We report results of a quantitative investigation of MFM sensitivity vs. tip coating thickness. Etched Si tips on cantilevers 225 pm in length were sputter-coate! with Co-Cr films of various thicknesses 150 d < t < 1500 A. Tip response was measured by scanning a specially-written hard disk with tracks of selected bit reversal densities. Tracking the shift in cantilever resonant frequency caused by the diskstray fields gave a measure of relative sensitivity, and hence tip moment. The main finding is a roughly linear increase in sensitivity (effective moment) up to a critical film thickness near 500 A beyond which saturation occurs. For 500 A coatings, sensitivity varies about 15% from tipto-tip, indicating the degree of uniformity that can be expected from batch fabrication. We estimate the effective tip moment to be about 10-l2 emu, implying that only a small portion of the tip's magnetic volume plays a role.
We present a technique for characterizing the magnetic state of a magnetic force microscopy (MFM) probe as a function of uniform external magnetic field H. A local magnetic field is generated by micron-scale current carrying conductors and directly imaged by MFM. As H alters the magnetic state of the probe, changes in image contrast yield componentwise measures of the tip’s net magnetic moment m, tip hysteresis loops and coercivities, and possible orientations (vertical vs lateral) of remanent states mr used for most MFM imaging. Results are presented for a variety of thin-film probes.
We present a technique for measuring the coercivity of magneto-optical and perpendicular recording media on a submicron scale using a magnetic force microscope and an electromagnet. Co–Cr coated silicon tips were used to write and image magnetic bits down to 150 nm in diameter. Bits were written when the sum of the tip stray field and an external field Hext exceeded the local, or ‘‘point’’ coercivity. Media can be characterized by a continuous write probability Pw(Hext) which differs significantly from bulk hysteresis loops. For an intermediate field range, writing was intermittent (0<Pw<1) due to spatial variations in media properties.
We have developed a technique to quantitatively image the magnetic field above a magnetic specimen using a modified magnetic force microscope (MFM). The technique depends on the nonlinear response of a magnetically soft MFM tip to the sample field and to an externally applied field, similar in principle to fluxgate magnetometry. We demonstrate the technique with high resolution, quantitative images of the magnetic field above a sample of longitudinal recording media. The magnetic field resolution is on the order of 1 Oe, with sub-100 nm spatial resolution comparable to standard MFM techniques.
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