Influence of energetic ions and neutral atoms on the L1 0 ordering of FePt films V. Cantelli * , J. von Borany, A. Mu ¨ cklich, Shengqiang Zhou, J. Grenzer Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf e. V., P.O. Box 510119, 01314 Dresden, Germany Available online 23 January 2007 Abstract The A1 ! L1 0 phase transition of Fe 50 Pt 50 films, deposited at room-temperature on amorphous SiO 2 by dc magnetron co-sputtering at 0.3 Pa, was studied with in-situ X-ray diffraction. An almost complete transition characterized by a long-range order parameter S > 0.8 is obtained already after a heat treatment at (320 ± 20) °C. A post-deposition He ion irradiation (50 keV, 1 · 10 15  3 · 10 16 cm 2 ) does not further reduce the transition temperature. Theoretical calculations reveal that, due to the negligible thermalization of the sputtered atoms and reflected ions in the plasma, a considerable fraction of energetic ions and atoms meet the substrate surface. The low transition temperature is explained by the impact of energetic ions and atoms which provoke significant adatom mobility and a decrease of the activation energy for atomic reordering by vacancies. Consequently, using deposition parameters leading to a strong thermalized plasma, the FePt films showed an increase of the transition temperature up to 400 °C, a lower S-value (S ffi 0.6) and a reduced coercivity. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Nz; 75.50.Bb; 75.50.Vv; 81.15.Cd Keywords: FePt; L1 0 -ordering; Structural phase transition; Hard magnetic properties; Magnetron sputtering 1. Introduction Due to its high magneto-crystalline anisotropy (0.7– 1 · 10 8 erg/cm 3 ) the face-centered tetragonal (fct) L1 0 phase of FePt alloys belongs to the preferred materials for future magnetic recording media, with the potential to achieve a storage density above 1 Tbit/in 2 [1]. Unfortunately, FePt films deposited at room temperature exhibit only the face- centered cubic (fcc) paramagnetic A1-phase and a subse- quent heat treatment at T > 400 °C is required to achieve the A1 ! L1 0 transition [2,3]. But, with respect to a feasible fabrication technology, it is necessary (i) to produce such films on amorphous substrates, and (ii) to reduce signifi- cantly the processing temperature (T 6 400 °C). Different methods have been explored to lower the transition temper- ature such as (i) third-element alloying (C, Ag, Cu) [4–6], (ii) sequential deposition of multiple Fe/Pt stacks [7], or (iii) ion irradiation [8,9]. In most cases, the decrease of the transition temperature T T is based on an increase of the Fe/Pt atoms mobility which supports the atomic rearrangement towards the chemically ordered L1 0 phase [10]. The present paper reports on the properties of FePt films deposited by magne- tron sputtering on SiO 2 /Si substrates using a large ion/atom ratio during deposition. 2. Experimental Equiatomic FePt films of about 70 nm thickness were prepared by dc co-sputtering from elemental targets (Fe/ Pt; 3.5N/5N purity) in a chamber equipped with two bal- anced magnetrons, each tilted 30° away from the substrate surface normal, with a target-substrate distance of 100 mm. Si(0 0 1) samples of 15 · 15 mm 2 size covered with 1.5 lm amorphous, thermally grown SiO 2 were used as substrates. The base pressure was below 5 · 10 4 Pa, and a low operat- ing pressure of 0.3 Pa (Ar, 5N) during deposition was applied. The deposition rate was (0.55 ± 0.02) A ˚ /s which 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.117 * Corresponding author. Tel.: +49 351 260 3350; fax: +49 351 260 3438. E-mail address: v.cantelli@fzd.de (V. Cantelli). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 257 (2007) 406–410 NIM B Beam Interactions with Materials & Atoms