Study of magnetic properties of magnetic force microscopy probes using micronscale current rings

Metal rings with inner diameters of 1 and 5 μm, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy (MFM). A MFM tip’s effective magnetic charge, q, and effective magnetic moment along the tip long axis, mz, can be determined by the current flowing in the ring. The magnetic moments in the directions transverse to the tip’s long axis were estimated by a straight current wire. It was found that for a silicon tip coated with 65 nm thick cobalt on the side, q=2.8×10−6 emu/cm, mz=3.8×10−9 emu, and mx=my=10−13 emu, which are negligible compared with mz. Furthermore, the tip’s sensitivity to the second derivative of the magnetic field was found to be about 0.1 Oe/nm2.