Electron spin resonance (ESR) measurements at room temperature and X-band microwave frequency were performed on highly crystalline FePt system thin films. Fairly high DC static magnetic field absorption of about 300？mT was observed in these films. We attribute the high field absorption to ferromagnetic resonance (FMR). Upon increasing iron content in FePt system, no detectable spin waves modes were identified already at room temperature. This signifies a homogeneous distribution of the magnetization across the films. We qualitatively attributed such homogeneity distribution in the films to self-assembly of these Fe–Pt system nanoparticles. The results revealed that the FePt system contains hyperfine coupling with sextet exhibiting a phase reversal behaviour compared to FMR line. Both iron content and crystallite size increased the FMR intensity making the films good candidates for large data storage mediums and spintronics. 1. Introduction Magnetic recording media plays a vital role in the development of nonvolatile data storage technologies. Particularly, magnetic hard disk drives are important parts in many devices such as video cameras and computers. The year 1956 marked the generation of first magnetic hard disk with recording density of 2？kB/in2 that was successfully built by IBM [1]. Since then, the areal density (the number of bits/unit area on a disk surface) has successively increased [2]. Nowadays, products with an areal density of more than 700？GB/in2 are commercially available [3]. The increase in the areal density needs to be continued due to the future demand for information storage that is drastically advancing. Due to advancement in information technology (IT) and computer science, areal density in a level of 1？Tb/in2 or more is inevitable. Iron platinum (FePt) nanoparticles (NPs) are actively being pursued as a potential candidate for larger storage capacities on hard-disk drives than any other materials due to its high magnetocrystalline anisotropy (MA) [4]. MA is a process when the atomic structure of a crystal of a certain material introduces preferential direction of magnetisation, and in most cases, it will be the easy axis of magnetisation [5]. This phenomenon is mostly common in ferromagnetic materials. Traditional magnetic recording materials such as Co/Cr have limitations since their magnetic direction of each recording bit would become unstable at room temperature due to thermal fluctuation [6]. FePt does not only possess higher magnetic anisotropy but also possesses better thermal stability [7]; this makes it a better
References
[1]
D. Weller and A. Moser, “Thermal effect limits in ultrahigh-density magnetic recording,” IEEE Transactions on Magnetics, vol. 35, no. 6, pp. 4423–4439, 1999.
[2]
Z. Z. Bandic and R. H. Victoria, “Advances in magnetic data storage technologies,” Proceedings of the IEEE, vol. 96, no. 11, pp. 1749–1753, 2008.
[3]
Toshiba Corporation, “Toshiba boosts performance with industry-leading areal density on 1TB 2.5-inch hard drive for PC consumer electronics applications,” 2011, http://www.toshibastorage.com.
[4]
S. Sun, C. B. Murray, D. Weller, L. Folks, and A. Moser, “Monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices,” Science, vol. 287, no. 5460, pp. 1989–1992, 2000.
[5]
H. Gavi, B. D. Ngomb, A. C. Beye, et al., “Low-field microwave absorption in pulse laser deposited FeSi thin film,” Journal of Magnetism and Magnetic Materials, vol. 324, no. 6, pp. 1172–1176, 2012.
[6]
K. Chokprasombat, “Synthesis of patterned media by self-assembly of FePt nanoparticles,” Walailak Journal of Science and Technology, vol. 8, no. 2, p. 87, 2011.
[7]
G. J. Li, C. W. Leung, Z. Q. Lei, K. W. Lin, P. T. Lai, and P. W. T. Pong, “Patterning of FePt for magnetic recording,” Thin Solid Films, vol. 519, no. 23, pp. 8307–8311, 2011.
[8]
A. Martins, S. C. Trippe, A. D. Santos, and F. Pelegrini, “Spin-wave resonance and magnetic anisotropy in FePt thin films,” Journal of Magnetism and Magnetic Materials, vol. 308, no. 1, pp. 120–125, 2007.
[9]
Q. Y. Jin, Y. B. Xu, S. M. Zhou, M. Lu, H. R. Zhai, and Y. H. Shen, “A study of interlayer coupling in Fe/Cu multilayers by spin wave resonance,” Physica Status Solidi (B), vol. 193, no. 2, pp. 457–461, 1996.
