Advanced Materials Volume 2 Issue 1 1990 [Doi 10.1002%2Fadma.19900020111] Dr. Steven Luitjens --...

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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



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



ADVANCED

MATERIALS

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

Advanced Materials Volume 2 Issue 1 1990 [Doi 10.1002%2Fadma.19900020111] Dr. Steven Luitjens --...

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