Current-Driven Magnetization Reversal in a Ferromagnetic Semiconductor $(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}$ Tunnel Junction

Current-driven magnetization reversal in a ferromagnetic semiconductor based $(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}$ magnetic tunnel junction is demonstrated at 30 K. Magnetoresistance measurements combined with current pulse application on a rectangular $1.5\times 0.3{\mu \mathrm{m}}^2$ device revealed that magnetization switching occurs at low critical current densities of $1.1–2.2\times {10}^5\mathrm{A}/{\mathrm{c}\mathrm{m}}^2$ despite the presence of spin-orbit interaction in the $p$-type semiconductor system. Possible mechanisms responsible for the effect are discussed.

Figure 1

Normalized magnetization curves of two $(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(d\mathrm{n}\mathrm{m})/(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}(\sim 35{\mathrm{m}\mathrm{m}}^2)$) magnetic tunnel junction layers at 5 K ($d=2\mathrm{n}\mathrm{m}$ and $d=6\mathrm{n}\mathrm{m}$). Magnetic field was applied along $[\overline{1}10]$. The inset shows $I\mathrm{\text{−}}V$ characteristics at 5 K of the two magnetic tunnel junction devices ($20\times 20{\mu \mathrm{m}}^2$) fabricated from these layers.

Figure 2

(a) Major (closed symbols) and minor (open symbols) magnetoresistance curves of a $1.5\times 0.3{\mu \mathrm{m}}^2$ magnetic tunnel junction sample at 30 K taken at a bias of $V_d=+10\mathrm{m}\mathrm{V}$. Magnetic field is applied along $a$. Three arrows indicate the sweep direction of magnetic field to prepare the different initial configurations A, B, and C. (b) Size $A$ dependence of coercive force ${\mu }_0{H}_C$. $H_C$ of the top (bottom) layer are indicated by closed (open) symbols.

Figure 3

(a) $\Delta R$ as a function of $I_{\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}}$ of the $1.5\times 0.3{\mu \mathrm{m}}^2$ device at 30 K, where $\Delta R$ is the resistance difference between the resistance of MTJ after application of $I_{\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}}$ (1 ms) and that at parallel magnetization configuration at $H=0$. Closed circles show the $I_{\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}}$ dependence of $\Delta R$ for initial configuration A (parallel $M$), whereas open triangles show the results for initial configuration C (antiparallel $M$). The inset shows $I\mathrm{\text{−}}V$ characteristics of the device. (b) Magnetic field dependence of critical current density $J_C$ (and critical current $I_C$) for the $2.0\times 0.4{\mu \mathrm{m}}^2$ device at 30 K. Dotted lines are linear fits to the data.

Figure 4

Magnetoresistance curves of the $1.5\times 0.3{\mu \mathrm{m}}^2$ device at 30 K measured at $V_d=+10\mathrm{m}\mathrm{V}$ starting from three different states. MR curves (a) and (b) are obtained from a state prepared by applying a positive current pulse with current density of $J_{\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}}=+2.2\times {10}^5\mathrm{A}/{\mathrm{c}\mathrm{m}}^2$ on initial configuration A (see the rightmost diagram for $M$ configuration). MR curves (c) and (d) are obtained from a state prepared by the same manner but starting from initial configuration B.