Ultrafast pulsed laser deposition as a method for the synthesis of innovative magnetic films V. Iannotti a, *, S. Amoruso b , G. Ausanio a , A.C. Barone c , C. Campana a , X. Wang b , L. Lanotte a a CNR-INFM Coherentia, Dipartimento di Scienze Fisiche, Universita ` degli Studi di Napoli ‘‘Federico II’’, P.le V. Tecchio 80, I-80125 Napoli, Italy b CNR-INFM Coherentia, Dipartimento di Scienze Fisiche, Universita ` degli Studi di Napoli ‘‘Federico II’’, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy c Nanobiotechnology Facilities – Istituto Italiano di Tecnologia (IIT), Via Morego 30, I-16163 Genova, Italy 1. Introduction Nanoparticles (NPs) are of great interest both in technological applications and fundamental research due to their size-depen- dent physical properties. They can be formed in different ways and the synthesis of NPs of controlled size is a challenge [1–3]. Different techniques have been used for NPs production, such as arc discharge, vapour and electrochemical deposition, sputtering and nanosecond pulsed laser deposition (ns PLD). Recently, ultrashort pulsed laser deposition (uPLD) in vacuum has been demonstrated to be a powerful and versatile tool for the production of metal and semiconductor NPs films [4–9]. The generation of NPs by femtosecond (fs) laser ablation is quite different from the well-known formation of NPs by ns PLD in an ambient gas [10]. NPs synthesis by fs laser ablation occurs under vacuum (the typical pressure is in the 10 7 to 10 3 mbar range) without gas phase condensation, and different theoretical inves- tigations have been reported to establish their formation mechanisms [11,12]. The different models and simulations are based on two important points: (i) the heat transfer from the laser pulse to the target occurs almost at solid density and (ii) the subsequent rapid expansion and cooling of the irradiated material result in NPs generation trough mechanisms like phase explosion and fragmentation [13–15]. Ultrafast laser ablation allows producing films of NPs which are pretty different from those obtained by the classical ns PLD method in terms of morphology, composition and structure [16]. The films produced by uPLD are constituted by random stacking aggregates of disk-shaped NPs, whose aspect ratio depends on the experimental parameters (laser intensity, wavelength, etc.). Moreover, the films are characterized by an ordinate disposition of the NPs with the major cross-section parallel to the deposition substrate [17,18]. Previous experimental studies evidenced that in uPLD the particles in the film tend to preserve their individuality, without complete coalescence, even at high NPs volume fractions, differently from what is obtained by means of other production techniques (e.g. ns PLD, sputtering, etc.), and an exchange interaction is active among the nearest NPs [18–21]. This paper reports an experimental investigation on the properties of Ni and Fe NPs films deposited by uPLD evidencing the strong correlation between the morphology and topology of the NPs films and their peculiar magnetic features. 2. Experimental details The experimental setup used in the present experiment has been reported earlier [22] and will be only briefly described here. The laser source was a Nd:glass laser system providing Applied Surface Science 255 (2009) 5224–5227 ARTICLE INFO Article history: Available online 6 November 2008 Keywords: Ultrashort pulsed laser deposition Nanogranular magnetic films High remanence ratio Coercive squareness ABSTRACT Exchange-coupled monocomponent magnetic films constituted of disk-shaped Ni and Fe nanoparticles were produced by ultrafast pulsed laser deposition, in vacuum. These films show a peculiar cauliflower- like structure, made of granular agglomerates of nanoparticles sticking to one another with a significant shape and orientation anisotropy. Both as-deposited Ni and Fe films present hysteresis loops with a high in-plane remanence ratio (0.61 and 0.81 at 250 K, respectively), relatively low values of the saturation and coercive fields and a steep slope near coercivity. At temperature of 10 K and 250 K, the magnetization curves confirm the strong influence of the production technique on the topologic structure of these films, and consequently on their magnetic properties. In perspective, the striking and intriguing properties of these nanogranular films appear very promising for potential application as permanent magnets and in data storage technology. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: iannotti@na.infn.it (V. Iannotti). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.10.088