Intrinsic magnetic anisotropy versus coupling in arrays of closely spaced circular Fe/GaAs(110) dots, patterned by focused ion beam G. Carlotti a,b, * , G.C. Gazzadi b , G. Gubbiotti a,c , M. Madami a , S. Tacchi a , P. Vavassori b,d a INFM—Dipartimento di Fisica, Universita ` di Perugia, Via A. Pascoli, 06123 Perugia, Italy b INFM—CRS S3, Dipartimento di Fisica, Via Campi 213/A, 41100 Modena, Italy c INFM—CRS SOFT, Universita ` di Roma ‘‘La Sapienza,’’ 00185 Roma, Italy d INFM—Dipartimento di Fisica, Universita ` di Ferrara, Via Paradiso 12, 44100 Ferrara, Italy Available online 19 January 2006 Abstract We present the results of a detailed magneto-optical Kerr effect and Brillouin light scattering investigation of an epitaxial Fe/GaAs(110) film, 9 nm thick, achieving a quantitative determination of its anisotropy constants. Starting from this film, three different arrays of circular dots with diameter of 200 nm and interdot spacings of 200, 60 and 30 nm, have been produced by focused ion beam patterning. The modification of both the magnetization curves and the spin wave spectrum of the patterned specimens are discussed in terms of structural imperfections, intrinsic magnetocrystalline anisotropy and interdot dipolar coupling. D 2005 Elsevier B.V. All rights reserved. PACS: 75.30.Gw; 5.70.-i; 75.75.+a; 75.30.Ds; 78.35.+c; 85.40.Hp Keywords: Nanomagnetism; Magnetic anisotropy; Ultrathin magnetic films; Brillouin scattering; Surface acoustic waves; Focused ion beam 1. Introduction Patterned arrays of magnetic elements in the submicrometric scale are attracting wide interest because of both the unique features of magnetism in low-dimensional systems and the potential applications in the technology of solid state devices and magnetic recording media [1]. One important issue in these laterally confined magnetic structures is the understanding of the interplay between shape and intrinsic anisotropy, as well as the influence of dipolar coupling among the dots. This reflects both on the quasistatic magnetic properties and on the high frequency dynamics of the magnetization, which can be investigated by magnetooptical Kerr effect (MOKE) and Brillouin light scattering (BLS) from spin waves, respectively [2,3]. Most of the previous MOKE and BLS investigations of magnetic dots arrays, however, focused on polycrystalline permalloy elements (negligible intrinsic magnetocrystalline anisotropy), fabricated by electron beam lithography (EBL), with lateral inter-dot spacings above 200–300 nm. In such conditions, interdot dipolar coupling is usually irrelevant; both the magnetization curve and the spin-wave spectrum are determined by the properties of individual elements, as shown in the experiments [4–7]. To the best of our knowledge, the only paper where a slight interdot coupling was measured by BLS was an array of circular dots of permalloy (1 Am diameter, 100 nm spacing). The in-plane frequency showed a twofold oscillation (of about 3%), reflecting the symmetry of the dot matrix, which was therefore attributed to the dipolar interaction between unsaturated parts of the dots [8]. Concerning the investigation of magnetic dots of Fe, rather than permalloy, a BLS investigation of polycrystalline elliptical Fe dots, performed by Grimsditch et al. [9] gave evidence of the effect of shape anisotropy but neither intrinsic anisotropy nor interdot coupling was observed. In this work, we present the results of a detailed MOKE and BLS investigation of an epitaxial Fe/GaAs(110) film, 9 nm thick, achieving a quantitative determination of its intrinsic anisotropy. Starting from this film, three arrays of circular dots with a diameter of 200 nm and different inter-dot distances have been produced by focused ion beam (FIB). The modification of both the magnetization curves and the spin- 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.12.258 * Corresponding author. Dipartimento di Fisica, Universita ` di Perugia; Via Pascoli, 06123 Perugia, Italy. Tel./fax: +39 075 585 2767. E-mail address: carlotti@fisica.unipg.it (G. Carlotti). Thin Solid Films 515 (2006) 739 – 743 www.elsevier.com/locate/tsf