Magnetization reversal and coercivity of magnetic-force microscopy tips

An experimental technique is presented that allows determining the magnetiz ation reversal and coercivity of magnetic-force microscopy (MFM) tips. An O mega -shaped current carrying gold ring with a radius of 2400 nm fabricated by electron-beam lithography and a lift-off technique is charged with a co nstant current in order to produce a magnetic stray field in the z directio n that is detected by MFM. While an oscillating MFM tip is continuously ras ter scanned across the center of the current ring, an external magnetic fie ld is applied in the z direction and increased in magnitude in order to rev erse the tip magnetization during imaging. Thus, the corresponding changes in the measured image contrast exclusively describe the magnetization rever sal and coercivity of the particular part of the tip that is used for imagi ng. We have investigated commercially available thin-film tips and we find that the hysteresis loops measured with MFM may be significantly different as compared to hysteresis loops measured by means of superconducting quantu m interference magnetometry on the respective magnetic tip coatings of the same tip. (C) 2001 American Institute of Physics.