Switching behaviour of patterned SmCo thin films
The domain structure of highly coercive, epitaxial SmCo5 thin films with well defined direction of the easy axes in the film plane was studied to understand the nature of the magnetization process. For MFM measurements, the film was patterned and magnetized up to 5 T to adjust different remanent states and afterwards the domain structure was imaged. In the thermally demagnetized (0 T) state magnetic contrast is visible at a length scale of 200 nm which is about 4-5 times larger than the size of the individual grains. Thus, one has to describe the magnetic state by interaction domains originating from exchange or dipolar coupling of neighbouring grains. Upon applying an external field, the stray field contrast inside the element reduces and magnetic charges of opposite sign build up at the two edges of the squares perpendicular to the field direction indicating a non zero net magnetization. Small areas within the element remain oppositely magnetized even in fields larger than the coercivity and only vanish upon full saturation at about 5 T indicating a pinning dominated switching behaviour The three line scans show the development of the domain size and the appearance of the stray field contrast at the element edges for the different applied magnetic fields. See: U. Wolff, A. Singh, L. Schultz, V. Neu, Switching behaviour of patterned SmCo5 thin films investigated by magnetic force microscopy, JMMM, 310, 2210 (2007)
Magnetic domain structures in [Co/Pt]/Ru multilayers
[Co/Pt]/Ru multilayer consists of several layers of Co/Pt stacks, each with strong perpendicular anisotropy, and separated by a Ru spacer layer which mediates an antiferromagnetic coupling between the Co/Pt stacks. Due to the competition of ferromagnetic dipolar coupling and antiferromagnetic coupling these samples display a large variety of different magnetic domain configuration.
The field-dependent domain structure of a [(Co(4Å)/Pt(7Å))8]/Ru(9Å)]18 multilayer was investigated by magnetic force microscopy (MFM). At RT, this sample stays in purely dipolar coupled state and displays the typical band domains for films with perpendicular anisotropy. Measurements were performed using a Digital Instruments Dimension 3100, upgraded for measurements with an external magnetic field up to 0.4 T applied perpendicular to the sample.
The figure shows the development of the typical band domain structure upon increasing an external perpendicular magnetic field. The domains modify gradually, without changing the general configuration, until they transform into a bubble domain structure at 0.38 T, which is about 80% of the saturation field of the sample.