Resonant torque magnetometry: a new in-situ technique for determining the magnetic properties of thin film MFM tips

A new high sensitivity Resonant Torque Magnetometry (RTM) technique has been developed enabling the determination of the magnetic properties of Magnetic Force Microscope (MFM) tips in-situ. A sensitivity of better than 10^-12 emu (10^-15 Am²) has been achieved at ambient temperature and pressure. We have studied the micromagnetic properties of a variety of tip coatings including hard CoCr and CoPt films and soft permalloy. In-situ determination of the magnetic properties of MFM tips is vital if quantitative interpretation of MFM images is to be achieved especially when images are made in the presence of bias fields. The m(μ₀ H) loops obtained for CoPt tips have a shape similar to a standard magnetisation loop when the field is applied parallel to the tip axis. With the field applied perpendicular to the tip both CoPt and CoCr demonstrate behaviour consistent with partial demagnetisation of the axial moment, to which the RTM is sensitive