Re: Magnetic fields and Storage Devices

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

On Monday, November 24, 2003, at 02:33 PM, John S. Denker wrote:

> On 11/24/2003 08:22 AM, J. Green wrote:
> > I was wondering the other day how big of a magnetic field would be
> > needed to "erase" a magnetic storage device (floppy, removable tape,
> > hard drive, etc...).
>
> As long as "etc." doesn't include MO (magneto-optical)
> devices, the coercivity of present-day media is typically
> 1700 Oersteds or less.  So that sets the order-of-magnitude
> of interest.  . . .

I recall that one Oersed in air corresponds to 1 gauss
in air. And 1 tesla=10,000 Gs. Thus the limit quoted by
JohnD is 0.17 tesla. Some modern magnets "are
associated" with magnetic fields of up to about one
tesla (?), at pole surfaces. Such a field would erase a
floppy. But can a small (but equally strong) neodymium
magnet (in my pocket) erase the same floppy from a
distance of 20 cm? I do not think so, but I am not sure.
Ludwik Kowalski