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

RIKEN Accel. Prog. Rep. 48 (2015)

Magnetic ground state of Cu6O8MCl (M = Y, Pb) with a caged structure
K. Kawashima,*1,*2 H. Takeda,*1 S. Yasuda,*1 S. Igarashi,*1 W. Ito,*1 I. Kawasaki,*2 I. Watanabe,*2 and J. Akimitsu*1＊1＊2Department of Physics and Mathematics, Aoyama Gakuin University.
RIKEN-RAL, Nishina Centerof Cu+, Cu2+, and Cu3+ 2). These conditions encumber theformation of the completely static magnetic ordered state inCu6O8PbCl. The observed behavior of ZF-SR spectra andFig. 2 data of Cu6O8PbCl indicate the growth of theshort-range magnetic interaction between S = 1/2 spins
below 20 K. Consequently, the magnetic ground state of
Cu6O8PbCl does not have a static long range magnetic
ordered state such as an antiferromagnetic state in high-Tc
cuprate. There is possibility that the short range interactionof Cu6O8PbCl forms the spin glass state below 20 K likeunder-doping material in high-Tc cuprate. The magnetic
ground state of Cu6O8MCl compound depends on thevalence state of the M site ion.

Corrected Asymmetry25(a)201510T = 60 K

T = 10 K
15K
20K
30K

024100K
200K
300K

68101214 02468101225

Corrected Asymmetry

14Time (s)Time (s)(b)201510T = 60 K

T = 10 K
15 K
20 K
30 K

024100 K
200 K300 K

68101214 0

2468101214Time (s)Time (s)Fig. 1 ZF-SR time spectra of Cu6O8MCl ((a) M = Y, (b) M= Pb) at various temperatures. Solid lines indicate the fitting
results of eq. (1).

-1

 (s )

a-relaxing

13-1

 (s )

Cu6O8MCl (M=cation) compound has a Cu6O8 cage
which forms a three-dimensional Cu-O network byconnecting their faces in its crystal structure 1). The formal
Cu valence in the Cu6O8 cage is +2.15 for M = Pb4+ and+2.33 for M = Y3+, suggesting the existence of Cu+ (3d10),
Cu2+ (3d9) with S = 1/2 spin, and Cu3+ (3d8) 2). If there ispartial existence of S = 1/2 spins on the Cu site in the Cu6O8cage, the static magnetic ordered state is expected in thesquare-lattice and the dynamical spin fluctuation in thetriangular-lattice i.e., the magnetic competition state isexpected in the magnetic ground state of Cu6O8MCl. To
elucidate the detailed physical properties of Cu6O8MCl, wefocused on clarifying the magnetic ground states of
Cu6O8PbCl, which is the semiconducting material, andcompared the observed data with the based material of
Cu6O8YCl, which is the metallic compound withparamagnetic behavior.
SR experiments were performed at the RIKEN-RALMuon facility at the Rutherford-Appleton Laboratory, UK.
Fig. 1 shows the zero field (ZF) SR spectra of Cu6O8MCl(M=Y, Pb) at various temperatures. With the decrease in thetemperature, the initial asymmetry of Cu6O8PbCl rapidly
decreased below 20 K (Fig. 1(b)). On the other hand, clear
decreasing behavior of the initial asymmetry was notobserved in the ZF-SR spectra of Cu6O8YCl down to 0.3
K, indicating that there is no magnetic ordered state in thissystem (Fig. 1(a)). The ZF-SR spectra in Fig. 1 wereanalyzed using the following function,P(t) = Aexp(-t)GKT(,t)+AB (1),where A is the initial asymmetry at t = 0,  is relaxation
ratio of the muon spin, and AB is the background signal.
GKT(,t) is the static Kubo-Toyabe function with ahalf-width of  describing the distribution of thenuclear-dipole field at the muon site 3). Results of thebest-fit of eq. 1 are indicated by the solid line in Fig. 1, andthe observed adjusted parameters A, , and  of Cu6O8MCl(M=Y, Pb) as functions of temperature are shown in Fig. 2.
A (a-relaxing) of Cu6O8YCl slightly decreases with thedecrease in the temperature (Fig. 2), whereas  and  of
Cu6O8YCl are almost constant, being temperature
independent. These facts indicate that there is no change ofspin dynamic and long range magnetic ordered state in
Cu6O8YCl, which is a metallic compound withparamagnetic behavior. For Cu6O8PbCl, the temperaturedependence of a-relaxing, , and  change below 20 K,
indicating the change in the magnetic spin state (Fig. 2).
However, clear precession signal is not confirmed in theZF-SR spectra below 20 K. The Cu6O8 cage has asquare-lattice and triangular-lattice on its surface, and theCu sites in the Cu6O8 cage are occupied by various valences

1211
10

M=Y

9
8
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0
0.15
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0.1
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M = Pb
M=YM = Pb

M=YM = Pb

050

100

150

200

250

300

T (K)

Fig. 2 Temperature dependence of the initial asymmetry A(a-relaxing), relaxation ratio  and  of Cu6O8MCl (M = Y,Pb) defined by the results of fitting for the Fig. 1 data.
References

1) I. Yazawa, R. Sugise, N. Terada, M. Jo, K. Oka, and H. Ihara,Jpn. J. Appl. Phys. 29 L1693 (1990).
2) G. Zouganel, K. Bushida, I. Yazawa N. Terada, M. Jo, H.
Hayakawa, and H. Ihara, Sol. St. Comm. 80 709 (1991).
3) Y. J. Uemura, T. Yamazaki, D. R. Harshman, M. Senba, and E. J.
Ansaldo, Phys. Rev. B 31 546 (1985).

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