Kerr microscopy observations of magnetization process in microfabricated ferromagnetic wires

The magnetization process in microfabricated NiFe wires was observed using a Kerr microscope. Magnetic wires were made from a 20-nm-thick NiFe film by using lift-off techniques. Their width W and length L were designed as W = 0.5, 1.0 and 2.0 mu m and L = 50 mu m, respectively. One end of the wire was connected to a square shaped head with a side of 2W, which is designed to act as a domain wall source. In each wire, necks with different width of 0.2W, 0.6W, and 0.8W were introduced as artificial pinning sites of a domain wall. By using an oil-immersion lens (NA = 1.3) and a Hg lamp, magnetization reversals in very narrow wires, as narrow as 0.5 mu m, were clearly observed. It is confirmed that domain wall penetration, pinning, depinning, and also the direction of wall motion are controllable using square shaped head and necks with optimized width. (C) 2000 American Institute of Physics. [S0021-8979(00)37608-3].