Magnetic Domain Wall Memory and Logic Devices

We are investigating the fabrication, material, and circuit properties of magnetic memory and logic devices. The research is divided into two main subjects: the first is the study of 360° domain walls, which show novel characteristics under DC and AC applied magnetic fields and currents, and are a promising data token in racetrack memory applications. The second subject is designing and fabricating an instantiation of magnetic logic that has the potential to be more energy efficient than today’s transistors.

In 360° domain walls (360DWs), the magnetization makes a full in-plane 360° turn in a localized region of a magnetic wire, while the rest of the wire is magnetized parallel to its edges. We show a 360 DW in a Co nanowire.1 Simulations2 indicate that 360 DWs have a response to a current that is qualitatively different from the behavior of 180 DWs. 360 DWs move at a velocity independent of applied magnetic fields and can be destroyed by a burst of applied current. The stability of the domain wall can be controlled by an externally applied field. These features make the 360 DW a candidate data token in novel domain wall logic and memory devices.

The heat dissipated per switching operation by logic transistors can potentially be greatly reduced by using a collective effect, such as the collective switching of magnetic moments. Thus, we are researching a device that uses the current-induced switching of a 180 DW in a soft ferromagnet to perform logic. The state of the logic gate is read out using a magnetic tunnel junction. Modeling of the device performance shows its potential for beyond-CMOS: it is nonvolatile, compatible with CMOS, has a fanout greater than one, a single device acts as a universal NAND gate, and the power dissipation per device operation scales well with device size. 3 We show a device prototype, using CoFeB as the soft ferromagnetic wire, with ends exchange bias with IrMn antiferromagnets to ensure a single 180 DW in the wire.