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DV NCED
MATERIALS
Table 6. Tissue response to stress at interface
Stress condition Response
Stresses without interfacial rel-
ative motion tion maturation
Stress with interfacial relative
motion cells
Stress shielded areas
cell adhesion, connective tissue forma-
no cell adhesion, macrophages and giant
macrophages and giant cells
The content of these Tables leads to the statement that
collagen producing fibroblasts were normally found only,
but reliably, along surfaces along which forces were present
without causing relative (tangential) micromovements and
which had surface undulations with a “wavelength” between
1and 3 Fm. This observation was widely independent of the
chemistry of the material. There are strong indications that
the collagen formation by osteoblasts will follow a very
similar pattern.-This discovery and its interpretation
might, if confirmed, open wide new possibilities for consider-
ably improved implant fixations.
[l] The Book of Abstracts of the 8th European Conference on Biomaterials
ISBN
90-72101-02-2) can be ordered from the Conference Secretary,
Dr. U. Soltesz, Fraunhofer Institut fur Werkstoffmechanik, Wohlerstr. 11,
D-7800 Freiburg (FRG) at a price of DM 40. The proceedings of this
conference will be published as Vol. 9 of Advance.r
in Biomaterials,
G. Heimke, U oltesz, A.
J C.
Lee (Eds.): Clinical Implant
Materials,
Elsevier Science Publishers, Amsterdam 1990.
[2] The Book of Abstracts of the 2nd International Symposium on Ceramics
in Medicine (ISBN 3-925543-04-X) can be ordered from the Deutsche
Keramische Gesellschaft e.V., Frankfurter Str. 196,
D-5000
Koln 90
(FRG) at a price of DM 30. The proceedings of this symposium will be
published as G. Heimke (Ed.): Bioceramics Vol. 2, Deutsche Keramische
Gesellschaft, Koln 1990 at a price of DM 185.
Conference Reports
Magnetic Recording Media
in
Rimini
By
Steven Luitjens
1.
Introduction
The M.R.M.39 (international conference on magnetic
recording media) was held for the fourth time in Italy, this
time in Rimini, from September
4-6,
1989. The conference
had a strong European accent, a lot of European universities
and companies presenting results, but the conference was
given true international character by the many American
and Japanese contributions. The scope of the conference was
limited to recording media and a lot of important aspects of
these materials were discussed. The contributions ranged
from considering the basic magnetic properties of particles
and thin films, tribology of the head-tape interface, and the
chemistry of the magnetic coating to the recording perfor-
mance of a tape or a disk.
A
small number of papers reported
on magneto-optic recording.
A
total number of 90 papers
were presented in planary and poster sessions, with the num-
ber of participants being about
200.
A nice feature of this
[*]
Dr.
S.
Luitjens
Philips Research Laboratories,
P.O.
Box
80000
NL-5600 JA Eindhoven (The Netherlands)
conference was the absence of parallel sessions, meaning that
all participants could take par t
in
the discussions on subjects
presented in the sessions.
The conference chairman S .B.
Luitjens)
stressed the im-
portance of recording performance in present and future
video recording systems. The performance of magnetic
recording systems has been increasing rapidly over the last
decade and this improved performance is mainly caused by
better recording heads and recording media. Figure
1
shows
the development of the areal density with time.”]
The high recording density for the high-quality video sys-
tems S-VHS and Hi8 are only possible due to the improved
recording performance of the media. The Hi8 system is the
most recent one, and is based on the existing
8
mm system.
Hi8 is the first video recording system which uses a thin film
medium called metal evaporated ME) tape, to become
available on the market. In general, thin film media are able
to store more information than the traditional particulate
media. As a consequence, ME tape may play an important
part in future high density recording systems for high defini-
tion television (HDTV). However, the tribological problems
with such a thin film tape are more severe. Thin film and
Adv. Muter.
2
(1990) No. 1 CH
Pkrlagsgesellschaft
mbH,
0-6940Weinheim, 1990
0935-9648/90/0iOi-O049
02.50/0
49
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ADVANCED
MATERIALS
Conference ReDorts
1o6
1o5
1o4
1o
10’
1o
1
o3
1o4
Track density tracksk m)
ig. 1. The areal densities for
various magnetic storage systems: video
recorders 0 ,
or
the
PAL
television system in the
long
play mode unless indicat-
ed otherwise), flexible disk systems + ) and rigid disk systems 0) . he data are
partly taken
from
[2]. PR indicates the expected density
for
perpendicular
recording. The track density and the linear density are on the horizontal and
vertical axes, respectively. Lines of constant areal density are shown.
