PhysOrg.com) -- Millions of people today carry around pocket-sized music players capable of holding thousands of songs, thanks to the discovery 20 years ago of a phenomenon known as the "giant magnetoresistance effect," which made it possible to pack more data onto smaller and smaller hard drives. Now scientists are on the trail of another phenomenon, called the "colossal magnetoresistance effect" (CMR) which is up to a thousand times more powerful and could trigger another revolution in computing technology.

Understanding, and ultimately controlling, this effect and the intricate coupling between electrical conductivity and magnetism in these materials remains a challenge, however, because of competing interactions in manganites, the materials in which CMR was discovered. In the June 12, 2009, issue of the journal Physical Review Letters, a team of researchers report new progress in using high pressure techniques to unravel the subtleties of this coupling.

To study the magnetic properties of manganites, a form of manganese oxide, the research team, led by Yang Ding of the Carnegie Institution's High Pressure Synergetic Center (HPSync), applied techniques called x-ray magnetic circular dichroism (XMCD) and angular-dispersive diffraction at the Advanced Photon Source (APS) of Argonne National Laboratory in Illinois. High pressure XMCD is a newly developed technique that uses high-brilliance circularly polarized x-rays to probe the magnetic state of a material under pressures of many hundreds of thousands of atmospheres inside a diamond anvil cell.

The discovery of CMR in manganite compounds has already made manganites invaluable components in technological applications. An example is magnetic tunneling junctions in soon-to-be marketed magnetic random access memory (MRAM), where the tunneling of electrical current between two thin layers of manganite material separated by an electrical insulator depends on the relative orientation of magnetization in the manganite layers. Unlike conventional RAM, MRAM could yield instant-on computers. However, no current theories can fully explain the rich physics, including CMR effects, seen in manganites.

"The challenge is that there are competing interactions in manganites among the electrons that determine magnetic properties," said Ding. "And the properties are also affected by external stimuli, such as, temperature, pressure, magnetic field, and chemical doping."

"Pressure has a unique ability to tune the electron interactions in a clean and theoretically transparent manner," he added. "It is a direct and effective means for manipulating the behavior of electrons and could provide valuable information on the magnetic and electronic properties of manganite systems. But of all the effects, pressure effects have been the least explored."