Nobel Prize in Physics 2007: Giant Magnetoresistance and Spintronics

This note covers the Nobel Prize in Physics 2007: who won it, what Giant Magnetoresistance (GMR) is and how it works, how the discovery of GMR unfolded, how it changed hard disk technology and gave rise to spintronics, and quick facts for exams.

What was the Nobel Prize in Physics 2007 awarded for?

The Royal Swedish Academy of Sciences awarded the prize jointly to Albert Fert and Peter Grünberg "for the discovery of Giant Magnetoresistance". This is the official citation, and it names a single phenomenon that both scientists found independently in 1988.

In plain words, Giant Magnetoresistance (GMR) is a situation where a very small change in a magnetic field produces a very large change in the electrical resistance of a specially built material.

Normal magnetic materials show only a tiny change in resistance when a magnetic field is applied, usually a few per cent at most.

Fert and Grünberg built thin, layered structures where this change became "giant" by comparison, sometimes tens of per cent. The official name of this award is the Nobel Prize in Physics, administered by the Royal Swedish Academy of Sciences.

Who are the laureates?

Albert Fert

Albert Fert was born on 7 March 1938 in Carcassonne, France. At the time of the award he was affiliated with Université Paris-Sud, Orsay, France, and with the Unité Mixte de Physique CNRS/THALES, Orsay, France, where he had been scientific director since 1995.

He received one half of the prize. According to the press release, Fert earned his doctorate in 1970 at Université Paris-Sud and became a professor there in 1976.

His group grew multilayer structures of iron and chromium, built up atom by atom, and observed a resistance change of up to 50 per cent when a magnetic field was applied.

The scientific background document notes that Fert's measurements were made at a very low temperature of 4.2 kelvin. He is credited with coining the term "Giant Magnetoresistance" in his first publication on the effect.

Peter Grünberg

Peter Grünberg was born on 18 May 1939 in Plzen, then Czechoslovakia (now the Czech Republic), and died on 9 April 2018 in Jülich, Germany.

At the time of the award he worked at the Forschungszentrum Jülich in Germany, where he had been a professor at the Institut für Festkörperforschung since 1972. He also received one half of the prize.

Grünberg's group used a simpler system of just two or three iron layers separated by chromium, and measured a smaller resistance change of up to 10 per cent.

The popular information page states that Grünberg also recognised the practical potential of the discovery straight away and filed a patent for it at the same time as writing his first scientific paper on the subject.

What problem were Fert and Grünberg trying to solve?

By the 1980s, scientists already knew that a magnetic field could change the electrical resistance of certain metals.

The British physicist Lord Kelvin had shown this as early as 1857: he found that the resistance of iron and nickel increased along the direction of magnetisation and decreased across it when a magnetic field was applied.

This effect, later called anisotropic magnetoresistance (AMR), was useful but weak, usually changing resistance by only a per cent or so.

The practical problem was how to read data from ever smaller hard disks. A hard disk stores information as tiny areas magnetised in different directions, and a read-out head scans the disk to detect these magnetic patterns and convert them into an electric signal.

As engineers tried to pack information more densely, each magnetised area became smaller and its magnetic field weaker. The old read-out technology, based on induction coils and later on AMR, could not keep up with this miniaturisation.

By the general consensus of the 1980s, it was thought that the performance of magnetic sensors based on magnetoresistance could not be significantly improved.

What made a new answer possible was a quite separate advance: new techniques developed from the 1970s onward for growing extremely thin layers of metal, only a few atoms thick.

This was an early form of what we now call nanotechnology. It was this capability, applied to magnetic materials, that let Fert and Grünberg build structures no one had been able to make before, and that is how they stumbled onto a far stronger effect than anyone expected.

Before this capability existed, researchers could not control the thickness of a material layer precisely enough to study what happens when magnetic and non-magnetic metals are stacked just a few atoms deep. Even before 1988, a few publications had reported small magnetoresistance effects of a few per cent in similarly thin layered films, but none of these observations had been recognised as a new effect.

