Magnon gap formation and charge density wave effect on thermoelectric properties in SmNiC2 compound

We studied the magnetic, electrical, and thermal properties of polycrystalline compound of SmNiC2. The electrical resistivity and magnetization measurement show the interplay between the charge density wave at T$_{\mathrm{CDW}} =$ 157 K and the ferromagnetic ordering of Tc $=$ 18 K. Below the ferromagnetic transition temperature, we observed the magnon gap formation of 4.3 $\sim$ 4.4 meV by $\rho $(T) and C$_{\mathrm{p}}$(T) measurements. The charge density wave is attributed to the increase of Seebeck coefficient resulting in the increase of power factor S$^{\mathrm{2}}\sigma $. The thermoelectric figure-of-merit ZT significantly increases due to the increase of power factor at T$_{\mathrm{CDW}} =$ 157 K. Here we argue that the competing interaction between electron-phonon and electron-magnon couplings exhibits the unconventional behavior of electrical and thermal properties. This research was supported by Basic Science Research Program (2011-0021335), Nano-Material Technology Development Program (2011-0030147), and Mid-career Research Program (Strategy) (No. 2012R1A2A1A03005174) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.