Using the latest methods of nanofabrication, a team led by physicists at Rice University has discovered a surprising new electronic property in one of the oldest and most studied magnetic minerals on Earth – magnetite, also known as name of magnetite.
By changing the voltage in their experiment, the researchers were able to get magnetite at temperatures below minus 250 degrees Fahrenheit to go 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 is possible now that we can make electronic devices to study materials at the nanoscale.”
The magnetic properties of magnetite, also known as magnetite, were documented in China over 2,000 years ago, and Chinese sailors sailed with magnetite compasses 900 years ago.
Magnetite is a particular iron oxide mineral. Its atoms are arranged in a crystalline structure with four oxygen atoms for every three iron atoms, 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 dramatically and rapidly at low temperatures. As 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.
“When we applied a high enough voltage to our nanostructures, we found that we could push the cooled magnetite out of its insulating phase and cause it to become a conductor again,” Natelson said. “The transition is very sharp, and when the voltage is then lowered below a lower critical value, the magnetite reverts to its insulating phase. We are not sure exactly why this switching occurs, but we believe that other experiments will shed light on this and the nature of the insulating state.
With engineers seeking to exploit new electronic materials for next-generation computers and hard drives, phase transitions between insulator and conductive states have become an increasingly hot topic of research in physics and materials science these days. last years.
The debate over the causes and specifics of the temperature-induced phase change of magnetite has simmered much longer. Natelson said physicists have long argued over the possible underlying physical and electronic causes of the phase transition. The discovery of this new voltage-controlled switching provides new clues, but more research is still needed, he said.
“The effect we discovered was probably not noticed in the past because nanotechnology only now allows the electrodes, nanoparticles and thin films needed for the study to be prepared with the precision needed to document the effect. “, did he declare.
Natelson’s team experimented with two types of magnetite. One, called a nanorouille, is made up of tiny particles of magnetite developed in the lab of Rice chemist Vicki Colvin, director of Rice’s Center for Biological and Environmental Nanotechnology. The second thin films of monocrystalline magnetite were produced by Igor Shvets’ research group at Trinity College, University of Dublin. These high-quality materials with precise compositions were essential to the study, Natelson said.
The research was published online December 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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