On the Elastic Moduli of Ferromagnetic Materials. Part IV.ΔE_Effect of Iron Single Crystals at High Temperature

Abstract

By repeating the measurements of ΔE-effect in iron single crystals at high temperatures, the influence of temperature on this effect is studied. SH=0 in the directions of the principal axes (SH=0 is 1/E of the magnetic origin at H=0) are measured at various temperatures in the same way as described in Part III. SH=0, [100] increases with the rise of temperature and after reaching a maximum at about 640°C it decreases steeply to zero at the Curie point ; while SH=0, [111] decreases monotonously. The ratio 1/k²₁SH=0, [100]/1/K²₃SH=0, [111], however, decreases with the rise of temperature. (k₁ and k₂ are the magnetostriction constants.) At high temperature, the undulatory nature of the SH-H curves (SH is 1/E, of the magnetic origin in a certain magnetic field) of crystals in certain orientations vanishes and they have the same form in all orientations. By plotting SH against I, it can be seen that in the orientations far from the [100]-direction SH becomes very small before the intensity of magnetization is saturated. It is assumed that the magnetization of an elementary domain may point to a direction slightly inclined- perhaps owing to the action of internal stresses to the direction which makes εm (the thermodynamical potential defined in Part III) minimum. By studying the distribution of the directions of the magnetic moments of the elementary domains concentrated around a direction of minimum εm, the effects of external forces on this distribution are discussed and SM=o is evaluated. Under such an assumption the vslucs of SH=0 in the directions of the principal axes of crystal can be evaluated from the ratio SH=0, [111]/SH=0, [111].The agreement of this result with the experiment is quite satisfactory