Sommerfeld coefficient enhancement and magnetic short-range order in a hyperkagome 3 system

Shamoto, Shinichi*; Yasui, Yukio*; Yoshizawa, Kanako*; Noda, Yukio*; Takahashi, Miwako*; Onuki, Yoshichika*; Haga, Yoshinori   ; Ishikado, Motoyuki*; Yamauchi, Hiroki   ; Huang, T.-C.*; Lee, M. K.*; Chang, L.-J.*

-Mn shows a large Sommerfeld constant of 70 mJ,,Mn,,K, which is one of the largest values in 3-electron systems. Although the origin has been attributed to the fluctuating magnetic moment, there are no material-dependent systematic studies in the 3-electron systems except for doped -Mn. The ordered -Mn structure compounds MnTX (T = Co, Rh, Ir; X = Si, Ge) also exhibit the enhancement. We have studied the enhancement in MnTX system. The enhancement has been often accompanied with magnetic short-range order. The mechanism of the magnetic short-range order is discussed based on the phase diagrams of MnTX system. The phase diagrams are categorized in two groups. One group of MnCoSi and MnRhSi exhibits the magnetic short-range order above the Nel temperature, whereas the others do not. The two groups can be separated by the spin-orbit coupling value, regardless of the cubic lattice parameter.