2025/12/25 by K. Nihongi, Takanori Kida, Nihongi, K. +25
Physics and Astronomy · Materials Science · #Physics of Superconductivity and Magnetism #Iron-based superconductors research #Advanced Condensed Matter Physics
paper · doi:10.48550/arxiv.2512.21682
We present a combined experimental and theoretical study of the triangular-lattice quantum antiferromagnet CsFeCl3 under high magnetic fields and high pressure. Pulsed-field magnetization for the magnetic field along the symmetric c direction at ambient pressure reveals a magnetization process from a nonmagnetic singlet ground state with a nearly linear increase between 3.7 and 10.7 T, a plateau-like region, and then a sharp stepwise metamagnetic transition near 32 T. Wide frequency--field range electron spin resonance indicates that the low-field regime originates from the J = 1 manifold, while the high-field metamagnetic transition suggests a level crossing between the J = 1 and J = 2 lowest states. Pulsed-field magnetic susceptibilities measured with a proximity detector oscillator under high pressure show that the low-field nonmagnetic singlet phase is gradually suppressed, while the high-field metamagnetic transition evolves into an increasingly rich pattern of fractional steps. While the observations at low to intermediate fields can be understood within the established spin-1 description, the high-field regime requires a new perspective, which we provide through a projected spin-1/2 framework built from Zeeman-selected crystal-field states not related by time reversal. This construction naturally allows emergent three-body interactions on triangular plaquettes and explains the asymmetric evolution of the fractional steps in the magnetization. Our findings reveal that high-field effective spin models in quantum magnets with separated yet accessible crystal-field multiplets are not constrained to even-body couplings, but can naturally host odd-body terms, opening a broader avenue for realizing field-asymmetric magnetization processes and exotic phases beyond conventional even-body physics.