Indian origin scientist shows electric fields can be used as ON/OFF switches

June 1st, 2009 - 4:33 pm ICT by ANI  

Washington, June 1 (ANI): Ramamoorthy Ramesh, a scientist of Indian origin, along with his colleagues at Berkeley Lab’s Materials Sciences Division in the US, successfully demonstrated that electric fields can be used as ON/OFF switches in doped multiferroic films.

Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist.

They are potential cornerstones in future magnetic data storage and spintronic devices provided a simple and fast way can be found to turn their electric and magnetic properties on and off.

Ramesh and his colleagues at the Berkeley Lab, working with a prototypical multiferroic, have successfully demonstrated just such a switch - electric fields.

“Using electric fields, we have been able to create, erase and invert p-n junctions in a calcium-doped bismuth ferrite film,” said Ramesh.

“Through the combination of electronic conduction with the electric and magnetic properties already present in the multiferroic bismuth ferrite, our demonstration opens the door to merging magnetoelectrics and magnetoelectronics at room temperature,” he added.

The next generation of computers promises to be smaller, faster and far more versatile than today’s devices thanks in part to the anticipated development of memory chips that store data through electron spin and its associated magnetic moment rather than electron charge.

Because multiferroics simultaneously exhibit two or more ferro electric or magnetic properties in response to changes in their environment, they are considered prime candidates to be the materials of choice for this technology.

Bismuth ferrite is a multiferroic comprised of bismuth, iron and oxygen (BiFeO3), and has commanded particular interest in the spintronics field.

In their study, Ramesh and his group first doped the bismuth ferrite with calcium acceptor ions, which are known to increase the amount of electric current that materials like bismuth ferrite can carry.

The addition of the calcium ions created positively-charged oxygen vacancies. When an electric field was applied to the calcium-doped bismuth ferrite films, the oxygen vacancies became mobile.

The electric field “swept” the oxygen vacancies towards the film’s top surface, creating an n-type semiconductor in that portion of the film, while the immobile calcium ions created a p-type semiconductor in the bottom portion.

Reversing the direction of the electric field inverted the n-type and p-type semiconductor regions, and a moderate field erased them.

“It is the same principle as in a CMOS device where the application of a voltage serves as an on/off switch that controls electron transport properties and changes electrical resistance from high (insulator) to low (conductor),” said Ramesh.

Whereas a typical CMOS device features an on/off switching ratio, Ramesh and his group achieved an on/off switching ratio of about a thousand in their calcium-doped bismuth ferrite films. (ANI)

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