  The bipartite entanglement is comprehensively investigated in the mononuclear
molecular complex (Et3NH)[Ni(hfac)2L]L, where HL denotes
2-(2-hydroxy-3-methoxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl
and hfacH stands for hexafluoroacetylacetone. From the magnetic point of view,
the molecular compound (Et3NH)[Ni(hfac)2L] consists of an exchange-coupled
spin-1 Ni2+ magnetic ion and a spin-1/2 nitronyl-nitroxide radical substituted
nitrophenol. The nickel-radical molecular complex affords an experimental
realization of a mixed spin-(1/2, 1) Heisenberg dimer with a strong
antiferromagnetic exchange coupling J/kB = 505 K and two distinct g-factors
gRad=2.005 and gNi=2.275. By adopting this set of magnetic parameters we
demonstrate that the Zeeman splitting of a quantum ferrimagnetic ground-state
doublet due to a weak magnetic field may substantially reinforce the strength
of bipartite entanglement at low temperatures. The molecular compound
(Et3NH)[Ni(hfac)2L] maintains sufficiently strong thermal entanglement even at
room temperature, vanishing only above 546 K. Specifically, the thermal
entanglement in the nickel-radical molecular complex retains approximately 40%
of the maximum value corresponding to perfectly entangled Bell states at room
temperature, which implies that this magnetic compound provides suitable
platform of a molecular qubit with potential implications for room-temperature
quantum computation and quantum information processing.
