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Re: Using magnetic permeability to store information

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On 9/11/2015 5:54 PM, Sam Wormley wrote:
> Using magnetic permeability to store information
>> http://phys.org/news/2015-09-magnetic-permeability.html
>

(replaced lousy phys.org vomitization - with the Abstract)

         It is about RAD HARD memory devolopment.

Abstract

Steps are described in the development of a new magnetic memory
technology, based on states with different magnetic permeability, with
the capability to reliably store large amounts of information in a
high-density form for decades. The advantages of using the permeability
to store information include an insensitivity to accidental exposure to
magnetic fields or temperature changes, both of which are known to
corrupt memory approaches that rely on remanent magnetization. The high
permeability media investigated consists of either films of Metglas 2826
MB (Fe40Ni38Mo4B18) or bilayers of permalloy (Ni78Fe22)/Cu. Regions of
films of the high permeability media were converted thermally to low
permeability regions by laser or ohmic heating. The permeability of the
bits was read by detecting changes of an external 32 Oe probe field
using a magnetic tunnel junction 10 ?m away from the media. Metglas bits
were written with 100 ?s laser pulses and arrays of 300?nm diameter bits
were read. The high and low permeability bits written using bilayers of
permalloy/Cu are not affected by 10 Mrad(Si) of gamma radiation from a
60Co source. An economical route for writing and reading bits as small
at 20?nm using a variation of heat assisted magnetic recording is discussed.

paper is here, free;


http://iopscience.iop.org/article/10.1088/0022-3727/48/40/405002/meta;jsessionid=1549C8E8C19DB18D68E73E66FA70A0E0.c1



5.Summary and conclusions

We have discussed the development of a technology based on bits with 
different values for their permeability that can be used to safely store 
information in credit and identification cards and in high density hard 
disks. This information is a read only memory that is unaltered by 
exposure to a magnetic field or temperature changes. Using the 
permeability for card applications has the advantages that it cannot be 
easily erased and that it cannot be read by someone passing by with an 
RF reader. There are no clear technological barriers to writing and 
reading permeability information cards. Data was presented that 
demonstrated that bilayers of permalloy and copper can be used to write 
readable permeability bits. The permeability bits written on the 
bilayers can be written by ohmic heating and are radiation hard. One can 
use laser writing to create bits with higher and lower permeability than 
the as deposited Metglas. The Metglas bits can be written in 100 ?s and 
can be as small as 300?nm. We wish to emphasize that the technology of 
heat assisted magnetic recording should provide a route for writing 
20?nm or smaller permeability bits. We have discussed a potential 
technology for high density memory with different challenges than the 
superparamagnetic limit. Though the permeability bits can be very small, 
there are many technical issues and scientific questions that need to be 
addressed before one can produce practical nanosized bits and read these 
bits at an acceptable rate. For example, the read head must be able to 
reliably read the bits' alteration of the probe field. As the bits get 
smaller, the probe field may have to be increased and the sensor will 
likely have to detect small changes in this larger field. Some 
scientific questions that need to be considered are: How abrupt is the 
change in permeability and atomic arrangement in nanosized regions of 
Metglas after one has applied a temperature gradient? How abrupt is the 
change in permeability in nanosized regions of permalloy/Cu with a 
composition gradient? What temperature and time will be needed to write 
permalloy/Cu bits?

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Using magnetic permeability to store information Sam Wormley <swormley1@gmail.com> - 2015-09-11 17:54 -0500
  Re: Using magnetic permeability to store information jimp@specsol.spam.sux.com - 2015-09-11 23:08 +0000
    Re: Using magnetic permeability to store information benj <nobody@gmail.com> - 2015-09-12 00:20 -0400
  Re: Using magnetic permeability to store information gilber34 <invalid@invalid.com> - 2015-09-11 20:18 -0500

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