tag:theconversation.com,2011:/us/topics/electron-spin-6008/articleselectron spin – The Conversation2016-10-26T18:02:15Ztag:theconversation.com,2011:article/676852016-10-26T18:02:15Z2016-10-26T18:02:15ZTurning diamonds’ defects into long-term 3-D data storage<figure><img src="https://images.theconversation.com/files/143343/original/image-20161026-11275-1ilzlvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Diamonds are a data storers' best friend?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-132329216/stock-photo-3d-abstract-crystal-clear-background-texture.html">Diamond image via www.shutterstock.com</a></span></figcaption></figure><p>With the amount of data storage required for our daily lives growing and growing, and currently available technology being almost saturated, we’re in desparate need of a new method of data storage. The standard magnetic hard disk drive (HDD) – like what’s probably in your laptop computer – has reached its limit, holding a maximum of a few terabytes. Standard optical disk technologies, like compact disc (CD), digital video disc (DVD) and Blu-ray disc, are restricted by their two-dimensional nature – they just store data in one plane – and also by a physical law called the diffraction limit, based on the wavelength of light, that constrains our ability to focus light to a very small volume. </p>
<p>And then there’s the lifetime of the memory itself to consider. HDDs, as we’ve all experienced in our personal lives, may last only a few years before things start to behave strangely or just fail outright. DVDs and similar media are advertised as having a storage lifetime of hundreds of years. In practice this may be cut down to a few decades, assuming the disk is not rewritable. Rewritable disks degrade on each rewrite.</p>
<p>Without better solutions, we face financial and technological catastrophes as our current storage media reach their limits. How can we store large amounts of data in a way that’s secure for a long time and can be reused or recycled?</p>
<p>In our lab, we’re experimenting with a perhaps unexpected memory material you may even be wearing on your ring finger right now: diamond. On the atomic level, these crystals are extremely orderly – but sometimes defects arise. <a href="http://doi.org/10.1126/sciadv.1600911">We’re exploiting these defects as a possible way to store information</a> in three dimensions.</p>
<h2>Focusing on tiny defects</h2>
<p>One approach to improving data storage has been to continue in the direction of optical memory, but extend it to multiple dimensions. Instead of writing the data to a surface, write it to a volume; make your bits three-dimensional. The data are still limited by the physical inability to focus light to a very small space, but you now have access to an additional dimension in which to store the data. Some methods also polarize the light, giving you even more dimensions for data storage. However, most of these methods are not rewritable.</p>
<p>Here’s where the diamonds come in. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=588&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=588&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=588&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=739&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=739&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143325/original/image-20161026-11256-1xuba6g.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=739&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The orderly structure of a diamond, but with a vacancy and a nitrogen replacing two of the carbon atoms.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Diamond_Structure.png">Zas2000</a></span>
</figcaption>
</figure>
<p>A diamond is supposed to be a pure well-ordered array of carbon atoms. Under an electron microscope it usually looks like a neatly arranged three-dimensional lattice. But occasionally there is a break in the order and a carbon atom is missing. This is what is known as a vacancy. Even further tainting the diamond, sometimes a nitrogen atom will take the place of a carbon atom. When a vacancy and a nitrogen atom are next to each other, the composite defect is called a nitrogen vacancy, or NV, center. These types of defects are always present to some degree, even in natural diamonds. In large concentrations, NV centers can impart a characteristic red color to the diamond that contains them.</p>
<p>This defect is having a huge impact in physics and chemistry right now. Researchers have used it to detect the <a href="http://doi.org/10.1126/science.aaa2253">unique nuclear magnetic resonance</a> signatures of <a href="http://doi.org/10.1126/science.aad8022">single proteins</a> and are probing it in a variety of <a href="http://doi.org/10.1038/nature15759">cutting-edge quantum mechanical experiments</a>.</p>
<p>Nitrogen vacancy centers have a tendency to trap electrons, but the electron can also be forced out of the defect by a laser pulse. For many researchers, the defects are interesting only when they’re holding on to electrons. So for them, the fact that the defects can release the electrons, too, is a problem.</p>
