Magnetostrictive film

In performing such experiments on isotropic materials, one is accustomed to express the elastic stiffness parameters in the experimentally more readily accessible technical parameters E (Young s modulus) and v (Poisson ratio). The relative change in length, in the direction of the tensile stress a is, by definition, given by (Al/t)i — a/E, whereas v = (Af/ )x/( A / )u. For several magnetostrictive films and substrates, E and v values are listed in table 1. Some useful relations are ... 

Young s modulus ( ) and Poisson s ratio (u) for several magnetostrictive films and different substrates... 

Optical microactuators like a micromirror for scanning applications have been proposed by Orsier et al. (1996). A two-dimensional bimorph (Si 4- magnetostrictive film) is driven remotely by two differently oriented magnetic fields working at different frequencies in order to obtain the bending and torsional vibrations due to the magnetostrictive strain. 

Here, t is the thickness, E is Young s modulus, v is Poisson s ratio, A is the magnetostriction f stands for film, and s for substrate. Numerical values of and Vs are illustrated in table 1 for several magnetostrictive films and related substrates. 

The EMD of a magnetostrictive film is directly related to the film s stress. The change of the orientation of the film s EMD can be determined by considering the minimum of the magnetoelastic energy for an isotropic ferromagnet (du Tremolet de Lacheisserie 1993) ... 

The torsion-based, drift-free microactuator [67], invented by CNRS Grenoble, is basically a unimorph structme composed of a single magnetostrictive film deposited on a passive substrate. The new feature is a square shape maintained by hinges at three corners (Fig. 6.46). 

Several standing-wave ultrasonic motors (SWUMs), have been designed at Cedrat [68] (Figs. 6.48 and 6.49). A linear motor is a self-moving silicon plate including magnetostrictive film. It is submitted to a 10 mT dynamic field produced by an external coil, which may be placed at some centimeters distance... 

Oriented In-Plane Texture. In this kind of film the properties (H and in the various in-plane directions (texture and nontexture directions) are different. The texture of the film can be supported by the texture of the substrate and the crystal lattice can be smaller in the texture direction than in the transverse direction. This can be the source for strain-induced magnetic anisotropy (magnetostriction). It is also found that the crystal is aligned in the texture direction (92). 

Giant magnetostriction in rare-earth-transition metal thin films.114... 

Magnetostriction of amorphous rare earth based thin films.116... 

The elastic properties of the substrate can be determined more accurately than those of the film. Hence, in principle, the magnetoelastic coupling parameter By-2 can be determined more accurately than the magnetostriction coefficient ky-2. An analogous conclusion can be drawn with respect to bending experiments (see e.g. section 3.1 the magnetoelastic cantilever method). 

Various experimental methods have been developed for investigating the magnetoelastic properties of thin films and nanoscale magnetic systems. In the following subsections, we discuss the most important ones (i) the magnetoelastic cantilever, (ii) strain induced anisotropy, (iii) magnetostriction in spin valves, (iv) strain modulated ferromagnetic resonance, (v) secondary-electron spin-polarisation, and (vi) strain-induced anisotropy due to the spontaneous strains. 

For thin films with a perpendicular anisotropy (easy axis normal to the film plane), Huang et al. (199S) determined magnetostriction (As) and anisotropy (Iff) values, by using the so-called initial-susceptibility method. An ac magnetic field was applied in the film direction, and the induced magnetisation component in the field direction was measured. These authors deduced K and As from the x 1 vs. o plots, using ... 

Fig. 10. Room-temperature magnetostriction for Tb i Fe films. After Miyazaki etal. (1997).

Fig. 11. Magnetostriction as a function of Tb concentration for Tbi-jFe films. After Quandt (1997) (upper panel) and Miyazaki et al. (1997) (lower panel).

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