Magnetic particles elongated

The effect of magnetic nanoparticles on the cyclic, thermomechanical tensile tests of TFX nanocomposites is shown in Fig. 22. Here TE and a nanocomposite from TFX and 7.5 wt% magnetic particles were compared. In these tests, the samples were elongated at a temperature 71,igh, which was higher than Tsv, but lower than Tians of the hard domains. Strain was kept constant for a certain time interval to allow relaxation. The elongated samples were cooled to fix the temporary shape. This step was performed under stress-control, which resulted in an increase of strain as a consequence of entropy elasticity. The SME was initiated by reheating the composite to... 

A good design for a hard magnetic material is to have small, elongated particles. 

Whether a phase displays SD, PSD orMD behaviour, can be determined from the shape of its hysteresis loop. In MD particles the Bloch walls can be moved by lower energies than the directions of magnetization in SD particles. The hysteresis loops of MD particles, therefore, are much narrower than those of SD particles (Fig. 7.12). For ferrimagnetic phases, the ratios Jrs/Js and Har/Hc (Fig. 7.9) (Day et al., 1977) can be used to distinguish between SD, PSD, and MD particles (Fig. 7.12, right). It should be kept in mind, however, that the coercive forces also depend on particle morphology. Calculations by Butler and Banerjee (1975) show that deviations from the rounded isometric shape towards elongated needles stabilize the SD behaviour and even SP particles may become SD (Fig. 7.13). 

Elongated iron particles may be superior particulate materials for magnetic recording media, but the problem associated with corrosion has not been completely overcome for long storage time. 

As the direction of magnetization of an elongated particle is reversed (from A to C), it must be magnetized in a direction that increases its magnetostatic and magnetocrystalline energies (B). 

Braun H-B (1993) Thermally activated magnetization reversal in elongated fenomagnetic particles. Phys Rev Lett 71 3557-3560... 

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