Thin film media with a perpendicular magnetic anisotropy
are used for perpendicular recording. This recording mode is
expected to sustain even higher linear densities because of the
favorable recording geometry. Perpendicular thin film media
often show a stripe domain structure which may cause noise
in a recording experiment. Studies with Kerr microscopy by
Aitlamine
et al. CNRS), and with Bitter fluid by
Simsova
et
al. University of Prague) reported
on
these domain struc-
tures. Ouchiet al. Tohoku University) described the record-
ing result of a Co-Cr film with a Co-Fe underlayer. The
recording output of such a layer using a ring head for reading
and writing improved considerably with respect to the out-
put of a Co-Cr film alone. The recording process of a ring
head and a perpendicular Co-Cr film was simulated with a
vibrating sample magnetometer by
Bernards
et al. Philips).
The applied field had a similar magnitude and direction with
respect to the sample, as encountered in a real recording
experiment. The results were in good agreement with the
actual recording experiment as reported by
Cramer
et al.
Philips). These results are a nice demonstration of a way to
correlate macromagnetic data with recording results. Using
the detailed knowledge obtained about the micromagnetics
and the recording processes in the perpendicular films, a bit
area of less than 1 pm2 might be realized in the near future.
particulate media, as well as tribology were important topics
discussed at this conference.
3. Particulate Media
2.
Thin
Film
Media
The detailed magnetic microstructure of longitudinal thin
film media was studied by
Alexopoulos
et al. IBM) using
magnetic imaging techniques in an STEM. Complete vortex
structures of the magnetization at a transition were observed
and it was shown that only well-defined regularly shaped
transitions demonstrate a high signal to noise ratio in a
recording experiment.
A
good understanding
of
the magnet-
ic microstructure is therefore very important in order to im-
prove the recording performance.
The magnetic microstructure is strongly correlated with
the structure of the thin film. As a consequence, the prepara-
tion conditions of the film are critical to the end result. Seven
papers dealt with the influence of a Cr nucleation layer on
the structural and magnetic properties of longitudinal thin
films.
A
thicker Cr layer causes a different structure of the
magnetic layer.
As
a consequence, the magnetic coupling
between
the
magnetic entities is changed and the coercivity
goes up. At the same time the signal to noise ratio in a
recording experiment improves considerably. A similar ef-
fect caused by a change in the Ar pressure during sputtering
of the metal film was reported by Werneret al. BASF). It is
clear that this is a very important topic for the production of
high performance thin film media which are used in rigid
disk storage systems.
Most of the tapes and disks which are used today have a
particulate coating which consists of magnetic particles in an
organic binder. The most interesting high density media are
those with metal particles MP) and barium ferrite. Barium
ferrite media were the major topic in the sessionson particu-
late media. Simmons et al. IBM) stated that the recording
performance of a rigid disk system with a barium ferrite
coating is better than the performance of a system with a thin
film medium. It is not clear why, although it seemed that the
thin film medium had a high medium noise level. Barium
ferrite may be an alternative in rigid disk systems because of
its good recording performance. It is evident that this kind of
comparison gives rise to a lot of questions and a lot of discus-
sion. Barium ferrite is also promising for tape application,
and seems to perform as well as MP for high densities.
Shar
rock
3M) reviewed the properties of barium ferrite media.
He emphasized the positive effects of a small particle size and
the narrow switching field distribution. In a second paper,
Sharrock
demonstrated the presence of large interaction
fields. The interaction between the magnetic entities in a
medium influences their magnetic properties considerably.
Models for the magnetic properties of assemblies of interact-
ing particles were presented by Chantrell et al. Lancaster
Polytechnic). The results obtained with these models showed
the large influence of these interactions on magnetic proper-
ties like remanence and coercivity.
50 CH Verlagsgesellschaft
m bH , 0-6940 Weinheim. 990
0935-9648/90~010l-005002.50/0 Adv. Mater.
2
1990)
No.
1
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ADVANCED
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Conference Reports
Workers from BASF presented some new results with the
existing CrO, particles. By doping with Fe they are able to
produce particles with an increased coercivity suitable for
use in S-VHS tape. I t is evident that there is still a lot of new
development in the area of particulate media aimed at per-
formance improvement and therefore, the work on the basic
properties of particulate media will still be of great interest in
the future.
