Table Of ContentHigh Density Digital Recording
NATO ASI Series
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Series E: Applied Sciences - Vol. 229
High Density
Digital Recording
edited by
K. H. J. Buschow
Philips Research Laboratories,
Eindhoven, The Netherlands
Gary J. Long
Department of Chemistry,
University of Missouri-Rolla,
Rolla, Missouri, U.S.A.
and
Fernande Grandjean
Institute of Physics,
University of Liege,
Sart-Tilman, Belgium
Springer Science+Business Media, B.V.
Proceeding s of the NATO Advanced Study Institute on
High Density Digital Recording
II Ciocco, Castelvecchio-Pascoli , Italy
7-19 June 1992
Library of Congress Cataloging-in-Publicatio n Data
High densit y digita l recordin g / edite d by K.H.J. Buschow, Gary J .
Long, and Fernande Grandjean.
p. cm. — (NATO ASI series . Serie s E, Applie d sciences ; vol .
229)
Includes index.
ISBN 978-94-010-4714-2 ISBN 978-011-1636-7 (eBook)
DOI 10.1007/978-94-011-1636-7
1. Optical storag e devices . 2. Optica l storag e devices-
-Materials . 3. Magnetooptica1 devices . 4. Magnetooptica1 devices-
-Materials . I . Buschow, K. H. J . II .L ong, Gary J. ,1 941-
III . Grandjean, Fernande, 1947. IV. Series : NATO ASI series .
Series E, Applie d sciences ; no. 229.
TA1635.H45 1993
621.39'767—dc20 92-40898
ISBN 978-94-010-4714-2
Printed on acid-free paper
All Rights Reserved
© 1993 Springer Science+Busines s Media Dordrecht
Originall y publishe d by Kluwer Academic Publisher s in 1993
No part of the material protected by this copyrigh t notice may be reproduce d or
utilized in any form or by any means, electroni c or mechanical , includin g photo-
copying , recordin g or by any informatio n storage and retrieval system, without written
permissio n from the copyrigh t owner.
TABLE OF CONTENTS
Preface vii
Chapter 1. Fundamental Concepts and Units in Magnetism and
Magnetic Recording. F. Grandjean and G. J. Long
Chapter 2. Digital Magnetic Recording. 27
S. B. Luitjens
Chapter 3. Magnetic Properties and Preparation of Thin-Film Magnetic 59
Recording Media. J. C. Lodder
Chapter 4. Properties of Particulate Recording Media. 101
R. W. Chantrell and K. O'Grady
Chapter 5. Metal Evaporated Tapes and Co-Cr Media for High 137
Definition Video Recording. H. Hibst
Chapter 6. Preparation, Microstructure, and Magnetic Properties 161
of Co-Cr Thin Films. J. C. Lodder
Chapter 7. High Density Video Recording: Media and Recording. 197
Considerations. H. J. Richter
Chapter 8. System Aspects of Digital Magnetic Recording. 217
S. B. Luitjens
Chapter 9. Magnetic Heads for High Density Recording. 251
J. M. Fedeli
Chapter 10. Tribology of Magnetic Head-Medium Interface. 281
B. Bhushan
Chapter 11. Ultra-Thin Film Magnetism. 315
U. Gradmann
Chapter 12. Introduction to Erasable Magneto-Optical Recording. 355
K. H. J. Buschow
Chapter 13. Materials Engineering towards a High Kerr Rotation. 377
J. Schoenes
Chapter 14. Structure and Stability of Amorphous Alloys. 401
K. H. J. Buschow
Chapter 15. Magnetic Properties of Materials for Magneto-Optical 429
Recording. P. Hansen
Chapter 16. Magneto-Optical Properties of Recording Materials. 445
P. Hansen
vi
Chapter 17. Co-Pt Multilayers for Magneto-Optical Recording. 461
C. -J. Lin
Chapter 18. Structural Origins of Magnetic Anisotropy in Amorphous 483
Non-S-State Rare Earth Transition Metal Films.
