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

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Zero-ﬁeld μSR measurements to investigate the magnetic ordering of
Nd2 Ru2 O7
U. Widyaiswari,∗1,∗2 H. Sakai,∗3 H. Hanasaki,∗3 D. P. Sari,∗4 B. Kurniawan,∗2 and I. Watanabe∗1,∗2Pyrochlore oxides have a general formula A2 B2 O7 ,where A and B represent trivalent rare-earth andtetravalent transition metal ions, respectively. The pyrochlore oxides are constructed from the interpenetrating corner-sharing tetrahedral lattices of A and B sites.1)
The spins at vertices of the tetrahedral lattice are magnetically frustrated and can lead to various novel physical properties.1) The magnetic frustration, competition
between the exchange and dipolar interactions, and crystal electric ﬁeld eﬀect control the nature of the groundstate of pyrochlore oxide.2)
Pyrochlore ruthenate, A2 Ru2 O7 , has Ru 4d4 electrons
in the low-spin state with S = 1. In Nd2 Ru2 O7 , both Ndand Ru are magnetic ions. The magnetic ground stateof Nd2 Ru2 O7 is an interesting research topic because we
can investigate the coupling between Nd and Ru spins
by comparing it with that of Nd2 Ir2 O7 known to have
Ir4+ ions with 5d electrons, and they show ferromagnetic coupling between Nd and Ir spins.3) Nd2 Ru2 O7
showed magnetic anomalies around 1.8 K, 21 K, and146 K.4,5) At 1.8 K and 146 K, the magnetic transition
were attributed to the ordering of Nd and Ru spins, respectively.4) The origin of the anomaly at 21 K remains
debatable.4,5) Accordingly, we investigated the magnetic properties of Nd2 Ru2 O7 using various measurement techniques such as muon spin relaxation (μ+ SR)
measurement.
The polycrystalline Nd2 Ru2 O7 was prepared using
a solid-state reaction method.
μ+ SR experiments
were carried out on an HiFi spectrometer at the ISIS,
Rutherford Appleton Laboratory in the UK and on theARTEMIS spectrometer at Material and Life Science
Experiment Facility (MLF), J-PARC in Japan. We measured the μ+ SR time spectra in the zero-ﬁeld (ZF) condition at a temperature range of 2–150 K on HiFi, whereas
the time spectra below 5 K down to 0.3 K were obtainedby using Heliox cryostat on ARTEMIS.
The oscillations do not occur in the ZF-μ+ SR time
spectra of Nd2 Ru2 O7 , as shown in Fig. 1(a). However,the decreases in the initial asymmetry at t = 0 was observed by decreasing the temperature indicating the appearance of a magnetic ordered state. The time spectra
were analyzed using two exponential functions asA(t) = A1 exp(−λ1 t) + A2 exp(−λ2 t)∗2∗3∗4rates.
The appearance of Ru ordering at 146 K is conﬁrmed
from a sharp peak observed in λ2 (T ), as shown in the inset of Fig. 1(b). λ1 decreases below 50 K with decreasing
temperature and shows a dip around 30 K; this anomaly
is not related to the anomaly at 21 K observed fromthe DC susceptibility measurement, which was expectedfrom the magnetic property of Nd3 RuO7 .6) Therefore,
the anomaly around 30 K in the temperature dependence of λ1 could be related to the short-range magnetic
interaction of Nd spins. The long-range ordering of Nd
spins was expected to appear around 2 K, as indicated bya peak in the temperature dependence of λ1 . Currently,
we cannot determine the magnetic interaction between
Nd and Ru spins. Further investigation using continuous muon beam is required to determine the internalﬁeld as a function of temperature that occurred in thissystem.

(1)

The ﬁrst and second components of Eq. (1) correspondto the slow and fast components of muon spin relaxation,
respectively, and λ represents the muon-spin relaxation∗1Fig. 1. (a) ZF-μ+ SR time spectra of Nd2 Ru2 O7 . (b) Temperature dependence of λ1 ; the inset shows the temperature dependence of λ2 .

RIKEN Nishina Center
Department of Physics, Universitas Indonesia
Department of Physics, Graduate School of Science, Osaka
University
Innovative Global Program, Shibaura Institute of Technology

References
1) J. S. Gardner et al., Rev. Mod. Phys. 82, 53 (2010).
2) B. C. D. Hertog et al., Phys. Rev. Lett. 84, 3430 (2000).
3) R. Asih et al., J. Phys. Soc. Jpn. 86, 024705 (2017).
4) S. T. Ku et al., J. Phys. Condens. Matter 30, 155601(2018).
5) M. W. Gaultois et al., J. Phys. Condens. Matter 25,186004 (2013).
6) U. Widyaiswari et al., Mater. Sci. Forum 1028, 3 (2021).

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