Temperature dependence of magnetic anisotropy constant in cobalt ferrite nanoparticles

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• 作者：Sunghyun Yoon ; ^{shyoon@kunsan.ac.kr}
• 关键词：Magnetic nanoparticle ; Magnetic anisotropy constant ; Particle size distribution ; Anisotropy energy barrier distribution ; Superparamagnetism ; Cobalt ferrite
• 刊名：Journal of Magnetism and Magnetic Materials
• 出版年：2012
• 期刊代码：31_03048853
• 类别：ph
• 出版时间：August, 2012
• 卷：324
• 期：17
• 页码：2620-2624
• 文件大小：783 K

摘要

The temperature dependence of the effective magnetic anisotropy constant K(T) of CoFe₂O₄ nanoparticles is obtained based on the SQUID magnetometry measurements and M枚ssbauer spectroscopy. The variation of the blocking temperature T_B as a function of particle radius r is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and the magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and T_B. The resultant effective magnetic anisotropy constant K(T) decreases markedly with increasing temperature from 1.1脳10⁷ J/m³ at 5 K to 0.6脳10⁵ J/m³ at 280 K. The attempt time 蟿₀ is also determined to be 6.1脳10^鈭?2 s which together with the K(T) best explains the temperature dependence of superparamagnetic fraction in M枚ssbauer spectra.