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May 14, 2015

Instant-start computers possible with new breakthrough

A conceptual illustration of the reversal of a magnetization (given by the compasses) with the application electric field (blue) applied across the gold capacitors. The compass needles under the electric field are rotated 180 degrees from those that are not under electric field (zero rotated). Furthermore, a two-step switching sequence is illustrated by the blurred compass needle in the compass under the electric field, making an intermediate state between the zero and 180 degrees rotated states while under the electric field. A team of researchers led by John Heron, a postdoctoral associate at Cornell University, performed this work.

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Magnetic memories and devices have historically relied on a current of electric charge to generate a magnetic field or the injection of a spin-polarized current to reverse the magnetization of a magnetic layer. These currents are the primary source of power consumption and heating in these devices.

This issue has triggered a new line of research in spintronics: The pursuit of 180 degrees magnetization switching with an applied electric field (i.e., no current flow). Nature has imposed great barriers that complicate such an endeavor; for instance, a compass needle is not sensitive to an electric field but is to a magnetic field. Magnetoelectric multiferroics (materials or heterostructures that possess more than one ferroic parameter with the electric and magnetic orders coupled) enable the electric field control of magnetism. However, the reversal of a magnetization by purely an applied electric field has been elusive due to material symmetry constraints.

In an article published in the Dec. 18, 2014, online issue of Nature, Heron et al. describe a pathway to the reversal of a magnetization with an applied electric field at room temperature using a multiferroic-based heterostructure (Co.90Fe.10/BiFeO3). They propose a mechanism for this switching that relies on the ferroelectric polarization and the canted moment of BiFeO3 switching together under the applied electric field in two sequential steps. The results are then used to demonstrate the electric field control of a traditional spintronic device at room temperature and indicate that the scaled energy consumption is ~ 1 order of magnitude smaller than switching the device with a spin-polarized current.

The research was supported in part by a grant from the National Science Foundation.

To learn more, see the Cornell Chronicle story Multiferroic heroics put instant-on computing in sight.

Or, read Heron's paper "Deterministic switching of ferromagnetism at room temperature using an electric field" in Nature Here. Or see the Nature News and Views story, "Materials science: Two steps for a magnetoelectric switch," Here. (Date of Image: December 2014)

Credit: John Heron

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