Thermoelectric Effect in Single-Molecule-Magnet Junctions

We study the spin-dependent thermoelectric transport through a single-molecule-magnet junction in the sequential tunneling regime. It is found that the intrinsic magnetic anisotropy of the single-molecule magnet can lead to gate-voltage-dependent oscillations of charge thermopower and a large violation of the Wiedeman-Franz law. More interestingly, the spin-Seebeck coefficient is shown to be greater than the charge-Seebeck coefficient, and a pure spin thermopower or/and a pure spin current can be obtained by tuning only the gate voltage. It needs neither an external magnetic field or irradiation of circularly polarized light on the molecule nor ferromagnetic leads to realize these interesting effects, indicating the powerful prospect of single-molecule-magnet applications in spintronic devices.

Figure 1

(a) Charge thermopower $S_c$ for nonmagnetic molecule ($D=J=0$) and SMM ($D=0.06\mathrm{meV}$, $J=0.2\mathrm{meV}$) with $U=0$; dashed lines: analytic result from Eq. (5); solid lines: numerical result. (b) $S_c$ and (c) Lorenz number $L/L_0$ for different $J$ and $U$; as functions of molecular level ${\epsilon }_0$. (d) Variation of the figure of merit $ZT$ with $J$ for ${\epsilon }_0=0.2$.

Figure 2

(a) Charge thermopower $S_c$ and spin thermopower $S_s$, (b) their ratio $S_c/S_s$, and (c) spin-dependent currents $I_{\uparrow (\downarrow )}$, charge current $I_c$, and spin current $I_s$, as functions of molecular level ${\epsilon }_0$.