High coercivity and superparamagnetic behavior of nanocrystalline iron particles in alumina matrix |
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| Affiliation: | 2. Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA;1. Clarkson University, 13699 Potsdam, NY, USA;2. SUNY Polytechnic Institute, 12203 Albany, NY, USA;3. Albany College of Pharmacy and Health Sciences, 12208 Albany, NY, USA;1. School of Materials Science and Engineering & RIGET, Gyeongsang National University, Jinju-daero 501, Jinju 52828, Republic of Korea;2. Department of Materials Engineering and Convergence Technology & RIGET, Gyeongsang National University, Jinju-daero 501, Jinju 52828, Republic of Korea;1. Particulate Materials Research Center, Department of Resources Engineering, National Cheng Kung University, Tainan, Taiwan, ROC;2. Department of Materials Science and Engineering, National United University, Miaoli, Taiwan, ROC;1. Key Laboratory of Optoelectronic Material and Device, Shanghai Normal University, 200234 Shanghai, People’s Republic of China;2. Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Institute of Applied Magnetics, Lanzhou University, Lanzhou 730000, People’s Republic of China |
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| Abstract: | Single-domain nanoscale magnetic iron particles have been embedded uniformly in an amorphous matrix of alumina using a pulsed laser deposition technique. Structural characterization by transmission electron microscopy (TEM) reveals the presence of a crystalline iron and an amorphous alumina phase. Fine particle magnetism have been investigated by carrying out field and temperature dependence of magnetization measurements using superconducting quantum interference device magnetometer. The particle size of Fe in Al2O3 matrices prepared by changing the deposition time of Fe, have been found to be 9, 7 and 5 nm from TEM studies. At 10 K, the coercivities of these samples are found be 450, 350 and 150 Oe, respectively. At 300 K, the coercivity of Fe–Al2O3 sample decreases from 100 to 50 Oe as the particle size decreases from 9 to 7 nm and finally the sample turns superparamagnetic when the Fe particle size becomes around 5 nm. Based on the calculated value of blocking temperature, TB, (481 K), magnetic anisotropy K (4.8×105 erg/cm3) for Fe, and the Boltzmann constant kB (1.38×10−16 erg/K) from TB=KV/25kB, the mean radius of Fe particles is found to be 9.3 nm. in one of the samples. This is in good agreement with the particle size measured using TEM studies. |
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