Composition, Size, Structure, and Magnetic Characterization of Iron-Platinum Nano-particles
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Composition, Size, Structure, and Magnetic Characterization of Iron-Platinum Nanoparticles N. Parekha, G. Younga, A. Singha, K. Parvinb , M. Kaurb ,D. Bruckc,S. Wongc ABSTRACT Iron-platinum (FePt) nano-particles were synthesized using a hot metal salt reduction reaction with iron chloride and platinum acetylacetonate as the precursor salts. The synthesis route was based upon work done previously by Sun et Al.[6]. The size and composition of the FePt nanoparticles were controlled by varying the surfactant to reagent molar ratio and refluxing time during synthesis. The average size of FePt nano-particles synthesized ranged from 4.08 nm to 5.23 nm. The composition of the nano-particles ranged from Fe60Pt40 to Fe55Pt45. The size was shown to increase as the surfactant to reagent molar ratio was changed from 1:6 to 1:1. The platinum composition increased from 40 % to 45 % with an increase in the refluxing time from 30 minutes to 60 minutes. The X-ray analysis (XRD) showed that the unannealed nano-particles had a FCC crystal structure. The FCC FePt nano-particles were superparamagnetic at room temperature. A blocking temperature (Tb) of 35 K was measured for 5.23 nm Fe55Pt45 nanoparticles. Annealing of the Fe55Pt45 nano-particles induced a FCT crystal structure with hardmagnetic properties. Coercivity (Hc) of approximately 13000 Oe was measured at room temperature. (a) Department of Chemical and Materials Engineering, San Jose State University (b) Department of Physics and Astronomy, San Jose State University (c) Department of Biological Sciences, San Jose State University INTRODUCTION Continuous miniaturization of bit cells on thin-film magnetic medium is necessary to accommodate the volume of digital data that is doubling every year. The bit cell is a small collection of crystalline grains with uniform magnetic properties [1]. Further miniaturization of bit cells of the thin-film magnetic recording media will result in superparamagnetic transformation of the magnetic medium, which will result in loss of data storage capacity [2]. Thus, it is becoming increasingly important to find materials with higher coercivity. FePt alloys are well known for their use as permanent magnets. Equiatomic FePt alloy with face-centered tetragonal (FCT) structure possess magnetocrystalline anisotropy (Ku) up to 107 J/m3. They are considered a potential material for ultrahigh density data storage applications. However, the limitations of grain size and composition control in the FCT FePt thin-film media have restricted their use in data storage applications [1-2]. The magnetic properties of nanoparticles are a function of their size, composition, and crystal structure. FePt nano-particles with larger diameter (~8 nm) and 1:1 Fe to Pt molar ratio have improved magnetic properties [3]. FePt nano-particles are commonly synthesized via a thermal decomposition chemical synthesis route. This route utilizes a high temperature polyol reduction of platinum acetylacetonate (Pt (acac)2) and the thermal decomposition of iron pentacarbonyl (
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