How does Giant Magnetoresistance actually work?

To understand GMR, it helps to know that an electric current in a metal is carried by electrons, and that resistance arises when electrons scatter off irregularities in the material.

In a magnetic metal, electrons also carry a property called spin, which can point in one of two directions, and this spin affects how strongly an electron scatters.

In a magnetic material, most electron spins line up in the same direction as the overall magnetisation, while a smaller number point the opposite way.

According to the Scientific Background, electrons with spin opposite to the local magnetisation tend to scatter more than electrons with spin aligned to it, especially at the boundary between a magnetic and a non-magnetic layer.

A basic GMR structure is a sandwich: a thin non-magnetic metal layer placed between two thin magnetic metal layers. The behaviour depends on whether the two magnetic layers are magnetised in the same direction or in opposite directions:

1. Electrons travel through the first magnetic layer, where those with spin opposite to the local magnetisation scatter more and face higher resistance.
2. The electrons cross the non-magnetic middle layer, where, according to the sources, all electrons scatter about equally regardless of spin.
3. The electrons reach the second magnetic layer. If this layer is magnetised in the same direction as the first, electrons that scattered least before continue to scatter least, so overall resistance stays low.
4. If the second layer's magnetisation is flipped (opposite to the first), the electrons that passed through easily now face strong scattering, and the total resistance of the whole stack becomes high.

This means a weak external magnetic field, strong enough only to flip one magnetic layer's magnetisation, can switch the whole stack between a low-resistance and a high-resistance state, a far bigger effect than old-style AMR.

Draw three horizontal layers: a non-magnetic metal strip in the middle, with a magnetic metal layer above and below it.

In one version, draw both magnetic layers' arrows pointing the same way (label "low resistance"). In a second version below it, draw the two magnetic layers' arrows pointing opposite ways (label "high resistance").

Fert's group achieved this using around thirty alternating layers of iron and chromium, grown atom by atom in near-vacuum conditions. Grünberg's group used a far simpler trilayer of iron-chromium-iron. Both approaches revealed the same underlying physics, even though the size of the effect they measured differed considerably.

How was the effect produced and observed in the laboratory?

Making a GMR structure demands exceptional precision, because the magnetic and non-magnetic layers must each be only a few atoms thick, just a few nanometres. The press release explains that this was only possible because of new techniques for growing extremely thin films that had developed from the 1970s onward.

Although Fert measured a far larger effect, the popular information page makes clear that the underlying physics in both experiments was identical: a new kind of magnetoresistance, much stronger than anything seen before, caused by spin-dependent scattering of electrons at the interfaces between magnetic and non-magnetic layers.

Both laboratories also recognised immediately that this was something new rather than a minor variation on old magnetoresistance.

Fert named the effect "Giant Magnetoresistance" in his very first paper on it, while Grünberg also applied for a patent while he was writing up his results, showing he saw its commercial promise straight away.

The laboratory method used by both groups, called epitaxy, was careful and expensive, suited to research but not to mass manufacturing.

It was Stuart Parkin, a British scientist working in the United States, who later showed that the same GMR effect could be produced using a cheaper, simpler technique called sputtering, which made large-scale industrial production possible.

How did the discovery unfold?

Why does Giant Magnetoresistance matter?

The most direct impact of GMR has been on hard disk storage. A GMR read-out head can detect the very weak and tiny magnetic fields created by densely packed data on a compact hard disk, converting magnetic information into a readable electric current.

According to the press release, this technology made it possible to shrink hard disks radically, enabling compact storage in laptops and portable music players, and the popular information page notes that home storage capacities soared to the terabyte range.

GMR is also described in the sources as one of the earliest major uses of nanotechnology in practice, because the effect only exists when layers are built to a thickness of just a few atoms. Beyond hard disks, GMR structures are used more generally as magnetic sensors.

Perhaps the most far-reaching consequence is that GMR opened the door to spintronics, a new branch of electronics that exploits the electron's spin as well as its electric charge.

