فرهنگستان سطنتي علوم سوئد جايزه نوبل
فيزيك 2007 را به دو فيزيكدان فرانسوي و آلماني اهدا كرد كه كشفياتشان
امكان مينياتوري كردن قطعات الكترونيكي را فراهم آورده و به اختراع
دستگاه هايي مانند رايانه هاي همراه و يا iPod انجاميده است.
به گزارش شبكه BBC ، آلبر فر ، فيزيكدان فرانسوي و پتر گرونبرگ،
فيزيكدان آلماني جايزه نوبل 2007 را به صورت مشترك و براي تحقيقاتي
دريافت مي كنند كه سال ها پيش و به صورت مستقل از يكديگر انجام داده و
منجر به دستاوردهاي نويني براي علم فيزيك شدند.
پتر گرونبرگ در سال در پيلسن ( پلزن امروزي در جمهوري چك) متولد شده
است. او در سال 1986 هنگامي كه در بخش فيزيك حالت جامد در انستيتوي
تحقيقاتي يوليخ در غرب آلمان به كار اشتغال داشت، به كشفياتي در زمينه
الكترومغناطيس رسيد كه دو سال بعد منجر شد او پديده اثر مقاومت بزرگ
مغناطيسي GMRرا كشف كند.
آلبر فر، فيزيكدان فرانسوي در سال 1938 در كاركاسون
متولد شده است. او نيز هم زمان با گرونبرگ در سال 1988 در دانشگاه
پاريس - جنوب در اورسي به شيوه ديگري پديده اثر مقاومت بزرگ مغناطيسي
GMRرا كشف كرد.
استفاده از اين پديده اين امكان را فراهم مي آورد كه داده هايي كه به
صورت مغناطيسي در ديسك هاي سخت CD ذخيره شده اند به سيگنال هايي
الكتريكي تبديل شوند كه براي رايانه ها قابل پردازش و فهم باشند.
به اين ترتيب امكان توليد قطعات مينياتوري در دستگاه هاي الكترونيكي و
رايانه اي فراهم آمد كه حاصل آن دستگاه هايي مانند رايانه هاي همراه و
يا «آي پاد» iPod است.
پتر گرونبرگ در زماني برنده جايزه فيزيك نوبل مي شود كه در دوران
بازنشستگي خود به سر مي برد اما آلبر فر همچنان در دانشگاه پاريس -
جنوب تدريس مي كند.
ا
رسال خبر : محمد
ميرزايي
منبع خبر : جام
جم آنلاين
نقل از هوپا
Nobel prize recognizes GMR pioneers
The 2007 Nobel Prize in Physics has been awarded jointly to Albert
Fert of the Université Paris-Sud in France and Peter Grünberg of the
Forschungszentrum Jülich in Germany "for the discovery of giant
magnetoresistance". Their discovery, which both physicists made
independently in 1988, led to a dramatic rise in the amount of data
that can be stored on computer hard-disk drives. Fert and Grünberg
share prize money totalling 10 million Swedish krone (about $1.5m).
Giant
magnetoresistance, or GMR, is the sudden change in electrical
resistance that occurs when a material consisting of alternating
ferromagnetic and non-magnetic metal layers is exposed to a
sufficiently high magnetic field. In particular, the resistance
becomes much lower if the magnetization in neighbouring layers is
parallel and much higher if it is antiparallel. This change in
resistance is due to "spin up" and "spin down" electrons scattering
differently in the individual layers.
Peter Grünberg
GMR has since been
used to develop extremely small and sensitive read heads for
magnetic hard-disk drives. These have allowed an individual data bit
to be stored in a much smaller area on a disk, boosting the storage
capacity greatly. The first commercial read heads based on GMR were
launched by IBM in 1997 and GMR is now a standard technology found
in nearly all computers worldwide and is also used in some digital
cameras and MP3 players.
Albert Fert
In Grünberg's
original work, he and his team studied an iron/chromium/iron
trilayer system that showed an decrease in resistance of 1.5%. Fert
and colleagues, in contrast, studied an iron/chromium multilayer
system in which the electrical resistance decreased by nearly 50%.
"These films
started out as being very esoteric, but it turned out that they
would have great practical importance," says Tony Bland, a physicist
from the University of Cambridge. "They paved the way for
substantial information densities of commercial disk drives. It also
paved the way for new physics, such as tunneling magnetoresistance
(TMR), spintronics and new sensor technology, for example
biosensors. The caveat is that GMR has already become old technology
and people are now interested in TMR for future technology."
