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

RIKEN Accel. Prog. Rep. 47 (2014)

Magnetic instability induced by Rh dopingin the Kondo semiconductor CeRu2 Al10
H. Guo,∗1,∗2 H. Tanida,∗1,∗3 R. Kobayashi,∗4,∗5 I. Kawasaki,∗1 M. Sera,∗3 T. Nishioka,∗6 M. Matsumura,∗6
I. Watanabe, ∗1 and Z. Xu∗2
The ternary compound CeT2 Al10 (T = Fe, Ru, andOs) is a unique system that shows Kondo semiconducting behavior at low temperatures, and it exhibits anantiferromagnetically (AFM) ordered state at T0 ∼ 30
K for T = Ru and Os, while a nonmagnetic groundstate is observed for T = Fe, as is usually the casefor Kondo semiconductors (or insulators).1–3) Since themagnetic susceptibility (χ) systematically decreases onchanging the transition metal element in the orderfrom T = Ru to Os to Fe, the 4f electron state is located in the vicinity of the boundary between localized
and non-localized states, as expected from the Kondo
semiconducting behavior. Thus, the c-f hybridization
between d- and 4f -electrons must play a key role for
their low-temperature properties involved in the originof the AFM order.
The AFM order is very unusual. T0 is quite highfor a usual Ce-based intermetallic compound when
taking into account, for instance, the long distanceof 5.2 Å between neighboring Ce ions.2) The magnetic anisotropy is also unusual. Although the easy
axis is the a axis with the large magnetic anisotropy(acb), the AFM ordered moment (mAF ) with amagnitude of 0.3−0.4 µB /Ce aligns in the c-axis direction.4,6) Recently, the Rh-doping effect on CeRu2 Al10
has been examined, where Rh (4d8 ) has one electron
more than Ru (4d7 ).7,8) On the basis of the results,
we infer that χ becomes more Curie−Weiss like anddecreases drastically below T0 for Ha. These results
imply that the Rh-doping breaks mAF c and mAF ais realized instead. In order to clarify the spin alignment and the critical Rh concentration xc from a microscopic point of view, we performed zero-field µSR
on Ce(Ru1−x Rhx )2 Al10 (x = 0, 0.03, 0.05, and 0.1).
Figure 1 shows the temperature dependence of theinternal magnetic field (Hsmall , Hlarge ) at the muon site
for Ce(Ru1−x Rhx )2 Al10 . Here, Hsmall (Hlarge ) represents the smaller (larger) component of internal magnetic fields. For the undoped sample, Hsmall shows
non-mean-field-like behavior, while Hlarge increases below T0 and saturates to a value of about 180 G below
†
∗1
∗2
∗3
∗4
∗5
∗6

Condensed from the article in Phys. Rev. B 88, 115206(2013).
RIKEN Nishina Center
Department of Physics and State Key Laboratory of Silicon
Materials, Zhejian University
AdSM, Hiroshima University
Neutron Science Laboratory, ISSP, Tokyo University
Quantum Condensed Matter Division, Oak Ridge National
Laboratory
Graduate school of Integrated Arts and Science, Kochi University- 255 -

Fig. 1. Temperature dependence of the internal magnetic
fields at the muon sites in Ce(Ru1−x Rhx )2 Al10 (x = 0,0.03, 0.05, and 0.1): (a) Hsmall (b) Hlarge .

about 15 K. On the other hand, for Rh-doped samples,
Hlarge reaches about 800 G at low temperatures. Thisstrongly suggests the spin-flop transition from mAF c
to mAF a on the basis of our dipolar field calculation
at the suggested muon site, which is consistent with thebulk properties.7,8) Since there is no Rh-concentration
dependence in Hlarge for x > 0.03, the boundary ofthe different magnetic ground states is identified ataround x ∼ 0.03. The drastic change of the magnetic
ground state by such a tiny Rh doping indicates thatthe magnetic structure in CeRu2 Al10 is not robust andcan be quite easily tuned using external perturbations
such as d-electron doping. On the basis of previous experimental results from thermal electric power,9) neutron scattering,4) and NQR measurements,10) the nonmean-field-like behavior of Hsmall for the x = 0 sample is attributed to the Fermi contact field from thepolarized electrons at the muon site, while the T dependence of Hlarge for the Rh-doped samples is still anunresolved question; whether it results from the Fermi
contact field or from the unusual ordering of Ce3+ moments should be clarified by future neutron scatteringexperiments.
References
1) A. M. Strydom: Physica B 404, 2981 (2009).
2) T. Nishioka et al.: J. Phys. Soc. Jpn. 78, 123705 (2009).
3) Y. Muro et al.: J. Phys. Soc. Jpn. 78, 083707 (2009).
4) D. D. Khalyavin et al.: Phys. Rev. B 82, 100405(R)(2010).
5) K. Kato et al.: J. Phys. Soc. Jpn. 80, 073701 (2011).
6) H. Tanida et al.: Phys. Rev. B 84, 233202 (2011).
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. Tanida et al.: J. Phys. Soc. Jpn. 79, 063709 (2010).
10) M. Matsumura et al.: J. Phys. Soc. Jpn. 78 123713(2009).