Frustrated random-singlet state with ice-type structural fluctuation in spinel titanates

花咲 徳亮*; 服部 崇幸*; 薦田 匠*; 源 拡栄*; 鳥越 秀平*; 山下 智史*; 中澤 康浩*; 中野 岳仁*; 吉見 光平*; 八島 光晴*; 椋田 秀和*; Widyaiswari, U.*; 渡邊 功雄*; 幸田 章宏*; 本田 孝志*; 大友 季哉*; 佐賀山 基*; 樹神 克明   ; 村川 寛*; 酒井 英明*

Hanasaki, Noriaki*; Hattori, Takayuki*; Komoda, Takumi*; Minamoto, Kakuei*; Torigoe, Shuhei*; Yamashita, Satoshi*; Nakazawa, Yasuhiro*; Nakano, Takehito*; Yoshimi, Kohei*; Yashima, Mitsuharu*; Mukuda, Hidekazu*; Widyaiswari, U.*; Watanabe, Isao*; Koda, Akihiro*; Honda, Takashi*; Otomo, Toshiya*; Sagayama, Hajime*; Kodama, Katsuaki; Murakawa, Hiroshi*; Sakai, Hideaki*

In ice, it is well-known that the orientation of HO molecules is disordered by geometrical frustration. Ice-analogous materials having a pyrochlore lattice display interesting phenomena such as the spin-ice state and the magnetic monopole. In the spinel titanate MgTiO, the Ti ions have a quantum spin in the pyrochlore lattice. The Ti ions are displaced, accompanied by the spin-singlet formation. Since this displacement pattern follows the ice rule, the title compound is a material analogous to ice. When a small quantity of Ti ions are replaced with Mg ions, the ice-type structural fluctuation exists. In this structural ice-type state, the spins are also fluctuating at a nanosecond scale down to 0.3K. We ascribed this phenomenon to the gapless frustrated random-singlet state, in which the spin-singlet pairs are resonating, and the orphan spins are hopping.