<p>But in our lab, we instead look at these nitrogen vacancy centers as a potential benefit. We think of each one as a nanoscopic “bit.” If the defect has an extra electron, the bit is a one. If it doesn’t have an extra electron, the bit is a zero. This electron yes/no, on/off, one/zero property opens the door for turning the NV center’s charge state into the basis for using diamonds as a long-term storage medium.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=747&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=747&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143342/original/image-20161026-11278-1qkd21l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=747&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Starting from a blank ensemble of NV centers in a diamond (1), information can be written (2), erased (3), and rewritten (4).</span>
<span class="attribution"><span class="source">Siddharth Dhomkar and Carlos A. Meriles</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Turning the defect into a benefit</h2>
<p>Previous experiments with this defect have demonstrated some properties that make diamond a good candidate for a memory platform.</p>
<p>First, researchers can selectively change the charge state of an individual defect <a href="http://doi.org/10.1088/1367-2630/15/1/013064">so it either holds an electron or not</a>. We’ve used a green laser pulse to assist in trapping an electron and a high-power red laser pulse to eject an electron from the defect. A low-power red laser pulse can help check if an electron is trapped or not. If left completely in the dark, the defects maintain their charged/discharged status virtually forever. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143340/original/image-20161026-11239-6taoxb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The NV centers can encode data on various levels.</span>
<span class="attribution"><span class="source">Siddharth Dhomkar and Carlos A. Meriles</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our method is still diffraction limited, but is 3-D in the sense that we can charge and discharge the defects at any point inside of the diamond. We also present a sort of fourth dimension. Since the defects are so small and our laser is diffraction limited, we are technically charging and discharging many defects in a single pulse. By varying the duration of the laser pulse in a single region we can control the number of charged NV centers and consequently encode multiple bits of information.</p>
<p>Though one could use natural diamonds for these applications, we use artificially lab-grown diamonds. That way we can efficiently control the concentration of nitrogen vacancy centers in the diamond.</p>
<p>All these improvements add up to about 100 times enhancement in terms of bit density relative to the current DVD technology. That means we can encode all the information from a DVD into a diamond that takes up about one percent of the space.</p>
<h2>Past just charge, to spin as well</h2>
<p>If we could get beyond the diffraction limit of light, we could improve storage capacities even further. We have one novel proposal on this front.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143327/original/image-20161026-32322-lvaitv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A human cell, imaged on the right with super-resolution microscope.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/zeissmicro/9132340803/">Dr. Muthugapatti Kandasamy</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Nitrogen vacancy centers have also been used in the execution of what is <a href="http://doi.org/10.1038/NPHOTON.2009.2">called super-resolution microscopy</a> to image things that are much smaller than the wavelength of light. However, since the super-resolution technique works on the same principles of charging and discharging the defect, it will cause unintentional alteration in the pattern that one wants to encode. Therefore, we won’t be able to use it as it is for memory storage application and we’d need to back up the already written data somehow during a read or write step.</p>
<p>Here we propose the idea of what we call charge-to-spin conversion; we temporarily encode the charge state of the defect in the spin state of the defect’s host nitrogen nucleus. Spin is a fundamental property of any elementary particle; it’s similar to its charge, and can be imagined as having a very tiny magnet permanently attached it.</p>
<p>While the charges are being adjusted to read/write the information as desired, the previously written information is well protected in the nitrogen spin state. Once the charges have encoded, the information can be back converted from the nitrogen spin to the charge state through another mechanism which we call spin-to-charge conversion.</p>
