Magnetostriction deformation

Fig. 87. Drift free microactuator (a) thermal deformation and (b) magnetostriction deformation. After Betz...

Hydrogenation of the Lu2Fei7 single crystal leads to a decrease of magnetostrictive deformations (see curve 7, Fig. 7). The experimentally obtained values of magnetostriction for the LuJenH] 5 hydride were three times less than that one in Lu2Fei7. 

The magnetostrictive measurements were made on the same Ni plate. In the external magnetic fields more than 100 mT the change of deformations were not essential. However, the GMR effect appeared as usual in such fields. There was not any correlation between the magnetostrictive deformation and the stepwise change of current of the Ni-polymer-Cu structure. 

It should be noted that the transverse component of the VV susceptibility depends on the orientation of the magnetic field in the plane perpendicular to the crystal c-axis. This dependence is due to the anisotropy of the electronic Zeeman interaction and to magnetostrictive deformation, as mentioned in sect. 3.2. In the weak fields such an angular dependence was registered only by NMR methods (Al tshuler et al. 1982). 

Fig. 6.47. Modeling of the microactuator shown in Fig. 6.46. a Magnetostrictive deformation, b thermal deformation...

It was assumed that the variation of tp with temperature was due to the magnetostriction deformations. From the experimental dependence (p T) the dl /d nc w 1500K and 9/2/9Inc ss 340K were determined (Landry 1967). These values differ considerably from the values of dl /d n c = 75K and dh/dlnc = 0 obtained by Bartholin and Bloch... 

The second term in eq. (88) was related to the change of the bonding forces between the atoms in a crystalline lattice due to the magnetostriction deformations in the magnetically ordered state. 

The two principle modes of the magnetostriction (A -° and As or Xy-2) introduced above are illustrated in fig. 2. With respect to the non-magnetic fictitious state, a spherical, isotropic sample exhibits a relative volume change AV/V = A" 0, when it becomes magnetic. In addition, when one forces the moments to be directed along an applied magnetic field B, an anisotropic deformation is induced, which transfers the sphere into an ellipsoid with the same volume. 

Fig. 3. The normal modes of deformation and the corresponding magnetostriction modes for cubic and uniaxial...

For uniaxial (hexagonal) symmetry the 6 strain components are subdivided in two (invariant) one-dimensional subsets (indicated by the superscript a, and subscripts 1 and 2 for the volume dilatation and the axial deformation, respectively), and two different two-dimensional subsets, indicated by y for deformations in the (hexagonal) plane, and by e for skew deformations. These modes are also depicted in fig. 3. In this case, the magnetostriction can be expressed as... 

Notice here the uniaxial deformation, X 0, independent of the direction of the magnetisation, and the contribution to the volume magnetostriction, X 2, which does depend on the magnetisation direction. 

Fig. 4. (a) Anticlastic deformation of a bimorph in a magnetic field (saddle form), (b) Fixation of a bimorph on its sample holder and measurement principle of the deformation of any magnetostrictive bimorph using the... 

The practical application of ultrasonics requires effective transducers to change electrical energy into mechanical vibrations and vice versa. Transducers are usually piezoelectric, ferroelectric, or magnetostrictive. The application of a voltage across a piezoelectric crystal causes it to deform with an amplitude of deformation proportional to the voltage. Reversal of the voltage causes reversal of the mechanical strain. Quartz and synthetic ceramic materials are used. 

Both crystal (ferromi etic) anisotropy and m netostriction tend to diminish as the Curie point is approached. (The magnetostriction may be regarded as an induced anisotropy brought about by deformation of the crystal by its own magnetic forces.) Hence the hysteresis is... 

The exchange interactions are isotropic to first order. They describe a coupling between the magnetic moments and dominate the magnetic ordering in the materials. The variation of these interactions with the interatomic distance is the reason for a spontaneous deformation (i.e., the volume magnetostriction). 

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