Physicists measure current-induced torque in nonvolatile magnetic memory devices

Mar 09, 2011
The geometry of a magnetic tunnel junction.

(PhysOrg.com) -- Tomorrow's nonvolatile memory devices – computer memory that can retain stored information even when not powered – will profoundly change electronics, and Cornell University researchers have discovered a new way of measuring and optimizing their performance.

Using a very fast oscilloscope, researchers led by Dan Ralph, the Horace White Professor of Physics, and Robert Buhrman, the J.E. Sweet Professor of Applied and Engineering Physics, have figured out how to quantify the strength of current-induced torques used to write information in called magnetic tunnel junctions. The results were published online Feb. 28 in the journal Nature Physics.

Magnetic tunnel junctions are memory storage devices made of a sandwich of two ferromagnets with a nanometers-thick oxide insulator in between. The electrical resistance of the device is different for parallel and nonparallel orientations of the magnetic electrodes, so that these two states create a nonvolatile memory element that doesn't require electricity for storing information. An example of nonvolatile memory today is flash memory, but that is a silicon-based technology subject to wearing out after repeated writing cycles, unlike magnetic memory.

What has held back magnetic memory technology is that it has required magnetic fields to switch the magnetic states – that is, to write information. This limits their size and efficiency because magnetic fields are long-ranged and relatively weak, so that large currents and thick wires are needed to generate a large-enough field to switch the device.

The Cornell researchers are studying a new generation of magnetic devices that can write information without using magnetic fields. Instead, they use a mechanism called "spin torque," which arises from the idea that electrons have a fundamental spin (like a spinning top). When the electrons interact with the magnets in the tunnel junctions, they transfer some of their angular momentum. This can provide a very strong torque per unit current, and has been demonstrated to be at least 500 times more efficient than using magnetic fields to write magnetic information, Ralph said.

To measure these spin torques, the researchers used an oscilloscope in a shared facility operated by Cornell's Center for Nanoscale Systems. They applied torque to the magnetic tunnel junctions using an alternating current and measured the amplitude of resistance oscillations that resulted. Since the resistance depends on the relative orientation of the two magnets in the , the size of the resistance oscillations could be related directly to the amplitude of the magnetic motion, and hence to the size of the torque.

The researchers hope such experiments will help industry make better devices by understanding exactly how to structure them, and also, what materials would best be used as the oxide insulators and the ferromagnets surrounding them.

Explore further: Better thermal-imaging lens from waste sulfur

Related Stories

Electric control of aligned spins improves computer memory

Jan 19, 2010

Researchers from Helmholtz-Zentrum Berlin (HZB, Germany) and the French research facility CNRS, south of Paris, are using electric fields to manipulate the property of electrons known as "spin" to store data permanently. ...

Tunneling Across a Ferroelectric

Jul 14, 2006

University of Nebraska-Lincoln physicist Evgeny Tsymbal's groundbreaking identification of an emerging research field in electronic devices earned publication this week in Science magazine.

Recommended for you

Better thermal-imaging lens from waste sulfur

3 hours ago

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

How to test the twin paradox without using a spaceship

Apr 16, 2014

Forget about anti-ageing creams and hair treatments. If you want to stay young, get a fast spaceship. That is what Einstein's Theory of Relativity predicted a century ago, and it is commonly known as "twin ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Eikka
not rated yet Mar 09, 2011
An example of nonvolatile memory today is flash memory, but that is a silicon-based technology subject to wearing out after repeated writing cycles, unlike magnetic memory.


Why would silicon make the memory device inherently fragile? DRAM is made out of silicon, and it doesn't wear out under repeated writing cycles.
Parsec
not rated yet Mar 09, 2011
An example of nonvolatile memory today is flash memory, but that is a silicon-based technology subject to wearing out after repeated writing cycles, unlike magnetic memory.


Why would silicon make the memory device inherently fragile? DRAM is made out of silicon, and it doesn't wear out under repeated writing cycles.

It also disappears when no power is applied. There are a bunch of applications where retaining data between power cycles is very important. Think hard drives.

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Robotics goes micro-scale

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...