Memory effects in a superparamagnetic γ-Fe2O3 system
Memory effects in a superparamagnetic γ-Fe2O3 system
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DOI：
10.1103/physrevb.72.014445
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发表时间：
2005-07
影响因子：
3.7
通讯作者：
G. Tsoi;L. Wenger;U. Senaratne;R. Tackett;E. C. Buc;R. Naik;P. Vaishnava;V. Naik
中科院分区：
文献类型：
--
作者：
G. Tsoi;L. Wenger;U. Senaratne;R. Tackett;E. C. Buc;R. Naik;P. Vaishnava;V. Naik
通过超导量子干涉装置的磁化强度测量，研究了平均纳米粒子尺寸为$4的非相互作用磁性纳米粒子系统($\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$-alginate复合材料的低温动力学。采用不同的温度和场方案，在低于阻挡温度${T}_{B}=38\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.的温度下，观察到了该纳米粒子系统的直流磁化和磁弛豫中的记忆现象老化实验表明，零场冷却后的磁场变化引起的磁化驰豫不存在等待时间依赖性，而场冷却后的等待时间依赖性较弱。这一观察结果将这一系统的动力学与经典自旋玻璃的行为区分开来，在经典自旋玻璃的行为中，沮丧和无序导致系统响应的年龄相关性。此外，这种纳米粒子系统的动力学被证明是由粒子尺寸分布和样品不均匀性引起的粒子弛豫时间的广泛分布所支配的。
The low-temperature dynamics of a noninteracting magnetic nanoparticle system ($\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$-alginate composite with an average nanoparticle size of $4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$) has been studied by superconducting quantum interference device magnetization measurements. Using different temperature and field protocols memory phenomena have been observed in the dc magnetization and magnetic relaxation of this nanoparticle system at temperatures below its blocking temperature ${T}_{B}=38\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Aging experiments show an absence of any waiting time dependence in the magnetization relaxation due to a field change after zero-field cooling and only a weak waiting time dependence after field cooling. This observation discriminates the dynamics of this system from the behavior of a classical spin glass, where frustration and disorder lead to an aging dependence of the system response. Moreover, the dynamics of this nanoparticle system is shown to be governed by a broad distribution of particle relaxation times arising from the distribution of particle sizes and sample inhomogeneities.