One descendant of GMR is Tunnelling Magnetoresistance (TMR), where electrons cross an extremely thin insulating layer using a quantum effect called tunnelling rather than passing through a non-magnetic metal.

TMR produces even bigger resistance changes and underlies newer read-out heads and a developing memory technology called MRAM (Magnetic Random Access Memory), which the popular information page describes as a possible universal memory combining the speed of working memory with the permanence of a hard disk.

The Scientific Background notes that this research area is an unusually clear example of fundamental science and new technology reinforcing each other, with thousands of scientists worldwide now working on related magnetoelectronic phenomena.

At the award ceremony, the presenting committee member said the discovery could reasonably be called "one prerequisite for the modern IT revolution", underlining how a laboratory curiosity in 1988 reshaped everyday consumer electronics within a decade. The Scientific Background and the popular information page both note that the discovery is an unusually clear case of fundamental science and engineering progress reinforcing one another, since nanometre-scale layer growth made GMR possible and GMR in turn pushed nanotechnology forward into new fields of research and industry.

How does this connect to what you study?

GMR connects directly to topics in electricity and magnetism taught in school physics: how a current is a flow of electrons, how resistance arises from scattering, and how magnetic fields interact with moving charges.

It is also a vivid example of how materials science, at the scale of individual atomic layers, can unlock entirely new physical effects not seen in bulk materials, a theme relevant to any introduction to nanotechnology.

Students who study the idea of electron spin in introductory quantum physics will recognise GMR as one of the clearest real-world demonstrations of why spin matters. Instead of treating the electron as simply a charged particle, GMR shows that its intrinsic spin direction changes how strongly it scatters inside a magnetic material, and this tiny quantum property becomes the basis of a large, measurable, everyday engineering effect used in computers.

The discovery is also a useful case study in how applied and fundamental science interact. The sources describe GMR as arising only once thin-film growth techniques from the 1970s made nanometre-scale layers possible, and then show how the new effect fed straight back into engineering, through sputtering methods and read-out heads, and onward into newer fields such as spintronics. This two-way relationship between pure research and practical technology is a theme that recurs across many areas of physics and chemistry taught at school level, from semiconductors to new battery materials, and GMR gives students a concrete, well-documented example of it rather than an abstract description.

Finally, anyone studying computer hardware or information technology at a basic level will meet the idea of a hard disk read-out head, and GMR explains, from first physics principles, how such a device actually senses the ones and zeros stored magnetically on a spinning disk.

Quick facts for exams

The Nobel Prize in Physics 2007 was awarded jointly to Albert Fert of France and Peter Grünberg of Germany for the discovery of Giant Magnetoresistance (GMR), an effect in which a weak magnetic field causes a large change in electrical resistance in specially layered materials.

The discovery was made independently by both scientists in 1988 and announced by the Royal Swedish Academy of Sciences on 9 October 2007.

GMR revolutionised hard disk read-out heads from 1997 onward, allowing disks to shrink dramatically, and it is considered one of the earliest practical uses of nanotechnology. The prize, worth 10 million Swedish kronor, was shared equally between the two laureates.

Note: Source. The prize facts in this note are from the Nobel Prize's official site, nobelprize.org.

Glossary

• Giant Magnetoresistance (GMR) — a large change in electrical resistance caused by a small change in an applied magnetic field, found in specially layered thin-film materials.
• Magnetoresistance — the change in a material's electrical resistance when it is placed in a magnetic field.
• Anisotropic Magnetoresistance (AMR) — the older, weaker form of magnetoresistance first described by Lord Kelvin in 1857, where resistance differs depending on the direction of the field relative to the current.
• Spin — a quantum property of the electron that behaves like a tiny magnetic direction, pointing either "up" or "down".
• Nanotechnology — techniques and science dealing with structures only a few nanometres (billionths of a metre) in size, often just a few atoms thick.
• Epitaxy — a laboratory method of growing thin material layers atom by atom on a surface.
• Sputtering — a simpler, industrial technique for depositing thin layers, shown by Stuart Parkin to be suitable for producing GMR materials at scale.
• Read-out head — the part of a hard disk drive that scans magnetised areas on the disk and converts them into an electric signal.
• Spintronics — a field of electronics that uses the electron's spin in addition to its electric charge.
• Tunnelling Magnetoresistance (TMR) — a related effect where electrons cross a thin insulating layer by quantum tunnelling, producing even larger resistance changes than GMR.
• MRAM — Magnetic Random Access Memory, a proposed fast and permanent computer memory based on TMR technology.
• Multilayer — a material built from alternating thin layers, such as iron and chromium, each only a few atoms thick.

