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When a Magnet Plays “Ping Pong”

A novel theoretical framework for a magnetic field tunable radio frequency oscillator has been developed.The proposed device, when realised, would play a major role in  the nanoelectronics field, specifically as integrable clocks in futuristic logic circuits.

With every second instrument incorporating a logic circuit, smart devices occupy an indispensable position in our day to day life. There are smartphones, ACs, refrigerators, calculators, and recently smart automobiles, and the list doesn't end here. At the heart of each of these devices is a logic circuit, which is composed of thousands of individual components or building blocks. An oscillator is one such building block of a logic circuit. The newly proposed nanoelectronic oscillator based on spintronics, if realized would make our smart instruments smarter, faster, and more efficient.  The proposal has been put forth by Prof. Bhaskaran Muralidharan, Prof. Ashwin Tulapurkar and Mr. Sanchar Sharma at the Department of Electrical Engineering, IIT Bombay.

An oscillator can be understood as a circuit which generates periodic oscillating signals. For example, an oscillator on a motherboard of a 2 GHz PC generates electric pulses after every 0.5 nanoseconds. In the proposed framework, the oscillations would come from the motion of a magnetic domain wall.

A domain wall is a thin interface separating group of atoms having different magnetic alignments. Under suitable conditions oscillations could be induced to the domain walls. Prof. Muralidharan and Prof. Tulapurkar explain that this wall moves periodically between two unstable positions, like a table tennis ball. Similar to the motion caused by two players,  a push by spin current plus a magnetic field on one side and only magnetic field on the other side of the wall. These oscillations may be read out via electrical currents  and then be used as timers or clocks.

An electron has three characteristics: charge, mass, and spin. The spin can be thought of as how much the electrons turn on their own axis. Just as any system with moving electrons has an electric current due to the moving charges, it will also have “spin current” due to moving spins. This spin current is exploited in the current work for producing oscillations.

The team now intends to realize this concept by building an actual logic circuit. The applications of the oscillators could be an important step toward realizing an all spin nanoscale logics driven exclusively by spin currents. The probable advantages of the device would be higher efficiency, speed, accuracy and lesser power consumption.

(This work was supported in part by IIT Bombay Seed Grant and the Department of Science and Technology (DST), Government of India under the Science and Engineering Board Grant.

The team acknowledges the support of the Centre of Excellence in Nanoelectronics (CEN), IIT Bombay.)

Sanchar Sharma, Bhaskaran Muralidharan, Ashwin Tulapurkar, Proposal for a Domain Wall Nano-Oscillator driven by Non-uniform Spin Currents, Nature Scientific Reports 5, Article number : 14647, (2015)DOI : 10.1038/srep14647

Patent : 3395/MUM2015

Write up prepared by (based on inputs from the authors) : Ajay Gupta, Sashwata Ghosh

Graphics by : Purushottam Gupta

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