Ion sculpting: A tool for tuning magnetic anisotropy in ultrathin films R. Moroni * , F. Bisio, F. Buatier de Mongeot, M. Canepa, C. Boragno, L. Mattera, U. Valbusa CNISM and Dipartimento di Fisica dell’Universita ` di Genova, via Dodecaneso 33, I-16146 Genova, Italy Available online 12 January 2007 Abstract The possibility of modifying the magnetic properties of ultrathin films by means of ion sculpting has been verified for Co/Cu(0 0 1) and Fe/Ag(0 0 1). For both these systems, ion sputtering at grazing incidence performed in a proper, material-dependent, temperature range induces the formation of ripples at the surface of the films. Following ripple formation, the magnetic anisotropy in the plane of the films undergoes dramatic changes brought about by the out-of-equilibrium distribution of defect sites induced by the ripple structure itself. Ó 2007 Elsevier B.V. All rights reserved. Pacs: 75.30.Gw; 75.75.+a; 75.70.i; 81.16.Rf Keywords: Ion sculpting; Nanoscale pattern; Magnetic anisotropy; Ultrathin films; Iron; Silver 1. Introduction For a material scientist, nanoscience deals with the pos- sibility of obtaining materials endowed with unusual and novel properties by reducing their size or by modifying their morphology at the nanometer scale. Indeed, nano- sized and nanostructured materials often exhibit electronic, magnetic and optical properties which may be very differ- ent from those of the parent bulk material. In the specific case of magnetic materials, novel properties are brought by boundary atoms which, as dimensions are reduced down to the nanoscale, give a relevant contribution to the overall magnetic properties of the system [1,2]. Historically, ultrathin magnetic films are among the first examples of nanosized magnetic systems. Here, the altered, non-bulk-like, atomic environment affects local magnetic properties of interface atoms, such as their magnetic moment and magnetic anisotropy. By reducing the film thickness below a few tens of monolayers (ultrathin-film regime), the contribution of interface atoms to the magnetic properties of the film becomes relevant, thus leading to the appearance of extremely interesting magnetic properties [3]. In view of applications, the possibility of modifying and tuning the magnetic anisotropy of ultrathin films has attracted a great deal of interest. Such interest is motivated by the fact that the magnetic behaviour of a system is greatly influenced by its magnetic anisotropy, which con- tributes to determine the response to external magnetic fields. In this respect, thanks to the strong sensitivity of magnetic anisotropy to interface-related symmetry break- ing effects, nanostructuring gives the opportunity of tailor- ing the magnetic properties of ultrathin films. In fact, the resulting modification of the film morphology at the nano- meter scale induces a redistribution of the different atomic sites (e.g. terrace, step and kink sites) at the surface of the film, each characterised by different magnetic anisotropy. In ultrathin films, where the role of interface atoms has become relevant or even dominant, nanostructuring opens therefore the possibility of tuning the magnetic anisotropy. In this respect, ion sculpting has been demonstrated to be a versatile technique to induce the formation of self- organized nanosized surface structures [4]. This technique consists in sputtering the sample surface with low-energy noble-gas ions in proper geometric conditions and 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.036 * Corresponding author. Tel.: +39 0103536287; fax: +39 010311066. E-mail address: moroni@fisica.unige.it (R. Moroni). URL: http://www.fisica.unige.it/surfmag (R. Moroni). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 257 (2007) 359–364 NIM B Beam Interactions with Materials & Atoms