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The Nobel Prize in Physics 2007
This year’s Nobel Prize in Physics is awarded to ALBERT FERT and PETER GRÜNBERG for their discovery of Giant Magnetoresistance. Applications of this phenomenon have revolutionized techniques for retrieving data from hard disks. The discovery also plays a major role in various magnetic sensors as well as for thedevelopment of a new generation of electronics. The use of Giant Magnetoresistance can be regarded as one of the first major applications of nanotechnology.

Better read-out heads for pocket-size devices
Constantly diminishing electronics have become a matter of course in today’s IT-world. The yearly addition to the market of ever more powerful and lighter computers is something we have all started totake for granted. In particular, hard disks have shrunk – the bulky box under your desk will soon be history when the same amount of data can just as easily be stored in a slender laptop. And with a music player in the pocket of each and everyone, few still stop to think about how many cds’ worth of music its tiny hard disk can actually hold. Recently, the maximum storage capacity of hard disks forhome use has soared to a terabyte (a thousand billion bytes).

Areal density (gigabits/cm 2 ) 100 10 1 0.1 0.01 0.001 1980 MR GMR

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Diagrams showing the accelerating pace of miniaturization might give a false impression of simplicity – as if this development followed a law of nature. In actual fact, the ongoing IT-revolution depends on an intricate interplaybetween fundamental scientific progress and technical fine tuning. This is just what the Nobel Prize in Physics for the year 2007 is about.

The Nobel Prize in Physics 2007 • The Royal Swedish Academy of Sciences • www.kva.se

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Portable computers, music players, and powerful search engines, all require hard disks where the information is very densely packed. Information on a hard disk isstored in the form of differently magnetized areas. A certain direction of magnetization corresponds to the binary zero, and another direction corresponds to the binary value of one. In order to access the information, a read-out head scans the hard disk and registers the different fields of magnetization. When hard disks become smaller, each magnetic area must also shrink. This means that themagnetic field of each bite becomes weaker and harder to read. A more tightly packed hard disk thus requires a more sensitive read-out technique. Towards the end of the 990s a totally new technology became standard in the read-out heads of hard disks. This is of crucial importance to the accelerating trend of hard disk miniaturization which we have seen in the last few years. Today’s read-outtechnology is based on a physical effect that this year’s two Nobel Laureates in Physics first observed almost twenty years ago. The Frenchman Albert Fert and the German Peter Grünberg, simultaneously and independently, discovered what is called Giant Magnetoresistance, GMR. It is for this discovery that the two now share the Nobel Prize in Physics.

From Lord Kelvin to nanotechnology
Originally,induction coils where used in read-out heads, exploiting the fact that a changing magnetic field induces a current through an electric coil. Even though this technology has not been able to keep pace with the demands of shrinking hard disks, induction coils are still in use for writing information onto the disk. For the read-out function, however, magnetoresistance soon proved better suited. It has longbeen known that the electric resistance of materials such as iron may be influenced by a magnetic field. In 857, the British physicist Lord Kelvin had already published an article showing that the resistance diminishes along the lines of magnetization when a magnetic field is applied to a magnetic conductor. If the magnetic field is applied across the conductor the resistance increases...