Fabrication and magnetic characterization of single domain Co91Fe9 nanostructures

Linear arrays of 15 nm thick, polycrystalline Co91Fe9 nanoelements have bee n fabricated using e-beam lithography, collimated sputtering and lift-off. The elements have widths of 0.17 and 0.25 mu m, lengths from 0.5 to 4 mu m, pointed ends, and center-to-center spacing of 0.5 mu m. Characterization b y magnetic force microscopy shows that in the virgin state these elements a re single-domain and have magnetizations parallel to their long axes. The f ield at which an element switches its magnetization direction is shown to d epend mainly on its width, and only slightly on its length. Fields of about 440 and 680 Oe are needed to switch completely the 0.25 and 0.17 mu m stru ctures, respectively. This separation in switching fields is adequate to al low elements of different widths to be switched independently. Also, magnet ic force microscopy and SQUID magnetometry analysis show that a capping lay er is necessary to protect the films from oxidation. Unprotected films show an altered hysteresis loop and their associated nanostructures are not con sistently single-domain. (C) 2000 American Institute of Physics. [S0021- 89 79(00)74308-8].