New magnetoelectric memory promises low-power, instant-on computing devices

December 19, 2014

A conceptual illustration of magnetization reversal, given by the compasses, with an electric field (blue) applied across the gold capacitors. The compass needles under the electric field are rotated 180 degrees from those not under the field (0 degrees rotated). The two-step switching sequence described in the paper is represented by the blurred compass needle under the electric field, making an intermediate state between the 0 and 180-degree rotated states. (Credit: John Heron)

A team led by postdoctoral associate John Heron of Cornell University has developed a room-temperature magnetoelectric memory design that replaces power-hungry electric currents with an electric field. It could lead to low-power, instant-on computing devices.

“The advantage here is low energy consumption,” Heron said. “It requires a low voltage, without current, to switch it. Devices that use currents consume more energy and dissipate a significant amount of that energy in the form of heat. That is what’s heating up your computer and draining your batteries.”

The researchers made their device out of bismuth ferrite, which is both magnetic and ferroelectric, meaning it’s always electrically polarized; and that polarization can be switched by applying an electric field.

This rare combination makes it a “multiferroic” material, allowing for it to be used for nonvolatile memory devices with relatively simple geometries. Other scientists have demonstrated similar results with competing materials, but at impractical cold temperatures, like 4 Kelvin (-452 Fahrenheit).

Their results were published online Dec. 17 in Nature, along with an associated “News and Views” article.

Collaborators from the University of Connecticut; University of California, Berkeley; Tsinghua University; and Swiss Federal Institute of Technology in Zurich where also involved in the research, which was supported by the National Science Foundation and the Kavli Institute at Cornell for Nanoscale Science.

Abstract of Deterministic switching of ferromagnetism at room temperature using an electric field

The technological appeal of multiferroics is the ability to control magnetism with electric field123. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii–Moriya (DM) interaction6789. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden1011. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work101112. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching1314. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics39, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics.