
It is emphasized that no disappearance of the initialasymmetry is observed. Below 3 K, time spectra are
well ﬁtted by the two component function as follows:
A(t) = A1 exp(−λ1 t)+A2 exp(−λ2 t). Here, A1 = 0.58,
A2 = 0.42. As shown in Fig. 1 (b), λ1 increases

0 210103HLF (gauss)

0104

Fig. 1. (a)Temperature dependence of the time spectra inthe LF of 200 gauss. (b) Temperature dependence ofthe muon spin relaxation rate in LF 200 gauss. (c) LFµSR time spectra above 200 gauss up to 3000 gauss at
0.27 K. (d) LF dependence of the muon spin relaxation
rate at 0.27 K.

with decreasing temperature. LF-dependence of timespectra at 0.27 K is shown in Fig. 1 (c), and LFdependence of relaxation rates is shown in (d). Muon
spin relaxation rates are inversely proportional to LF,
and such change indicates “white” frequency spectra,
which means the spectra are described by summationof continuously distributed frequencies using the Redﬁeld formula. These results suggest that the internal ﬁelds ﬂuctuate, and are consistent with reported
macroscopic results at least down to 0.27 K.
References
1) H. C. Jiang et al.: Phys. Rev. Lett. 101, 117203 (2008).
2) R. R. P. Singh et al.: Phys. Rev. B 77, 144415 (2008).
3) M. Muller et al.: Z. Anorg. Allg. Chem. 621, 993 (1995).
4) T. Ono et al., Phys. Rev. B 79, 174407 (2009).
5) K. Matan et al., Nature Phys. 6, 865 (2010).
6) K. Katayama et al.: arXive:1412.5770v1 [cond-matt.strel].

College of Engineering, Shibaura Institute of Technology
Department of Physics, Tokyo Institute of Technology
Department of Physics, Sophia University
RIKEN Nishina Center- 260 -

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