Spin-dependent thermoelectric figure of merit in a quantum dot

•Thermoelectric efficiency in the presence of spin current is analyzed in a quantum dot.•The condition that the spin accumulation across the system is zero yields a higher ZT value.•ZT decreases as the spin polarization degree of the ferromagnetic lead is increased.

We theoretically investigate the spin-dependent thermoelectric effects in a quantum dot that is connected with a normal metal lead and a ferromagnetic metal lead, by using the nonequilibrium Green's function method. The thermoelectric figure of merit ZT   can be evaluated in several different ways, for example, by imposing a condition that the spin accumulation across the system is zero (Δμs=0Δμs=0) or that the spin current is zero (Is=0Is=0). We find that ZT   in the case of Δμs=0Δμs=0 is always greater, especially when the spin polarization degree of the ferromagnetic lead is large. Meanwhile, in each case the ZT value drops when the spin polarization degree is increased. Effects of electron interaction on thermoelectric properties are also discussed briefly.