  We demonstrate the quantitative measurement of the magnetization of
individual magnetic nanoparticles (MNP) using a magnetic force microscope
(MFM). The quantitative measurement is realized by calibration of the MFM
signal using an MNP reference sample with traceably determined magnetization. A
resolution of the magnetic moment of the order of 10^(-18) Am^2 under ambient
conditions is demonstrated which is presently limited by the tip's magnetic
moment and the noise level of the instrument. The calibration scheme can be
applied to practically any MFM and tip thus allowing a wide range of future
applications e.g. in nanomagnetism and biotechnology.
