Abstract In this paper we investigate the effective magnetic anisotropy constant Keff of single-core magnetic nanoparticles (MNPs) as a function of temperature applying two approaches, which both are based on the Stoner-Wohlfarth model: First, the coercive field is used to determine the anisotropy field and second the descending branch of the magnetic moment-vs.-magnetic field (m-H) curve measured on immobilized MNPs is fitted with an empirical model. In particular, we compare the analysis with and without considering the distribution of core size, which is estimated from fitting the m-H curve measured on MNP suspensions. Good agreement between the Keff(T) curves estimated with both methods is found if the size distribution is included while significant deviations are observed especially at high temperatures if the size distribution is ignored. Additionally, the blocking temperature was obtained from the maximum of the temperature derivation of the difference between the field-cooled (FC) and zero-field-cooled (ZFC) magnetization curve. The Keff value determined from the blocking temperature showed reasonable agreement with those obtained from coercive field and m-H curve. We also found that the magnetic moment of both studied single-core MNP systems exhibits a significant paramagnetic-like contribution even at 7 T.

中文翻译：

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磁性纳米粒子有效各向异性常数的测定——两种方法的比较

摘要 在本文中，我们采用两种方法研究单核磁性纳米粒子 (MNP) 的有效磁各向异性常数 Keff 作为温度的函数，这两种方法均基于 Stoner-Wohlfarth 模型：首先，矫顽场用于确定各向异性场和第二个在固定的 MNP 上测量的磁矩与磁场 (mH) 曲线的下降分支拟合有经验模型。特别是，我们比较了在考虑和不考虑核心尺寸分布的情况下的分析，这是通过拟合在 MNP 悬浮液上测量的 mH 曲线估计的。如果包含尺寸分布，则使用两种方法估计的 Keff(T) 曲线之间具有良好的一致性，而如果忽略尺寸分布，则会观察到显着偏差，尤其是在高温下。此外，阻塞温度是从场冷 (FC) 和零场冷却 (ZFC) 磁化曲线之间差异的温度推导的最大值中获得的。从阻塞温度确定的 Keff 值与从矫顽力和 mH 曲线获得的值显示出合理的一致性。我们还发现，即使在 7 T 时，两个研究的单核 MNP 系统的磁矩也表现出显着的类似顺磁的贡献。