Effects of ion irradiation on structural and magnetic properties of Fe/Si multilayers prepared by helicon plasma sputtering Setyo Purwanto a,1 , I. Sakamoto a, * , M. Koike a , H. Tanoue a , S. Honda b a National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan b Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan Abstract Helicon plasma sputtering has been used to prepare Fe/Si MLs with an Fe layer thickness around t Fe ¼ 2–5 nm for a Si spacer fixed at the thickness of t Si ¼ 1 and 1.5 nm. Present study found that the Fe/Si MLs of the Si spacer thickness at t Si ¼ 1 nm exhibit antiferromagnetic nature, but the other Fe/Si MLs are ferromagnetic. The maximum value of magnetoresistance (MR) ratio in Fe/Si MLs appears at t Fe ¼ 3 nm, t Si ¼ 1 nm and is about 0.22%. We performed 400 keV Ar ion irradiation to investigate the behavior of magnetic properties in Fe/Si MLs. The magnetization measure- ments of Fe/Si MLs after 400 keV Ar ion irradiation show the degradation of antiferromagnetic behavior and the values of MR ratio after ion irradiation decrease. X-ray diffraction (XRD) patterns indicate that the peak intensity of a satellite peak originated in superlattice structure does not change within the range of ion dose used. These results imply that the interface structures after ion irradiation become rough although the superlattice structures remain. Therefore, we consider that the change of MR properties in Fe/Si MLs by 400 keV Ar ion irradiation is due to the thickness dependence of Si layers like metallic superlattice structures. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 61.80.L; 73.21.A; 75.70.C; 75.70.P Keywords: Irradiation effects; Multilayers; Magnetic properties; Magnetoresistance 1. Introduction Since the evidence of giant magnetoresistance (GMR) phenomenon in Fe/Cr metallic multilayers (MLs) was found in 1988 by Baibich et al. [1], investigations in this kind of materials are in- creasing rapidly. In addition, many interesting phenomena were observed when the metallic spacer between Fe film was substituted by non- metallic materials like Si. Fullerton et al. [2] in- vestigated the strong antiferromagnetic coupling with switching fields of 6 kOe at room temperature (RT) in sputtered Fe (3 nm)/Si (1.5 nm) MLs. In this case, the interface layer was found to be a crystalline interdiffused Fe–Si alloy. Furthermore, Inomata et al. [3] determined the existence of two different antiferromagnetic interlayer couplings as a function of Si layer thickness. The first one appeared in Fe (2.6 nm)/Si (1.2 nm) MLs, with the magnetoresistance (MR) ratio of 0.15% at RT. * Corresponding author. Tel.: +81-298-61-5689; fax: +81- 298-61-5673. E-mail addresses: setyofzm@batan.go.id (S. Purwanto), isao-sakamoto@aist.go.jp (I. Sakamoto). 1 On leave from R&D Center for Materials Science and Technology, National Nuclear Energy Agency (BATAN), Puspiptek-Serpong, Tangerang 15314, Indonesia. 0168-583X/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0168-583X(03)00755-9 Nuclear Instruments and Methods in Physics Research B 206 (2003) 326–329 www.elsevier.com/locate/nimb