Shape effects in the magnetic structure and properties of ferromagnetics

Abstract

1. Flat ferromagnetic specimens can show changes in structure and properties (λ, μ, Hc) dependent on the shape during annealing if there is the appropriate relation between Δfs and Δfσi. The effects are pronounced only if ¦Δfs ≃ ≃ Δfσi ¦. 2. The precise effects are dependent on the orientation of the crystal relative to the plane of the sheet and to the magnetic field; the best is {110} [100] (for cubic crystals with k1. > 0). 3. The effects should be very much dependent on the thickness of the sheet, each material having an optimal thickness, which is dependent on the state as well as on the material. This thickness tends to increase as the internal stress is reduced. 4. The additional magnetic texture arises during annealing by relief of the additional magnetostriction stresses produced by reversal in those parts of domains for which ¦Δfs¦ > Δfσi ¦. This effect is governed by the temperature dependence of k1 and λ100 (for ki > 0) or λ111(ki > 0); it is large only in materials for which λ100 (or λ111) is large at temperatures sufficient to relieve these magnetostriction stresses. 5. E310 and E330 transformer steels satisfy all these conditions; they obey ¦Δfs Δfσi ¦ after annealing at sufficiently high temperatures. 6. The form texture in E310 or E330 should decrease as the temperature rises towards 550 °C, because ¦Δfs/Δfσi ¦ then falls.