AIST Stories No1
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From AIST to the Innovative World6magnetoresistance (GMR) effect*5 in 1988 by Albert Fert of France and Peter Grünberg of Germany. The MR ratio in GMR has values of 5–15%, sufficient for practical applications. The high MR ratio means that the sensitivity when reading magnetic signals is high, so when GMR is employed in a magnetic head that reads data in an HDD, the density of data recording in the HDD can be raised. The development of devices using GMR was pursued internationally, and GMR heads capable of greatly increasing the recording density were commercialized in 1997. Fert and Grünberg were awarded the Nobel Prize in Physics in 2007.In 1995, Terunobu Miyazaki of Tohoku University and Jagadeesh Moodera of Massachusetts Institute of Technology separately discovered tunnel magnetoresistance (TMR) effect, which gives a high MR ratio, 20–70% at room temperature, by the use of a magnetic tunnel junction (MTJ)*6 in which an ultrathin layer of amorphous*7 aluminum oxide is used as an insulator (a tunnel barrier). This revolutionary achievement enabled further miniaturization of recording components, and in 2004 ultra-high density HDD magnetic heads (TMR heads) were commercialized. These increased the recording density of HDDs, leading to reductions in power consumption by greatly improving energy efficiency.This achievement also led to the realization of the world’s first non-volatile working memory (MRAM).World-beating results from individual researchUpon joining the Electrotechnical Laboratory (now AIST) in 1996, Shinji Yuasa was involved in the research and development of HDD magnetic heads and second-generation non-volatile memory using aluminum oxide (Al-O)-based MTJs. He soon felt that the Al-O-based MTJs had reached their limits.“At that time, the spread of information technology into society was progressing rapidly and there was a need for MTJs with higher MR ratios, and particularly for MR ratios of well over 100%. I thought that it would probably be impossible to achieve these by further development of conventional methods, and that using crystals rather than amorphous materials would be better.” In 2002, he applied to the “Sakigake” (PRESTO) program*8 of the Japan Science and Technology Agency (JST), a relatively small program that supports individual research. His proposal that stated a clear end product, achieving an ▲A laboratory tool that produces thin films with magnesium oxide. It started operation in 2003 and is still in use. The aluminum foil wrapped round the apparatus is a measure to prevent uneven baking when the apparatus heats up to 200°C and an ultra-high vacuum is created inside the chamber.*5 Giant magnetoresistance (GMR) effect: A phenomenon in which, when a current flows in a multilayer film of a ferromagnetic metal and a non-magnetic metal, the electrical resistance falls if the spins in the ferromagnetic layers are arranged in parallel, or increases if the spins are arranged in anti-parallel. *6 Magnetic tunnel junction (MTJ): A component that exhibits tunnel magnetoresistance (TMR) effect. An insulating layer (a tunnel barrier) with a thickness of no more than a few nm (1 nm=10–9 m) is sandwiched between two ferromagnetic metal layers.*7 Amorphous: An arrangement of the atoms or molecules structuring a

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