Scientists have discovered that the magnetic strength of magnetite — the most abundant magnetic mineral on Earth — declines drastically when put under pressure. Researchers from the Carnegie Institution’s Geophysical Laboratory, together with colleagues at the Advanced Photon Source of Argonne National Laboratory, have found that when magnetite is subjected to pressures between 120,000 and 160,000 times atmospheric pressure its magnetic strength declines by half. They discovered that the change is due to what is called electron spin pairing.

Magnetism comes from unpaired electrons in magnetic materials. The strength of a magnet is a result of the spin of unpaired electrons and how the spins of different electrons are aligned with one another. This research showed that the drop in magnetism was due to a decrease in the number of unpaired electrons.

“Magnetite is found in small quantities in certain bacteria, in brains of some birds and insects, and even in humans,” commented Yang Ding, the study’s lead author with the Carnegie-led High-Pressure Synergetic Consortium. “Early navigators used it to find the magnetic North Pole and birds use it for their navigation. And now it is used in nanotechnology. There is intense scientific interest in its properties. Understanding the behavior of magnetite is difficult because the strong interaction among its electrons complicates its electronic structure and magnetic properties.”

To study the mineral, the researchers developed and applied a novel technique, called X-ray Magnetic Circular Dichroism (XMCD) at the Advanced Photon Source, a high-energy synchrotron facility. The technique uses high-brilliance circularly polarized X-rays to probe the magnetic state of magnetite as a diamond anvil cell subjects a sample to many hundreds of thousands of atmospheres. The researchers combined their experimental results with theoretical calculations by collaborators* to pinpoint why the magnetic strength changes. The study, to be published in February in Physical Review Letters, reveals the electron-spin configuration in the iron sites of the mineral to be the origin of the phenomenon.

This discovery not only shows the profound effects of pressure on magnetism, it also discloses, for the first time, that pressure induced a spin pairing transition that results in changes in the electron mobility and structure.

“The discovery is important,” Ding said. “It advances our understanding of the correlation of magnetism, electron transport, and structural stability in materials with strong electron interactions, like magnetite.”

“It is not surprising to see that a new phenomenon has been trigged by pressure in the oldest magnet. Pressure can directly change electron-electron interactions by squeezing the spacing between them,” said Ho-kwang Mao, the director of the High-Pressure Synergetic Consortium and the High-Pressure Collaborative Access Team. “In the future, the integration of high pressure with novel synchrotron techniques will no doubt lead to more new discoveries.”

*Collaborators are at the Kirensky Institute of Physics (Russia). Other authors in the paper are Daniel Haskel, Sergei G. Ovchinnikov, Jonathan C. Lang, Yuan-Chieh Tseng, and Yuri S. Orlov.

This work was supported by the U.S. Department of Energy (Basic Energy Sciences and NNSA), the National Science Foundation, the W.M. Keck Foundation and the Carnegie Institution.

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ESA’s orbiting gamma-ray observatory, Integral, has made the first unambiguous discovery of highly energetic X-rays coming from a galaxy cluster. The find has shown the cluster to be a giant particle accelerator.

The Ophiuchus galaxy cluster is one of brightest in the sky at X-ray wavelengths. The X-rays detected are too energetic to originate from quiescent hot gas inside the cluster and suggest instead that giant shockwaves must be rippling through the gas. This has turned the galaxy cluster into a giant particle accelerator.

Most of the X-rays come from hot gas in the cluster, which in the case of Ophiuchus is extremely hot, at 100 million degrees Kelvin. Four years ago, data from the Italian/ Dutch BeppoSAX satellite showed a possible extra component of high-energy X-rays in a different cluster, the Coma cluster.

“Two groups analysed the data. One group saw the component but the other did not,” says Dominique Eckert, Integral Science Data Centre (ISDC), University of Geneva, Switzerland. So Eckert and colleagues from ISDC launched an investigation into the mystery.

They turned to Integral and its five-year, all-sky survey and found that ESA’s orbiting gamma-ray observatory did show an unambiguous detection of highly energetic X-rays, coming from the Ophiuchus cluster of galaxies. These X-rays can be produced in two ways, both of which involve high-energy electrons.