<p>With these advanced protocols, the storage capacity of a diamond would surpass what existing technologies can achieve. This is just a beginning, but these initial results provide us a potential way of storing huge amount of data in a brand new way. We’re looking forward to transform this beautiful quirk of physics into a vastly useful technology.</p><img src="https://counter.theconversation.com/content/67685/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Support for this work was provided by National Science Foundation.</span></em></p><p class="fine-print"><em><span>The research is funded by the National Science Foundation</span></em></p>With current modes up against their limits, we need new data storage solutions. Tiny defects in diamonds’ atomic structure might turn them into a new medium for memory.Siddharth Dhomkar, Postdoctoral Associate in Physics, City College of New YorkJacob Henshaw, Teaching Assistant in Physics, City College of New YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/580062016-04-29T10:06:06Z2016-04-29T10:06:06ZA new state of matter: quantum spin liquids explained<figure><img src="https://images.theconversation.com/files/120548/original/image-20160428-28040-ojld52.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Spin, liquid – just add quantum.</span> <span class="attribution"><span class="source">Panom Pensawang/shutterstock.com</span></span></figcaption></figure><p>Magnetism is one of the oldest recognised material properties. Known since antiquity, records from the 3rd century BC describe how <a href="http://www.oceannavigator.com/January-February-2003/Lodestone-and-needle-the-rise-of-the-magnetic-compass/">lodestone</a>, a naturally occurring magnetised ore of iron, was used in primitive magnetic compasses. Today, thanks to the theory of quantum mechanics we now understand the nature of magnetism, too, with the concept of spin explaining the behaviour of elementary particles such as electrons in the material that make it magnetic.</p>
<p>Spin, a property of sub-atomic particles such as electrons and quarks, makes each individual electron behave as if it were a tiny magnetic compass needle. The millions or billions of electron spins in a piece of material interact with each other in various ways and stabilise to form the different possible magnetic states found in solid matter. Taken together in such large numbers, the spin of the material’s electrons grants the same magnetic properties to the material itself.</p>
<p>Magnetism is essential for the basic trappings of modernity: magnetic materials form the basis of modern electronics and information storage. With this in mind, scientists have pursued the discovery of materials with entirely new magnetic behaviours or new states of matter with unprecedented and potentially beneficial properties. </p>
<p>One is that of a <a href="http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Quantum%20Spin%20Liquids">quantum spin liquid</a>, first proposed by the Nobel Prize-winning theoretical physicist PW Anderson in the early 1970s. In a paper published in the journal Nature Materials, a research team led by Professor Stephen Nagler at the Oak Ridge National Laboratory in the US has <a href="http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4604.html">demonstrated the quantum spin liquid nature</a> of the magnetic material ruthenium trichloride (α-RuCl₃).</p>
<h2>How do quantum spin liquids form?</h2>
<p>Quantum spin liquids are frequently found in a class of materials known as <a href="http://phys.org/news/2015-04-frustrated-magnets-reveals-clues-discontent.html">frustrated magnets</a>. In a conventional magnet, the interactions between spins result in stable formations, known as their <a href="http://www.britannica.com/science/long-range-order">long-range order</a>, in which the magnetic directions of each individual electron is aligned.</p>
<p>In a frustrated magnet, the arrangement of electron spins prevents them from forming an ordered alignment, and so they collapse into a fluctuating, liquid-like state. In a true quantum spin liquid, the electron spins never align, and continue to fluctuate even at the very lowest temperatures of absolute zero, at which the spins in other magnetic states of matter would have already frozen.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/120520/original/image-20160428-28044-1rvjot9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Herbertsmithite, a candidate quantum spin liquid source.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Herbertsmithite-herb03a.jpg">Rob Lavinsky/iRocks.com</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The conditions required for a quantum spin liquid to form are often found in nature. The most famous example is the copper-based mineral <a href="http://www.mindat.org/min-26600.html">Herbertsmithite</a>, for which there is significant evidence to suggest that a quantum spin liquid state exists within the frustrated magnetic layers of copper ions that make up its structure. </p>
<h2>Where do we find quantum spin liquids?</h2>
<p>A challenge for scientists is to recreate the conditions required to synthetically grow candidate quantum spin liquid materials in the laboratory to allow for a complete understanding of their properties.</p>
