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Dive into the research topics where K. Mackay is active.

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Featured researches published by K. Mackay.


Journal of Applied Physics | 1997

Giant magnetostrictive spring magnet type multilayers

Eckhard Quandt; Alfred Ludwig; J. Betz; K. Mackay; D. Givord

Thin film magnetostrictive materials can be extremely useful as the active material in microactuators. In this article, some results on a novel type of multilayer structure which combines exchange coupled giant magnetostrictive materials and materials with large magnetic polarizations are presented for the first time. Giant magnetostrictions are achieved at low fields, due to the polarization enhancement in such multilayers. Therefore such composite materials should be much more appropriate for applications than the simple homogeneous alloy films studied up to now.


Journal of Applied Physics | 1996

Giant magnetostriction in amorphous (Tb1−xDyx)(Fe0.45Co0.55)y films

N. H. Duc; K. Mackay; J. Betz; D. Givord

The magnetization and magnetostriction have been studied in amorphous (Tb1−xDyx)(Fe0.45Co0.55)y films. A well‐defined easy axis is created by magnetic field annealing and the sperimagnetic cone structure, characteristic of these amorphous alloys, is reduced. The anisotropy has a minimum at x=0.73 as in the R Fe2 Laves phase. This points to the similarity between the local environments in the amorphous and crystalline states. A giant magnetoelastic coupling coefficient b of 60 MPa is developed at 300 K in low applied field for x=0, optimally annealed films. Assuming a Young’s modulus and a Poisson ratio of 80 GPa and 0.31, respectively, the magnetostriction is evaluated at 1020×10−6. This is much larger than previously reported values in other amorphous films.


Journal of Applied Physics | 2000

50 T pulsed magnetic fields in microcoils

K. Mackay; Marlio Bonfim; D. Givord; A. Fontaine

In this article we present a system based on microcoils capable of generating pulsed magnetic fields up to 50 T. We discuss the current generation and the measurement techniques currently used. We have measured the Faraday rotation for different paramagnetic materials, glass, gadolinium gallium garnet, Pr gallium garnet, and Si and have used the results to calibrate the magnetic field achieved. We discuss the relative merits of such a system compared to conventional ones, as well as the field characteristics obtained.


Journal of Magnetism and Magnetic Materials | 1996

Properties of rare-earth—transition-metal sandwich films

D. Givord; J. Betz; K. Mackay; J.C. Toussaint; J. Voiron; S. Wüchner

Abstract In sandwich systems made by stacking coupled layers with typical thicknesses 100 nm, a specific type of domain wall may be found. This extends over the whole film surface and is termed the extended domain wall (EDW). As a result, peculiar magnetisation processes are observed, some typical examples of which are described in this paper. The formation of EDWs occurs by nucleation/propagation. Experimental evidence for the existence of EDWs is obtained from optical Kerr effect measurements. Magnetization processes are described in both analytical and numerical approaches. High susceptibility in low fields and large magnetostriction anomalies may occur in these systems.


Journal of Applied Physics | 2000

Magnetic and magnetostrictive properties in amorphous (Tb0.27Dy0.73)(Fe1−xCox)2 films

N. H. Duc; K. Mackay; J. Betz; D. Givord

Magnetic and magnetostrictive properties have been investigated for amorphous (Tb0.27Dy0.73)(Fe1−xCox)2 thin films. An increase in the 3d magnetic moment due to the enhancement of T–T interactions in substituted (Fe, Co) alloys was found. This leads to stronger R–(Fe, Co) exchange energies and then to enhancements of R–sublattice magnetization as well as magnetostriction in these amorphous R(Fe, Co) thin films. In addition, a well-defined in-plane anisotropy is created by magnetic-field annealing for the Co-rich films. A large magnetostriction of 480×10−6 developed in low fields of 0.3 T was observed for films with x=0.47 after magnetic-field annealing. The differing roles of Fe and Co atoms on the magnetization process have also been discussed.


Journal of Applied Physics | 2000

Elastic properties of magnetostrictive thin films using bending and torsion resonances of a bimorph

Zs. Sárközi; K. Mackay; Jean-Claude Peuzin

The modification of the elastic properties of giant magnetostriction alloy films due to an applied magnetic field (the ΔE effect), has been studied. Two different types of films were deposited on Si substrates: (i) single layers of TbDyFeCo alloys typically 1000 nm thick and (ii) nanocomposite multilayer films of FeCo/TbFeCo each having a typical thickness of 6 nm. Both types of films were rendered magnetically anisotropic with a well defined in-plane easy axis. Rectangular samples were cut out of these bimorphs and firmly glued at one end to a heavy base to form a simple cantilever structure. The variations of film elastic moduli were deduced from the shifts of the cantilever resonance frequencies as a function of bias field for two basic configurations: (i) field applied along the easy axis and (ii) field applied along the hard axis. In contrast with previous work, both flexural and torsion resonance modes were excited and studied. As a result the field induced variations of both planar traction modulus...


