Ni nanowires were fabricated by electrochemical deposition in the pores of alumina and polycarbonate membranes, with the diameter around 200 run and 30 run, respectively. To study the magnetic and electrical properties of Ni nanowires, individual nanowires were selected and connected with metal electrodes. Single and multiple constrictions were formed oil the nanowires by FIB. The wires were further thinned using oxygen plasma oxidation and chemical etching. Magnetoresistance curves were studied and compared before and after FIB trimming, oxidization and chemical etching. 3-D micromagnetic modeling was used to Simulate the magnetoresistance of the nanowires with and without constrictions. (c) 2005 Elsevier B.V. All rights reserved.