Magnetic Force Microscopy (MFM)

Magnetic force microscopy (MFM) is a phase imaging mode that uses atomic force microscope cantilevers with a thin magnetic coating in order to probe the magnetic field between a sample and a magnetized tip. This method is commonly used to image any materials with heterogeneous magnetic properties such as magnetic-based hard disk drives. It can be operated in single, interlaced and dual scan line modes. Any of these modes require optimization of the height above the sample at which the magnetic force microscopy image is collected.

The MFM measurements below show 80 µm topography (left) and magnetic force microscopy (center) images of polished stianless steel, plus a zoomed in image of the MFM signal (right). The topography shows minor topographical features, whereas the corresponding magnetic force microscopy image reveals 3 distinct areas: the areas showing meandering being the magnetic ferrite phase, in which contrast and frequency depend on the domain orientations.

AFM topography image of stainless steel
Topography of a polished stainless steel sample. Scan size: 80 µm. Height range: 50 nm.
Magnetic force microscopy (MFM) image of stainless steel
Magnetic force microscopy (MFM) of the same 80 µm × 80 µm area. Phase range: 10°.
Magnetic force microscopy (MFM) image of stainless steel (zoomed in)
Magnetic force microscopy (MFM) of a smaller area. Scan size: 13 µm. Height range: 50 nm.

Two further examples of magnetic force microscopy (MFM) measurements come from the field of data storage. The first two images show the topography and MFM data of a hard disk drive platter, while the third image shows magnetically stored data on a digital backup tape. Magnetic force microscopy can play a crucial role in studying material or product defects.

AFM topography image of a harddisk platter
Surface topography measurement (dynamic force mode) of a hard disk drive platter. The recording tracks, as evident in the MFM image, run parallel to the grooves. Scan range: 2 µm. Height range: 5 nm.
Magnetic force microscopy (MFM) image of a harddisk platter
Magnetic force microscopy (MFM) measurement of a hard disk drive platter (same area). White and black areas show magnetization reversal, where white stands for repulsive forces and black for attractive forces. Scan range: 2 µm. Phase range: 5°.
Magnetic force microscopy (MFM) image of digital backup tape
Magnetic force microscopy (MFM) of digital backup tape with magnetically stored data. Scan size: 50 µm.