V. G. Harris, W. T. Elam, and N. C. Koon
Chapter 19. Magneto-Optic Drive Systems. 519
E. W. Williams
Chapter 20. Noise in Magneto-Optic Drive Systems. 531
H. C. Patel, R. H. Noyau, and E. W. Williams
Chapter 21. Magneto-Optical Recording Applications. 539
E. W. Williams
Appendix List of ASI Participants 545
Author Index 549
Subject Index 565
Preface
High density digital magnetic and magneto-optical storage devices are widely used in audio,
video, and data processing information technology, as well as in CAD/CAM computer
systems. These widespread uses generate a continually increasing demand for both increased
information storage densities and capacities, and for reduced access times. Hence, the materials
engineering of high density storage media, with a high signal to noise ratio, and the associated
design of sophisticated read and write heads, form the basis of major technological research.
This research is especially complex because, ideally, the recorded information should be both
erasable and, at the same time, secure and accessible over periods of many decades. As a
result, research on these complex problems requires a multidisciplinary approach which utilizes
the expertise in such widely differing fields as organic, inorganic, and solid state chemistry,
metallurgy, solid state physics, electrical and mechanical engineering, and systems analysis.
Often, further research specialization is necessary in each of these different disciplines. For
instance, solid state physics and chemistry address the problems of crystallographic structure
and phase diagram determination, magnetism, and optics, but more advanced research
methods, such as high resolution electron microscopy and electronic band structure
calculations, are necessary to understand the microstructure of particulate recording media or
the electronic spectra of magneto-optical recording media.
Unfortunately, there are only a few research centres throughout the world which have the
broad range of research expertise required to solve these technological problems. Even further,
much of the highly specialized research, and the associated methodology, is found in only a
few countries within the NATO community. As a result, the dissemination of current research
results between scientists working in these different disciplines is relatively slow and there is
an obvious need to promote scientific and engineering research exchange and to foster
international contacts, even within the NATO community. Students, the main consumers of
knowledge, are the final link in a long chain which begins with the knowledge of specialized
scientists and engineers in one country, proceeds via the knowledge of scientists and
engineers, perhaps in another country, to the teachers in a further country. The teachers bring
the knowledge of specialized scientists and engineers, in a suitably digested form, to the
students. It was the belief of the organizers of the NATO Advanced Study Institute on High
Density Digital Recording that the transfer rate along this chain is much too slow, especially in
view of the worldwide impact of information storage and computer technology on our
economic and social life.
In order to promote both international contacts between scientists and dissemination of
advanced knowledge in the field of high density digital recording, the organizing committee for
this Advanced Study Institute has made an extensive effort to open the meeting to a broad range
of nationalities. As a result, participants came from Belgium, France, Germany, Greece, Italy,
the Netherlands, Russia, Switzerland, Turkey, the United Kingdom, and the United States of
America. In addition to the fornml scientific program, there were many contacts and exchanges
of scientific and engineering experience on a personal level. It was a special pleasure to meet
several Russian scientists during the meeting. Hopefully, these contacts will lead to both
intermediate and long teml cooperation between both the participants and their scientific
institutes.
vii
viii
The success of an Advanced Study Institute is very dependent upon the venue and its
meeting facilities. In this respect, 11 Ciocco, located in Castelvecchio-Pascoli, a few kilometers
from the beautiful village of Barga, in the Serchio valley of Tuscany, Italy, has served ideally.
II Ciocco is a conference and sports centre with accomodation and meeting facilities which are
perfect for an Advanced Study Institute. Indeed, one of the advantages is its isolation which
insures excellent attendance by the participants throughout the scientific sessions, as well as at
the coffee breaks, meals, and other sports and social functions. The organizers are still
uncertain whether more personal contacts were-established during discussions in the lecture
hall or during the frequent informal ball games which occured after the lectures.
Virtually all of the lecturers honored the request of the organizing committee to present their
lectures at a tutorial level which would be appropriate for graduate students. The resulting
lectures, and the informal and friendly atmosphere of II Ciocco, encouraged the students to
participate actively in the various discussions. During the lectures, there were interruptions
whenever clarification was required by the students. The AS! ended with a panel discussion in
which the main issues of the lectures and possible future developments in the field were
discussed. Students were also invited to present their research in the field, either as short oral
talks, or as posters. Their posters were on display during the entire ASI in the coffee break
area. It is gratifying to report that these posters served as nucleation centers for numerous
discussions. A group of students, who did not have posters on display, selected the
contribution by Steffen Porthun and Peter ten Berge as the best poster presentation. The
directors selected the talk by Vincent Harris as the best oral research presentation and have
included his contribution as a chapter in this volume. A prize for the most colorful
transparencies was awarded to Jean-Marc Fedeli. Hans-JOrgen Richter and Allan Bell were
selected, through student evaluation forms, as the best junior and senior lecturers. A wine
tasting contest was enjoyed by all the participants and Carl Che was found best at judging the
relative cost of the different wines.