<p>Quantum spin liquids’ evasive character make it notoriously difficult to confirm their existence and pinpoint their exact nature. The presence of a quantum spin liquid can be inferred from a lack of alignment of electron spins, but definitive confirmation is tricky: absence of evidence is not evidence of absence, as the adage goes. A more sophisticated approach is to uncover the more distinctive and unique characteristics of the quantum spin liquid to allow for a positive confirmation.</p>
<p>This is why Nagler’s study is particularly noteworthy. In experiments using <a href="http://www.spectroscopyonline.com/neutron-spectroscopy">neutron spectroscopy</a>, the team revealed that α-RuCl₃ realises something extremely close to a special flavour of quantum spin liquid called a <a href="http://www.esrf.eu/home/news/spotlight/content-news/spotlight/spotlight236.html">Kitaev spin liquid</a>. A prerequisite for this particular quantum spin liquid state is that the spins of the magnetic ruthenium ions form a frustrated honeycomb network: a layered, two-dimensional hexagonal structure, similar to that assumed by carbon atoms in graphite.</p>
<p>In their experiment, a beam of neutron particles created by a particle accelerator was scattered from the sample of α-RuCl₃ transferring energy between the neutrons and the sample in the process. This energy transfer was quantified by a set of detectors surrounding the sample, and the response observed fits that described by the theory developed for the Kitaev quantum spin liquid in particular.</p>
<h2>What can we do with quantum spin liquids?</h2>
<p>We now recognise that the quantum spin liquid comes in several different varieties with subtly different properties, but that they all share the ability to support peculiar quantum mechanical phenomena. This is exciting, and not just from a purely scientific perspective: these states could be used in the development of quantum computers and other transformative quantum technologies that are expected to provide revolutionary changes to how we process and store data throughout the 21st century. </p>
<p>In the age of quantum computing, we will be able to perform calculations that are currently unsolvable on even the most powerful supercomputers of today. This will allow for breakthroughs in a vast array of fields in which we are tackling some of the biggest challenges of our time, from drug discovery to the design of smarter materials for a whole host of applications. As we discover more candidate quantum state liquid materials and better understand their behaviour, we will unravel ever more exotic physics and discover ways to manipulate and control this novel state of matter to our advantage.</p><img src="https://counter.theconversation.com/content/58006/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucy Clark receives funding from The Leverhulme Trust. </span></em></p>Here’s how they could revolutionise science.Lucy Clark, Research Fellow, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/458642015-09-02T05:35:34Z2015-09-02T05:35:34ZShift from electronics to spintronics opens up possibilities of faster data<figure><img src="https://images.theconversation.com/files/93345/original/image-20150828-19943-1q97o15.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/levoodoo/3979665458">levoodoo</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Electronics is based on measuring the tiny electrical charge of electrons passing through electronic circuits. An alternative approach under development is spintronics, which instead relies not on electrons’ charge, but on another of their fundamental quantum-mechanical properties: <a href="http://www.nature.com/milestones/milespin/index.html">spin</a>. </p>
<p>Spin can be visualised as the Earth turning on its own axis while rotating around the sun. In the same way, an electron spins on its own axis while rotating around an atom’s nucleus. Spin is either “up” or “down”. In the same way traditional electronics uses charge to represent information as zeros and ones, the two spin states can be used to represent the same binary data in spintronics. </p>
<p>Spin can be measured because it generates tiny magnetic fields. Ferrous metals such as iron become magnetic, for example, when enough particles have their spin set in the same direction, generating a magnetic field of the same polarity as the spin.</p>
<p>Spintronics has <a href="http://www.ias.ac.in/meetings/myrmeet/pjm1_talks/bipulpal/bipulpal.pdf">several advantages over conventional electronics</a>. Electronics require specialised semiconductor materials in order to control the flow of charge through the transistors. But spin can be measured very simply in common metals such as copper or aluminium. Less energy is needed to change spin than to generate a current to maintain electron charges in a device, so spintronics devices use less power. </p>
<p>Spin states can be set quickly, which makes transferring data quicker. And because electron spin is not energy-dependent, spin is non-volatile – information sent using spin remains fixed even after loss of power.</p>
