In spinel-type nickelate NiRh2βO4β, magnetic ordering is observed upon
the sample synthesized via kinetically controlled low-temperature solid-state
metathesis, as opposed to previously-reported samples obtained through
conventional solid-state reaction. Our findings are based on a combination of
bulk susceptibility and specific heat measurements that disclose a NeΛel
transition temperature of TNβ = 45 K in this material, which might feature
spin-orbit entanglement in the tetragonally-coordinated d8 Mott insulators.
The emergence of magnetic ordering upon alteration of the synthesis route
indicates that the suppression of magnetic ordering in the previous sample was
rooted in the cation-mixing assisted by the entropy gain that results from
high-temperature reactions. Furthermore, the Jeffβ = 0 physics, instead
of solely the spin-only S=1, describes the observed enhancement of
effective magnetic moment well. Overseeing all observations and speculations,
we propose that the possible mechanism responsible for the emergent magnetic
orderings in NiRh2βO4β is the condensation of Jeffβ = 0 exciton,
driven by the interplay of the tetragonal crystal field and superexchange
interactions.Comment: 7 pages, 5 figures, accepted in Physical Review Material