Temperature dependence of lancet domains in grain-oriented Fe-3%Si steels

Grain-oriented Fe-3%Si steels are industrially important soft magnetic materials that are usually used in transformer cores but have also recently started to be used in motor cores. Further improvements in the magnetic properties of grain-oriented steels are required to increase the efficiency of electrical machinery. The magnetic properties of grain-oriented steels strongly depend on the magnetic domain structures. The magnetic domains in grain-oriented steels mainly consist of the 180° basic domains and supplementary domains, such as lancet domains. The lancet domains, which occur due to a tilt angle of the [001] easy axis out of the steel surface (β), affect not only iron losses but also magnetostrictive noise. Therefore, it is important to understand the behavior of the lancet domains in order to further improve the magnetic properties. Many studies of the lancet domains have been performed, for example, under applied stresses and external magnetic fields at the room temperature (RT). However, the behavior of lancet domains in the region above RT has not yet been investigated even though the operating temperature of transformers and electric motors are generally above RT. In this paper, the changes in the lancet domains of grain-oriented steels over the range from RT to the Curie point were observed using photoemission electron microscopy combined with X-ray magnetic circular dichroism (XMCD-PEEM). Moreover, the domain theory enabled us to quantitatively explain the observed temperature dependence of the lancet domains.