[10]
R. F. Soohoo, Magnetic Thin Films, Harper & Row, New York, NY, USA, 1965.
[11]
A. T. Costa, R. B. Muniz, and D. L. Mills, “Theory of spin waves in ultrathin ferromagnetic films: the case of Co on Cu(100),” Physical Review B, vol. 69, no. 6, Article ID 064413, 5 pages, 2004.
[12]
B. W. Mwakikunga, A. Forbes, E. Sideras-Haddad, M. Scriba, and E. Manikandan, “Self assembly and properties of C？:？WO3 nano-platelets and C？:？VO2/V2O5 triangular capsules produced by laser solution photolysis,” Nanoscale Research Letters, vol. 5, no. 2, pp. 389–397, 2010.
[13]
S. S. Nkosi, B. W. Mwakikunga, E. Sideras-Haddad, and A. Forbes, “Synthesis and characterization of potential iron-platinum drugs and supplements by laser liquid photolysis,” Nanotechnology, Science and Applications, vol. 5, pp. 27–36, 2012.
[14]
C. C. Yang and Y. W. Kim, “Distant electron-nuclear double resonance and dynamic nuclear polarization in ruby,” Physical Review B, vol. 20, no. 3, pp. 1291–1292, 1979.
[15]
J. Lambe, N. Laurance, E. C. McIrvine, and R. W. Terhune, “Mechanisms of double resonance in solids,” Physical Review, vol. 122, no. 4, pp. 1161–1170, 1961.
[16]
A. Abragam and B. Bleaney, Electron Paramagnetic Resonance of Transition Lons, Clarendon Press, Oxford, UK, 1970.
[17]
A. W. Overhauser, “Polarization of nuclei in metals,” Physical Review, vol. 92, no. 2, pp. 411–415, 1953.
[18]
C. A. Ross, H. I. Smith, T. Savas et al., “Fabrication of patterned media for high density magnetic storage,” Microelectronic Engineering, vol. 53, no. 1–4, p. 67, 2000.
[19]
B. D. Terris, “Fabrication challenges for patterned meida,” Journal of Magnetism and Magnetic Materials, vol. 321, no. 6, pp. 512–517, 2009.
[20]
V. Nandwana, K. E. Elkins, N. Poudyal, G. S. Chaubey, K. Yano, and J. P. Liu, “Size and shape control of monodisperse FePt nanoparticles,” Journal of Physical Chemistry C, vol. 111, no. 11, pp. 4185–4189, 2007.
[21]
K. Zaghib, A. A. Salah, N. Ravet, A. Mauger, F. Gendron, and C. M. Julien, “Structural, magnetic and electrochemical properties of lithium iron orthosilicate,” Journal of Power Sources, vol. 160, no. 2, pp. 1381–1386, 2006.
[22]
M. H. Hong, K. Hono, and M. Watanabe, “Microstructure of FePt/Pt magneticthin films films with high perpendicular coercivity,” Journal of Applied Physics, vol. 84, no. 8, pp. 4403–4409, 1998.
[23]
A. E. Berkowitz, W. J. Schuele, and P. J. Flanders, “Influence of crystallite size on the magnetic properties of acicular γ-Fe2O3 particles,” Journal of Applied Physics, vol. 39, no. 2, pp. 1261–1263, 1968.
[24]
M. Chen, J. P. Liu, and S. Sun, “One-step synthesis of FePt nanoparticles with tunable size,” Journal of the American Chemical Society, vol. 126, no. 27, pp. 8394–8395, 2004.
[25]
B. W. Mwakikunga, M. Maaza, K. T. Hillie, C. J. Arendse, T. Malwela, and E. Sideras-Haddad, “From phonon confinement to phonon splitting in flat nanostructures: a case of VO2@V2O5 core-shell nanoribbons,” Vibrational Spectroscopy, vol. 61, pp. 105–111, 2012.
[26]
B. W. Mwakikunga, A. E. Mudau, N. Brink, and C. J. Willers, “Flame temperature trends in reacting vanadium and tungsten ethoxide fluid sprays during CO2-laser pyrolysis,” Applied Physics B, vol. 105, no. 2, pp. 451–462, 2011.
[27]
M. Govender, L. Shikwambana, B. W. Mwakikunga, E. Sideras-Haddad, R. M. Erasmus, and A. Forbes, “Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres,” Nanoscale Research Letters, vol. 6, article 166, 2011.
