A COMBINED MAGNETO-OPTIC-MAGNETIC FORCE MICROSCOPE STUDY OF AMORPHOUS AND MULTILAYER FILMS

Abstract

We have combined a Magnetic Force/Atomic Force Microscope (MFM/AFM) with a Magneto-optic (MO) microscope. This instrument combines the high spatial resolution of the MFM/AFM and its capability to correlate magnetic structure with the structure of the sample surface with the real-time imaging capability and large field of view of the MO microscope. Using this instrument, we studied nucleation and displacement of domain walls (DW) in amorphous TbFe alloy films and Co/Pd multilayer films. We found that in Co/Pd multilayer film with 20 Co/Pd layer pairs and 16 nm total thickness, nucleation of domains during sample remagnetizations occurs repeatedly in the same points, and that displacement of domain walls is unidirectional. The high topographic resolution of the AFM allowed us to show that domains nucleate at small defects (1-2 nm in depth) on the sample surface. The unidirectional displacement of the domain walls was found to correlate with the anisotropic structure of the sample surface. We observed reversible bending of domain wall segments pinned to defects and irreversible, jump-like displacement of domain wall segments in an applied magnetic field. The maximum reversible displacement of domain walls was 50-100 nm and the length of the segments which reversibly curved in the field was about 150 nm. Measurement of the change in radius of curvature of a DW segment in response to an applied field allowed estimation of the DW energy density and local self-demagnetizing field of the film acting on the DW. The irreversible displacement of a DW was not a continuous process. The 200 - 400 nm long DW segments exhibited jump-like motion over distances of 100-150 nm.