Journal of Magnetism and Magnetic Materials 290–291 (2005) 731–734 Modification of the magnetic properties of exchange coupled NiFe/FeMn films by Ga + ion irradiation S. Blomeier a,à , D. McGrouther b , R. O’Neill b , S. McVitie b , J.N. Chapman b , M.C. Weber a , B. Hillebrands a , J. Fassbender c a Fachbereich Physik and Forschungsschwerpunkt MINAS, Erwin-Schro¨dinger-Strasse 56, Technische Universita¨t Kaiserslautern, 67663 Kaiserslautern, Germany b Department of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK c Institut fu¨r Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Postfach 510119, 01314 Dresden, Germany Available online 8 December 2004 Abstract The influence of 30 keV Ga + ion irradiation on the magnetic properties of polycrystalline NiFe/FeMn exchange bias layers was investigated. In this context, it was of particular interest to determine whether a previously observed enhancement of the bias field value for the irradiation with 5 keV He + ions is a material-specific or an ion-specific effect. Moreover, the capability of magnetic micro-patterning using Ga + ions from a focused ion beam source was tested. It is demonstrated that magnetic patterning with a lower width limit in the range of 100–1000 nm is possible. r 2004 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 75.30.Gw; 75.70.Cn Keywords: Exchange bias; Ion irradiation; Micro-patterning 1. Introduction Recently it has been demonstrated that ion irradia- tion can be used as an excellent tool to modify the magnetic properties of thin films without affecting their surface topography. Active research has been focused on this field, as the respective experimental techniques, in combination with methods of high spatial resolution, have considerable potential for the fabrication of magnetic structures on the nanometer scale. Previous experiments indicated an ion-induced change in the anisotropy behavior of Co/Pt multilayers [1,2] and FePt alloys [3], and in the exchange coupling of Ni 81 Fe 19 /Fe 50 Mn 50 films by irradiation with 5keV He + ions [4,5]. In the latter case it was demonstrated that the exchange bias field can be changed both in magnitude and direction. In particular, within a fluence regime of 1  10 15 –8  10 15 ions/cm 2 an enhancement of the local exchange bias field was observed. At higher fluences it was found that the bias field is reduced below its initial value. A model was established that ascribes the observed modifications to the creation of point defects within the irradiated stack and relates the normalized exchange bias field (H EB /H EB,initial ) to the applied ion dose N according to H EB =H EB;initial ¼ð1 þ aptNÞ expðbNÞ: (1) Here, t is the thickness of the antiferromagnetic layer, p is the number of defects created per ion, and a and b ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.278 à Corresponding author. Tel.: +496312054203; fax: +496312054095. E-mail address: blomeier@physik.uni-kl.de (S. Blomeier).