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.
With respect to the study of magnetic multilayers for magnetoresistive sensors, research has been carried out in order to increase the understanding of the fundamental physics and materials science aspects of the spin value magnetoresistance (MR) effect in magnetic multilayer materials.
Initially many multilayer thin films were studies. The fundamental work concentrated on cobalt copper, iron chromium and iron palladium multilayers. Both the magnoresistance effect for current in plant and perpendicular to the thin film plane were optimized 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 was evaluated by Conversion Electron Moessbauer Spectroscopy. The effect of temperature on the interface roughness and the magnetoresistance was studied for some specific cases. A separate study of the interface roughness of nickel iron-copper-cobalt-copper was done. Other multilayers suitable for application in low magnetic fields have been optimized. 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.
APPROACH AND METHODS
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 (Juelich, 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 Moessbauer spectroscopy (Juelich). 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.
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.
5600 MB Eindhoven