Phenomenological model aids in understanding the mechanisms responsible for the easy-axis coercive force in thin magnetic films of NiFe, MnBi, and gadolinium iron garnet

Baldwin, J. A.

English

NASA Technical Reports Server

September 1970	 Brief 70-10221 
NASA TECH BRIEF F INASAI 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Coercive Force of Thin Magnetic Films 
A simple phenomenological model has been devel-
oped which may lead to a better understanding of 
the physics of thin-film magnetic-optic devices. 
The study of coercive force in thin magnetic films 
has been confined primarily to films of NiFe, mainly 
because of the widespread application of this alloy 
in computer memories. Other films, such as MnBi 
and gadolinium iron garnet, also have shown promise 
of being useful in the area of computer memories. It 
is of both academic and practical importance to under-
stand the mechanisms responsible for the easy-axis 
coercive force, Hc, in order that this parameter may 
be controlled in practice. 
In the simple phenomenological model which has 
been developed, Hc contains a term which varies as 
t- 1 , due to surface effects, plus another term which is 
independent of t. The constant term is the sum of a 
positive term due to the bulk material plus a surface-
tension term which may be either positive or negative. 
The experimental data of other researchers have been 
found to fit this simple theory quite well, the coef-
ficient of t' 1 having been found to be 0.2 Oe- p m for 
NiFe films at the zero-magnetostriction composition 
(81%Ni-19%Fe). When compared with low scatter
data, the surface term varied as t- 1 , and not t 4/3 the 
value previously theorized. It is felt that this simplified 
relationship will lead to a better understanding of the 
physics of thin-film magnetic-optic devices, and should 
permit further understanding and advancement of the 
art. 
Notes: 
1. See J.A. Baldwin, Jr., J. AppI. Phys. 38, 501 (1967) 
for the comprehensive development of the mathe-
matical model. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B70-10221 
Patent status: 
No patent action is contemplated by NASA. 
Source: John A. Baldwin of 
Caltech/JPL 
under contract to 
NASA Pasadena Office 
(N P0-10750) 
Category 03 
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.
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Coercive force of thin magnetic films

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