Finally, the editors would like to thank the organizing committee and especially Profs. 1. C.
Lodder and E. W. Williams for many helpful suggestions during the planning of this ASI and
each of the authors for their timely and infommtive chapters. The editors also thank Ms. S.
Maquet of the University of Liege and Mr. B. Giannasi, of II Ciocco, for their help in the ASI
organization. Of course, this ASI could not have taken place without the financial support
provided by the NATO Scientific Affairs Division. We also gratefully acknowledge support
provided by Lake Shore Cryotronics, the US National Science Foundation, the University of
Liege, and the University of Missouri-Rolla.
August 1992 K. H. J. Buschow
Liege, Belgium Gary J. Long
Fernande Grandjean
Chapter 1
FUNDAMENTAL CONCEPTS AND UNITS IN MAGNETISM AND
MAGNETIC RECORDING
Fernande Grandjean
Institut de Physique, B5
Universite de Liege
B-4000 Sart-Tilman
Belgium
and
Gary 1. Long
Department of Chemistry
University of Missouri-Rolla
Rolla, MO 65401, USA
1. Introduction
Our generation has seen a dramatic change in the way in which information is stored
and retrieved. For almost 500 years, since the invention of movable type, the principal
method of storing information was through the printed word. About 100 years ago,
methods for analog recording were developed, but these methods have seldom been used
for information storage and have mainly been applied to the storage and retrieval of music.
About 50 years ago, magnetic recording was developed for analog signals and in the last
25 years magnetic recording has become an important method for storing information in
digital form. As more information was created with time, it became essential to improve
the efficiency of information storage. Hence the technology for information storage has
improved from ca. three letters or characters per cm2 in GUtenberg books, to ca. 20 letters
or characters per cm2 in this book, and to ca. 170 letters or characters per cm2 in the
microprint edition of the Oxford English Dictionary.[1] Such books have the disadvantage
of relatively low storage density but the advantage of rapid access by the final user, the
reader, at least if his library contains the appropriate books. This storage density can be
improved somewhat through the use of microfilm and micro-photographic techniques, but
with the added disadvantage of more difficult access by the reader. Figure I shows the
improvement of areal storage density with time.
The last 50 years have seen the development of methods for the digital storage of
information. In the past few years these methods have become quite widespread, and now
perhaps half of the newly published archival information is stored in digital form.
However this does not mean that the access time of the user to this information is
necessarily faster. At this point if the user has available in his or her office either a printed
form of the information or a digital computer file with the same information, the access
time is probably about the same. However, the access time to digital information will, no
doubt, improve with time as more information is stored in a digital form and as more
computer networks become available for the dissemination of digital information. Hence it
is necessary to develop ever more efficient methods for the storage of digital information.
Indeed as is shown in Figure I, the last 50 years have shown a dramatic increase in the
areal digital storage density.
K. H. J. Busclww et al. (eds.), High Density Digital Recording, 1-25.
II:) 1993 Kluwer Academic Publishers.
2
1010
C\I 108
I
E
0
...
~ 106
'iii
c:
Q)
C
104
Q)
.C..)
.c.t.I
0
en
102
100
1500 1600 1700 1800 1900 2000
Year
Figure 1. The areal storage density as a function of time in printed and magnetic fonns,
We must also, however, be concerned with how long we will continue to have
access to the stored infonnation. It is still relatively easy, at least if one is located near the
appropriate library, to read books printed as long as 500 years ago. However, the same
is not necessarily true for digital infonnation stored in a non-current fonnat. For
instance, it is now far from easy to obtain access to the digital infonnation stored as little
as 20 years ago on either paper tape or punched cards. The same is also true with early
magnetic tapes.
Write head Read head
Energizing
Coil ...- -....
Input
Current
Magnetization
Moying media
Vector
Figure 2. The schematic of a magnetic recording system in perpendicular geometry.
