Quantification of magnetic force microscopy using a micronscale current ring

Metal rings with inner diameters of 1 and 5 mu m, 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's long axis, m(z), can be determined from the MFM signal of the ring at a different scan height and a different electric current 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 Si tip coated with 65 nm cobalt on one side, q is 2.8X10(-6) emu/cm, m(z) is 3.8X10(-9) emu, and m(x) and m(y) are in the order of 10(-13) emu, which are negligible compared with m(z). Furthermore, the MFMs sensitivity to the second derivative of the magnetic field was determined from the minimum ring current for a measurable MFM signal to be 0.1 Oe/nm(2). (C) 1997 American Institute of Physics.