Journal of Magnetism and Magnetic Materials 272–276 (2004) 2439–2441 Influence of the morphology on the magnetism of iron arborescences Vasile Heresanu, Rafik Ballou, Pierre Molho* Laboratoire Louis N ! eel, CNRS, BP 166, Grenoble Cedex 9 38042, France Abstract Iron arborescences grown by electrodeposition have been studied. Their magnetic properties are very sensitive to the morphology, which can be varied by changing the growth parameters, initial salt concentration and voltage, or applying a magnetic field during the growth. Faster growing arborescences are more coercitive and arborescences grown on a substrate exhibit anisotropic magnetic properties. r 2003 Elsevier B.V. All rights reserved. PACS: 75.90.+w; 61.43.Hv; 81.15.Pq Keywords: Electrodeposition; Fractals; Magnetic properties 0. Introduction Arborescent morphologies, observed in many differ- ent natural systems, may be generated by electrodeposi- tion [1]. We are interested in iron arborescences, the magnetic properties of which should depend on the morphology and the various length scales existing in them. Different morphologies are obtained, according to the growth parameters, initial salt concentration and voltage, or on applying a magnetic field during the growth. ‘Sparse’ arborescences, with few thick branches, behave like bulk iron. ‘Dense’ ones, with many thin branches, obtained for lower concentration, exhibit a behavior interpreted as ‘small grains’ or ‘spin glass like’ [2]. Different dense morphologies have been obtained, showing that the magnetic properties are sensitive to slight morphology changes. Another way to change the morphology is to grow the arborescences on a substrate [3]. Magnetic properties are then very different. 1. ‘Dense’ arborescences The experimental cell was already described in a previous paper [4]. Instead of glass plate, we used kapton film to recover the samples after growth and avoid the complex magnetic contribution of glass. Grown samples were protected against oxidation by a thin film of gold. Magnetic measurements were per- formed on a set of five samples to increase the sensitivity, applying field cycles up to 8 T. The dense morphology (initial salt concentration of 0.06M) shows slight changes on increasing the voltage and thus the growth velocity: no effect is found out at the macro- scopic scale, but SEM observations reveal that faster growing branches are thinner (Fig. 1). This change is reflected in the coercivity, which increases when the growth voltage increases (Fig. 2). Similar slight changes also occur when a magnetic field, up to 0.05 T, normal to the plane of growth, is applied during the growth. At a macroscopic scale almost no field effect is observed, in particular no spiraling, but at a small scale the growing branches are affected [5]. One may think that the field effect, which is to bend the small branches and to favor the nucleation of new thin ones, is similar to a thinning at a given scale, analogous to a faster growing one. However, this effect ARTICLE IN PRESS *Corresponding author. Tel.: +33-4-76-88-79-19; fax: +33- 4-76-88-11-91. E-mail address: molho@grenoble.cnrs.fr (P. Molho). 0304-8853/$-see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.461