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

Hanasaki, Noriaki; Hattori, Takayuki; Komoda, Takumi; Minamoto, Kouei; Torigoe, Shuhei; Yamashita, Satoshi; Nakazawa, Yasuhiro; Nakano, Takehiko et al. · Proc Natl Acad Sci U S A · 2026

basic_science · Level V

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Abstract

In ice, it is well known that the orientation of H<sub>2</sub>O 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 MgTi<sub>2</sub>O<sub>4</sub>, 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 0.3 K. 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.