Journal of Magnetism and Magnetic Materials 272–276 (2004) 1684–1685 Ferromagnetic resonance studies of Co nanowire arrays O. Yal@ın a, *, F. Yıldız a , M. . Ozdemir b , B. Akta - s a , Y. K . oseo & glu c , M. Bal d , M.T. Tuominen d a Department of Physics, Gebze Institute of Technology, Cayirova-Gebze/Kocaeli 41410, Turkey b Physics Department, Faculty of Art and Science, Marmara University, G . oztepe/Istanbul, Turkey c Physics Department, Faculty of Art and Science, Fatih University, Istanbul 34900, Turkey d Physics Department, University of Massachusetts, Amherst, MA 01003, USA Abstract Co nanowires grown by electrodeposition technique on di-block copolymers composed of polystyrene and polymethylmethacrylate, P(S-B-MMA), have been studied. Two samples with the same wire length of 1 mm and different wire diameters of 12 and 24 nm have been prepared. The nanowires are perpendicular to the film plane and arrayed in hexagonal symmetry in the lateral dimensions. Ferromagnetic resonance (FMR) technique has been used to investigate magnetic parameters of the system. The FMR spectra are very broad (a few kG) for every direction of the external field with respect to the sample plane. The FMR spectra exhibit considerable anisotropic behavior as the field is rotated both in sample plane and from the film plane towards the film normal direction. r 2003 Elsevier B.V. All rights reserved. PACS: 75.30.Gw; 75.75.+a; 76.50.+g Keywords: Magnetic nanowires; Nanostructures; Ferromagnetic resonance; Dipolar interaction 1. Introduction Since arrays of magnetic nanowires are promising candidates for ultra-high-density recording media, fab- rication of highly ordered arrays of magnetic wires and understanding of their magnetic behaviors have recently become of growing interest. The magnetic anisotropies of nanowire arrays were of primary interest in the studies by various techniques (see, for instance, Ref. [1– 5]). FMR experiments had been performed for some nanowire arrays with wire diameters ranging from 35 to 500nm, and the dipolar interaction fields have been characterized [1, 6–9]. In this study we have investigated (by FMR technique) two samples of Co nanowire (one micron in length and 12 and 24nm in diameter, respectively) that nanowires are perpendicularly ordered in hexagonal symetry in lateral dimensions polymethyl- methacrylate (PMMA) film. The cylindrical nano-wire axes are almost parallel to the film normal and the distance between the nearest neighboring wire axes are 24 and 48 nm for 12 and 24-nm thick wires, respectively. 2. Experimental results and discussions The ultrahigh-density nanowire arrays were obtained from the co-polymer film used as a template for dc electrodeposition method, as described elsewhere [10]. FMR measurements were performed at room tempera- ture using X-band spectrometer. The angular-dependent FMR lines were recorded for both in-plane (the applied field is in the film plane-IPG) and out-of-plane geometries (the applied field makes an angle with the film normal-OPG). The ESR spectra taken from Co nanowire arrays of 12 and 24 nm in diameter at out-of- plane geometry for some selected angles are given in ARTICLE IN PRESS *Corresponding author. Tel.: +90-262-6538-497X1149; fax: +90-262-6538-490. E-mail address: orhanyalcin@penta.gyte.edu.tr, fizik51@hotmail.com (O. Yal@ın). 0304-8853/$-see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.561