Development of High Resolution Magnetic Force Microscopy with High Sensitivity and Low Noise and Its Application to Nano-scale Magnetic Imaging

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Magnetic force microscopy (MFM) is widely used for magnetic domain observation. However the spatial resolution of commercial MFM is about several 10nm and is not enough to observe the recording bits of high density recording media. The purpose of this study is development of high resolution MFM and its application to nano-scale magnetic imaging. The following results were obtained.1. Development of high resolution MFM(1.1) Low noise MFM using tip coolingLow noise MFM was developed by adding the tip cooling equipment to high vacuum MFM. The noise of the MFM was reduced to the theoretical limit of thermodynamic noise of MFM cantilever by cooling a tip. The MFM can decrease the tip temperature and sample temperature to 42K and 32K, respectively. Low noise measuring condition can be obtained within 1 hour.(1.2) Fabrication of high resolution MFM tipsHigh-coercivity tip was fabricated by depositing FePt film on a surface oxidized Si tip made by O_2 plasma oxidation treatment and post-annealing of the tip. The coercivity of the tip is above 15 kOe and MFM resolution is about 10 nm. For further improvement of MFM resolution, a new high-resolution MFM tip using the cross section of an exchange-spring trilayer film [hard (low M_s) /soft (high M_s)/hard (low M_s)] was proposed and clarified the theoretical resolution is less than 5 nm by computer simulation. FePt/FeCo/FePt trilayers was fabricated for the application of MFM tip.2. Nano-scale magnetic imaging of high density magnetic recording mediaMedium noise-coercivity overlapping method was developed by using magnetic force microscopy and was used to study the origin of medium noise of 400~600 Gbit/inch^2 class perpendicular media. It was made clear that medium noise arises from (1) a spatial fluctuation of magnetization reversal filed in the media, where fluctuation length extends to about 100nm, (2) an insufficient magnetic field gradient of recording head.