As the feature size of disk surfaces in magnetic recording continues to decrease and the head hovers just 50 nm above the disk surface, there is an increasing need to ensure precise and contaminant-free surfaces. AFM can be employed to check the surface for defects as well as contamination. The mapping of magnetic forces to topography AFM scans can be used to characterize the domain structure of magnetic materials, as well as to visualize information bits recorded to magnetic media.

The AFM technique used for the characterization of the magnetic field distribution over a sample surface is known as magnetic force microscopy (MFM). This is a two-pass mode, where the surface topography is measured in tapping mode during the first pass and magnetic forces are mapped on the second pass with respect to the topography data.

Magnetic Force Microscopy (MFM)

Cantilevers with a magnetic Co-Cr coating should be used for MFM research. The coating is formed on both sides of the cantilever to prevent the bending from intrinsic stress and increase the reflection of the laser beam.

The spring constant and resonant frequency of the cantilever should be chosen to provide stability in tapping mode, as well as high sensitivity to weak magnetic forces during the second pass.

Though the cantilevers are magnetized at the facility, you may need a magnetizer to magnetize them additionally. It is recommended to keep the probes in a dessicator to prolong prolong their shelf life, which is limited to approximately 6 months due to oxidation. Low or absent magnetic signal implies that the coating has been oxidized by ambient humidity.

Note that the structure of "soft" magnetic samples like Permalloy or garnet films can be significantly changed by the field of the Co-Cr coated probe, which has a relatively high coercitivity of 300-400 Oe.