System Bits: Aug. 27

The triple point; strange magnetism.

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Material that conducts and insulates
It is well known to scientists that the three common phases of water – ice, liquid and vapor – can exist stably together only at a particular temperature and pressure, called the triple point. Also well known is that the solid form of many materials can have numerous phases, but it is difficult to pinpoint the temperature and pressure for the points at which three solid phases can coexist stably.

Scientists at the University of Washington have made what they believe is the first-ever accurate determination of a solid-state triple point in a substance called vanadium dioxide, which is known for switching rapidly – in as little as one 10-trillionth of a second – from an electrical insulator to a conductor, and thus could be useful in various technologies.

In 1959, researchers at Bell Laboratories discovered vanadium dioxide’s ability to rearrange electrons and shift from an insulator to a conductor, called a metal-insulator transition. Twenty years later it was discovered that there are two slightly different insulating phases. The new research shows that those two insulating phases and the conducting phase in solid vanadium dioxide can coexist stably at 65 degrees Celsius, give or take a tenth of a degree (65 degrees C is equal to 149 degrees Fahrenheit).

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The researchers regard this work as a significant step in understanding the metal-insulator transition in vanadium dioxide, which could lead to development of new types of electrical and optical switches.

Strange magnetic behavior
They’re not exactly the peanut butter and jelly of semiconductors, but when you put lanthanum aluminate and strontium titanate together, something magical happens, according to researchers at Ohio State University. Alone, neither exhibit any particularly notable properties but when they are layered together, they become not only conductive, but also magnetic.

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, the researchers said.

The whole question is how to 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 tween them, charge begins to flow and interesting magnetic effects happen?

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

They showed how the elemental units of magnetism, called “local moments,” are formed at the interface of the two materials. They then showed 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 there were conduction and magnetism available in the same platform, it could be possible to integrate computer memory with data processing enabling different kinds of computation.

While those applications are a long way off, the the physicists hope in the short term that their theoretical explanation for the strange magnetic behavior will enable other researchers to perform experiments and confirm it.

~Ann Steffora Mutschler