A combined magnetooptic/magnetic force microscope study of Co/Pd 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 capabilities and large field of view of the MO microscope. Our MO/MFM setup is based on the Nanoscope III Multimode™ MFM/AFM (Digital Instruments, Santa Barbara, CA). Currently, the spatial resolution of the MO microscope is about 3 μm and polarization sensitivity is on the order of 0.5°. Using this instrument, we observed domain structures in Co/Pd multilayerfilms. We found that in a 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 on the sample surface. The depth of the defects is 1–2 nm, they are 20–30 nm wide and up to 500 nm long. The unidirectional displacement of the domain walls was found to correlate with the anisotropic structure of the sample surface.