Imaging Magnetic Domains

There are many different ways to image magnetic domain structures in a material. All the microscopy techniques we described in Chapter 10 can be used, although, in some cases, deviations from the usual operating procedure are necessary to obtain the desired images. It is also possible to use X-ray topography to study magnetic domains. In this section, we will briefly describe three techniques the oldest, one of the newest, and the trickiest. 

FIGURE 33.18 Magnetic domains on the basai surface of a hexagonai ferrite, Co2Ba2Fe2s046, reveaied by the Bitter technique. 

The effect of M on the reflected light intensity is known as the Kerr effect. The polar Kerr effect refers to a situation in which the sample has a component of M normal to the surface and normal incidence illumination is used. The longitudinal Kerr effect is used when M is parallel to the surface and the illumination is oblique. 

FIGURE 33.19 Domain pattern in a YIG thin film revealed by the Faraday effect. The stripes are 12pm wide. 

FIGURE 33.20 Schematic of MFM of a magnetized pattern on a hard drive. 

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By using circularly polarized X-rays from a synchrotron source the intensity of photoemission becomes dependent on the magnetisation of the sample. This can be used to provide element specific magnetic contrast for imaging magnetic domains whose behaviour can then be studied in real time. 

Element specific magnetic contrast capability for imaging magnetic domains. Real time element specific imaging. 

Figure 6 Scanning Karr image of the magnetization changes in the indirection for a thin-film head having a 1-MHz, 5-mA p-p coil current, and the magnetic domain pattern deduced for this head from the observed domain wall motion. ...

The second mode of operation is the non-contact mode, in which the distance between tip and sample is much larger, between 2 and 30 nm. In this case one describes the forces in terms of the macroscopic interaction between bodies. Magnetic force microscopy, in which the magnetic domain structure of a solid can be imaged, is an example of the non-contact mode operation. 

The essence of the topographic methods is that they map the interrsity of the diffracted beam over the surface of the crystal. Defects affect the diffracted intensity, so give contrast in the image. The methods are quite sertsitive enough to reveal individual dislocatiorrs, precipitates, magnetic domains and other long-range strain fields but cannot reveal point defects except in dense clusters. 

Figure 10.5 Real-time image, with no computer processing, of magnetic domains and low-angle boundaries in iron-silicon taken using the Bede Scientific HI-RES detector at Daresbury Laboratory. The white radiation topograph was taken with X-rays of fundamental wavelength 1 A...

Figure 3. AFM (A and C) and MFM images (B and D) of a CoCrPt thin film medium directly patterned by FIB. Magnetic-domain images taken by spin-SEM after electron bombardment of a centered square for 1200 s (E) in-plane, and (F) out-of-plane magnetization component.

Microscopy electron, light (with video enhancement), scanning tunneling, atomic forces, IR microscopy, NMR imaging, thermal and magnetic domain microscopy. 

Fig. 8-37 Borrmann effect, (a) Formation of topographic images, (b) Topograph of a crystal of Fe + 3 percent Si, 0.36 mm thick, showing magnetic domains (black and white stripes) and dislocations (white lines). 020 reflection, Co Ka radiation. (Courtesy of Carl Cm. Wu [8.26].)...

Fig. 7.1 Magnetic domain images were observed through the Kerr effect of Co-Ni-Fe-P soft magnetic underlayer on a disk substrate electroless-deposited (a) without and (b) with an external appUed magnetic field. The thickness of each sample is 1 pm [15]. 2004 IEEE...

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