Linear magnetostriction

Fig. 86. (a) A side view of the cantilever actuator fabricated by combining TbFe and SmFe films. After Honda ei al. (1994). (b) Two-leg linear magnetostrictive micromotor. After Honda et al. (1994). 

Fig. 88. Many-leg linear magnetostrictive micromotor. After Claeyssen et al. (1997).

This simplified theory provides an understanding of some important features of linear magnetostrictive drivers of actuators, transducers, etc. It shows, for instance, that a driver may be limited either by the stress or by the field, and that the strain at resonance may be much larger than that of a static system and yet may require much less field. However, because of the assumptions on the field shape, the strain uniformity and so on, it is not possible to accurately predict the behavior of the device, especially its exact limits. So, without a good knowledge of these limits, it is difficult to use the full potential of the device. That is why a more accurate model is required and has been developed. 

Here, the parameter k expresses the changes of the magnetostriction due to the change in composition of the residual amorphous matrix with the evolution of crystallisation. In fact, a linear approximation A.am(p) = A.am(0) + kp is applied. The last term describes the surface effects in which R is the effective radius of the grains, i.e. 3IR is the surface to volume ratio for the spherical grains (5/ V in table 4). Figure 69a shows the... 

The spontaneous magnetostriction has been measured by single crystal x-ray diffraction between 10 and 300 K (Kusz et al. 2000). As can be seen from figs 38 and 39, both compounds show pronounced linear as well as volume effects. Gd3Ni is characterized by a large positive spontaneous magnetostriction in a-direction (the estimated value at 0 K is (Aa/a)mag 2.9 x 10 3), whereas the effects in b- and c-direction are about two... 

Thermal expansion, magnetostriction and magnetic susceptibility under pressure have been measured on a polycrystalline CeAgSb2 sample by Thornton et al. (1999). It was observed that in zero magnetic field the magnetic contribution to the linear thermal expansion coefficient... 

Linear position Linear motion is typically driven by the use of lead screws, ball screws, or worm drives with ranges from less than a 25 mm to over 6 m. Linear sensors for position feedback in the lower range include LVDTs, magnetic, and optical encoders. For longer strokes, the linear feedback devices include encoders and magnetostrictive position transducers. Optical encoders are practical up to 2 m. Magnetostrictive position transducers can be used up to 20 m. 

The magnetic phase diagram for the Co system is shown in fig. 25 and table 13 lists the important properties. The ferromagnetic alloys are regarded as itinerant because of the linearity of the Arrott plots over a wide range of temperature and also of the Mathon plots of M02 as a function of x (Hilscher and Kirchmayr 1975). Calculations of the density of states (Terao and Shimizu 1983) show that the itinerant-electron model gives a volume magnetostriction consistent with the experimental value (Muraoka et al. 1980, 1983). 

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. 

The crystalline electric-field (CEF) interactions are the principle origin of the magnetocrystalline anisotropy. They cause a notable contribution to the (linear) Joule magnetostriction. 

The main magnetoelastic effects, such as magnetostriction and alterations of sound velocity in a magnetic field, may be described by considering only those terms in the corresponding series expansion of the free energy, which are linear and quadratic in the deformation parameters Uap, Wa(A). It should be noted that the function / depends on the deformation parameters both explicitly, through He-], and implicitly, because of the dependence of molecular field constants on the lattice structure ... 

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