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

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.