The first option is that the electrons are caught in the magnetic field threading through the cluster. In this case, the electrons would spiral around the magnetic field lines, releasing synchrotron radiation in the form of X-rays.

The electrons would be extremely energetic, carrying over 100 000 times the energy of the electrons in the alternative scenario, which is that the electrons are perhaps colliding with microwaves left over from the origin of the Universe and now bathe all of space. In such collisions, the electrons lose some energy, emitted as X-rays.

Determining which of these scenarios is correct is the next job for the team. They plan to use radio telescopes to measure the magnetic field of the galaxy cluster. They also plan to use the High Energy Stereoscopic System (HESS) in Namibia. This giant telescope looks for the brief flash of light generated when highly energetic gamma rays collide with particles in Earth’s atmosphere. If HESS sees such flashes coming from Ophiuchus, then the astronomers will know that the synchrotron scenario is correct.

Either way, the electrons themselves are most likely to be accelerated to high energies by shockwaves travelling through the cluster gas. The shockwaves are set up when two clusters collide and merge. The question is how recently Ophiuchus swallowed its companion cluster.

In the synchrotron scenario, the highly energetic electrons cool very quickly. If the team find this to be the case, then the collision must still be in progress. In the case of microwave scattering, cooling takes a long time and the collision could have taken place at any time in the past.

Once the scientists know, they will be able to properly understand the history of the cluster. One thing is already certain; nature has transformed the galaxy cluster into a powerful particle accelerator, perhaps 20 times more powerful than CERN’s Large Hadron Collider (LHC), which begins operation in Switzerland this summer.

“Of course the Ophiuchus cluster is somewhat bigger,” says Stéphane Paltani, a member of the ISDC team. While LHC is 27 km across, the Ophiuchus galaxy cluster is over two million light-years in diameter.”

Journal reference: ‘Integral discovery of non-thermal hard X-ray emission from the Ophiuchus cluster’ by D. Eckert, N. Produit, S. Paltani, A. Neronov and T. Courvoisier is to be published in a forthcoming issue of Astronomy and Astrophysics.

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Fossil hunters have uncovered the greatest rodent that ever lived — a one-ton behemoth that bestrode the swamplands of South America some four million years ago.

The newly identified species is the greatest-known member of the order Rodentia and by comparison makes the biggest rodent alive today, the 60-kilo (132-pound) capybara, look like a pygmy shrew.

The skull of the extraordinary beast was found in a broken boulder on Kiyu Beach on the coast of Uruguay’s River Plate region, paleontologists reported in a study on Wednesday.

Measuring a whopping 53 centimeters (21 inches), the skull has massive incisors several centimeters long.

Despite this fearsome look, the creature was not carnivorous and looked more like a hippo than a rat.

Its small grinding teeth suggest it had only weak masticatory muscles for chewing food, and probably tucked into soft vegetation, fruit and squidgy aquatic plants in deltas, the experts say.

Its food intake must have been vast, given its huge size.

Other denizens of this world of marsh and forest would have included saber-toothed cats, flesh-eating birds and armadillos.

The species has been dubbed Josephoartigasia monesi, in honor of Alvaro Mones, a Uruguayan paleontologist who specialized in South American rodents.

Authors Andres Rinderknecht of the National Museum of Natural History and Anthropology and Ernesto Blanco of the Institute of Physics in Montevideo say there are several ways to estimate J. monesi’s size.

The ranges run from 468 kilos (1,029 pounds) to 2.5 tons.

But, they say, the most reliable figure is an average of 1,008 kilos (1.008 tons, 2,217 pounds) which is derived from comparing the giant to its closest living relatives, called hystricognath rodents.

The previous rodent record-breaker, Phoberomys pattersoni, was found in Venezuela in 2003 and was estimated at 700 kilos (1,540 pounds) in its prime.

The study is published by Proceedings of the Royal Society B., The Royal Society is Britain’s de-facto Academy of Sciences.

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