Novel ground state in the frustrated S=1 tetramer antiferromagnet K2Ni2(MoO4)3

Quantum materials wherein frustration, the topology of the electronic band structure, spin correlations, and subtle interplay between emergent degrees of freedom are at play can host a panoply of novel quantum states spanning from spin liquids to Bose-Einstein Condensation with exotic fractionalized excitations. Herein, we focus on a new frustrated antiferromagnet K2Ni2(MoO4)3 in which Ni2+ ions constitute a tetramer. The magnetic susceptibility and specific heat on the single crystal and polycrystal exhibit short-range spin correlations without a gap in the spin excitation spectrum. The presence of a sharp peak at around ~ 1.1 K in magnetization and specific results suggest the presence of long range magnetic order. Remarkably, the external magnetic field induces magnetic phenomena akin to the BEC of triplon excitations in spin gap magnets. T-H phase boundary follows a power law (T-T_N)∝H^(2/3) as predicted for the BEC scenario. Our thermodynamic results suggest the titled material is located in the proximity of a quantum critical point (QCP), which separates the magnetically ordered and spin-gap regions of the phase diagram. We propose a μSR study much below the sub-Kelvin temperatures to unambiguously confirm the BEC state, extract the relevant order parameter, and critical exponents essential to establish universality class in BEC of magnetic excitations in this novel frustrated antiferromagnet.