New property discovered in ancient mineral magnetite

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Using the latest nanofabrication methods, a team led by physicists from Rice University has discovered a startling new electronic property in one of the oldest and most studied magnetic minerals on Earth – magnetite, also known as magnetite name.

By changing the voltage in their experiment, the researchers were able to get magnetite at temperatures below minus 250 degrees Fahrenheit to change from an insulator to a conductor.

“It’s fascinating that we can still find surprises in a material like magnetite that has been studied for thousands of years,” said lead researcher Doug Natelson, associate professor of physics and astronomy. “This kind of discovery is really a testament to what’s possible now that we can make electronic devices to study materials at the nanoscale.”

The magnetic properties of lodestone, also known as magnetite, were documented in China over 2,000 years ago, and Chinese sailors were sailing with magnetite compasses as early as 900 years ago.

Magnetite is a special iron oxide mineral. Its atoms are arranged in a crystalline structure with four atoms of oxygen for three of iron, and their arrangement gives the mineral its characteristic magnetic and electrical properties. Physicists have known for over 60 years that the electronic properties of magnetite change drastically and rapidly at low temperatures. When the material cools below a critical temperature near minus 250 degrees Fahrenheit, it changes from an electrical conductor to an electrical insulator – an electrical transformation akin to the physical change that water undergoes when it freezes into ice cream.

“When we applied a high enough voltage to our nanostructures, we found that we could kick the cooled magnetite out of its insulating phase and make it conductive again,” Natelson said. “The transition is very sharp, and when the voltage is then lowered below a lower critical value, the magnetite returns to its insulating phase. We do not know exactly why this switching occurs, but we believe that other experiments will shed light on this and the nature of the insulating state.”

As engineers seek to exploit new electronic materials for next-generation computers and hard drives, phase transitions between insulating and conducting states have become an increasingly hot topic of research in physics and materials science. these last years.

The debate over the causes and specifics of the temperature-related phase change of magnetite has simmered much longer. Natelson said physicists have long discussed the possible underlying physical and electronic causes of the phase transition. The discovery of this new voltage-driven switching provides new clues, but more research is still needed, he said.

“The effect we discovered has probably not been noticed in the past because nanotechnology only now makes it possible to prepare the electrodes, nanoparticles and thin films needed for study with the precision needed to document the effect. “, did he declare.

Natelson’s team experimented with two types of magnetite. One, called nanorust, consists of tiny magnetite particles developed in the lab of Rice chemist Vicki Colvin, director of Rice’s Center for Biological and Environmental Nanotechnology. The second single crystal magnetite thin films were produced by the research group of Igor Shvets at Trinity College, University of Dublin. These high-quality materials with precise compositions were critical to the study, Natelson said.

The research was published online Dec. 16 and will be included in the February print edition of Nature Materials. The research was funded by the Department of Energy.

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Material provided by rice university. Note: Content may be edited for style and length.

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