  Although abundant research has focused recently on the quantum criticality of
itinerant magnets, critical phenomena of insulating magnets in the vicinity of
critical endpoints (CEP's) have rarely been revealed. Here we observe an
emergent CEP at 2.05 T and 2.2 K with a suppressed thermal conductivity and
concomitant strong critical fluctuations evident via a divergent magnetic
susceptibility (e.g., chi''(2.05 T, 2.2 K)/chi''(3 T, 2.2 K)=23,500 %,
comparable to the critical opalescence in water) in the hexagonal insulating
antiferromagnet HoMnO3.
