George D. Skidmore

Improved spatial resolution in magnetic force microscopy

Electron beam deposited spikes for use in magnetic force microscopy have been grown onto atomic force microscope tips and coated with magnetic thin films using thermal evaporation. The resulting magnetically active regions are a close approximation to monopoles or dipoles located on the very end of the spikes. We show that these tips image with increased spatial resolution and less sample perturbation than the standard, commercially available tips.

Quantitative magnetic field measurements with the magnetic force microscope

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.

Magnetization reversal processes in perpendicular anisotropy thin films observed with magnetic force microscopy

Abstract We have carried out studies of the magnetic reversal process of a rare earth–transition metal thin film with perpendicular magnetic anisotropy using a magnetic force microscope (MFM) capable of applying in situ magnetic fields. The magnetization of the microscopic area shown in MFM images was determined for a number of field values comprising a complete hysteresis loop. This microscopic hysteresis loop was found to be nearly identical to a bulk hysteresis loop. Changes in the magnetization of the film as the hysteresis loop was traversed can be linked to individual microscopic domain changes evident in the MFM images. These studies show that the magnetization of this film was characterized by a two-stage process – fast and slow rates of change of magnetization with applied field. A second experiment in which the film was incompletely saturated and brought back to zero field showed that domain nucleation was not responsible for the rate of the fast process, but rather all magnetization changes were primarily limited by the low domain wall mobility. These observations are linked to previous work on magnetization processes in similar magnetic systems.

Microscopic magnetization reversal in perpendicular anisotropy CoCr thin films

Magnetic force microscopy was used to observe the magnetization reversal in a CoCr thin film on a grain/subgrain scale. The combination of high resolution topographic and magnetic images were used to relate microscopic magnetization changes to the microstructure of the sample. Both uniformly and partially magnetized grains and both uniform and partial magnetization reversal were observed. Statistically, the uniform magnetic state was more prevalent. In addition, there was a visualization of the flux closure between grains.

Magnetic reversal of tapered permalloy bars with holes in the center

The magnetic reversal mechanism of tapered permalloy bars with holes in the center was studied using a Magnetic Force Microscope with in situ magnetic field capability. The samples studied were lithographically patterned from a 20-nm-thick NiFe film using a subtractive process to create tapered bars 18 wide×348 μm long. The easy axis of the permalloy is parallel to the long axis of the bar. In the center of the tapered bar was either a 10, 5, or 3 μm diameter hole. The remnant state after saturation parallel to the long axis of the bar is a large domain magnetized along the saturating field direction except near the hole. The magnetization at the edge of the hole can be explained by considering edge pinning and the last direction of a saturating magnetic field. An inplane magnetic field parallel to the long axis of the bar reverses the magnetization by domain nucleation at the edge of the hole. After the bar has reversed, the same type of wall structure is seen as in the remnant state. As the magnetic fie...

Localized magnetostrictive magnetization reversal using scanning probe tips

Localized magnetic reversal of a perpendicular anisotropy thin film has been performed using the magnetostrictive response of the film to a force applied by probe tips of scanning force microscope cantilevers. Non-magnetic and magnetic cantilever tips were used to apply local stresses which alter the local magnetization through magnetostriction. The magnetic field of the tip, if any, and the local demagnetizing field of the film reverse the stressed area for stresses exceeding a critical value. These findings were in agreement with a simple model.

Direct observation of the high frequency write response of recording heads using the magnetic force microscope (abstract)

A direct measure of the high frequency (HF) response of recording heads is becoming increasingly important as storage densities head toward 10 Gb/in.2. One of the quantities for characterizing head response is the value of the magnetic field at high write frequencies. Typical, HF testing of heads has been mostly indirect; the recording head is used to write data to a disk and the head performance is evaluated based on the readback signal. The results of the testing depend on the test media and the readback system in addition to the actual HF performance of the recording head. To our knowledge, the only direct testing of HF head response was done with a scanning magneto-optic photometer which images the dynamic domain structure of the recording head.1 Unlike these other techniques, the magnetic force microscope (MFM) responds directly to the magnetic field above the recording head. Normally, the MFM response time is limited by the resonant frequency of the cantilever, typically 60–80 kHz in our system. How...