Common errors and misconceptions

• Misconception: GMR and ordinary magnetoresistance are the same thing. Correct: GMR produces a far larger resistance change than the older anisotropic magnetoresistance first observed by Lord Kelvin.
• Misconception: Fert and Grünberg worked together on the discovery. Correct: they discovered GMR independently of each other in 1988, in separate laboratories.
• Misconception: GMR is only relevant to computer hard disks. Correct: GMR is also used in magnetic sensors generally and led to the wider field of spintronics.
• Misconception: both laureates measured the same size of effect. Correct: Fert's group measured a resistance change of up to 50 per cent while Grünberg's group measured up to 10 per cent, though the underlying physics was identical.
• Misconception: the thin layers used in GMR can be any thickness. Correct: the layers must be only a few nanometres, a few atoms thick, for the effect to appear.
• Misconception: GMR read-out heads were commercialised immediately after the 1988 discovery. Correct: the first commercial GMR-based read-out head was not launched until 1997.

Exam-style questions with model answers

Q1. For what discovery was the Nobel Prize in Physics 2007 awarded? [2 marks]

1. It was awarded for the discovery of Giant Magnetoresistance, an effect where a small magnetic field change causes a large change in electrical resistance.

Q2. Name the two laureates of the Nobel Prize in Physics 2007 and state their countries of affiliation at the time of the award. [2 marks]

1. Albert Fert, affiliated with Université Paris-Sud and CNRS/THALES in Orsay, France, and Peter Grünberg, affiliated with Forschungszentrum Jülich in Germany.

Q3. Explain, step by step, how a GMR sandwich structure produces different resistance depending on the magnetisation of its layers. [4 marks]

1. A GMR sandwich has a non-magnetic metal layer placed between two magnetic metal layers.
2. Electrons carry a spin, and in a magnetic layer, electrons with spin opposite to the local magnetisation scatter more and face higher resistance than those aligned with it.
3. If both magnetic layers are magnetised in the same direction, electrons that scatter least in the first layer continue to scatter least in the second, giving low overall resistance.
4. If the two magnetic layers are magnetised in opposite directions, electrons that passed through the first layer easily are scattered strongly in the second, giving high overall resistance; this is how a weak external field flips the structure between low- and high-resistance states.

Q4. Compare the experimental approaches of Fert's group and Grünberg's group in discovering GMR. [4 marks]

1. Fert's group built about thirty alternating layers of iron and chromium and measured their magnetoresistance at a very low temperature of 4.2 kelvin, observing a resistance change of up to 50 per cent.
2. Grünberg's group used a simpler trilayer of iron and chromium and made measurements at room temperature, observing a smaller resistance change of up to 10 per cent.
3. Despite the difference in the size of the effect and in experimental conditions, the underlying physics causing the resistance change was identical in both cases: spin-dependent scattering of electrons at magnetic and non-magnetic interfaces.
4. Both researchers recognised they had found a genuinely new phenomenon rather than a variant of existing magnetoresistance, with Fert naming it "Giant Magnetoresistance" and Grünberg promptly filing a patent.

