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Higher manganese silicides (HMSs) have emerged as promising candidates for environmentally friendly thermoelectric (TE) materials due to their earth-abundant and non-toxic composition. We report grain boundary engineering in ruthenium-doped HMSs via a melt-quenching followed by annealing method. This approach promotes the formation of MnSi nanoprecipitates and nanopores, preferentially near grain boundaries. The presence of these nanostructures results in a weak temperature-dependent thermal conductivity, resembling glass-like thermal transport behavior. A two-channel model incorporating propagons and diffusons describes this glass-like thermal conductivity, with diffusons contributing about 60 % of the lattice thermal conductivity at 300 K. Furthermore, the quench-annealing process enhances electrical conductivity while preserving a large Seebeck coefficient, which is attributed to a high density-of-states effective mass. As a result of improved power factor and reduced thermal conductivity, the figure of merit zT value increases by 33 % at 300 K compared to undoped HMS synthesized via solid-state reaction. These findings present a promising strategy for manipulating phonon dynamics in functional materials and designing efficient TE systems. 

Magnons are quasiparticles of spin waves, carrying both thermal energy and spin information. Controlling magnon transport processes is critical for developing innovative magnonic devices used in data processing and thermal management applications in microelectronics. The spin ladder compound Sr14Cu24O41 with large magnon thermal conductivity offers a valuable platform for investigating magnon transport. However, there are limited studies on enhancing its magnon thermal conductivity. Herein, we report the modification of magnon thermal transport through partial substitution of strontium with yttrium (Y) in both polycrystalline and single crystalline Sr14−xYxCu24O41. At room temperature, the lightly Y-doped polycrystalline sample exhibits 430% enhancement in thermal conductivity compared to the undoped sample. This large enhancement can be attributed to reduced magnon-hole scattering, as confirmed by the Seebeck coefficient measurement. Further increasing the doping level results in negligible change and eventually suppression of magnon thermal transport due to increased magnon-defect and magnon-hole scattering. By minimizing defect and boundary scattering, the single crystal sample with x = 2 demonstrates a further enhanced room-temperature magnon thermal conductivity of 19Wm−1K−1, which is more than ten times larger than that of the undoped polycrystalline material. This study reveals the interplay between magnon-hole scattering and magnon-defect scattering in modifying magnon thermal transport, providing valuable insights into the control of magnon transport properties in magnetic materials.