The oxidation behavior and magnetic properties of iron carbonitride ultrafine particles
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The oxidation behavior and magnetic properties of iron carbonitride ultrafine particles X. Q. Zhao Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China and National Laboratory for RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China
Y. Liang and Z. Q. Hu National Laboratory for RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, China
B. X. Liu Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China (Received 8 November 1995; accepted 15 July 1996)
Iron nitride and iron carbonitride (ICN) ultrafine particles (20–80 nm in size) have been synthesized by laser-induced pyrolysis of the Fe(CO)5 –NH3 –C2 H4 system. The oxidation behavior, surface morphologies, and structural characteristics as well as magnetic properties of these particles are reported and discussed. It is found that the presence of very thin carbon coating (1 –2 nm) on the ICN particles plays an important role in preventing the oxidation of the particles. Accordingly, the ICN ultrafine particles exhibit higher saturation magnetization (142 emuyg) than the iron nitride ones (124 emuyg).
High-density magnetic recording demands high performance magnetic particles with high saturation magnetization and coercivity as well as ultrafine particle size.1,2 In recent years, iron nitride particles have been considered as a potential candidate for magnetic recording media due to their high saturation magnetization and better chemical stability than the iron particles,1,3 so that much attention has been paid to the preparations and investigations on the magnetic properties of iron nitride particles, especially emphasized on g 0 –Fe4 N and Fe8 N.1,3–8 However, iron nitride particles still oxidize in air and cannot present excellent magnetic properties. For example, the ultrafine g 0 –Fe4 N particles only exhibited a saturation magnetization of below 120 emuyg,4,5 which is far below the value of the corresponding bulk materials (193 emuyg),5,6 although some results on acicular particles on micrometer scale in size are encouraging.3 In this report, we synthesized iron carbonitride (ICN) and iron nitride ultrafine particles by laser-induced pyrolysis, and then investigations on the structural and magnetic characteristics as well as the oxidation behavior of these particles were present. A 1 kW CW CO2 laser (l 10.6 mm) was used as the irradiation source to induce the pyrolysis of the premixed precursors, i.e., Fe(CO)5 (99.9%) vapor, NH3 (99.99%), and C2 H4 (99.99%). The synthesis devices and the detailed procedures have been given in a previous report.9 The NH3 and C2 H4 absorbed the laser energy, and a portion was transferred and absorbed by Fe(CO)5 molecules; thus, under the nozzle a pyrolysis reaction was induced. In the reaction, Fe(CO)5 , NH3 , and C2 H4 J. Mater. Res., Vol. 11, No. 11, Nov 1996
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