Fabrication and magnetic characterization of single domain Co91Fe9 nanostructures

Linear arrays of 15 nm thick, polycrystalline Co91Fe9 nanoelements have been 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 by magnetic force microscopy shows that in the virgin state these elements are single-domain and have magnetizations parallel to their long axes. The field at which an element switches its magnetization direction is shown to depend 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 structures, respectively. This separation in switching fields is adequate to allow elements of different widths to be switched independently. Also, magnetic force microscopy and SQUID magnetometry analysis show that a capping layer is necessary to protect the films from oxidation. Unprotected films show an altered hysteresis loop and their associated nanostructures are not consistently single-domain. (C) 2000 American Institute of Physics. [S0021- 8979(00)74308-8].