Replacing electrical currents with electromagnetic fields

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, Cornell university

To store (and read) one bit in a flash memory you need to have an electrical current. This implies moving electrons and in turns requires energy that in part will be wasted as heat.

To move electrons, that is to have a current, you need to apply an electric filed, and on the reverse, moving electrons generate an electric field. Wait. This is true if you have a conductor, not if you have an insulator. In an insulator electrons remain bound to their atomic "cage" and don't move around from atom to atom. So if we apply an electric field to an insulator there won't be any electrons movement, no current and no heat dissipation!

This is what researchers at the Cornell University have been doing creating a magnetoelectric memory that can be written are read using an electric field at room temperature.

Notice that this does not mean you can store and read bits at no energy cost, using an electric field still engage energy transfer, but the amount of energy involved is minuscule with respect to the one involving electrons movement.

The memory is based on bismuth ferrite, a material that shows both magnetic and electrical properties. It has a permanent magnetic field of its own and has ferroelectric properties meaning that it is always electrically polarised. This polarisation can be switched by applying an electric field and this is what allows you to store a "bit", associating 0 to one polarisation state and 1 to the other.

Bismuth ferrite is part of the ferroic materials, an interesting class discovered on the year 2000. Their properties have been studied theoretically and experimented at very low temperatures (4°K), so low that they made their application economically unsustainable. The big advance made at Cornell is the possibility of using this material at room temperature.

It is not yet a "go" for an industrial application, though. They have shown how to store a bit, but what you need is to store billions of them... Nevertheless, it is a first step in the direction of radically change the approach to storage getting rid of electrons and using electric fields.

Author - Roberto Saracco

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