Surface spin disorder in ferrite nanoparticles (invited)
Surface spin disorder in ferrite nanoparticles (invited)
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DOI：
10.1063/1.364659
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发表时间：
1997-04-15
影响因子：
3.2
通讯作者：
Foner, S
中科院分区：
文献类型：
--
作者：
Kodama, RH;Berkowitz, AE;Foner, S
以前已经报道过有机涂层NiFe2O4纳米颗粒的异常磁性（Berkowitz等人）。(5)高磁场下磁化强度低，磁化率差大，磁场冷却后磁滞回线移位，穆斯堡尔谱显示材料的磁有序。在本研究中，我们发现高场的不饱和伴随着高达160 kOe的不可逆性（即迟滞回路打开）。此外，粒子在70koe的外加磁场中表现出随时间变化的磁化特性。高场不可逆性和环路位移在50 K以上消失。我们提出了一个由铁磁排列的核心自旋和自旋玻璃状表面层组成的粒子磁化模型。我们发现该模型的定性特征可以通过自旋分布的数值计算再现。讨论了该模型对这些材料中可能存在的宏观量子隧道效应的影响。(C) 1997年美国物理研究所。
Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).(5) These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mossbauer spectra indicated that all of the material was magnetically ordered. In the present study, we find that the lack of saturation in high fields is accompanied by irreversibility (i.e., hysteresis loops are open) up to 160 kOe. In addition, the particles exhibit time dependent magnetization in 70 kOe applied field. The high field irreversibility and the loop shift both vanish above 50 K. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. The implications of this model for possible macroscopic quantum tunneling in these materials are discussed. (C) 1997 American Institute of Physics.