We imaged the magnetic domain of an extremely rough surface (with a roughness of ∼1 μm) of the anisotropic Sr ferrite sintered magnet without any topographic crosstalk by alternating magnetic force microscopy (A-MFM) using a sensitive FeCo-GdOx superparamagnetic tip. The magnetic moment of the FeCo-GdOx superparamagnetic tip is driven by an external AC magnetic field applied out of the plane direction to the magnetic sample. The static magnetic field is from the rough fractured ferrite sample parallel to the direction of the external AC magnetic field and is imaged by modulating the magnetic moment of the superparamagnetic tip. By using the frequency demodulation phenomena, A-MFM can extract the magnetic signal without any topography crosstalk versus the conventional MFM method. The intensity and the polarity of the static magnetic field originate from highly rough fractured hard magnetic Sr ferrite samples, and these were successfully detected and identified. This technique with the as-fabricated FeCo-GdOx superparamagnetic tips gives information about the intensity as well as polarity of magnetic fields from the magnetic domain structure of very rough fractured magnetic materials without any topographic crosstalk. This is crucial for the development of high performance hard magnets and magnetic devices.

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