Magnetoelastic coefficient

The relative influence of the surface (or interface) effects, of course, must decrease with increasing thickness t of the layer(s). Since the surface effects contribute per unit surface area , one defines, for the layer, effective parameters such that Beff, or heff, equals gbuik 2bsurt/t. Here, the factor 2 is put in, because a layer has two surfaces. In practice, this simple l/t dependence works satisfactorily. For nanocrystallites, both the volume fraction and the volume to surface ratio of the crystallites (i.e. their radius) must be taken into account (see also section 8). In connection to these effects, (non-linear) contributions to the magnetoelastic coefficients due to surface strains and surface roughness are expected to be considerable. 

Fig. 42. Magnetoelastic coefficient versus magnetic field applied parallel and perpendicular to the long axis of the cantilever (parallel measurement direction) of an as-sputtered TbFe/Fe multilayer deposited (a) without a dc field (H

The two magnetoelastic coefficients measured along the two applied field directions are... 

Fig. 20. Calculated stress a as a function of film thickness for Tb-Co films. The variations of perpendicular anisotropy and magnetoelastic coefficient as functions of composition are shown in the inset. After Betz et al.

A comparison of the critical field, calculated within the frozen lattice model, in terms of the microscopic crystal field and magnetoelastic coefficients gives... 

Since thin magnetic films are deposited on a non-magnetic substrate, the actual strains, and thus the induced anisotropy, depend on the magnetoelastic coupling coefficients of... 

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). 

Fig. 40. A comparison of the magnetoelastic coupling coefficient of an annealed (Tb4oFego)/(FesoCoso) multilayer with the optimised Tb Fego. SmFeB (a) and (Tb gFe82)/(Fe75Co25), (TbDyFe)/(FeSiCuNbB), (Tb33Fe67)/(Fe8oB2o) (b) ones. After Ludwig and Quandt (2000).

Fig. 45. Normalised magnetoelastic coupling coefficient of a Tbo.4Feo.6f7 nm)/Feo.sCoo.5(9 nm) multilayer, as a function of external field at different temperatures. After Ludwig and Quandt (2000).

Fig. 4. Field dependence of the magnetoelastic and magnetostrictive coefficients for a vacuum-evaporated nickel thin film. After Betz (1997).

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