Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3-xO4 nanoparticles
Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3-xO4 nanoparticles
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DOI：
10.1063/1.4935146
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发表时间：
2015-07
影响因子：
3.2
通讯作者：
T. Torres;E. Lima;Alvaro Mayoral;Alfonso Ibarra;C. Marquina;C. Marquina;M. Ibarra;Gerardo F. Goya
中科院分区：
文献类型：
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作者：
T. Torres;E. Lima;Alvaro Mayoral;Alfonso Ibarra;C. Marquina;C. Marquina;M. Ibarra;Gerardo F. Goya
本文系统研究了Fe(acac)3和Co(acac)2热分解制备的CoxFe3−xO4磁性纳米颗粒的结构和磁性。大的磁晶各向异性导致了高的阻挡温度（42 K < TB < 345 K, 5 < d < 13 nm）和大的矫顽力场（T = 5 K时HC≈1600 kA/m）。最小的粒子（⟨d⟩=5 nm）揭示了磁硬、自旋无序表面的存在。整个系列样品的静态和动态磁性能的热依赖性可以在Neel-Arrhenius弛豫框架内通过包括磁晶各向异性常数K1(T)的热依赖性来解释，而无需特别修正。该方法使用经验Brukhatov-Kirensky关系，提供了与静态或动态磁测量的块状材料非常相似的K1(0)值，以及响应时间（τ0≈10−10s）的实际值。最小颗粒体各向异性值的偏差可以根据K1(T)和M(T)之间的齐纳关系定性地解释。
We report a systematic study on the structural and magnetic properties of CoxFe3−xO4 magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac)3 and Co(acac)2. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < TB < 345 K for 5 < d < 13 nm) and large coercive fields (HC ≈ 1600 kA/m for T = 5 K). The smallest particles (⟨d⟩=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Neel–Arrhenius relaxation framework by including the thermal dependence of the magnetocrystalline anisotropy constant K1(T), without the need of ad-hoc corrections. This approach, using the empirical Brukhatov-Kirensky relation, provided K1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (τ0 ≈ 10−10s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener's relation between K1(T) and M(T).