Magnetic switching of a single molecular magnet due to spin-polarized current

Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic leads (electrodes) is investigated theoretically. Magnetic moments of the leads are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through the barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system, as well as the spin relaxation times of the SMM, are calculated from the Fermi golden rule. It is shown that spin of the SMM can be reversed by applying a certain voltage between the two magnetic electrodes. Moreover, the switching may be visible in the corresponding current-voltage characteristics.

Figure 1

(Color online) (a) Schematic picture of the system under consideration for two collinear configurations of the electrodes’ spin moments; parallel (blue arrows) and antiparallel (red arrows). Dashed lines represent the two possible tunneling processes: direct tunneling (the top line) and tunneling with scattering on the SMM’s spin due to exchange interaction (the bottom line). (b) Energy levels corresponding to different spin states of the SMM. The grey dot represents the initial spin state $\mid -S⟩$ of the molecule.

Figure 2

(Color online) (a) The mean value of the SMM’s spin $⟨S_z⟩$ and the current $I$ flowing through the system as a function of voltage $V$ in the case of nonmagnetic electrodes, and for $c=10\mathrm{kV}∕\mathrm{s}$ and $T=0.01\mathrm{K}$. The inset shows schematically the density of states and the allowed tunneling processes (the solid arrows correspond to electrons tunneling without spin reversal, whereas the dashed arrows correspond to electrons tunneling with simultaneous spin flip). (b) Schematic representation of the DOS and tunneling processes for both parallel and antiparallel magnetic configurations, shown in the case when the left electrode is made of a half-metallic ferromagnet while the right one is either a typical $3d$ ferromagnet or a half-metallic ferromagnet.

Figure 3

(Color online) The mean value of the SMM’s spin $⟨S_z⟩$ and the current $I$ flowing through the system as a function of voltage $V$ for indicated polarization parameters in the parallel $\left(P\right)$ (a)–(c) and antiparallel (AP) (d)–(f) configurations, and for $c=10\mathrm{kV}∕\mathrm{s}$ and $T=0.01\mathrm{K}$. Part (g) corresponds to the case where one electrode is nonmagnetic.

Figure 4

(Color online) The mean value of the SMM’s spin $⟨S_z⟩$ and the current $I$ as a function of the voltage $V$ for various voltage sweeping speeds $c$ in the parallel magnetic configuration of the system. The numerical results are for $T=0.01\mathrm{K}$, $P^L=1$, and $P^R=0.9$.