Below -148 °C (125 Kelvin), magnetite (Fe3O4) – the oldest magnetic material known to us – changes from metal to insulator. At that particular temperature, the material undergoes drastic transformations in its crystal structure, as well as its electric and thermal properties. Known as the Verwey transition, this physical process was discovered over 80 years ago. It remains arguably one of the most important and challenging problems in condensed matter physics, still lacking a complete understanding.
Using magnetite nanoparticles, researchers at Seoul National University and colleagues explored the effects of the introduction of oxygen (oxygen doping) on magnetite. They oxidised magnetite nanoparticles at room temperature and checked the changes in their Verwey transition temperature over a period of three years.
Oxidation changes the charge of the iron in the magnetite and affects the ordering pattern inside the material. As more and more oxygen molecules penetrate deep into the magnetite nanoparticles, a gradual decrease would be expected in the Verwey transition temperature to a minimum value. Instead, the researchers observed an intriguing and previously unreported variation of the Verwey transition temperature: it lowered to a minimum of approximately -203 °C (70 Kelvin) after 72 days of oxidation before rising to -178 °C (95 Kelvin). The team has explained this phenomenon with an elegant diffusion model.
The researchers calculated how many oxygen atoms could diffuse into the nanoparticles over time. They chose to use nanoparticles because studying the Verwey transition upon oxidation at room temperature in a larger block of magnetite would be prohibitively slow. “Nanoparticles have a large surface where oxidation can take place, so they allow us to study this process on a reasonable timescale. The same experiment on a larger piece of magnetite would require an incredible number of years… I would say it would take forever,” explains Taehun Kim, one of the researchers who took part in this study.
It is still a slow experiment though. After approximately 140 days, only about 70 oxygen atoms are incorporated into each magnetite nanoparticle per day. The team took advantage of this slow pace to understand the various aspects and limits of the oxidation.
While at the beginning of the oxidation process oxygen concentration is higher in the outer than inner layers of the nanoparticles, this initial gradient reduces over time. “We suggested that the increase and decrease of the oxygen concentration gradient may be related to the drop and recovery of the Verwey transition temperature,” points out Kim. “However, it is unclear why such a small quantity of oxidation (or doping) has such a big influence on the Verwey transition. This could be the next direction of this research.”
“A much bigger lesson we learned from this work is that our experimental approach can be adapted to many different nanoparticles. It will open a completely new door to the oxidation problem on nanometer scales. If successful, it will be a much wider consequence of this work going beyond the advances our understanding of the effect of oxidation on the Verwey transition in magnetite,” says Je-Geun Park, who led this study at Seoul National University.
Notes for editors
Kim T., et al. Slow oxidation of magnetite nanoparticles elucidates the limits of the Verwey transition. Nature Communications (2021).
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For further information or to request media assistance, please contact Prof. Je-Geun Park (Center for Quantum Materials, Department of Physics & Astronomy, Seoul National University, Seoul 08826, Korea, +82-2-880-6613, email@example.com).
Slow oxidation of magnetite nanoparticles elucidates the limits of the Verwey transition
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Hubble Looks at Spiral Galaxy NCG 7329 – Sci-News.com
The NASA/ESA Hubble Space Telescope has captured an amazing photo of the spiral galaxy NCG 7329.
Otherwise known as ESO 109-12, IRAS 22369-6644 and LEDA 69453, it resides 149 million light-years away in the constellation of Tucana.
The galaxy is a member of the NGC 7329 group (LGG 462), an assembly of more than 10 galaxies bound together by gravity.
This new image of NCG 7329 is made up of observations from Hubble’s Wide Field Camera 3 (WFC3) in the infrared and optical parts of the spectrum.
“Creating a colorful image such as this one using a telescope such as Hubble is not as straightforward as pointing and clicking a camera,” Hubble astronomers said.
“Commercial cameras will typically try to collect as much light of all visible wavelengths as they can, in order to create the most vibrant images possible.”
“In contrast, raw images collected by Hubble are always monochromatic, because astronomers typically want to capture very specific ranges of wavelengths of light at any time, in order to do the best, most accurate science possible.”
“In order to control which wavelengths of light will be collected, Hubble’s cameras are equipped with a wide variety of filters, which only allow certain wavelengths of light to reach the cameras’ CCDs (a CCD is a camera’s light sensor — phone cameras also have CCDs).”
“How are the colorful Hubble images possible given that the raw Hubble images are monochromatic? This is accomplished by combining multiple different observations of the same object, obtained using different filters,” they added.
“This image of NCG 7329, for example, was processed from Hubble observations made using four different filters, each of which spans a different region of the light spectrum.”
“Specialized image processors and artists can make informed judgements about which optical colors best correspond to each filter used.”
“They can then color the images taken using that filter accordingly.”
“Finally, the images taken with different filters are stacked together, and voila!”
“The colorful image of a distant galaxy is complete, with colors as representative of reality as possible.”
SpaceX Tapped For 3 More Possible Commercial Crew Flights To Space – Forbes
SpaceX’s Crew Dragon is just going to get busier shuttling astronauts in the coming years.
NASA announced it intends to issue a sole-source modification to SpaceX’s long-term contract to send astronauts to the International Space Station. This follows an agency call for proposals back in October for more flight options to send people to space.
Boeing’s Starliner spacecraft, which is the other major system, is not quite yet ready for humans following a difficult uncrewed test flight in 2019 that never saw the spacecraft reach the ISS. Starliner has spent some time fixing computer glitches and other issues (including a valve problem that delayed an expected 2021 launch) and is now expecting a second uncrewed test flight by 2022.
The October solicitation, NASA noted, confirms SpaceX is the only viable choice for the time being, given the agency’s safety requirements and the need to keep the space station staffed continuously in the coming years.
“It’s critical we begin to secure additional flights to the space station now so we are ready as these missions are needed to maintain a U.S. presence on station,” Kathy Lueders, associate administrator of NASA’s space 0perations mission directorate, said in a blog post. “Our U.S. human launch capability is essential to our continued safe operations in orbit and to building our low-Earth orbit economy.”
NASA stated it would use these new flights “as early as 2023”, and that the contract (in securing flights and allowing the agency to task personnel elsewhere) will help them get Boeing’s Starliner system ready to fly astronauts once it’s been certified.
“NASA and Boeing will provide additional updates on the status of Starliner’s next mission as we work through the investigation and verification efforts to determine root cause and effective vehicle remediation,” said Phil McAlister, director of commercial spaceflight at NASA, in the same statement.
The latest issue holding up the flight was an oxidizer isolation valve that was found in August, and NASA and Boeing together elected to pull the spacecraft back to the hanger to figure out how to fix the issue before sending the spacecraft aloft.
Another pressing issue for NASA’s future will be extending the planned retirement of the ISS from 2024 to at least 2028, which the agency has said for years it wants to do. It is in negotiations with Congress and with its international partners to do this, and in the meantime, last week the agency also announced it has secured three early-stage contracts for future private space stations to fly late in the 2020s.
See what food challenges astronauts face in space – CGTN America
For the first time ever, NASA and the Canadian Space Agency hosted the Deep Space Food Challenge.
The competition brought universities and companies together to propose solutions on how to feed astronauts on a long mission. Last month, NASA announced that the winners and one of the international winners of the Phase 1 competition came from a group of students in a university in South America.
CGTN’s Michelle Begue reports Colombia.
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