Temperature dependence of 180° domain wall width in iron and nickel films analyzed using electron holography

Although numerous studies have been dedicated to magnetic domain walls since their discovery, some issues concerning their essential features remain unclear. For bulk ferromagnets, the Bloch-type 180° domain wall width is scalable by the characteristic length A / K, where A is the ferromagnetic exchange stiffness constant and K is the magnetocrystalline anisotropy constant. This relationship has long been thought to be applicable to the domain walls that we can commonly observe using electron microscopy and other magnetic imaging techniques. In this study, we investigated the temperature dependence of the Bloch-type 180° domain wall width introduced in thin (100) iron and (110) nickel films using electron holography and elucidated that the temperature dependence of the domain wall width does not follow that of A / K. The domain wall width changed non-monotonically, showing an obvious discrepancy with A / K that dramatically increases with increasing temperature. This discrepancy may arise from the contribution of the magnetostatic energy to the total domain wall energy, which has been overlooked or less often considered. The magnetostatic energy plays a key role in squeezing the domain wall near the specimen surfaces. A revised energy landscape can reproduce the temperature dependence of the observed domain wall width and hence provides an easy-to-use approach to exploit the magnetic properties of A and K over a very wide temperature range below the Curie temperature.