Wednesday, 20 August 2014
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New spin on computer memory

A new magnetic phenomenon may spell the end of having to wait for computers to boot up.

The application of 'displaced vortex states' - small magnetic circular movements of just a few thousandths of a millimetre - may expedite development of a new type of magnetic memory that is not erased when a computer is switched off.

A team of scientists from the Universitat Autònoma de Barcelona (UAB), in collaboration with colleagues from the US Argonne National Laboratory and the French laboratory Spintec, has for the first time produced microscopic magnetic states, known as "displaced vortex states", that will allow an increase in the size of Magnetic Random Access Memory (MRAM).

The use of MRAM would mean that computers do not have to load operating systems and other programs and would be ready to work almost instantaneously. SRAM and DRAM are currently used in computers, but they do not allow this. Although quick, they are volatile, being deleted when the computer is switched off. Flash memory, such as that used in digital cameras, is not deleted but is slow.

The "displaced vortex states", first observed by UAB researchers, are small circular movements of just a few thousandths of a millimetre that form in the tiny zones where the data is stored. Orientating these zones in specific directions saves the information on hard drives. The zones pointing upwards, for example, codify a 1, and those pointing downwards a 0. The smaller and more compact these zones are, the greater the capacity of the hard drive. But if they are too close together, the magnetic field created by one can affect the neighbouring zone and wipe the data. However, if the field is saved in a whirlpool form, in "vortex state", it does not leave the tiny zone to which it is confined and does not affect the neighbouring data, thus making it possible for a much larger hard drive capacity.

The scientists have achieved these "vortex states" on small, circular structures that are smaller than a micrometre (a thousandth of a millimetre) and combine layers of material with opposing magnetic properties - a layer of ferromagnetic material and a layer of antiferromagnetic material. What makes the configuration of the magnets observed by the UAB scientists new is that the vortex states are "displaced". Once the magnetic field is no longer applied, the eye of the whirlpool moves off-centre in relation to the circular structure on which it formed. This seemingly insignificant detail is the key to applying the technique to increasing the capacity not only of hard drives but also Magnetic Random Access Memories (MRAMs) that are fast, non-volatile, but until now with small storage capacity.

"The phenomenon observed could also be applied to other fields, such as improving the read heads of hard drives", said Jordi Sort, a UAB-ICREA physicist and the coordinator of the research. "But the reason that motivated us is even more fundamental: this is a very peculiar physical state that can be observed only in extremely small magnetic structures."

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