We studied the electrical, thermal, and thermoelectric properties of the polycrystalline compound of SmNiC${}_2$. The electrical resistivity and magnetization measurement show the interplay between the charge density wave at $T_{\mathrm{CDW}}=150$ K and the ferromagnetic ordering of $T_c=18$ K. Below the ferromagnetic transition temperature, we observed the magnon gap formation of $\Delta \simeq 4.3$–4.4 meV by $\rho \left(T\right)$ and $C_p\left(T\right)$ measurements. The charge density wave is attributed to the increase of the Seebeck coefficient resulting in the increase of the power factor $S^2\sigma$. The thermal conductivity anomalously increases with increasing temperature along the whole measured temperature range, which implies the weak attribution of Umklapp phonon scattering. The thermoelectric figure of merit $ZT$ significantly increases due to the increase of the power factor at $T_{\mathrm{CDW}}=150$ K. Here we argue that the competing interaction between electron-phonon and electron-magnon couplings exhibits the unconventional behavior of electrical and thermal properties.

• Received 20 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.235101