Magnetic Nanoparticle Assemblies Imaged in an Applied Magnetic Field with the VFM.

The interactions between the tip and sample change from attractive (bright), to repulsive (dark) and back to attractive as the applied field is switched between zero and 1,100 Oe. Before this sequence of images were acquired, the sample was magnetized in a -2,000 Oe field. 5 µm x 10 µm scan. Imaged with the MFP-3D AFM. Sample courtesy of G. Agarwal, Ohio State.