Synergetic Enhancement in Thermoelectric Performance via Localized Magnetic Moments and Lattice Softening

Magnetism‐assisted transport is achieved in Mn‐containing SnSe magnetic nanocomposites, where superparamagnetic MnSe nanoprecipitates are introduced to modulate both carrier and phonon scattering. Transmission electron microscopy reveals well‐dispersed 5–10 nm MnSe inclusions embedded within the SnSe matrix. Magnetization measurements identify a blocking temperature of 165 K and temperature‐dependent hysteresis behavior consistent with Néel relaxation, confirming active s–d exchange between localized Mn moments and itinerant carriers. Compared to pristine SnSe, the composites exhibit an enhanced power factor alongside reduced total thermal conductivity. Integrated crystal‒orbital Hamilton population analysis reveals that Mn substitution weakens bonding, while phonon calculations indicate a decrease in group velocities; together, these effects account for the observed suppression in lattice thermal conductivity. The combined influence of spin‐fluctuation scattering and phonon softening results in a peak figure of merit ( zT ) of 1.98 at 820 K for Sn 0.97 Mn 0.03 Se. These findings demonstrate that integrating superparamagnetic dynamics with lattice softening enables decoupling of the Seebeck coefficient and electrical conductivity while simultaneously reducing thermal conductivity in earth‐abundant chalcogenides.