Physics of Magnetism

CHAPTER 11. MAGNETIC ANISOTROPY 99

Equating the two torques leads to the relation

The value of H that makes parallel with the field is reached when The

anisotropy field is then given by

In some materials, is negligible and measurements of are sufficient for the

determination of

A frequently used method to determine and has been developed by Sucksmith

and Thompson (1954) and is based on the relation

which holds for the magnetization curve of a single crystal obtained in comparatively small
fields applied perpendicular to the easy direction. Under these circumstances, one may
assume that the value of the saturation polarization does not change with field strength
and hence Substitution into Eq.(11.6) then leads to Eq.(11.8). When H/J is
plotted versus the anisotropy constant in Eq. (11.8) may be derived from the vertical
intercept and the anisotropy constant from the slope of the straight line.
Substantial errors may arise from misalignment when this method is used for deter­
mining and on aligned powder samples. Misalignment leads to curvature of the
magnetization, similar to what would be the effect of a larger value of Somewhat better
in this respect is a method based on the Sucksmith–Thompson plot, as proposed by Ram and
Gaunt (1983). In this modification, is plotted versus