We explore the world of giant magnetoresistance and spintronics with a pioneer researcher.
By TAN KIT HOONG email@example.com
Imagine sitting on a merry-go-round moving at great speed — faster even than real merry-go-rounds can go — and then imagine trying make out every detail of your surroundings, including being able to count every pebble on the ground.
This is essentially what a modern hard disk drive does as each magnetic platter spins at up to 10,000rpm (revolutions-per-minute) while a tiny head on an actuator arm reads and writes the magnetic equivalent of ones and zeroes.
Frankly, it’s mind-boggling and it’s partly thanks to the work of Nobel Prize laureate Professor Albert Fert that modern hard disk drives are able to store and read gigabytes of data packed into a relatively small 3.5in platter.
In.Tech had the opportunity to sit down for a lecture and Q&A session with Fert, who was invited to speak at University Malaya on his work in the field of “spintronics.”
Fert shares the 2007 Nobel Prize in Physics with Peter Grünberg for discovering the giant magnetoresistance (GMR) effect, utilised in modern hard disk drive read/write heads which has consequently made larger capacity hard disk drives possible.
GMR was discovered in 1988 by Fert and Grünberg simultaneously and independently of each other, and essentially deals with how electrical resistance changes when adjacent ferromagnetic layers separated by thin non-ferromagnetic barriers are magnetised in parallel or non-parallel alignments.
It is the GMR (and later, TMR or Tunnel Magnetoresistance) effect which has allowed hard disk drive heads to sense the minute changes in magnetism on a modern high-capacity hard disk platter.
Fert’s work has also led to the emerging technology dubbed spintronics which grew out of his research in GMR, and exploits the intrinsic spin of electrons and the ability to manipulate the spin using a magnetic field.
Manipulating the spin of electrons is a departure from traditional electronics, which deals with manipulating the charge in electrons.
According to Fert, spintronics is one of the technologies that could help move the electronics world currently dominated by semiconductors based on CMOS (complementary metal-oxide semiconductor) to something beyond CMOS.
“It’s well-known that in 10 years or so, conventional semiconductor technology will have reached its physical limits. Perhaps spintronics could help bridge the gap between current semiconductor technology and the technology beyond CMOS,” Fert told In.Tech.
Current CPU technology, for example, is commonly made up of a logic unit (which is the brain of the processor) and some form of memory unit which is used for the processor’s temporary storage.
Today, both CPU and memory units are based on current semiconductor technology but according to Fert, work is already underway by various technology companies to replace the memory unit with one based on STT-RAM (Spin Torque Transfer Random Access Memory) — a form of memory based on TMR.
The main advantage of STT-RAM is that it’s non-volatile memory, i.e. it stores information even when there is no power (much like Flash memory today), but has a read-and-write speed that’s as fast as volatile memory, like that of SDRAM used in computers now.
According to Fert, STT-RAM is still about two or three years away from going commercial and it will revolutionise storage as we know it.
Because of its speed and non-volatile nature, STT-RAM has the potential to replace not only SDRAM but also non-volatile storage like SD cards and the like, and eventually even hard disk drives.
“With STT-RAM, we could have computers that can be completely shut down and then started up instantly, while saving energy by a factor of two (due to the non-volatile nature of the RAM),” said Fert.
In the past, the future
The road to the Nobel prize has been a long and storied one for Fert, and becoming a physicist was not his first choice when considering a career.
“I was good in mathematics and physics, but my feeling was that everything had already been found. I was not so attracted to physics at first, as I didn’t think there was anything new to discover.
“However, I began to be really attracted to it when I did my PhD and after doing experiments in a lab I realised that there are many new discoveries yet to be made,” he said.
The interesting thing about Fert’s GMR discovery is that when he first started research on it, his theories could not have been effectively tested until modern technology had caught up.
The problem was that to properly test the GMR effect requires depositing layers of ferromagnetic material and non-ferromagnetic layers just a few nanometres in thickness, and the technology to do that did not exist until years after he formed his theories.
In that interim period, Fert worked on research in other areas and when the technology finally caught up some 15 years later, he resumed his research into GMR.
As for spintronics, that technology is on an upspin, so to speak, because there is a lot of research going on right now on how spintronics can be applied to carbon nanotubes and nanowires.
Currently, Fert is working on research into spin transfer oscillators, which could have an application in the telecommunications industry because such oscillators can help make a highly-tunable radio-frequency emitter. But that’s a story for another time.
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