How fast is the rate of "switch" for the domains to align with an exterior field? Possibly in milliseconds? I assume it won't take much time since domains are very small, and they only turn from a certain degree to another.

I know this would depend on a lot of factors, but if powerful large magnet can attract a ferromagnet with a force of nearly 4,000, brining it closer to it would take 0.005 seconds, then surely the magnetization was a lot faster than that. Since magnetization occurs before attraction.


http://news.sciencemag.org/math/2012/02/hot-idea-faster-hard-drive : "Each bit in a magnetic recording medium is in fact a nanometer-sized patch or "domain" that can be magnetized in either of two directions—say, up and down—to encode a 0 or a 1. That information is read out by the read head, a tiny electromagnet that passes over the rotating disk and measures each domain's orientation. The same head also writes the information to the disk by applying a magnetic field that flips a bit's orientation. But the traditional electromagnetic read head struggles to keep up. For a while now, the time needed to write one bit has been stuck at about 1 nanosecond, limiting the rate of data transfer."

  • $\begingroup$ A NANOSECOND! THAT'S UNBELIEVABLE. Magnetization could be that fast or a bit more... amazing. $\endgroup$ – AxtII Dec 9 '13 at 6:08
  • $\begingroup$ And it's struggling as well, this is mind boggling! $\endgroup$ – AxtII Dec 9 '13 at 6:22
  • $\begingroup$ @XCIX: "Today’s widely used mass storage devices, based on magnetic domain flipping by the giant magnetoresistance(GMR) effect (1,2), are limited to access times in the nanosecond range. (arxiv.org/abs/1209.1280 ) $\endgroup$ – akhmeteli Dec 9 '13 at 6:24
  • $\begingroup$ @XCIX: "Traditionally, magnetization dynamics was studied under quasi-equilibrium conditions and thought of as a rather slow process, limited to the nanosecond regime [1] by domain-wall motion and spin–lattice relaxation time." physik.uni-kl.de/fileadmin/hillebrands/Internal/Book_chapters/… $\endgroup$ – akhmeteli Dec 9 '13 at 6:29
  • $\begingroup$ This is beyond my current level of understanding. But thank you for point out how fast domain's flip. Wow, in the nanosecond rage... Remarkable. $\endgroup$ – AxtII Dec 9 '13 at 7:31

I agree with the above quoted evaluations for the magnetization switching, but a precisse calculation concerns solving the Landau–Lifshitz–Gilbert equation (http://en.m.wikipedia.org/wiki/Landau%E2%80%93Lifshitz%E2%80%93Gilbert_equation) and particullarly knowing the value of the damping factor alfa. The phenomenological character of this parameter is a great difficulty and only experimental works and numerical simulations can elucidate this issue. Fortunately, there are now several works that point values in the region of microwaves.


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