Contrasting magnetothermal conductivity in sibling Co-based honeycomb-lattice antiferromagnets

Honeycomb-lattice antiferromagnets have attracted wide attention for exploration of exotic heat transport and their interplay with magnetic excitations.In this work, we have revealed a contrasting behavior in the magneto-thermal conductivity (MTC) between two Co-based honeycomb-lattice magnets Co4M2O9 (M = Nb, Ta), despite their identical lattice structures and quite similar magnetism.Co4Ta2O9 exhibits enhanced MTC of about 550 % at 9 T of an in-plane magnetic field, comparable to other honeycomb-magnets, while MTC for Co4Nb2O9 reaches only ∼ 30 %.This marked difference is ascribed to distinct features in the field-induced evolution of magnetic excitations that resonantly scatter phonons.This finding sheds light on implicit impacts of non-magnetic ions on thermal transport, and hints at the potential for broad heat-transport tunability while preserving magnetism and lattice structures.