No abstract

The magnetization reversal in a sputtered Sm 40 Fe 60 (88 nm)/Ni 80 Fe 20 (62 nm) hard/soft bilayer with induced uniaxial anisotropy was investigated by Kerr microscopy and magnetometry. In the reversible regime of the hysteresis loop a twisting of magnetization across the thickness of the soft magnetic film could be derived. The hard layer reverses by the nucleation and growth of regular domains. They are separated from the nonswitched areas by tilted domain walls, the angle of which can be predicted by considering the net magnetic moments of the bilayer system.

No abstract

A wide-field polarization microscope, optimized for Kerr microscopy was extended with a mode-locked pulsed laser illumination source to investigate time-dependent magnetization processes with picosecond resolution, thus providing the possibility to directly compare the quasistatic with the dynamic magnetization response. Square-shaped Ni 81 Fe 19 elements were excited by fast magnetic field pulses aligned along and diagonally to the elements, respectively. Starting from the Landau ground state, the magnetic response to the excitation is dominated by a fast rotation of magnetization followed by slow relaxation, mostly through domain wall motion, back into the Landau state. Spike domains in the corners of the element form during the fast rotational process. Low angle domains with oscillatory behavior develop in the low dynamic permeability closure domains. Slow motion of the center vortex over several nanoseconds is recorded. The direct comparison of the dynamic and the static domain patterns is necessary for a understanding of all details of the magnetization processes.

We used Kerr microscopy to investigate the magnetization processes of NiFe-Co/Cu/Co/ FeMn spin-valve meanders for magnetoresistive sensors and compared them to processes in related single films and bilayers. We observed irregular switching, characterized by the irreversible decay of blocked domains or by domain nucleation at 360 walls, in the related films and in the free layer of the spin-valve system. Both effects are connected with hysteresis. Edge-curling walls are responsible for rotational hysteresis in the giant magnetoresistance signal of the spin valves, occurring during field rotation in clockwise and counterclockwise directions. The U-turns of the meanders and their shape have no relevant influence on the magnetization behavior and hysteresis effects.