Chirality-induced spin current through spiral magnets

Spin-polarized current through helimagnets and the conductance modulation due to the chirality mismatch are studied numerically. The one-dimensional spiral magnet structure is obtained by taking into account the Dzyaloshinskii-Moriya interaction and the ferromagnetic interaction. Although the spiral magnetic structure consists of the $y\text{−}z$ components of the magnetization, the conduction electron through the spiral magnet is polarized in the $x$ direction, and its sign depends on the chirality of the spiral structure. We also investigate charge transport through the junction system consisting of two helimagnets. Similar to the giant magnetoresistance in the uniform ferromagnet, the conductance is reduced significantly by attaching the helimagnets with different chiralities. It is possible that our proposed mechanism can make use of the chirality measuring method by using electron transport and an alternative type of magnetoresistance using a topological property.

Figure 1

Schematic view of the helimagnet. (a) Left-handed system. The chirality ($\lambda ={[\vec{M}\left(\vec{r}\right)\times \vec{M}(\vec{r}+\vec{x})]}_x$) is negative. (b) Right-handed system $(\lambda >0)$. The spatial period of the spiral structure is determined by the ratio between the strength of the DMI and the strength of the FM. For calculating transport properties, the conduction electrons propagate in the $x$ direction.

Figure 2

The spin polarization of the conduction electron $\left(P_x\right)$ through the helimagnet. $E_{\mathrm{F}}$ is the Fermi energy of the conduction electrons. For the positive value of the DMI, the helimagnet forms the right-handed system in the $y\text{−}z$ plane. The sign of $P_x$ is determined by the chirality of the helimagnet.

Figure 3

Wave-packet dynamics through the helimagnet. (a) The initial state ($t=0$) of the wave packet. (b) The wave packet at $t=100t_0$, where $t_0(=\hslash /V_0\sim 0.028$ ps) is the unit time of the calculation.

Figure 4

(a) Schematic view of the junction system. (b),(c) The conductance modulation $G_{\mathrm{RR}}-G_{\mathrm{RL}}$ by changing the chirality of the helimagnet in the junction system. The angle at the interface of the junction system is (a) $\theta =0$ and (b) $\theta =\pi$.

Figure 5

Wave-packet dynamics through the junction system at $t=100t_0$. The initial state is the same as that in Fig. 3. The wave packet is reflected at the interface of the junction system RHS/LHS.