Magnetostriction determination

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). 

For technical applications (sensors), Hristoforou et al. (1998) have developed an interesting method to determine the field-dependence of the magnetostrictive strain, based on measuring the delay due to Bloch-wall motion. 

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 ... 

In traditional discussions based on eq. (20), the resonance conditions have been expressed in terms of the magnetostriction coefficients. However, Du Tremolet de Lacheisserie (1995) has found that the elastic coefficients of the substrate (S 1 and S 2s) have entered his formulas of the resonance frequency. He showed that in the SMFMR method only the bY,2 and ba2 coefficients can be determined. 

Nan and Weng (1999) have developed a Green function method to determine self-consistently the effective magnetostrictive properties of composites. The authors claim that their method, in principle, can be used to study the effects of material constants and microstructure, such as anisotropy, particle shape and orientation relative to the applied magnetic field. 

Additional comment deserve magnetostriction measurements near the ordering temperature 7c reflecting critical phenomena. Few data for critical expansion is available, such as have been reported by Dolejsi and Swenson (1981) for the case of Gd metal. The thermal expansion coefficient in the critical region should assume the form 1(7 — Tc)/Tc °-The critical exponent or should be the same as for the specific heat and depend only on the universality class (dimensionality, No. of degrees of freedom) of the system. For Gd metal this universality class has been determined by Frey et al. (1997). 

Summary of the spontaneous magnetostriction (estimated values at 0 K) of the systems with very small or not determined (n.d.) anisotropic effects. The table is ordered... 

The measurement of the sound speed in filaments and yams requires special techniques, viz. by means of a magnetostrictive oscillator (see Ballou et al. 1944/1949). The dynamic modulus, determined in this way is considerably larger than the Young modulus from stress-strain experiments Edyn 1-5 Estat-... 

For Tb2C, an unusual magnetostriction along c was found by determining the linear thermal expansion coefficient between 4 and 298 K. This may be correlated with the fact that the direction of the ferromagnetic moment is parallel to the c axis in Tb2 C. 

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