FePt grains for magnetic storage on layer of self-assembled silica nanoparticles
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Arata Tsukamono and Akiyoshi Itoh College of Science and Technology, Nihon University, 7-24-1 Narashino-dai Funabashi, Chiba 274-8501, Japan (Received 4 May 2010; accepted 2 August 2010)
Small FePt grain size is one of the candidates for ultrahigh density magnetic recording material. We investigate increasing grain density of FePt grains fabricated on nanostructured substrates. One of them is nanodent-array (NDA) (period 5 14 nm), and another is self-assembled silica nanoparticles (SASP) (period 5 18 nm). In this paper, the influence of difference in nanostructured substrates on grain density Np is investigated in detail. FePt films were fabricated by sputtering and rapid thermal annealing (RTA) [Y. Itoh, T. Aoyagi, A. Tsukamoto, K. Nakagawa, A. Itoh, and T. Katayama, Jpn. J. Appl. Phys. 43(12), 8040 (2004)]. FePt grains on those substrates show almost the same areal density; however, experimental results show that FePt grains on SASP has the largest Np while the initial film thicknesses are the same. Electron diffraction measurements indicate the existence of ordered FePt crystalline. The magnetic hysteresis loops are also shown.
I. INTRODUCTION
L10-FePt small grain having high magnetic anisotropy is one of the promising candidates for the ultrahigh density magnetic or heat-assisted magnetic recording. Epitaxial c-axis oriented FePt nanoparticles were synthesized on Si (100) using TiN intermediate layer as a template.1 From a detailed analysis of structure–magnetic property correlations, it was shown that individual nanoparticles in a single domain state have larger coercivity than continuous thin film. Magnetic multilayers on nanospheres2 and the template-directed self-assembled magnetic structures3 have been reported. We have already reported that isolated FePt crystal grains having 7 nm average diameter can be fabricated directly on flat SiO2/Si substrate by rapid thermal annealing (RTA)4 with out any intermediate layers. It is also reported5 that nanodent array (NDA) made by using the polymer micelles technique is effective for increasing the grain density of FePt fabricated on it. This paper describes the method of fabrication for the single layer of self-assembled silica nanoparticles (SASP) having small diameter silica spheres, as small as 18 nm. It also reports in detail that the grain density Np of FePt can be fabricated on the different substrates. The comparison of the value of Np for FePt and FeCuPt fabricated on the different substrates such as flat SiO2, NDA, and SASP has been shown. The results of the electron diffraction
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.11 J. Mater. Res., Vol. 26, No. 2, Jan 28, 2011
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measurements and magnetic hysteresis loops are also shown. II. FABRICATION OF SASP
Figure 1 shows the method of making the monolayer particle array. The toluene solution includes silica particles and polymethylphenylsilane (PMPS). The role of the PMPS is to reinfo
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