High resolution magnetic domain images under magnetic field

The dependence of the domain structure of thin magnetic films on the size of the sample, its thickness, shape, and the effect of the underlying layer on the domain structure will be imaged using magnetic force microscopy. We will be able to improve the performance of magnetic devices by better understanding the response of magnetic domains under magnetic fields.

An example of this type study is shown in Fig. 1. In this case, the magnetic field was applied along the hard axis [110] of a patterned epitaxial (110) Fe film. The sample has a 10 µm width, 200 µm length, and 100nm thickness. The magnetization curve was measured by a SQUID magnetometer. The detailed domain evolution can clearly be seen, showing that we are able to directly correlate the magnetic domain patterns with the magnetization curve. Very different domain patterns were observed when the applied magnetic field was along the easy axis [001] (that is not shown here).

Fig. 1 There are magnetic domain structures of a patterned epitaxial (110) Fe film under a magnetic field. The film was magnetized at -5,000 Oe before the measurement. (a) at -400 Oe, the edge domain wall is formed, (b) at -300 Oe to -270 Oe the domain wall starts to propagate from the edge into the sample. It shows a rapid change of magnetization, (c) at -260 Oe the domain struture is formed in the film. (c) (d) (e) (f) Between -260 Oe and 260 Oe, the domain walls only move within a short distance. This shows flux closure domains. (g) at 300 Oe the domain wall is start to disappear, domain walls exist only at the edge and at the surface (The surface domain walls has a much lower signal i.e. light color.) (h) at 400 Oe, it is close to the saturation magnetization, however, the surface domain wall is still visible. In contrast, there is no surface domain in the domain pattern (a) (that was magnetized at -5,000 Oe before the measurement). The surface domain disappears at about the applied magnetic field of 600 Oe. Sample provided by A. D. Kent at the New York University

Fig. 2 These are the details of magnetic domain structures of a patterned epitaxial (110) Fe film under a magnetic field range from 290 Oe to270 Oe. It clearly shows that the domain wall starts to propagate from the edge into the sample. These is a rapid change of magnetization from (a) 290 Oe, (b) 280 Oe, (c) 275 Oe, to (d) 270 Oe.