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

RIKEN Accel. Prog. Rep. 47 (2014)µSR study on CeRu2 Al10 under pressure
H. Guo,∗1,∗2 H. Tanida,∗3 I. Kawasaki,∗1 M. Sera,∗3 T. Nishioka,∗4 M. Matsumura∗4 I. Watanabe,∗1 and Z. Xu∗2
CeT2 Al10 (T = Fe, Ru, and Os), which has the orthorhombic YbFe2 Al10 −type structure, can be categorized as a Kondo semiconductor and is of interest
because of numerous anomalous electronic behaviors
due to the c − f hybridization effect.1–3) For instance,
the antiferromagnetic (AFM) transition temperature(T0 ) is quite high compared to that usually expected
for Ce-based intermetallic compounds,2) and the spinalignment in the AFM ordered state is mAF  c, although the easy magnetization axis is the a-axis withthe large magnetic anisotropy a  c  b.4,5) In addition, the magnetic structure is easily changed frommAF  c to mAF  b or mAF  b to mAF  c by application of non-magnetic La doping, magnetic field, orexternal pressure.6) Furthermore, tiny d-electron doping, such as Rh(4d8 )-doping in Ru(4d7 ), easily breaks
the mAF  c ordering, and mAF  a ordering is realized instead.7) These results indicate that the magnetic structure of CeRu2 Al10 is not robust and is easily
tuned by such perturbations.
Regarding the effect of pressure on CeRu2 Al10 , T0
is enhanced up to about P = 2 GPa, beyond which
it exhibits a slight decrease; at approximately Pc =4 GPa, CeRu2 Al10 exhibits a first-order-like transition
from the AFM Kondo semiconducting state to the nonmagnetic Fermi liquid state.2) Since T0 is enhanced
at low pressures, the bulk magnetization is expected
to also be enhanced by pressure. However, the magnetization is strongly suppressed by pressure.8) At P
= 1 GPa, the magnetization becomes nearly half ofthat at ambient pressure. That is, the pressure enhances T0 but suppresses the magnetization. These
results seem to contradict each other. In order to verify whether mAF is suppressed on applying pressure,
we performed µSR experiments on CeRu2 Al10 underpressures up to about P = 0.6 GPa. From the µSR
experiment, the pressure dependence of mAF can beclarified through the change in the internal magnetic
field at the muon site. To our knowledge, this is thefirst attempt at investigating the effect of pressure on
the mAF in CeT2 Al10 (T = Ru, Os).
Figure 1 shows the temperature dependence of theinitial asymmetry of CeRu2 Al10 at ambient pressure
and at P = 0.6 GPa. The initial asymmetry is extracted from the transverse field (TF) measurement.
The decrease in the initial asymmetry below T0 is agood indicator of the appearance of a magnetically ordered state. We clarified that T0 is enhanced by pres∗1∗2∗3∗4RIKEN Nishina center
Department of Physics, Zhejiang University
AdSM, Hiroshima University
Graduate school of Integrated Arts and Science, Kochi University- 256 -Fig. 1. Temperature dependence of the initial asymmetryof CeRu2 Al10 at ambient pressure and at P = 0.6 GPa.
The initial asymmetry is extracted from transverse field(TF) measurements.

sure by observing bulk properties. The temperaturedependence of the initial asymmetry at ambient pressure is consistent with our previous µSR experiment.7)
As seen below for T =10 K, the temperature dependence of the asymmetry is different between the data
at ambient pressure and at those P = 0.6 GPa, indicating that the evolution of the mAF is different between
these two cases. This would be attributed to a change
in the hyperfine process through the Fermi contact field
caused by pressure.7) We aimed to clarify a change inthe magnitude of mAF under pressure. However, owing to the fraction of stopping muons in the sample
being less and the strong restriction of the time resolution of the double-pulsed muon beam, we could notobserve the muon spin precession, and thus, from thezero field measurement, no quantitative information on
Hint could be achieved directly under ambient or highpressure. In order to obtain detailed information on
mAF , further studies are needed.
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) H. Tanida et al.: Phys. Rev. B 84, 233202 (2011).
6) H. Tanida et al.: Phys. Rev. B 88, 045135 (2013).
7) H. Guo et al.: Phys. Rev. B88, 115206 (2013).
8) H. Tanida et al.: Phys. Rev. B 86, 085144 (2012).