Featured Research

from universities, journals, and other organizations

Wobbly Polarity Is Key To Preventing Magnetic Avalanches On Disk Drives

Date:
July 17, 2007
Source:
University of California - Santa Cruz
Summary:
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.

Closeup of the platters and read/write head of a computer hard drive.
Credit: iStockphoto/Jim Jurica

Push two magnets together and you'll set off an avalanche of activity, forcing atoms on each magnet to align their polarity with the intruding magnetic field. It may sound like a party trick for physicists, but you do it every time you press "Save" on your computer.

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."


Story Source:

The above story is based on materials provided by University of California - Santa Cruz. Note: Materials may be edited for content and length.


Cite This Page:

University of California - Santa Cruz. "Wobbly Polarity Is Key To Preventing Magnetic Avalanches On Disk Drives." ScienceDaily. ScienceDaily, 17 July 2007. <www.sciencedaily.com/releases/2007/07/070716190833.htm>.
University of California - Santa Cruz. (2007, July 17). Wobbly Polarity Is Key To Preventing Magnetic Avalanches On Disk Drives. ScienceDaily. Retrieved July 27, 2014 from www.sciencedaily.com/releases/2007/07/070716190833.htm
University of California - Santa Cruz. "Wobbly Polarity Is Key To Preventing Magnetic Avalanches On Disk Drives." ScienceDaily. www.sciencedaily.com/releases/2007/07/070716190833.htm (accessed July 27, 2014).

Share This




More Matter & Energy News

Sunday, July 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins