Giant Magneto Resistance-A key to modern data storage devices
In this article,I would like to highlight one of the very important physics principle which revolutionized the fabrication of hard-disk read-heads, magnetic field sensors and magnetic memory chips. Giant Magneto Resistance is the principle behind the enhancement of storage capacity and miniaturization of the size of the storage devices. This revolutionary idea was put forward by two independent research groups in the year 1988 by Albert Fert of France’s national research agency, CNRS, in Orsay, France and Peter Grunberg of Julich Research Centre in Germany. Soon afterwards ,researchers and engineers began their effort to implement the principle in read out heads. I transcended to a mystical state when I chance encountered to interact with Peter Grunberg. That memory really propelled me to write this article.
The GMR based hard-disk read-heads were released in the year 1997. Due to the incessant improvement of storage density, reduction of bit size, a good scalability and high sensitivity , now the GMR based devices have become indispensible in all realms of life. When we are glued to our computers for hors together playing video games or listening to music on i-pod, it is the outcome of we have directly benefitted from the efforts of the winners of the 2007 Nobel Prize in Physics. The maximum storage capacity in the modern computers is credited to the finding of GMR. The GMR effect elaborates us how an unforeseen scientific discovery could give rise to completely new technologies, new science and new profitable products.
Today’s high data storage is not possible without a detailed understanding of the physics of GMR, which requires a quantum-mechanical perspective into spin dynamics in magnetic thin films. Even before the discovery of GMR, scientific community knew that applying magnetic field to materials such as iron or nickel could influence the electrical conductivity. Electric current used to flow less readily equivalent to the direction in which the material was magnetized and more willingly across it. Technologists exploited the effect to make read heads which sense the setting of attracted bits in computer hard drive. But the effect known as anisotropic magnetoresistance was insufficient. The resistance changed by a limited percent. Both Grünberg and Fert found that they could significantly increase the change in resistance if they made layer-cake films with layers of iron detached by layers of nonmagnetic chromium only a few atoms thick. If two neighboring iron layers are magnetized in the same direction, then electrons spinning in one direction will pass along the film readily, whereas electrons spinning in the other direction will not. If, however, the iron layers are magnetized in opposite directions, then all electrons run into greater resistance, irrespective of how they are spinning. That makes a GMR film an enormously sensitive magnetic field detector. As a result, all the bits and hardware in a disk drive can be designed at a micro-miniscule size.
GMR based sensor is applied to observe the magnetization direction of the bits on the magnetic recording medium, which are logical 0 or 1. In a GMR based system ,very feeble magnetic variations give rise to large difference in electrical resistance ,making such system as a required tool for reading data from hard disks when information registered magnetically must be converted to electric current.
Mr. Stuart Parkin of IBM’s Almaden Research Center in San Jose, California invested two years in a lab in the early 1990s, trying to bargain a way to commercialize an odd magnetic effect of quantum mechanics. With the support of a research assistant, he was able to deploy the configuration of electronics to alter the magnetic state of tiny areas of a magnetic data storage disc, making it possible to store and retrieve information in a smaller amount of space. But sadly, Mr. Stuart Parkin who cultivated the GMR was not honored enough by the society.
In 2005 alone, the amount of data that could be stored by all the spin-valve-enabled hard drives sold equated all of the analog data available in the world at that time—roughly 100 exabytes. GMR also bargains the ability to improve signal to noise, increase resolution, or reduce the required field level for a given solution (smaller magnets, larger air gaps, etc.).
A huge rise in digital storage made is possible by giant magnetoresistance made consumer audio, video iPods and Google-style data centers, into a reality. This huge increase in storage capacity made possible the evolution of giant data centers in the “cloud.” Perhaps most importantly, the ability to store and access huge amounts of data in worldwide networks helped create the information-based world of today. The findings of GMR helped further for the evolution of spintronics which led to invent computer memory that holds information even after losing the power and microchips for performing the quantum computation.