| Magnetic force microscope (MFM) has been widely used to characterize thedomain structures of the hard disk and read/write head in magnetic recording industrysince it was invented. Nowadays, the coating materials of high-resolution MFM tipinclude cobalt-based alloy and iron-platinum alloy, which are the recording layer usedas the current perpendicular recording media and as a candidate for next generationmagnetic recording media, respectively. As the rapid growth of the areal density, it isurgent to develop higher resolution MFM tips to image and quantitatively explain thenano-scaled domain structures of magnetic materials in the magnetic recording system.However, it is difficult to characterize the microstructure and magnetic properties oftip-coating by experiments. Moreover, the effective magnetic dipole and its exactposition are not well discussed in thepoint probe model of the tip. In this thesis, theposition of the effective dipole in a MFM tip is determined by the multipole expansiontheory in classical electromagnetism. The magnetic moment distribution in a MFM tipcan be calculated by micromagnetic simulation. An accurate3-D micromagnetic tipmodel is set up, and the relationshipsamong the tip shape, magnetic properties andmicrostructure of tip-coating and the MFM image resolution have been systematicallystudied. The result obtained is in good agreement with experiments and explains furtherfor the improved resolution in the recent experimental reports. The understanding fromthis study throws light on designing MFM tips for high resolution.Intrinsic magnetic properties of theL10-FePt thin film media and the CoCrPt-basedperpendicular media with soft magnetic underlayer (SUL) are studied. This study is thefoundation for accurately setting up the MFM tip model and the sample model. Grainsize, inter-grain exchange coupling and lattice mismatch between different layers areincluded in the model. The simulated out-of-plane loop of L10-FePt thin film matchesthe experimental loop very well. The mechanism responsible for magnetizationreversalandpotential application of the thin film are studied and discussed. Amicromagnetic model of CoCrPt-based perpendicular disk media is set up, whichincludes a thick amorphous soft under layer (a-SUL). The a-SUL will decrease thecoercivity (Hc) of the recording layer (RL), which is beneficial for the writing process.However, due to the large saturation magnetization (Ms) and its large volume, a-SUL affects much on the measurement of crystalline anisotropy constant (K1) of RL bymeasuring torque curves of the whole disk media, which should be etched away beforemeasuring.An accurate pyramid tip model is set up, which includes polyhedron cells in the tipsurfaces and edges. The analytical solution of the demagnetizing matrix of a trianglewas obtained earlier by our group. Calculated tip stray field and the effective dipole arein good agreement with experiments. Furthermore, a micromagnetic model of pyramidtip coated by hard magnetic thin film is set up with the grain structure included in thethin film;and magnetic properties and microstructure of tip-coating arestudied. The tipwith perpendicular magnetic anisotropy (PMA tip) can measure the micromagneticstructures of granular thin film medium with a linear density of1600kfci accurately atlow scan heights of2nm to8nm, and tip with in-plane magnetic anisotropy (IMA tip) isa good choice for measuring the domain structure of bit patterned media with an areadensity of2.5TB/in~2at a low scan height of2nm. |
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