Quantum spin dynamics in a metallic spin chain Ti₄MnBi₂

One-dimensional spin chain systems provide platforms to explore, both experimentally and theoretically, a wealth of novel quantum phenomena. So far, almost all spin chain systems studied have been insulating. We investigated a new metallic compound, Ti₄MnBi₂, whose structure consists of chains of S = 1/2 Mn ions that extend along the c-axis. The close spacing of the Mn atoms in the chains and the relatively weak correlations found in heat capacity and susceptibility suggest an antiferromagnetic (AFM) order. We have performed inelastic neutron scattering (INS) measurements using AMATERAS@J-PARC on single-crystal Ti₄MnBi₂. A gapped magnetic excitation continuum is found roughly between 0.5 and 2 meV unchanged in the AFM state to temperature as low as 0.3 K. The gap decreases above T_N, and quasielastic scattering emerges. µSR measurements have been performed at M15/M20D@TRIUMF, finding that 20% of the spins are frozen at temperature below 1K. The µSR, INS, and specific heat measurements all find that substantial magnetic fluctuations persist in the AFM state, an indication of the importance of quantum fluctuations and unconventional AFM order in this system.