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Unveiling Strange Magnetic Behaviour At Semiconductor Interfaces

A new discovery could one day lead to electronic materials that provide both computation and data storage
Alone, neither lanthanum aluminate nor strontium titanate exhibit any particularly notable properties. But when they are layered together, they become not only conductive, but also magnetic.


In the current online edition of Nature Physics, researchers at The Ohio State University report what they say is the first-ever theoretical explanation to be offered for this phenomenon since it was discovered in 2004.


Understanding how these two semiconductors interact at their interface could someday lead to a different kind of material - one that provides a single platform for computation and data storage, says Mohit Randeria, co-author of the paper and professor of physics at Ohio State.


“The whole question is, how can you take two materials which do not conduct electricity and do not have magnetic properties, make a sandwich out of them and - lo and behold - at the interface between them, charge begins to flow and interesting magnetic effects happen?" he says.


“It’s like taking two pieces of bread and putting them together and having the sandwich filling magically appear."


By making calculations and modelling the basic physical properties of both materials, Randeria’s team has hit upon an explanation for the behaviour that seems ironic: the interface between two non-magnetic materials exhibits magnetism.


"Randeria’s team has hit upon an explanation for the behaviour that seems ironic: the interface between two non-magnetic materials exhibits magnetism."


The team showed how the elemental units of magnetism, called “local moments," are formed at the interface of the two materials. They then demonstrated how these moments interact with the conducting electrons to give rise to a magnetic state in which the moments are arranged in an unusual spiral pattern.


If the physicists’ explanation is correct, then perhaps someday, electronic devices could be constructed that exploit the interface between two oxides. Theoretically, such devices would combine the computational abilities of a silicon chip with the magnetic data storage abilities of permanent magnets like iron.


“If you had conduction and magnetism available in the same platform, it could be possible to integrate computer memory with data processing. Maybe different kinds of computation would be possible," Randeria comments.


But those applications are a long way off. Right now, the physicists hope that their theoretical explanation for the strange magnetic behaviour will enable other researchers to perform experiments and confirm it.


This work is described in detail in the paper, "Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO3/SrTiO3 interface," by Sumilan Banerjee et al in Nature Physics (2013) published online on 25th August 2013. doi:10.1038/nphys2702


This research was sponsored by the U.S. Department of Energy, the National Science Foundation (NSF), and Ohio State’s Centre for Emergent Materials, one of a network of Materials Research Science and Engineering Centres funded by NSF.


 




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