Magnetic Force Microscope - MFM Components

MFM Components

The main components of an MFM system are: Piezoelectric scanning

• Moves the sample in an x, y and z directions.
• Voltage is applied to separate electrodes for different directions. Typically, a 1 volt potential results in 1 to 10 nm displacement.
• Image is put together by slowly scanning sample surface in a raster fashion.
• Scan areas range from a few to 200 micrometers.
• Imaging times range from a few minutes to 30 minutes.
• Restoring force constants on the cantilever range from 0.01 to 100 N/m depending on the material of the cantilever.

Magnetized tip at one end of a flexible lever (cantilever); generally an AFM probe with a magnetic coating.

• In the past, tips were made of etched magnetic metals such as nickel.
• Nowadays, tips are batch fabricated (tip-cantilever) using a combination of micromachining and photolithography. As a result, smaller tips are possible, and better mechanical control of the tip-cantilever is obtained.
• Cantilever can be made of single-crystalline silicon, silicon dioxide (SiO₂), or silicon nitride (Si₃N₄). The Si₃N₄ cantilever-tip modules are usually more durable and have smaller restoring force constants (k).
• Tips are coated with a thin (< 50 nm) magnetic film (such as Ni or Co), usually of high coercivity, so that the tip magnetic state (or magnetization M) does not change during the imaging.
• The tip-cantilever module is driven close to the resonance frequency by a piezoelectric crystal with typical frequencies ranging from 10 kHz to 1 MHz.