New research brings models of magnetic avalanches much closer to reality, helping physicists understand both why they happen and why they don't run out of control, wiping disk drives clean. The research, by Joshua Deutsch, professor of physics at the University of California, Santa Cruz, and Andreas Berger, who did the research while at Hitachi Global Storage Technologies, appeared in the July 13 online edition of Physical Review Letters. The knowledge may help engineers design more reliable materials for disk drives.
Correcting even a single typo in an e-mail means changing dozens of bits of information. For each bit, a magnetic head grazes a tiny patch of your disk drive, forcing its polarity, or "spin," to align up or down--the magnetic equivalent of a one or a zero. The patch's polarity in many magnetic materials changes in a haphazard series of large and small jumps that physicists liken to an avalanche--though Deutsch's research shows it often behaves more like an explosion or runaway fire.
"The big advance in this paper is that in previous models of avalanches, the spin just flips from up to down as soon as they apply a magnetic field, and they're done. But that's not the way spin behaves in the real world," Deutsch said.
Deutsch and Berger realized that such an ideal model overlooked an effect, called spin precession, that each magnetic field exerts on its neighbors. They envisioned an individual bit of information as a tiny pincushion bristling with individual magnetic fields. As the disk drive head nears, each pin tends to wobble in a widening circle--pointing neither up nor down but somewhere in between--before it settles on its new polarity. That wobbling is called precession and resembles the way a spinning top draws out circles as it rotates.
"It takes around a few nanoseconds for a precession to die down," said Deutsch. "That's not that fast compared to computers today. It's not as fast as the time-scale you get for a transistor to switch." (A nanosecond is one-billionth of a second.) During that brief time, each magnetic field contributes forces that affect the precession of neighboring fields.
"There's a lot of stored energy in a magnet. It's sort of a battery in a way," Deutsch said. "As each spin flips from up to down, it liberates a small amount of energy that can do more work."
The combined effects can add up to a wave of energy that topples adjacent pins and spreads across the magnet's surface.
Deutsch and Berger suggested that one of the reasons that avalanches die down is because the magnetic material has an inherent ability to damp out the spin precession. The damping comes from the way the spins interact with their nonmagnetic surroundings, including electrons and minute vibrations called phonons.
Materials with poor damping are susceptible to long-running avalanches, and those with higher damping would be better candidates for use in disk drives. But all real materials feature much lower damping than the infinite damping assumed in previous models, Deutsch said.
"Obviously, disk drive makers have already learned by an enormous amount of ingenuity and trial and error what materials make good disks," Deutsch said. "But now we understand a lot better one of the reasons why--because the materials are good at damping, and we can quantify how damping will stop runaway avalanches. We still can’t calculate their damping, but at least we can measure it."
Hugh Powell | EurekAlert!
Will Earth still exist 5 billion years from now?
08.12.2016 | KU Leuven
Home computers discover a record-breaking pulsar-neutron star system
08.12.2016 | Max-Planck-Institut für Radioastronomie
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
08.12.2016 | Materials Sciences
08.12.2016 | Materials Sciences
08.12.2016 | Physics and Astronomy