4. ribology
Tribology is very important for the proper functioning of
magnetic recording systems. In video recorders, the head is
in contact with the tape, and wear and friction can present
problems. In rigid disk data storage systems the head is fly-
ing but contact is still present during the takeoff and touch-
down
of
the head during the start and stop of the disk.
Certainly for the thin film media, wear is critical because
the layer is very thin and can wear away easily. However,
there has been much progress in this area and a lot of prob-
lems have been solved.
Lee
Ampex) discussed the choice of
lubricants for ME tape. Papers from
CyfJlca
et al. Universi-
ty of Bochum/BASF) and Harth et al. BASF) showed re-
sults from wear experiments carried out with thin film media.
Broese van Groenou Philips) presented a theory which de-
scribes the friction using the microroughness of the tape and
head, and concluded that friction and wear should be consid-
ered at the level of the tape pigment. In a second paper
Broese
van
Groenou et al. described the difference in level
between the high saturation soft magnetic metal layer close
to the gap of the head and the surrounding ferrite. This is an
important problem because the head-to-tape distance in-
creases considerably and, as a consequence, the recording
performance degrades. A proper choice of alloys for the soft
magnetic layer keeps the level difference at an acceptable
value.
Not all details of the many interesting papers can be dis-
cussed in such a short report. However, the papers will ap-
pear in the January 1990 issue of the IEEE Transactions of
Magnetics.
[l]
S. B.
Luitjens: Magnetic recording trends: media developments and future
(video) recording systems. To be published in I€E€
Trans. Magn.
January
1990.
[2] H. Sugaya et al., in C. D. Mee,
E.
D. Daniel: Mugnef ic Recording, Vol. 111
McGraw Hill, London, 1988.
Optical Communication
in
Gothenburg
By
Peter A. Andrekson and Per 0 Andersson
For the first time in the series of ECOC conferences,
ECOC was held in Sweden, hosted by Chalmers University
of Tephnology in Gothenburg, from September 10- 14,1989.
It was organized by the Department
of
Optoelectronics and
Electrical Measurements at Chalmers. ECOC European
Conference on Optical Communication)
About 800 participants from 30 different countries rang-
ing from the Faroe Islands to New Zealand and from China
to Brazil were gathered together during this meeting. The
conference was generally judged as having a very high tech-
nical standard, which was reflected in the paper acceptance
rate which was only
55 .
The number of presented papers
was, nevertheless, the largest ever at an ECOC. The technical
sessions consisted of 162 contributed papers and 28 invited
papers. Of these, 32 were poster and 20 post-deadline papers.
The papers came from all over the world, with Japan con-
tributing the most 51), followed by the United States
(28),
United Kingdom 21), West Germany 17), France 12),
Sweden 1
),
and others 22).
The plenary session was held in the beautiful Gothenburg
Concert Hall, and directly approached the problems of the
role of fiber-optic communication in the information com-
munity. The session started with two Swedish presentations
discussing present and future national services as well as
international trends. Optical communication in Sweden is
considered a well established technology for expansion of the
network today and a necessity for the introduction of new
services with good economy in the future. I t was also pointed
out that the power of optics can best contribute to this evo-
lution if there is a continuous dialogue between demand and
technology people.
M .
Uenohara of the NEC Corporation
emphasized the importance of optical integrated circuit tech-
nology by comparing the trends in opto- and microelectron-
ics. Semiconductor optoelectronics device technology is fol-
lowing the path of microelectronics quite closely, but lagging
by about 20 years.
This year, a panel discussion was introduced into the con-
ference program. On Monday evening, nine distinguished
scientists from Europe, Japan, and the United States dis-
cussed “Optical Communication in the Year 2000 and Be-
yond”, a very well attended and lively discussion chaired by
[*] Dr.
P. A.
Andrekson,
Dr.
P.
0.
Anderson
Department
of
Optoelectronics and Electrical Measurements,
Chalmers University of Technology, S-412 96 Gothenburg (Sweden)
Adv.
Mater .
2 1990) No. 1
CH Verlagsgesellschaft
mbH.
D-6940 Weinheim,
YYO 0935-Y648~90/010i-0OS1 02.50/0 51