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 w as connected to a square shaped head with a side of 2W, which is designed t o 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 domai n wall. By using an oil-immersion lens (NA = 1.3) and a Hg lamp, magnetizat ion reversals in very narrow wires, as narrow as 0.5 mu m, were clearly obs erved. It is confirmed that domain wall penetration, pinning, depinning, an d also the direction of wall motion are controllable using square shaped he ad and necks with optimized width. (C) 2000 American Institute of Physics. [S0021-8979(00)37608-3].