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

Ⅲ-2. Atomic & Solid State Physics (Muon)µSR studies on antiferromagnet RRu2 Al10 (R = Sm, Gd)
H. Tanida,∗1,∗3 H. Guo,∗1,∗2 I. Kawasaki,∗1 M. Sera,∗3 T. Nishioka,∗4 M. Matsumura,∗4I. Watanabe, ∗1 and Z. Xu ∗2

∗1
∗2
∗3
∗4

RIKEN Nishina Center
Department of Physics and State Key Laboratory of Silicon
Materials, Zhejian University
AdSM, Hiroshima University
Graduate school of Integrated Arts and Science, Kochi University

25Raw Asymmetry (%)

The Kondo semiconductor CeT2 Al10 (T = Ru, Os)with an orthorhombic-type structure shows a uniqueantiferromagnetic (AFM) order at T0 ∼ 30 K.1,2) This
compound exhibits numerous unusual electronic properties that can be ascribed to the strong electron correlation between conduction and localized 4f electrons,
namely, the c − f hybridization effect, by which arenormalized quasi-particle state with heavy effective
electron mass is formed in the case of many Ce- or
Yb-based intermetallic compounds. However, in theclass of materials known as the Kondo semiconductors
or insulators, a temperature-dependent energy gap isformed instead. One of the most salient features ofthis system is magnetic anisotropy in the AFM ordered state. Since the magnetic susceptibility showsa large anisotropy of χa χc χb , an AFM orderedmoment (mAF ) is expected to be parallel to the a-axis
in the AFM ordered state. However, mAF c is realized, as was revealed by neutron scattering and 27 Al
NMR/NQR studies.3–5) The AFM structure is not robust and is easily tuned by magnetic field4) , pressure6) ,or chemical doping.7–9) This indicates that magnetic
exchange interactions are not a key parameter for thismagnetic ordering, but there could be an unknown parameter related to the strong c−f hybridization effect,
which must be related to the extraordinary high transition temperature of T0 ∼30 K.
We previously performed µSR experiments on theabove undoped and Rh-doped CeRu2 Al10 . The results have been published elsewhere.9) One of the residual problems is the serious inconsistency in the temperature dependence of internal fields (Hint ) between
two muon sites, that is, one component shows a usualmean-field behavior, but the other does not. To address this problem, we planned to perform zero-fieldµSR on related antiferromagnets with more localized
4f -electron character, RRu2 Al10 (R = Nd, Sm, andGd). These compounds are worthy of investigation for
their AFM ordered state; for instance, in the sample R= Gd, mAF is suggested to be parallel to the [011] direction, although a simple dipole-field calculation suggests that mAF prefers the a-axis direction.10) In ref.
9, a possible origin of this discrepancy was suggestedto be the zig-zag chain structure of Gd sites along thec-axis direction.
Figure 1 shows the zero-field time spectra ofGdRu 2 Al 10 ZF
double pulse

2020 K
15 K

151050Background = 11.426

51015Time (µs)
Fig. 1. Zero-field time spectra of GdRu2 Al10 at T = 20 and
15 K under double-pulse-beam condition.

GdRu2 Al10 at T = 20 K and 15 K; the data wererecorded under double-pulse-beam condition. We
found that the initial asymmetry is reduced when thetemperature is lowered below the AFM transition temperature of TN = 17 K. This is clear evidence for magnetic ordering. Since Hint is expected to be large because of the large magnetic moment of Gd-4f electrons, we should use single-pulse condition with muchgreater time resolution than that of the double-pulse
condition. However, we had to use the double-pulse
condition within our beam time because we could notbreak the extrinsic noise resulting from the kicker operation. Within the present resolution, we could not
identify any muon-spin precession behavior, and thus,from the zero field measurement, we could not obtain
quantitative information on Hint .
References
1) A. M. Strydom: Physica B 404, 2981 (2009).
2) T. Nishioka et al.: J. Phys. Soc. Jpn. 78, 123705 (2009).
3) D. D. Khalyavin et al.: Phys. Rev. B 82, 100405(R)(2010).
4) H. Tanida et al.: Phys. Rev. B 84, 233202 (2011).
5) M. Matsumura et al.: J. Phys. Soc. Jpn. 78 123713(2009).
6) H. Tanida et al.: Phys. Rev. B 88, 045135 (2013).
7) A. Kondo et al.: J. Phys. Soc. Jpn. 82, 054709 (2013).
8) R. Kobayashi et al.: J. Phys. Soc. Jpn. 82, 093702(2013).
9) H. Guo et al.: Phys. Rev. B 88, 115206 (2013).
10) M. Sera et al.: Phys. Rev. B 88, 100404(R) (2013).

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