Magnetic domain structure of thin magnetic films
The domain structure of thin magnetic films and multilayers is likewise dependent on intrinsic properties such as bulk and surface anisotropies, exchange coupling constants or saturation magnetization and on extrinsic properties such as the film geometry or the precise microstructure. To fully understand the domain structure for a given magnetic history several energy terms (effective anisotropies, exchange, strayfield) have to be considered while looking for the minimum in the total energy of the complete system. Vice versa, the microscopic study of the domain structures of thin films and multilayers allows to evaluate the influence of the different energy terms and thus can quantify intrinsic parameters by comparing experimentally observed domain structures with domain theory.
The MFM picture above shows the stripe domain structure of small isolated Nd2Fe14B grains in the thermally demagnetized state. The epitaxial growth of the NdFeB film guarantees a very good alignment of the easy magnetization axis (the crystallographic c-axis) perpendicular to the surface. The strong uniaxial anisotropy of the Nd2Fe14B phase therefore leads to the formation of stripe domains with alternating ‘up-down’ magnetization which is imaged as a ‘bright-dark’ contrast in the MFM measurement. The image on the right shows the good agreement of the measured domain width for grains of different heights with the values expected from domain theory of extended films by considering the intrinsic properties of the Nd2Fe14B phase. See: V. Neu et al., Phys. Rev. B 70, 14418 (2004).
- V. Neu, S. Fähler, A. Singh, A.R. Kwon, A.K. Patra, U. Wolff, K. Häfner, B. Holzapfel, and L. Schultz, Domain structure and magnetic properties of epitaxial Rare Earth – Transition Metal thin films, J. Iron Steel Res. Int. 13, Suppl. 1, 102-111 (2006).
- V. Neu, S. Melcher, U. Hannemann, S. Fähler, L. Schultz, Growth, microstructure and magnetic properties of highly textured and highly coercive Nd-Fe-B films, Phys. Rev. B 70, 144418 (2004).
- K. Khlopkov, O. Gutfleisch, V. Neu, D. Hinz, K.-H. Müller, L. Schultz, Evolution of interaction domains with texture studied by magnetic force microscopy, Proc. 18th Int. Workshop on High Performance Magnets and their Applications, Annecy (2004) 478.