Managanese bismuthide films are used in the development of a random access memory device of high packing density and nondestructive readout capability. Memory entry is by Curie point switching using a laser beam. Readout is accomplished by microoptical or micromagnetic scanning

Lewicki, G. W.

Tchernev, D. I.

English

NASA Technical Reports Server

December 1967	 Brief 67-10633 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Development of Curie Point Switching for Thin Film, 
Random Access, Memory Device 
The problem: 
A need has existed for an easily entered, small 
size, high bit density, random access memory device 
which can be read out nondestructively. Prior art 
memory devices have included flip-flop storage 
means, magnetic tape recording techniques, and mag-
netic recording techniques on disks. Other techniques 
have employed individual memory cores and thin film 
devices based on the same principle as the magnetic 
core. Disadvantages of these devices and techniques 
included large size, low density, difficult access, and 
destructive readout. 
The solution: 
The use of manganese bisniuthide (MnBi) films in 
the development of a random access memory device 
of high packing density and nondestructive readout 
capability. Memory entry is by Curie point switching 
using a laser beam. Readout is accomplished by 
micro-optical or micromagnetic scanning. 
How it's done: 
Curie point writing refers to a particular method of 
reversing the magnetization direction within a selected 
region of a film. The region is heated past its Curie 
temperature and then allowed to cool in a magnetic 
field having the' direction desired for the remanent 
magnetization and a magnitude sufficient to insure 
complete switching. This magnetic field is, however, 
too small to affect portions of the film not having 
been taken through the temperature cycle. 
Thin films of MnBi about 700 angstroms thick were 
used as the storage material. The writing was done 
with a bio-laser system designed for biological and 
biomedical research. The instrument consists of a 
pulsed, high-intensity ruby laser, flashlamp, focusing 
cavity, and a pinhole aperture which is imaged on a 
microscope stage. A Leitz Ortholux microscope was
used with the bio-laser and the recorded bits of in-
formation were observed using the Faraday effect in 
MnBi with polarized light. 
The intensity of the laser was attenuated sufficiently 
in order to heat the spots on the MnBi films above 
the Curie point (360°C) without destroying the ma-
terial (decomposition temperature is 420 0 C). Since the 
bio-laser produces a diffraction-limited spot of one 
micron at the lie point, by properly reducing the laser 
intensity, spots smaller than one micron could be 
recorded by using only the peak of the diffraction 
limited intensity distribution to heat areas to the 
Curie point. Because of the diffraction limit on the 
smallest spot observable by the Faraday effect, it is 
estimated that the size of the smallest bits that have 
been recorded is less than 0.5-0.7 micron. The limita-
tion is in the observation method rather than the 
material or the recording process. 
The recorded bits of information when viewed 
through a set of crossed polarizers appear as dark 
(or light) spots against a light (or dark) background, 
depending on the setting of the axis of the analyzer. 
Notes: 
I. The advantages and new features characteristic of 
the MnBi film memory are: 
a. Smaller and lighter for a given bit density 
b. Greater bit storage capacity 
c. Fewer memory core wires and less wiring 
d. Nondestructive readout 
e. Random access 
f. Operation at much higher temperatures than 
prior devices 
g. Optical switching of areas as small as one 
micron in diameter 
h. Possible bit storage densities as great as 10/ 
cm (continued overical) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000632 2020-03-11T21:34:28+00:00Z
2. Inquiries concerning this development may be di-
	 Patent status: 
rected to:	 Inquiries about obtaining rights for the commercial 
Technology Utilization Officer
	 use of this invention may be made to NASA, Code 
NASA Pasadena Office
	 GP, Washington, D.C. 20546. 
4800 Oak Grove Drive	 Source: G. W. Lewicki and D. 1. Tchernev 
Pasadena, California 91103
	 Jet Propulsion Laboratory 
Reference: B67-10633 	
.	 (N P0-10402) 
Brief 67-10633	 Category 02


Development of Curie point switching for thin film, random access, memory device

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