Fully Electrical Read-Write Device Out of a Ferromagnetic Semiconductor

We report the realization of a read-write device out of the ferromagnetic semiconductor (Ga,Mn)As as the first step to a fundamentally new information processing paradigm. Writing the magnetic state is achieved by current-induced switching and readout of the state is done by the means of the tunneling anisotropic magnetoresistance effect. This 1 bit demonstrator device can be used to design an electrically programmable memory and logic device.

Figure 1

Scanning electron microscope picture of the read-write device. A metallic air bridge made out of gold contacts the central disk. Each of the four nanobars connected to the central disk is contacted by two Ti/Au wires.

Figure 2

(a) TAMR measurements of the central disk summarized in a polar plot. (b) AMR measurements of one of the nanobars which shows a uniaxial magnetic anisotropy. Magnetic field sweeps for various in-plane angles in steps of $\Delta \phi =10°$ from along the long axis of the nanobar ($M\parallel H$) to perpendicular to it ($M\perp H$).

Figure 3

(a) Switching the magnetization of the central disk due to an electrical current from the 90° to 180° direction and back. The device can be written into a “1” (180°) by applying a current along 180°. For switching back the magnetization in the “0” state one applies the same current in the 90° direction. Having prepared the “0” state and applying a current in the 90° direction, the magnetization of the central disk does not change (control pulse). (b) Full TAMR traces for the central disk [90° gray (red) 0° black] and back sweep of the static magnetic field to zero after switching of the magnetization (light gray). (c) Sketch of the experimental configuration.

Figure 4

Proposed programmable logic element. The two central disks serve as two memory bits as well as two input bits of the logic device. The constriction between the two central disks is the key to reading out the result. The resistance from contact 1 to 2 will be dominated by the constriction which is dependent on the magnetization configurations of the input bits. In this configuration the input bits have four possible magnetization states: twice “Head-to-Tail,” “Head-to-Head,” “Tail-to-Tail.” Truth table as it could be programmed as an exclusive OR ($A$ XOR $B$) gate.