Material and system research defines accurate memory characteristics in regard to write, read, erase and data operations of manganese bismuth materials

Aagard, R. L.

Chen, D.

Liu, T. S.

Schmit, F. M.

English

NASA Technical Reports Server

1972.	 B72-10107 
NASA TECH BRIEF 
Marshall Space Flight Center 
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Manganese Bismuth Thin Film for Large Capacity Digital Memories 
The problem: 
Research into the employment of manganese bismuth! 
(Mn/Bi) for thin films used in optical memories, was in 
the past, very limited. To obtain accurate memory char-
acteristics in regard to the write, read, erase, and data 
retention operations was very difficult. 
The solution: 
Material and system research was done which defined 
more clearly the characteristics of manganese bismuth 
materials, relevant for use in an optical memory system. 
How it's done: 
Optical memory characteristics of Mn/Bi involve the 
laser Curie point writing properties, the repeated cycling 
effect, the read-out signal characteristics, the erasure 
field requirements, the information retention character-
istics, and the effect of film demagnetization. 
Mn/Bi has two crystal structure phases: the normal 
(low temperature phase) and the quenched (high temper-
ature phase). The Curie temperatures of the -normal 
phase and quenched phase are 360°C and 180°C re-
spectively. 
Mn/Bi films, prepared in its quenched state, will 
slowly transform back to its low temperature phase 
under normal operating conditions. Repeated heat cycling 
on quenched films can be done, without interference 
from this transformation. When film spots are heat 
cycled, the transformation time-constant increases as the 
temperature rises. At 180°C the time-constant is equal 
to about 40 milliseconds. If the spot is above 180°C for 
0.5 .z sec during laser writing, we should see an effect 
upon the optical memory characteristics after about 105 
cycles. Spots have been cycled up to 106 times before 
the signal-to-noise ratio becomes less than one. When 
examined under the microscope, there is no evidence of 
physical damage. However, the signal will disappear as
the writing power increases due to the quenched film 
gradually transforming into the normal phase. 
Temperature is one of the properties that affects the 
memory read-out characteristics. The maximum read-out 
signal is attained when the film is operating at about 
250°C. 
To erase a written spot, an external magnet field 
must be applied. The field required for a perfect erasure 
(for the normal and quenched phase films) is approx-
imately 500 oersteds. 
There is no evidence of spontaneous loss of stored 
information in either phase of the material within a 
temperature range of room temperature to 300°C. Al-
though the quenched film transforms back to the normal 
phase, the magnetization direction remains unchanged. 
Therefore no loss of information occurs. Cooling of 
films in liquid nitrogen will cause demagnetization, as 
will heating through the Curie temperature. The operating 
temperature is therefore limited to a range between 
77°K and 633°K. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A & TS-TU 
Huntsville, Alabama 35812 
Reference: B72l0 107 
Patent Status: 
Source:	 D. Chen, R. L. Aagard, F. M
. 
Schmit 
and T. S. Liu of 
Honeywell Inc. 
under contract to 
Marshall Space Flight Center 
(MFS-21246) 
Category 03 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
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Manganese bismuth thin film for large capacity digital memories

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