Wolfgang Rupprecht <wolfgang@wsrcc.com> writes:
> woods@weird.com (Greg A. Woods) writes:
> > [ On , May 22, 2001 at 07:27:17 (-0700), Wolfgang Rupprecht wrote: ]
> > > According to my resident magnetics expert, folks have always known how
> > > to make magnetically hard layers.
> > three atoms thick?  Known theoretically, or practically?
> 
> According to my expert making single atom layers is not difficult.
> Folks have been doing that for a long time.  The trick is making thin
> layers that retain their magnetic domains and don't "fade" as a
> function of time.  The normal trick for making such magnetic domains
> is to make the material very magnetically "hard".  That is, hard to
> magnetize and conversely hard to demagnetize.  The media that
> leading-edge folks are toying with now (and are drooling over) are too
> magnetically "hard" to magnetize with current heads.

The May Physics Today had an article on layered magnetic structures, a
bit or two of which is still in my short term memory--the 3 atom layer
of ruthenium creates an antiferromagnetic coupling between the thin
film magnetic media above and below it, which gives the layered
structure properties radically different from bulk magnetic media.
Possibly relevant is a strong perpendicular anisotropy to the
hysteresis curve, where perpendicular fields saturate much more
rapdily than parallel fields--which I guess could make the magnetic
domains less susceptible to the superparamagnetic effects that cause
small domains to fade.

Anyway, it isn't a traditional magnetically hard media, but a more
complicated layered anisotropic media, closely related to the highly
sensitive "giant magnetoresistance" read heads that made a large jump
in densities possible a few years back.  I gather this is something
that lots of people have been working on for a while, so the only real
"breakthrough" here is that IBM is the first to have an economical
procedure for reliable bulk production on the scale of disk drive
platters.  This isn't a trivial accomplishment--while thin films of a
few atoms are routine, the interlayer exchange coupling for these
structures oscillates between ferromagnetic and antiferrogmagnetic as
a function of the thickness of the intervening material, so the
precise thickness of the ruthenium spacer layer is critical.  It's no
surprise that IBM is first to get a commercial product out, given the
quality of (pure & applied) physics research IBM supports, but I'd
expect others to follow pretty quickly.

Apparently there's also talk of bringing back magnetic "core" memory
using similar layered thin film materials, replacing DRAM.

> PS.  For the last few years I've only bought IBM drives -- they do
>      make a darn good product.  I'm just not a big fan of their
>      over-the-top press releases.

We buy a lot of different drives, and have generally been happy with
the IBM's.  There also seems to have been some sort of reliability
bump at 9 GB--we've had lots of trouble with 9 GB drives, less with 18
GB, even less with 50 GB, and almost no trouble with the 72 GB and 180
GB drives we've been buying recently.
-- 
Dan Riley                                         dsr@mail.lns.cornell.edu
Wilson Lab, Cornell University      <URL:http://www.lns.cornell.edu/~dsr/>
    "History teaches us that days like this are best spent in bed"