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Mapping of magnetic stray field distribution over the surface of a sample in MFM require probes with magnetic coating. The probe is sharp enough to image magnetic domains on surface.

The Co-Cr coating on most MFM probes creates a magnetic moment of about 1400 emu/cc. Imaging in external magnetic field is a way to enhance the sensitivity further as it may increase the moment of both the MFM tip and the sample. Note that the magnetic structure of some samples having low coercitivity (permalloy, garnet films, etc.) may be significantly affected by the magnetized Co-Cr coated probe.

Though the Cr provides a protection for Cobalt from oxidizing, magnetic probes have a limited shelf life that ranges from weeks to months and depends mostly on humidity. However, there may be other reasons why probes loose sensitivity. Sometimes, magnetization with an arbitrary stong magnet may help to restore the probes, e.g. SmCo or NdFeB.
Height image obtained in Tapping mode. MFM map of the same area showing magnetic domain structure.
Height and phase images of the magnetic dipoles obtained using Co-Cr cantilevers. The structure is formed in a layer of Fe0.7C0.3 by annealing with interfering laser impulses . Images are courtesy of Prof. Sheviakov (MIET, Moscow).

 

Probes

Co-Cr coated
 

Magnetic Co-Cr coating is a Co layer of about 60-nm thickness on the tip and backside of the cantilever, which is protected from oxidation by 20-nm Cr film. The resulting curvature radius of the tip is 90 nm . The cobalt layer is formed as a polycrystalline film, which allows steady permanent magnetization in the direction of the tip axis.

Typical coercitivity Hc of the Co-Cr coating ranges from 300 to 400 Oe.


 
magnetic

Probes with magnetic coating for MFM.

90 nm radius magnetic tip
Co-Cr coated
 
 

 

 

 

 
 
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