Skip to main content

Resistance is utile: Magnetite nanowires with sharp insulating transition

Magnetite (Fe3O4) is best known as a magnetic iron ore, and is the source of lodestone. It also has potential as a high-temperature resistor in electronics. In new research led by Osaka University, published in Nano Letters, ultra-thin nanowires made from Fe3O4 reveal insights into an intriguing property of this mineral.
When cooled to around 120 K (-150°C), magnetite suddenly shifts from a cubic to a monoclinic crystal structure. At the same time, its conductivity sharply drops -- it is no longer a metal but an insulator. The exact temperature of this unique "Verwey transition," which can be used for switching in electronic devices, depends on the sample's properties, like grain size and particle shape.
Magnetite can be made into thin films, but below a certain thickness -- around 100 nm -- the Verwey transition weakens and needs lower temperatures. Thus, for electronics at the nano-scale, preserving this key feature ofFe3O4 is a major challenge. The Osaka study used an original technique to produce magnetite nanowires of just 10 nanometer length, which had exquisite Verwey behavior.
As described by study co-author Rupali Rakshit, "We used laser pulses to deposit Fe3O4 onto a template of MgO. We then etched the deposits into wire shapes, and finally attached gold electrodes on either side so we could measure the conductivity of the nanowires."
When the nanowires were cooled to around 110 K (-160°C), their resistance sharply increased, in line with typical Verwey behavior. For comparison, the team also produced Fe3O4 as a thin film with a large surface area on the millimeter scale. Its Verwey transition was not only weaker, but required temperatures down to 100 K.
"The nanowires were remarkably free of crystal defects," says study leader Azusa Hattori. "In particular, unlike the thin film, they were not dogged by antiphase domains, where the atomic pattern is suddenly reversed. The boundaries of these domains block conduction in the metal phase. In the insulator phase, they stop resistivity from emerging, so they flatten out the Verwey transition."
The nanowires were so pristine that the team could directly study the origin of the Verwey transition with unprecedented accuracy. The insulating properties of magnetite below 120 K are believed to come from "trimerons" repetitive structures in the low-temperature crystal. The researchers estimated the characteristic length scale of trimerons, and it closely matched the true size according to previous research.
"The Verwey transition has a host of potential uses in energy conversion, electronics and spintronics," says Hattori. "If we can fine-tune the transition by controlling the amount of defects, we can envisage producing very low-powered, yet advanced devices to support green technology."
Story Source:
Materials provided by Osaka University. 
Note: Content may be edited.

Comments

Post a Comment

Popular posts from this blog

Dark matter may be older than the Big Bang

Dark matter, which researchers believe make up about 80% of the universe's mass, is one of the most elusive mysteries in modern physics. What exactly it is and how it came to be is a mystery, but a new Johns Hopkins University study now suggests that dark matter may have existed before the Big Bang. The study, published August 7 in  Physical Review Letters , presents a new idea of how dark matter was born and how to identify it with astronomical observations. "The study revealed a new connection between particle physics and astronomy. If dark matter consists of new particles that were born before the Big Bang, they affect the way galaxies are distributed in the sky in a unique way. This connection may be used to reveal their identity and make conclusions about the times before the Big Bang too," says Tommi Tenkanen, a postdoctoral fellow in Physics and Astronomy at the Johns Hopkins University and the study's author. While not much is known about its origins,...
Post a Comment
Read more

All of the starlight ever produced by the observable universe measured

All of the starlight ever produced by the observable universe measured The team's measurement, collected from Fermi data, has never been done before. This map of the entire sky shows the location of 739 blazars used in the Fermi Gamma-ray Space Telescope’s measurement of the extragalactic background light (EBL). The background shows the sky as it appears in gamma rays with energies above 10 billion electron volts, constructed from nine years of observations by Fermi’s Large Area Telescope. The plane of our Milky Way galaxy runs along the middle of the plot. From their laboratories on a rocky planet dwarfed by the vastness of space, Clemson University scientists have managed to measure all of the starlight ever produced throughout the history of the observable universe. Astrophysicists believe that our universe, which is about 13.7 billion years old, began forming the first stars when it was a few hundred million years old. Since then, the universe has become a st...
Post a Comment
Read more

Reflecting antiferromagnetic arrangements

Reflecting antiferromagnetic arrangements : Brookhaven Lab physicists Claudio Mazzoli (left) and Mark Dean at the Coherent Soft X-ray Scattering (CSX) beamline at the National Synchrotron Light Source II. Mazzoli and Dean are part of the team of scientists led by Rutgers University that used the CSX beamline to image some magnetic domains in an iron-based 'antiferromagnetic' material. The ability to image these domains is key to developing spintronics, or spin electronics, for practical applications. A team led by Rutgers University and including scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory has demonstrated an x-ray imaging technique that could enable the development of smaller, faster, and more robust electronics. Described in a paper published on Nov. 27 in  Nature Communications , the technique addresses a primary limitation in the emerging research field of "spintronics," or spin electronics, using magneti...
Post a Comment
Read more