The Nobel Prize in Physics 2007 （General）

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 the development 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 to take 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 for home use has soared to a terabyte (a thousand billion bytes).I
n actual fact, the ongoing
IT-revolution depends on an intricate interplay between fundamental scientific progress and
technical fine tuning. This is just what the Nobel Prize in Physics for the year 2007 is about.
Portable computers, music players, and powerful search engines, all require hard disks where
the information is very densely packed. Information on a hard disk is stored 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 the magnetic 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 1990s 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-out technology 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 long been known that the electric resistance of materials such as iron may be influenced
by a magnetic field. In 1857, 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 instead. This (anisotropic) magnetoresistance (MR) was the direct predecessor
to giant magnetoresistance as a standard technology in read-out heads. GMR took over
at a point when an even more sensitive technology had become necessary.
A prerequisite for the discovery of the GMR-effect was provided by the new possibilities of
producing fine layers of metals on the nanometre scale which started to develop in the 1970s.
A nanometre is a mere billionth of a meter, and nanotechnology is concerned with layers
consisting of only a few individual strata of atoms. Deep down at atomic level, matter behaves
differently and therefore nanometre-sized structures will often exhibit totally new material
properties. This is true not only for magnetism and electric conductivity, but also for properties
like strength or the chemical and optical qualities of a material. In this sense, the GMRtechnology
may also be regarded as one of the first major applications of the nanotechnology
that is now so popularin
a very diverse range of fields.