Spintronic Memristor

Topics: Magnetic field, Magnetism, Ferromagnetism Pages: 20 (6428 words) Published: August 6, 2011

Generally when most people think about electronics, they may initially think of products such as cell phones, radios, laptop computers, etc. others, having some engineering background, may think of resistors, capacitors, etc. which are the basic components necessary for electronics to function. Such basic components are fairly limited in number and each having their own characteristic function. Memristor theory was formulated and named by Leon Chua in a 1971 paper. Chua strongly believed that a fourth device existed to provide conceptual symmetry with the resistor, inductor, and capacitor. A device linking charge and flux (themselves defined as time integrals of current and voltage), which would be the memristor, was still hypothetical at the time. However, thirty-seven years later, on April 30, 2008, a team at HP Labs led by the scientist R. Stanley Williams announced the discovery of a switching memristor. Based on a thin film of titanium dioxide, it has been presented as an approximately ideal device. The reason that the memristor is radically different from the other fundamental circuit elements is that, unlike them, it carries a memory of its past. When you turn off the voltage to the circuit, the memristor still remembers how much was applied before and for how long. That's an effect that can't be duplicated by any circuit combination of resistors, capacitors, and inductors, which is why the memristor qualifies as a fundamental circuit element. Memristor has very broad applications that include non-volatile memory, signal processing, control and learning system etc. Shortly after the demonstration of memristance, researchers began looking for this property in spintronics—a relatively new branch of electronics itself. In this ever changing world of technology, products of technology have evolved at an extremely quick rate.  Computers have been doubling in speed in no time flat, audio recording has evolved, though more slowly, from albums now to mpeg players that can store around 700 minutes worth of music, and the gaming console business, not to mention all the other areas of advancement.  But, getting back to computer speed and storage, the advancement in this category is starting to slow down (there can only be so many “switches/transistors” placed on a chip).  So to deal with storage and speed advancements some new research is being done.  One of these areas is that of spintronics.  Spintronics is at the heart of recent advances in hard-drive data density and the niche nonvolatile memory known as MRAM. The formal definition of spintronics is “the study of the role played by electron (and more generally nuclear) spin in solid state physics, and possible devices that specifically exploit spin properties instead of or in addition to charge degrees of freedom”. A simpler definition is that spintronics is a “new branch of electronics in which electron spin, in addition to charge, is manipulated to yield a desired outcome”. Nano-scale spintronic memristor has been proposed based upon spin torque induced magnetization motion and spin transport at semiconductor/ferromagnet junction . Realizing memristive effects in spintronic device not only provides understanding of a wide range of current-voltage behaviours observed in nanoscale spintronic system, but also sheds light on how we should look at existing/proposed magnetic devices and herald new applications.

Fig. 1


The transistor was invented in 1925 but lay dormant until finding a corporate champion in Bell Labs during the 1950s.Then in 2008,Hewlett-Packard Labs demonstrated a practical memristor, the fourth passive circuit element after the resistor, and the capacitor the inductor into the electronics mainstream. Postulated in 1971, the “memory resistor” represents a potential revolution in electronic circuit theory similar to the invention of transistor.Now, researchers have come up with a new type...

References: * X. Wang, Y. Chen, H. Xi, H.Li and D. Dimitrov, Spintronic memristor through spin torque induced magnetization motion’ IEEE Device Letters, vol. 30,n o. 3, pp. 294-297,2009. ‡
* L. O. Chua, “Memristor”, The missing circuit element, IEEE Tran.Circuit Theory, vol. CT-18, no. 5, pp. 507 - 519, Sep. 1971.
* Neil Savage , Spintronic Memristors , IEEE Spectrum, March 2009 .
* X. Wang, Y. Chen, Y. Gu, H.Li, Spintronic memristor temperature sensor, IEEE Electron Device Letters, Vol . 31, No . 1,January 2010. ‡
* Xiaobin Wang, Yiran Chen -‘Spintronic Memristor Devices and Application’, Design, Automation & Test in Europe Conference & Exhibition (DATE), 2010 , v.50,
no .1, p.5-23,January 2010. ‡
* R. Stanley Williams, How we found the missing memristor, IEEE Spectrum , December 2008, pp 25-31.
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