Peter Grünberg

Giant-Magnetoresistance Effect (GMR)

Technical field
Computer technology
Jülich Research Centre
An advancement of its predecessor, magnetoresistive head technology, Giant-Magnetoresistance Effect (GMR) vastly increases the data volume stored per square inch of hard drive. The invention enabled an up to fifty-fold increase in the hard drive capacity of typical workstations.

Driving Into the New Millennium

In 1988, Professor Peter Grünberg made a discovery that would go on to set a new standard for next-generation hard drive storage. In fact, the impact of his invention is omnipresent today, affecting numerous areas of everyday life, from computer use to mobile entertainment.

Grünberg, to this day a leading physicist at the Jülich Research Centre in Germany, saw his patent published in 1994. Four years later he was awarded the German Future Prize for his invention, which has in no small way gone on to revolutionize data storage.

An advancement of its predecessor, magnetoresistive head technology, Grünberg’s Giant-Magnetoresistance Effect (GMR) vastly increased the data volume stored per square inch of hard drive. The invention enabled an up to fifty-fold increase in the hard drive capacity of typical workstations (from approximately 10 GB in 1997 to between 100 and 500 GB today).

But Grünberg’s invention also paved the way for the commercial production of hard drive video recorders and the ongoing development of MRAM, a technology that will enable computers to boot instantly.

The emergence of lightweight miniature hard drives also ushered in a new epoch for compact mobile devices, such as MP3 players and digital cameras. Take, for example, the pocket generation and the transformation of sales at Apple, manufacturer of the world’s best known MP3 player, the hard drive-based iPod. In Q1 of Apple’s 2006 fiscal year, the iPod generated revenues of $2.9 billion, a 51 percent share of the company’s total revenue.

So how does the underlying technology work? Data on a hard drive is layered onto hard drive platters and stored as a consecutive sequence of magnetised areas, each of which has one of two possible polarisations which constitute the smallest unit of digital data – the bit. The sequence of the polarisations on the rotating platter represents the data’s digital code, which is accessed by a read head, a process resembling a stylus playing a record on a record player. The read head works by measuring the voltage of the electric current induced by the bits. The easiest way to improve a hard drive’s storage capacity is to use smaller magnetised areas, but these have weaker field strengths and corresponding voltages which are more difficult for the read head to detect.

This is where GMR comes into play as an affordable new method for detecting even very small magnetic fields. With GMR, the read head consists of a sandwich of two ultra-thin ferromagnetic layers with a third non-ferromagnetic layer in the middle. When the first of the two magnetic layers comes into proximity with the bit on the platter, the pole of the magnet of the layer is realigned so that its polarisation is changed according to the polarisation of the bit.

Meanwhile, the second ferromagnetic layer is permanently magnetised and detects the magnetic field direction of the magnet in the other layer which is reading the bit. An electric current then passes through the two magnetic layers. When the two magnetic layers have the same magnetic field direction, resistance is low and voltage is high; when they have opposing magnetic field directions, resistance is high and voltage is low.

With previous technologies, smaller bits were unable to be read because the magnetic field was too weak for the read head to detect. GMR, however, enables the measurement of weaker magnetic fields and thus a decrease in the size of the magnetised area.

IBM became the first licensee of GMR in 1995 and launched its first product in 1997. This new technology caused the price of 1 MB memories to plummet, from 20 cents in 1997 to less than half a cent in 2001. During that same period, the global revenue for hard drives grew by 66 percent, from $126 million to $209 million.

Today more than 90 percent of all hard drive read heads are based on Grünberg’s discovery. However, this versatile technology has also been successfully used in devices other than hard drives, notably non-volatile memory chips and a variety of sensors ranging from ABS brake systems to currency handling applications and medical implants.


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