Q5. Discuss why the discovery of Giant Magnetoresistance is considered important for both science and technology, with reference to how it unfolded from Lord Kelvin's observations to modern spintronics. [6 marks]

1. The story of GMR begins with Lord Kelvin's 1857 observation that a magnetic field changes the electrical resistance of iron and nickel, an effect later called anisotropic magnetoresistance, which remained weak for well over a century.
2. In the 1970s, new techniques for growing metal layers only a few atoms thick began to develop, creating, for the first time, the possibility of building artificial layered structures with properties unlike any bulk material.
3. Using these techniques, Albert Fert and Peter Grünberg independently discovered, in 1988, that carefully layered magnetic and non-magnetic metals could show a vastly larger resistance change than anything seen before, which they and others soon called Giant Magnetoresistance.
4. This discovery mattered scientifically because it revealed a genuinely new physical mechanism, spin-dependent electron scattering, and mattered technologically because, from 1997, it became the basis of standard read-out heads that let hard disks shrink dramatically while storing much more data.
5. GMR is described in the sources as one of the first major applications of nanotechnology, since the effect depends entirely on building layers at the nanometre scale.
6. The discovery also opened the door to spintronics, including Tunnelling Magnetoresistance and the proposed MRAM memory, showing how a single fundamental discovery can give rise to a whole new branch of technology over time.

Q6. Who demonstrated that GMR could be produced using sputtering, and why was this significant? [3 marks]

1. Stuart Parkin, a British physicist working in the United States, showed that the GMR effect could be achieved using sputtering, a much simpler technique than the epitaxy used by Fert and Grünberg.
2. This showed GMR did not depend on having very perfectly ordered layers.
3. This was significant because it meant GMR materials could be manufactured on an industrial scale rather than only in a research laboratory.

Q7. What is the difference between GMR and Tunnelling Magnetoresistance (TMR)? [3 marks]

1. In GMR, a non-magnetic metal layer separates two magnetic layers, and electrons pass through it directly while experiencing spin-dependent scattering.
2. In TMR, an electrically insulating layer separates the magnetic layers instead of a metal, and electrons cross it only through quantum tunnelling.
3. TMR can produce even larger resistance changes than GMR and underlies newer read-out heads and the developing MRAM memory technology.

Key takeaways

• Albert Fert and Peter Grünberg shared the 2007 Nobel Prize in Physics for independently discovering Giant Magnetoresistance in 1988.
• GMR is a large change in electrical resistance caused by a small change in an applied magnetic field, found in thin layered magnetic structures.
• The effect relies on spin-dependent scattering of electrons at interfaces between magnetic and non-magnetic layers.
• GMR could only be discovered once nanotechnology allowed scientists to grow layers just a few atoms thick.
• Fert measured a resistance change of up to 50 per cent at low temperature, while Grünberg measured up to 10 per cent.
• The first commercial GMR read-out head launched in 1997 and quickly became the standard for hard disk technology.
• Stuart Parkin made GMR industrially viable by showing it could be produced through sputtering rather than costly epitaxy.
• GMR opened the field of spintronics, including Tunnelling Magnetoresistance and the proposed MRAM memory.

Test yourself

What does GMR stand for?

GMR stands for Giant Magnetoresistance, a large change in electrical resistance caused by a small change in magnetic field.

When was the Nobel Prize in Physics 2007 announced?

It was announced on 9 October 2007 by the Royal Swedish Academy of Sciences.

Who first observed magnetoresistance, and when?

Lord Kelvin first observed magnetoresistance in iron and nickel in 1857, over a century before GMR was discovered.

What structure did Fert's group use to discover GMR?

Fert's group used about thirty alternating nanometre-thick layers of iron and chromium, grown atom by atom.

Where was Peter Grünberg affiliated at the time of the award?

Peter Grünberg was affiliated with Forschungszentrum Jülich in Germany at the time of the award.

What year did the first commercial GMR read-out head appear?

The first read-out head based on GMR was launched commercially in 1997 and soon became standard.

What field of electronics did GMR help to create?

GMR helped create spintronics, a field of electronics that exploits both the spin and the charge of electrons.

Who showed that GMR could be manufactured industrially?

Stuart Parkin showed GMR could be produced using sputtering, a simpler technique suitable for industrial-scale manufacturing.