  We report the synthesis and characterization of a new quantum magnet
[2-[Bis(2-hydroxybenzyl)aminomethyl]pyridine]Ni(II)-trimer (BHAP-Ni3) in
single-crystalline form. Our combined experimental and theoretical
investigations reveal an exotic spin state that stabilizes a robust 2/3
magnetization plateau between 7 and 20 T in an external magnetic field.
AC-susceptibility measurements show the absence of any magnetic order/glassy
state down to 60 mK. The magnetic ground state is disordered and specific-heat
measurements reveal the gapped nature of the spin excitations. Most
interestingly, our theoretical modeling suggests that the 2/3 magnetization
plateau emerges due to the interplay between antiferromagnetic Heisenberg and
biquadratic exchange interactions within nearly isolated spin $S$ = 1
triangles.
