从2007年诺贝尔物理学奖看科学创新
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2007年诺贝尔物理学奖揭晓，法国科学家Albert Fert 和德国科学家Peter Gruenberg 因发现巨磁电阻效应而获此殊荣。

与往届的那些天体物理，量子物理等看起来很神秘的理论发现不同，今年的诺奖就在我们身边，你正用的电脑的硬盘就是基于这次得奖的发现：巨磁电阻效应。

所谓巨磁电阻效应 (Giant Magnetoresistance, or GMR) 并不是很神秘的东西。通俗地讲，在铁磁介质中，其电子的自旋状态不是均衡的，这种倾向于某一方向的自旋使其在磁场下被磁化。当电子通过铁磁介质时，只有那些自旋方向和介质电子自旋状态相同的电子才容易通过，所以当电流通过两层自旋方向相反的介质时，几乎所有电子都被滤掉，使电流强度大幅下降，这就是巨阻效应。

虽然不是开天辟地的理论发现，但27年前，当这一效应被Fert和Gruenburg发现以后还是立马引起了科学和工程界的重视。IBM获知这一发现以后，立刻组成了研究小组对巨阻现象进行研究。在他们看来，电阻的骤然变化实际上提供了一种构造高灵敏传感器的新途径，可以读出电脑硬盘上微小的磁信号变化。

Fert 和Gruenberg最初的实验是在低温强磁场环境下进行的，而所用材料也是实验室里一点点生成的，极为稀少和繁杂。IBM实验室的Parkin和同事们尝试用通常的磁介质材料进行实验，并很快获得成功；以后又在室温，常规磁场条件下做大量相关实验，最终获得突破性进展。他们几年下来的劳动成果是一块基于GMR的16.8G的硬盘存储器。此后，所有硬盘更新换代，GMR 成为主流。Parkin因其杰出的工作和格林贝格尔与费尔一道，获1997年Hewlett-Packard物理学家奖。10年以后，这项成就终于迎来了诺贝尔奖的加冕， Parkin虽然没有诺奖之名，想必也是心潮彭湃。

这段历史很鲜活地展现了一个实验结果是如何登上诺贝尔奖坛的，而这其中一个关键人物就是IBM的Parkin 。可以想象，如果没有Parkin 和他的同事们开创性的工作，也许那两位最初的发现者怕是要等更长时间才能拿到诺奖的奖金。正是这种科学家创造的热情，工程师对科学的敏感，大公司的高瞻远瞩，才成就了这段佳话，也成就了在电脑前读我这些文字的网友们。Fert 和 IBM 他们当然是在为自已的兴趣和利润而工作，又何尝不是在为全世界所有人在工作？

比较一下中国现在的科研环境，恐怕还有很多地方值得反思。IBM在其网站上有一句话很让人深思，"To IBM Research, 10 years = a revolution. ",十年等于一次革命。我想对于很多国内的研究机构，甚至IBM的中国研发机构，恐怕来不及等这次革命，早把一些半生不熟拼出的东西拿出去凑数了。竞争太激烈，一年不出点儿东西老板就会不满意了，人人都想挣面子分，人人都往短平快了搞，别说关注科学，怕是把IEEE的文章拿出来读一读的都算敬业的了。这么一个环境，又怎么可能做出创造性的成果，又怎么能指望拿世界的最高荣誉呢？

要想打鱼当然要先养鱼，鱼的成长是有一定周期的，如果在长成之前就把些半大的小鱼捞上来，不仅卖不了什么价钱，更失去了出大鱼的希望。而之所以这么多人喜欢捞小鱼，因为管鱼塘的本身不是养鱼的，他不懂也不关心鱼最终养成个么样，他只要见着鱼，向上面交差挣够了面子，就可去管养骆驼了。长此以往，中国怕是只能在小鱼小虾上做点儿文章了。

诺贝尔奖不是盼来的，不是等来的，更不是骂来的。只有真正营造出一个自由的学术环境，思想环境，这个国家才有可能走向世界的奖台。

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Science Daily: Discoverers Of Giant Magnetoresistance Used In Hard Drives Win 2007 Nobel Prize In Physics

Science Daily — The Royal Swedish Academy of Sciences has awarded the Nobel Prize in Physics for 2007 jointly to Albert Fert, of Unité Mixte de Physique CNRS/THALES, Université Paris-Sud, in Orsay, France, and Peter Grünberg, of Forschungszentrum Jülich in Germany for the discovery of giant magnetoresistance.

This year's physics prize is awarded for the technology that is used to read data on hard disks. It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. Sensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance.

In 1988 the Frenchman Albert Fert and the German Peter Grünberg each independently discovered a totally new physical effect – Giant Magnetoresistance or GMR. Very weak magnetic changes give rise to major differences in electrical resistance in a GMR system. A system of this kind is the perfect tool for reading data from hard disks when information registered magnetically has to be converted to electric current. Soon researchers and engineers began work to enable use of the effect in read-out heads. In 1997 the first read-out head based on the GMR effect was launched and this soon became the standard technology. Even the most recent read-out techniques of today are further developments of GMR.

A hard disk stores information, such as music, in the form of microscopically small areas magnetized in different directions. The information is retrieved by a read-out head that scans the disk and registers the magnetic changes. The smaller and more compact the hard disk, the smaller and weaker the individual magnetic areas. More sensitive read-out heads are therefore required if information has to be packed more densely on a hard disk. A read-out head based on the GMR effect can convert very small magnetic changes into differences in electrical resistance and there-fore into changes in the current emitted by the read-out head. The current is the signal from the read-out head and its different strengths represent ones and zeros.

