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Principle of the SM-MFM technique. Two scans are performed at low lift distance (1–20 nm) with tip magnetization (arrow close to the tip) reversed by an external field B ext.
(a) and (b) SEM picture of the fabricated SM-MFM probe coated with 20 nm Py triangle. Left is the side view of the probe, and on the right panel is the top view. The Py triangle is in magnetic single domain state. External field of BEXT ∼8 mT switches its magnetization to the desired (up or down) direction. (c),(d) SEM images of the tip apex before (c) and after (d) evaporation of 20 nm Py layer showing the change in the tip's radius.
The dependence of the magnetization switching field of the 20-nm thick Py triangle with cone angle 36° on inverse triangle height as calculated by OOMMF simulator (inset).
Semicontact mode height amplitude or topography (a),(b) and MFM phase images of written bits in a high-density parallel recording medium (30 Gb/in2) at a scan height of 10 nm (d),(e) for SM-MFM tip of positive (left column) and negative (middle column) polarities. The width of the scanning area is 2 μm, topography amplitude is 15 nm, phase contrast 2°. Image (c) is calculated by adding the phase images with opposite tip polarities (d) and (e), and image (f) represents the difference of the phase images (d) and (e) obtained with opposite tip polarities.
(a) and (b) Semicontact mode height amplitude (topography) images using commercial (a) and SM-MFM (b),(c) tips. Phase images from scans at lift height of 5 nm obtained using commercial (e) and SM-MFM (f),(g) tips on a sample of flat high-density perpendicular recording medium (625 Gb/in2). Images (b) and (f) are taken with positive magnetization of the SM-MFM tip and (c) and (g) with negative one. Calculated topography (d) = (f) + (g) and MFM (h) = (f) − (g) signals from the phase images (f) and (g). Image area is 1 × 0.6 um2. The white dotted rectangle shows of the bit track pattern.
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