Hybrid spintronics and straintronics

Applies Physics Letters – Hybrid spintronics and straintronics: A magnetic technology for ultra low energy computing and signal processing

The authors show that the magnetization of a magnetostrictive/piezoelectricmultiferroic single-domain shape-anisotropic nanomagnet can be switched with very small voltages that generate strain in the magnetostrictive layer. This can be the basis of ultralow power computing and signal processing. With appropriate material choice, the energy dissipated per switching event can be reduced to ∼45 kT at room temperature for a switching delay of ∼100 ns and ∼70 kT for a switching delay of ∼10 ns, if the energy barrier separating the two stable magnetization directions is ∼32 kT . Such devices can be powered by harvesting energy exclusively from the environment without the need for a battery.

Note that in order to increase the switching speed by a factor of 10, the dissipation needs to increase by a factor of 1.6. Therefore, dissipation increases sub-linearly with speed, which bodes well for energy efficiency. With a nanomagnet density of 10^10 cm−2 in a memory or logic chip, the dissipated power density would have been only 2 mW/cm2 to switch in 100 ns and 30 mW/cm2 to switch in 10 ns, if 10% of the magnets switch at any given time (10% activity level). Note that unlike transistors, magnets have no leakage and no standby power dissipation, which is an important additional benefit.

Such extremely low power and yet high density magnetic logic and memory systems, composed of multiferroic nanomagnets, can be powered by existing energy harvesting systems that harvest energy from the environment without the need for an external battery.

These processors are uniquely suitable for implantable medical devices, e.g. those implanted in a patient’s brain that monitor brain signals to warn of impending epileptic seizures. They can run on energy harvested from the patient’s body motion. For such applications, 10- 100 ns switching delay is adequate. Speed is not the primary concern, but energy dissipation is. These hybrid spintronic/straintronic processors can be also incorporated in “wrist-watch” computers powered by arm movement, buoy-mounted computers for tsunami monitoring (or naval applications) that harvest energy from sea waves, or structural health monitoring systems for bridges and buildings that are powered solely by mechanical vibrations due to wind or passing traffic.

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