Abstract. In this paper, magnetic force microscopy (MFM) probes with different coating materials were characterized under AC magnetic field. A perpendicular magnetic write head similar to those used in hard disk drives was employed as the AC magnetic field generator. In order to measure a response of MFM probes to AC magnetic field, a MFM probe under test was scanned, at a scan height of 10 nm, across the surface of the magnetic write head. During MFM imaging, the write head was biased by a sufficient magnitude of AC current, approximately 30 mA. A spectral analysis for a frequency sweep from 1 kHz to 100 MHz was extracted from post-processing MFM images. As expected, a MFM probe coated with hard magnetic alloys, i.e. FePt, has the lowest response to AC magnetic fields. MFM probes coated with soft magnetic alloys, i.e. NiFe and NiCoCr, have a relatively high and flat response across the frequency range. Ni coated MFM probe has the highest response to AC magnetic fields. In addition, CoCr and NiCo coated MFM probes show lower response than NiFe and NiCoCr probes at low frequencies; however, theirs response to AC magnetic field increase for the AC magnetic field with a frequency above 50 kHz. This can be implied that those MFM probes are a good candidate for being used to study the high-frequency performance of perpendicular magnetic write heads. Noting that response of all MFM probes significantly decreased when driven frequencies above 1 MHz due to the limitation of the hardware, i.e. response of quadrant photodiode and op-amp in a pre-amplifier.

Magnetic force microscopy (MFM) was employed to characterize the magnetic field distribution of two different designs of perpendicular magnetic writers with fully wrap-around shield (WAS). Typical magnetic write heads, located on a slider at the so-called air bearing surface (ABS), are composed of a magnetic write pole and a magnetic return pole. The write pole has a much small cross section area at the ABS than the return pole which is connected to magnetic shield. The write pole and the shield are separated by a non-magnetic gap layer. The shield structure is designed in such a way that it can confine the magnetic fields without significantly degrading field strength. In this work, MFM imaging was used to investigate the relationship between the gap structure and magnetic field strength/gradient. Magnetic field distributions of two different head designs were compared and discussed in detail. Experimental results revealed that the magnetic field intensity is linearly proportional to pole dimensions, especially the pole width. The field gradient, however, is dependent on not only spacing gap between shields and the write pole, but also the pole widths and thicknesses.

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Almost all previous studies on a thermal-induced pole-tip protrusion (PTP) were mainly focused on the extension of the main pole which in turn affects the flying height of magnetic recording heads and the hard-disk drive reliability. None was reported the PTP effect on a variation of write filed profiles that is directly related to the track width of the magnetic data. In this work, a method to characterize the magnetic field distribution of perpendicular recording heads with a protrusion in a pole-tip region was proposed and implemented. A magnetic head under test was biased with two current sources, one for the write coil and the other for the heater. The write field was then observed by magnetic force microscopy (MFM). MFM images were post-processed in order to investigate the field profiles. Two models of magnetic write heads having different heater designs were employed as test samples. We observed the variations in the area of the write field for the write heads having the protrusion of the pole tip, while the magnitude of the field intensity was almost constant.