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

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Partial order of conduction electrons in Mn3 CoSi
S. Shamoto,∗1,∗2,∗3,∗4 D. P. Sari,∗5,∗3 I. Watanabe,∗3 H. Yamauchi,∗4 and L. -J. Chang∗1
Unconventional phase transitions have been discovered in various materials.1) One of them is a phase separation at the tri-critical point of quantum phase transition.2) Partial magnetic order has been observed in a
non-centrosymmetric compound of MnSi near the quantum phase transition under pressure.3,4) On the searchof new unconventional magnetic transition, we discovered the highest-temperature magnetic short-rangeorder (SRO) in a new noncentrosymmetric magnet
Mn3 RhSi by the complementary use of muon spin relaxation (HiFi and ARGUS at ISIS), neutron, X-ray scattering, electron diﬀraction, and magnetization measurements.5) It has a hyperkagome network of magnetic Mnions. We think that the unconventional magnetic SRO
emerges due to the spatially inhomogeneous order parameter, where the Lifshitz condition is violated by theDzyalonshinskii-Moriya interaction in a noncentrosymmetric magnet. The intriguing point of the SRO is not
limited in the highest-temperature record of magnetic
SRO, but also in the observed Q-position diﬀerent fromlong-range antiferromagnetic (AF) order Q-position. At
present, however, the mechanism is still unknown. To
reveal the mechanism, we believe that it is necessary tocomplete the phase diagram (Fig. 2) by measuring therelated family compounds such as Mn3 CoSi (a = 6.28 Å)with a diﬀerent lattice constant resulting in a diﬀerent

Fig. 2. Phase diagram of β-Mn type structure alloys.

bandwidth from that of Mn3 RhSi (a = 6.47 Å). The Néeltemperature of Mn3 CoSi is about 100 K, whereas that ofMn3 RhSi is 190 K. However, it was unknown which theSRO transition temperature of Mn3 CoSi becomes lower
than that of Mn3 RhSi.
TF µSR measurement of Mn3 CoSi (RB2070006) successfully showed SRO anomaly above Néel temperaturein the asymmetry as shown in Fig. 1. The magnetic
SRO of Mn3 CoSi is found to start at about 250 K. From
this result, we may conclude that the SRO temperature
increases with increasing the lattice constants as shownin Fig. 2. This result suggests that the present world
record of SRO temperature may further increase withincreasing the lattice constant.
ReferencesFig. 1. Temperature dependence of TF µSR asymmetry ofMn3 CoSi.
∗1
∗2
∗3
∗4
∗5

Department of Physics, National Cheng Kung University
Comprehensive Research Organization for Science and Society
RIKEN Nishina Center
Advanced Science Research Center, Japan Atomic Energy
AgencyCollege of Engineering, Shibaura Institute of Technology

1) S. Shamoto, J. Phys. Soc. Jpn. 88, 081008 (2019),
arXiv:1905.03905.
2) D. Belitz, T. R. Kirkpatrick, T. Vojta, Rev. Mod. Phys.
77, 579 (2005).
3) C. Pfleiderer et al., Nature 427, 227 (2004).
4) Y. J. Uemura et al., Nat. Phys. 3, 29 (2007).
5) H. Yamauchi, D. P. Sari, I. Watanabe, Y. Yasui,
L. -J. Chang, K. Kondo, T. U. Ito, M. Ishikado, M. Hagihara, M. D. Frontzek, S. Chi, J. A. Fernandez-Baca,
J. S. Lord, A. Berlie, A. Kotani, S. Mori, S. Shamoto,Commun. Mat. 1, 43 (2020).

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