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 Wand length L were designed as W= 0.5, 1.0 and 2.0 /Lm and L= 50/Lm, respectively. One end of the wire was connected to a square shaped head with a side of 2 W, 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 /Lm, 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.