Magnetic force microscope (MFM) tips coated by soft magnetic materials can achieve a spatial resolution above 10 nm. It is interesting to analyze why tips coated with soft magnetic materials can achieve such a high resolution. In experiment, an MFM tip coated by amorphous FeB can achieve a resolution of 8 nm; therefore, we chose an FeB tip as an example and establish a micromagnetic model to understand the measurement mechanism of the soft magnetic MFM tip. In the FeB film simulation, the random crystalline anisotropy results in a soft magnetic loop with an in-plane coercivity of 0.2 Oe, and the film surface roughness will raise the coercivity to the order of 1 Oe. In the tip simulation, it is found that the FeB-coated tip can be switched in a uniform field of the order of 100 Oe, but can remain near a remanent state in a stray field resulting from media. A simple model is set up to analyze the MFM images of bits in hard disk drivers using the simulated magnetic properties of the tip and resolution ∼ 10 nm is confirmed.
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