The GMR effect was discovered thanks to new techniques developed during the 1970s to produce very thin layers of different materials. If GMR is to work, structures consisting of layers that are only a few atoms thick have to be produced. For this reason GMR can also be considered one of the first real applications of the promising field of nanotechnology.

Albert Fert is a French citizen. Born 1938 in Carcassonne, France, he received his Ph.D. in 1970 at Université Paris-Sud, Orsay, France. He is a professor at Université Paris-Sud, Orsay, France, since 1976, and scientific director of Unité mixte de physique CNRS/Thales, Orsay, France, since 1995.

Peter Grünberg is a German citizen. Born 1939 in Pilsen, he received his Ph.D. in 1969 at Technische Universit&>28;t Darmstadt, Germany. He is a professor at Institut für Festk&>46;rperforschung, Forschungszentrum Jülich, Germany, since 1972.

Note: This story has been adapted from material provided by Nobel Foundation.

IBM: The Giant Magnetoresistive Head: A giant leap for IBM Research

What is it?

The "giant magnetoresistive" (GMR) effect was discovered in the late 1980s by two European scientists working independently: Peter Gruenberg of the KFA research institute in Julich, Germany, and Albert Fert of the University of Paris-Sud . They saw very large resistance changes -- 6 percent and 50 percent, respectively -- in materials comprised of alternating very thin layers of various metallic elements. This discovery took the scientific community by surprise; physicists did not widely believe that such an effect was physically possible. These experiments were performed at low temperatures and in the presence of very high magnetic fields and used laboriously grown materials that cannot be mass-produced, but the magnitude of this discovery sent scientists around the world on a mission to see how they might be able to harness the power of the Giant Magnetoresistive effect.

IBM Research Arrives on the Scene

Stuart Parkin and two groups of colleagues at IBM's Almaden Research Center, San Jose, Calif, quickly recognized its potential, both as an important new scientific discovery in magnetic materials and one that might be used in sensors even more sensitive than MR heads.

Parkin first wanted to reproduce the Europeans' results. But he did not want to wait to use the expensive machine that could make multilayers in the same slow-and-perfect way that Gruenberg and Fert had. So Parkin and his colleague, Kevin P. Roche, tried a faster and less-precise process common in disk-drive manufacturing: sputtering. To their astonishment and delight, it worked! Parkin’s team saw GMR in the first multilayers they made. This demonstration meant that they could make enough variations of the multilayers to help discover how GMR worked, and it gave Almaden's Bruce Gurney and co-workers hope that a room-temperature, low-field version could work as a super-sensitive sensor for disk drives.

 

The Nitty Gritty

The key structure in GMR materials is a spacer layer of a non-magnetic metal between two magnetic metals. Magnetic materials tend to align themselves in the same direction. So if the spacer layer is thin enough, changing the orientation of one of the magnetic layers can cause the next one to align itself in the same direction. Increase the spacer layer thickness and you'd expect the strength of such "coupling" of the magnetic layers to decrease. But as Parkin's team made and tested some 30,000 different multilayer combinations of different elements and layer dimensions, they demonstrated the generality of GMR for all transition metal elements and invented the structures that still hold the world records for GMR at low temperature, room temperature and useful fields. In addition, they discovered oscillations in the coupling strength: the magnetic alignment of the magnetic layers periodically swung back and forth from being aligned in the same magnetic direction (parallel alignment) to being aligned in opposite magnetic directions (anti-parallel alignment). The overall resistance is relatively low when the layers were in parallel alignment and relatively high when in anti-parallel alignment. For his pioneering work in GMR, Parkin won the European Physical Society's prestigious 1997 Hewlett-Packard Europhysics Prize along with Gruenberg and Fert.

Searching for a useful disk-drive sensor design that would operate at low magnetic fields, Bruce Gurney and colleagues began focusing on the simplest possible arrangement: two magnetic layers separated by a spacer layer chosen to ensure that the coupling between magnetic layers was weak, unlike previously made structures. They also "pinned" in one direction the magnetic orientation of one layer by adding a fourth layer: a strong antiferromagnet. When a weak magnetic field, such as that from a bit on a hard disk, passes beneath such a structure, the magnetic orientation of the unpinned magnetic layer rotates relative to that of the pinned layer, generating a significant change in electrical resistance due to the GMR effect. This structure was named the spin valve.

To see an animation of how MR and GMR recording heads work, click here. Gurney and colleagues worked for several years to perfect the sensor design that is used in the new disk drives. The materials and their tiny dimensions had to be fine-tuned so they 1) could be manufactured reliably and economically, 2) yielded the uniform resistance changes required to detect bits on a disk accurately, and 3) were stable -- neither corroding nor degrading -- for the lifetime of the drive. "That's why it's so important to understand the science," Parkin says. "IBM's intensive studies of GMR enabled us to enhance considerably the performance of some low-field sensors."

The chief source of GMR is "spin-dependent" scattering of electrons. Electrical resistance is due to scattering of electrons within a material. By analogy, consider how fast it takes you to drive from one town to another. Without obstacles on a freeway, you can proceed quickly. But if you encounter heavy traffice, accidents, road construction and other obstacles, you'll travel much slower.

Depending on its magnetic direction, a single-domain magnetic material will scatter electrons with "up" or "down" spin differently. When the magnetic layers in GMR structures are aligned anti-parallel, the resistance is high because "up" electrons that are not scattered in one layer can be scattered in the other. When the layers are aligned in parallel, all of the "up" electrons will not scatter much, regardless of which layer they pass through, yielding a lower resistance.

For an animation showing how electrons of different spins scatter within a GMR structure, click here.

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One Step Beyond...

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