Their results, published in the Physical Review Letters,* point to more efficient methods to predict the dynamics of magnetic materials and to improve the design of key materials for magnetic devices.
The ability to control the dynamics of magnetic materials is critical to high-performance electronic devices such as magnetic field sensors and magnetic recording media. In a computer’s magnetic storage—like a hard disk—a logical bit is represented by a group of atoms whose electron “spins” all are oriented in a particular direction, creating a minute magnetic field. To change the bit from, say, a one to a zero, the drive’s write head imposes a field in a different direction at that point, causing the electrons to become magnetically excited. Their magnetic poles begin precessing—the same motion seen in a child’s spinning top when it’s tilted to one side and begins rotating around a vertical axis. Damping is what siphons off this energy, allowing the electron spins to settle into a new orientation. For fast write speeds—magnetization reversals in a nanosecond or faster—a hard disk wants strong damping.
On the other hand, damping is associated with noise and loss of signal in the same drive’s read heads—and other magnetic field sensors—so they need materials with very weak damping.
The design of improved magnetic devices, particularly at the nanoscale, requires a palette of materials with tailored damping rates, but unfortunately the damping mechanism is not well understood. Important damping mechanisms have not been identified, particularly for the so-called intrinsic damping seen in pure ferromagnetic materials, and no quantitative calculations of the damping rate have been done, so the search for improved materials must be largely by trial and error.
To address this, CNST researchers calculated the expected damping parameters for three commonly used ferromagnetic elements, iron, cobalt and nickel, based on proposed models that link precession damping in a complex fashion with the creation of electron-hole pairs in the metal that ultimately dissipate the magnetic excitation energy as vibration energy in the crystal structure. The calculation is extremely complex, both because of the intrinsic difficulty of accounting for the mutual interactions of large numbers of electrons in a solid, and because the phenomenon is inherently complex, with at least two different and competing mechanisms. Damping rises with temperature in all three metals, for example, but in cobalt and nickel it also rises with decreasing temperature at low temperatures.
By comparing the calculated damping effects with experimental measurements, the team was able to identify the dominant mechanisms behind intrinsic damping in the three metals, which at room temperature and above is tied to electron energy transitions. The results, they say, point to materials design techniques that could be used to optimize damping in new magnetic alloys.
Michael Baum | EurekAlert!
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
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In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
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