TMR gives rise to a more pronounced resistance change in small
applied fields than is found in GMR devices.
Albert Fert was
born in 1938 in Carcassone, France, and received a PhD in physics in
from Université Paris-Sud, Orsay in France. He is now also
scientific director of CNRS/Thales Unité Mixte de Physique in Orsay.
Peter Grünberg was born in 1939 in Pilsen (now in Czech Republic)
and is a German citizen. He gained his PhD in physics from the
Technische Universität Darmstadt, Germany.
Grünberg, who holds
a patent on GMR, originally submitted his paper slightly
before Fert, although Fert's was
published first. "But whereas Fert was able to describe all the
underlying physics, Grünberg immediately saw the technological
importance," adds Bland.
Source: Physicsworld
'Ubiquitous' technology
Professor Ben Murdin of the University
of Surrey, UK, said giant magnetoresistance, or GMR, was the science
behind a ubiquitous technological device. "Without it you would not
be able to store more than one song on your iPod!" he explained.
"A computer hard-disk reader that uses
a GMR sensor is equivalent to a jet flying at a speed of 30,000
kmph, at a height of just one metre above the ground, and yet being
able to see and catalogue every single blade of grass it passes
over."
The breakthrough underpins how data is read from hard disks
GMR involves structures consisting of
very thin layers of different magnetic materials.
For this reason it can also be
considered "one of the first real applications of the promising
field of nanotechnology", the Royal Swedish Academy of Sciences said
in a statement.
"Applications of this phenomenon have
revolutionised techniques for retrieving data from hard disks," the
prize citation said. "The discovery also plays a major role in
various magnetic sensors as well as for the development of a new
generation of electronics."
Source: BBC
Giant magnetoresistance
Giant magnetoresistance (GMR)
is a quantum mechanical effect, a type of magnetoresistance effect,
observed in thin film structures composed of alternating
ferromagnetic and nonmagnetic metal layers.
The effect manifests itself as a
significant decrease in electrical resistance in the presence of a
magnetic field. In the absence of an applied magnetic field the
direction of magnetization of adjacent ferromagnetic layers is
antiparallel due to a weak anti-ferromagnetic coupling between
layers, and it decreases to a lower level of resistance when the
magnetization of the adjacent layers align due to an applied
external field. The spins of the electrons of the nonmagnetic metal
align parallel or antiparallel with an applied magnetic field in
equal numbers, and therefore suffer less magnetic scattering when
the magnetizations of the ferromagnetic layers are parallel.
The effect is exploited commercially by
manufacturers of hard disk drives. The 2007 Nobel Prize in physics
was awarded to Albert Fert and Peter Grünberg for the discovery of
GMR.
Founding results of Fert et
al.
Multilayer
GMR
Two or more ferromagnetic layers are
separated by a very thin (about 1 nm) non-ferromagnetic spacer (e.g.
Fe/Cr/Fe). At certain thicknesses the RKKY coupling between adjacent
ferromagnetic layers becomes antiferromagnetic, making it
energetically preferable for the magnetizations of adjacent layers
to align in anti-parallel. The electrical resistance of the device
is normally higher in the anti-parallel case and the difference can
reach more than 10% at room temperature. The interlayer spacing in
these devices typically corresponds to the second antiferromagnetic
peak in the AFM-FM oscillation in the RKKY coupling.
The GMR effect was first observed in
the multilayer configuration, with much early research into GMR
focusing on multilayer stacks of 10 or more layers.
Spin valve
GMR
Two ferromagnetic layers are separated
by a thin (about 3 nm) non-ferromagnetic spacer, but without RKKY
coupling. If the coercive fields of the two ferromagnetic electrodes
are different it is possible to switch them independently.
Therefore, parallel and anti-parallel alignment can be achieved, and
normally the resistance is again higher in the anti-parallel case.
This device is sometimes also called a spin valve.
Spin-valve GMR
Spin valve GMR is the configuration
that is industrially most useful, and is used in hard drives.
Granular GMR
Granular GMR is an effect that occurs
in solid precipitates of a magnetic material in a non-magnetic
matrix. In practice, granular GMR is only observed in matrices of
copper containing cobalt granules. The reason for this is that
copper and cobalt are immiscible, and so it is possible to create
the solid precipitate by rapidly cooling a molten mixture of copper
and cobalt. Granule sizes vary depending on the cooling rate and
amount of subsequent annealing. Granular GMR materials have not been
able to produce the high GMR ratios found in the multilayer
counterparts.
Source: Wikipedia
CPH Theory articles