Journal of Applied Physics | 1997

Torsional resonances in magnetoelastic bimorphs

Jean-Claude Peuzin; K. Mackay

In this paper, we show that torsional as well as flexion modes can be excited rather naturally in a magnetoelastic bimorph. This behavior is in contrast with that of usual piezoelectric bimorphs in which only flexion modes can be excited. We describe experimental results on the torsional resonances of bimorphs composed of a glass substrate and a highly magnetostrictive thin film of (TbDy)(FeCo)2 and show how basic linear piezomagnetic constants may be extracted from the resonance data. Finally, we discuss some possible applications of torsional resonance in magnetoelastic bimorphs.


Journal of Applied Physics | 2000

Nanosecond resolved techniques for dynamical magnetization reversal measurements

M. Bonfim; K. Mackay; S. Pizzini; M-L. Arnou; A. Fontaine; G. Ghiringhelli; S. Pascarelli; T. Neisius

In this article we present three techniques developed by our group for probing magnetization dynamics in the nanosecond time scale. All these techniques are based on the magneto-optical interaction of materials with polarized light. Magnetic excitation is provided by microcoils able to generate field pulses of some teslas within a few nanoseconds. Standard Kerr/Faraday dynamic measurements and imaging can be performed as well as time-resolved x-ray magnetic circular dichroism where chemical selectivity can be achieved.


Journal of Physics: Condensed Matter | 2000

Magnetic and magnetostrictive properties in amorphous (Tb0.27Dy0.73)(Fe1-xCox)2 films

N H Duc; K. Mackay; J Betz; Zs Sárközi; D Givord

Magnetic and magnetostrictive properties have been investigated for amorphous (Tb0.27Dy0.73)(FexCo1-x)2 thin films. An increase in the 3d magnetic moment and Curie temperatures higher than 550 K due to the enhancement of T-T interactions (T = transition metal) in substituted (Fe, Co) alloys were found. A well defined in-plane anisotropy is created by magnetic field annealing for the Co-rich films. A large magnetostriction of 480×10-6 was developed in 1.8 T magnetic field and 350×10-6 in low fields of 0.06 T for films with x = 0.47 after magnetic field annealing. The differing roles of Fe and Co atoms in the magnetization process have also been investigated.


Smart Structures and Materials 1998: Smart Structures and Integrated Systems | 1998

Micromotors using magnetostrictive thin films

Frank Claeyssen; Ronan Le Letty; Francois Barillot; J. Betz; K. Mackay; D. Givord; Philippe Bouchilloux

This study deals with a micromotor based on the use of magnetostrictive thin films. This motor belongs to the category of the Standing Wave Ultrasonic Motors. The active part of the motor is the rotor, which is a 100 micrometers thick ring vibrating in a flexural mode. Teeth (300 micrometers high) are placed on special positions of the rotor and produce an oblique motion which can induce the relative motion of any object in contact with them. The magnetic excitation field is radial and uses the transverse coupling of the 4 micrometers thick magnetostrictive film. The film, deposited by sputtering on the ring, consists of layers of different rare-earth/iron alloys and was developed during a European Brite-Euram project. The finite element technique was used in order to design a prototype of the motor and to optimize the active rotor and the energizer coil. The prototype we built delivered a speed of 30 turns per minute with a torque of 2 (mu) N.m (without prestress applied on the rotor). Our experimental results show that the performance of this motor could easily be increased by a factor of 5. The main advantage of this motor is the fact that it is remotely powered and controlled. The excitation coil, which provides both power and control, can be placed away from the active rotor. Moreover, the rotor is completely wireless and is not connected to its support or to any other part. It is interesting to note that it would not be possible to build this type of motor using piezoelectric technology. Medical applications of magnetostrictive micromotors could be found for internal microdistributors of medication (the coil staying outside the body). Other applications include remote control micropositioning, micropositioning of optical components, and for the actuation of systems such as valves, electrical switches, and relays.

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D. Givord

Centre national de la recherche scientifique

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J. Betz

Centre national de la recherche scientifique

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Jean-Claude Peuzin

Centre national de la recherche scientifique

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A. Fontaine

Centre national de la recherche scientifique

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N. H. Duc

Centre national de la recherche scientifique

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J. Voiron

Centre national de la recherche scientifique

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