Work Area: Alternative Advanced Semiconductor Materials, Devices and Process Steps
Keywords magnetic multilayers, magneto-resistance, exchange interactions, magnetic domain structures, magneto-resistive field sensors
Start Date: 1 September, 1992 / Duration: 36 months / Status: running
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Abstract SMMMS aims to increase the understanding of the fundamental physics and materials science aspects of the spin valve magneto-resistance (MR) effect in magnetic multilayer materials. From this study it should be possible to assess the usefulness of these materials for typical sensor applications. The project includes multilayer growth, microstructural and magnetic measurements, and experimental and theoretical studies of properties relevant for sensor applications.
The recently discovered "spin valve" magnetoresistance in magnetic multilayers, with effects up to 65% at room temperature, has an entirely different physical origin than the well-known so-called anisotropic magnetoresistance effect in normal alloys. The latter effect is only relatively small: 2-3% at room temperature in thin films. The aims of the project are to increase understanding of the physical origin of the spin valve magnetoresistance in multilayers, to search for improved and novel systems, to realise optimal growth and analysis procedures, and to assess the usefulness of these materials for sensor applications.
For the application of magnetic multilayers in the read heads of digital magnetic recording, the currently available multilayer systems operating at low magnetic fields will have to be optimised.
The consortium brings together a broad expertise on multilayer preparation and in situ and ex situ techniques for the analysis of the growth process and for the microstructural characterisation of the films. Several types of magnetic measurement techniques will be further developed and applied to (micro)-magnetic analysis. The microstructural and macromagnetic properties of these multilayer thin films will be correlated with the magnetoresistance (Paris-Sud), interlayer exchange coupling (Jülich, Philips) and the magnetisation process (Erlangen). Special attention will be given to the atomic configuration of the interfaces, using X-ray diffraction (Philips) and high resolution TEM (Thomson), nuclear techniques (NMR, FMR; Eindhoven and Strasbourg) and Mössbauer spectroscopy (Jülich). The industrial partners will optimise the deposition process, using techniques feasible for industrial use, for various multilayer thin films, suitable for application in high and low magnetic fields. Two industrial partners (Philips and Thomson) will focus on the realisation of sensor materials for read heads and a microcompass.
In the first (diverging) phase of the project many multilayer thin films have been studied. The fundamental work has concentrated on Co/Cu, Fe/Cr and Fe/Pd multilayers. Both the magnoresistance effect for current in plane and perpendicular to the thin film plane were optimised experimentally. Good agreement was found with the theoretical models developed. Interlayer exchanged coupling was studied in detail using multilayers in which certain layers have a continuous thickness variation (wedge samples). Interface quality, which was evaluated by Conversion Electron Mössbauer Spectroscopy, showed that fairly sharp can be made. The effect of temperature on the interface roughness and the magnetoresistance was studied for some specific cases too. A separate study of the interface roughness of [NiFe/Cu/Co/Cu]n was done. Other multilayers suitable for application in low magnetic fields have been optimised. For example in NiFE/Cu/NiFe/MnFe the interplay between interlayer exchange coupling and exchange biasing was measured and the Cu thickness was optimised. Very good progress was made in the development of theories on the magnetoresistance effect and on interlayer exchange coupling. The work on the applicability of these materials for recording heads and other magnetic field sensor was initiated.
Possible applications are in read magnetic heads for high-density magnetic recording of audio, video and data, and in position, acceleration and torque sensors. Thin-film recording read heads are key elements in consumer electronic products and in professional disk drives.
Up to September 1993 the consortium has published 37 papers in the open literature and 53 papers were submitted for publication. Several members of the consortium play an active role in organising conferences or conference sessions.
Philips Research Laboratories - NL
Prof. Holstlaan 4
NL - 5656AA Eindhoven
KFA-Jülich - D
Universität Erlangen - D
Siemens AG - D
Thomson CSF - F
Université de Paris-Sud - F
University Louis Pasteur-Strasbourg - F
Technische Universiteit Eindhoven - NL
Dr. R.H.J. Fastenau
tel +31/40 742189
fax +31/40 743352
SMMMS - 6146, August 1994
please address enquiries to the ESPRIT Information Desk
html version of synopsis by Nick Cook