Quantum critical behavior of the hyperkagome magnet MnCoSi

Yamauchi, Hiroki   ; Sari, D. P.*; Yasui, Yukio*; Sakakura, Terutoshi*; Kimura, Hiroyuki*; Nakao, Akiko*; Ohara, Takashi   ; Honda, Takashi*; Kodama, Katsuaki   ; Igawa, Naoki   ; Ikeda, Kazutaka*; Iida, Kazuki*; Ueta, Daichi*; Yokoo, Tetsuya*; Frontzek, M. D.*; Chi, S.*; Fernandez-Baca, J. A.*; Kojima, Kenji M*; Arseneau, D.*; Morris, G.*; Hitti, B.*; Cai, Y.*; Berlie, A.*; Watanabe, Isao*; Hsu, P.-T.*; Chen, Y.-S.*; Lee, M. K.*; Hall, A. E.*; Balakrishnan, G.*; Chang, L.-J.*; Shamoto, Shinichi  

-Mn-type family alloys Mn have three-dimensional antiferromagnetic (AFM) corner-shared triangular network. The antiferromagnet MnRhSi shows magnetic short-range order (SRO) over a wide temperature range of approximately 500 K above the Nel temperature = 190 K. MnCoSi has the smallest lattice parameter and the lowest in the family compounds. The quantum critical point (QCP) from AFM to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 of MnCoSi is only 140 K, quantum critical behavior is observed in MnCoSi as the enhancement of the electronic specific heat coefficient . We study how the magnetic SRO appears in MnCoSi by using neutron scattering, SR, and physical property measurements. The experimental results show that the neutron scattering intensity of the magnetic SRO does not change much regardless of the suppressed magnetic moment in the long-range magnetic ordered state compared to those of MnRhSi. The initial asymmetry drop ratio of SR above becomes small, and the magnetic SRO temperature is suppressed to 240 K. The results suggest that the MnCoSi is close to the QCP in the Mn system.