Magnetic AFM Probes

Co-Cr coated AFM tip close-up

Typical radius of uncoated AFM tip
8nm
Resulting AFM tip radius with the coating
<60nm
Full AFM tip cone angle*
40°
Total AFM tip height
12-18µm
AFM Probe material
n-type silicon
AFM Tip coating
Magnetic
Detector coating
Aluminum

*The full cone angle may be less than 40° at the last 200nm of the AFM tip end.

The coating consists of a Co layer on the tipside of the AFM cantilever. The Co layer is formed as a polycrystalline film, which allows steady permanent magnetization in the direction of the AFM tip axis. The Co coating is protected from oxidation by a thin Cr layer, resulting in longer AFM cantilever performance. Typical coercivity Hc of the Co-Cr coating ranges from 300 to 400 Oe.

All chips are pre-magnetized at the facility before shipping to end users. In some cases additional magnetization by an arbitrary strong magnet is required, e.g. SmCo or NdFeB.

1-AFM Cantilevers series

3-AFM Cantilevers series

Application

AFM probes with magnetic Co-Cr AFM tip coating can be used for Magnetic Force Microscopy (MFM) research. Mapping of magnetic stray field distribution to topography AFM scans can help characterize the domain structure of the magnetic materials.

The Co-Cr coating on most MFM probes creates a magnetic moment of about 10-13emu. 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 coercivity (permalloy, garnet films, etc.) may be significantly affected by the magnetized Co-Cr coated AFM probe.

Though chromium provides protection for cobalt from oxidizing, magnetic AFM probes have a limited shelf life that ranges from weeks to months that depends mostly on humidity. However, there may be other reasons why AFM probes lose sensitivity. Sometimes, magnetization with an arbitrary stong magnet may help to restore the AFM probes, e.g. SmCo or NdFeB.

Height and phase images of the magnetic dipoles obtained using Co-Cr AFM cantilevers. The structure is formed in a layer of Fe_0.7C_0.3 by annealing with interfering laser impulses . Images are courtesy of Prof. Sheviakov (MIET, Moscow).