<h2>Upgrading hard disks using spin</h2>
<p>The first application of spintronics to computers saw Professors Albert Fert and Peter Grünberg awarded the <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2007/">2007 Nobel Prize in Physics</a> for their discovery of <a href="http://www.research.ibm.com/research/gmr.html">giant magnetoresistance</a> (GMR). They realised it was possible to use electron spin to increase the rate at which information could be read from a hard disk drive and developed ground-breaking technology to harness this feature. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93353/original/image-20150828-19946-u6xs0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A hard drive, showing circular platters and read/write head mounted at the tip of the arm.</span>
<span class="attribution"><span class="source">drive by mike mols/shutterstock.com</span></span>
</figcaption>
</figure>
<p>A hard disk drive stores data as ones and zeros encoded magnetically on rotating disk platters within the drive. The magnetic field is generated when electrons flow through wire coils mounted in the drive write heads which move across the face of the platters, changing the alignment of the magneto-sensitive particles on the platter surface. Reversing the electron flow reverses the field; the two directions represent one and zero. To read from the disk the process works in reverse.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=545&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=545&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=545&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=684&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=684&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93203/original/image-20150827-326-1g24luk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=684&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A hard disk drive read/write head.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/amagill/89623319/">amagill</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>A GMR drive head consists of two ferromagnetic layers, one with a fixed magnetic field direction and the other free to align with the magnetic field encoded on the disk, with a non-magnetic layer sandwiched in between. </p>
<p>When an electron passes through a magnetic field its spin state may change, known as scattering. Where electrons have random, scattered spin states this creates greater resistance to electric current.
By aligning electrons’ spin state to that of the magnetic field in the layers of the drive head, GMR technology dramatically reduces resistance, speeding up data transfer. First <a href="http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/spintronics/">introduced by IBM in 1997</a>, GMR technology has led to faster and higher-density drives than was previously possible.</p>
<h2>Putting a fresh spin on memory</h2>
<p>Spintronics researchers have since been working on introducing the same technology to computer memory, aiming to replace electric current-based dynamic random access memory (DRAM) with magnetic RAM (MRAM). The first commercial product by <a href="https://www.everspin.com/">Everspin</a> has been used in Airbus aircraft and BMW motorbikes due to its reliability under heat stress or cosmic-ray exposure – something that affects aircraft cruising at high altitudes. </p>
<p>MRAM exploits the same spin-based magnetic field approach, but uses a magnetoresistance cell to store data rather than a spinning disk platter as in a hard drive. While it is not as fast as DRAM, magnetic cells are able to maintain their stored spin orientations, and so the data they represent, without power. MRAM is likely to replace commonly used flash memory such as SD cards and compact flash first, as it is faster and doesn’t suffer from flash memory’s limited lifespan.</p>
<p>Other manufacturers such as Intel, Qualcomm, Toshiba and Samsung are developing MRAM to use as processor cache memory, where by virtue of their smaller size MRAM chips of greater capacity can be incorporated into smaller packages that will be faster, and use <a href="http://www.mram-info.com/toshiba-shows-new-stt-mram-test-chip-consumes-about-80-less-power-sram-memory">up to 80% less power</a> than current cache memory.</p>
<p>As electronics approaches the limits of silicon, spintronic components will play an important role in ensuring we enjoy steady performance gains, and faster, higher-capacity storage at lower power and cost.</p><img src="https://counter.theconversation.com/content/45864/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Atsufumi Hirohata receives funding from EPSRC (EP/I000933/1, EP/K03278X/1 and EP/M02458X/1), Royal Society Industry Fellowship and EU FP-7 (NMP3-SL-2013-604398).</span></em></p>When silicon circuits shrink too small to handle electrons, the future of electronics is spintronics.Atsufumi Hirohata, Professor in Nanoelectronics, University of YorkLicensed as Creative Commons – attribution, no derivatives.