Bridging exchange bias effect in NiO and Ni(core)@NiO(shell) nanoparticles
Bridging exchange bias effect in NiO and Ni(core)@NiO(shell) nanoparticles
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DOI：
10.1016/j.jmmm.2015.07.060
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发表时间：
2016-02
影响因子：
2.7
通讯作者：
N. Rinaldi-Montes;P. Gorria;D. Martínez-Blanco;A. B. Fuertes;L. Barquín;I. Puente-Orench;J. Blanco
中科院分区：
文献类型：
--
作者：
N. Rinaldi-Montes;P. Gorria;D. Martínez-Blanco;A. B. Fuertes;L. Barquín;I. Puente-Orench;J. Blanco
在所有双磁核（过渡金属）@壳（过渡金属氧化物）纳米粒子（NP）中，Ni@NiO 表现出交换偏压（EB）效应的起始温度远低于块体反铁磁 NiO 的尼尔温度。在此框架中，通过比较 NiO 和 Ni@NiO 纳米颗粒的微观结构和磁性，研究了 NiO 磁性在纳米尺度上所起的作用。为了桥接两个系统，选择 NiO 纳米颗粒的直径（~4 nm）与 Ni@NiO 纳米颗粒的壳厚度（~2 nm）相当。 Ni@NiO NPs 中的 EB 效应归因于核和壳之间的交换耦合，界面交换能为 ΔE~0.06 erg cm−2，因此与之前关于薄膜和 NP 形态的 Ni/NiO 界面的报道相当。相比之下，在 NiO NP 中检测到的 EB 在图中得到解释，其中位于磁无序表面壳上的未补偿自旋与反铁磁核交换耦合。在所有研究的纳米颗粒中，EB 场随温度的变化是根据具有相似衰减常数的负指数定律来描述的，在 T~40–50 K 左右产生消失的 EB 效应。此外，NiO 和 Ni@NiO 纳米颗粒中 EB 效应的起始温度似乎普遍依赖于 NiO 微晶尺寸。
Among all bi-magnetic core(transition metal)@shell(transition metal oxide) nanoparticles (NPs), Ni@NiO ones show an onset temperature for the exchange bias (EB) effect far below the Néel temperature of bulk antiferromagnetic NiO. In this framework, the role played by the magnetism of NiO at the nanoscale is investigated by comparing the microstructure and magnetic properties of NiO and Ni@NiO NPs. With the aim of bridging the two systems, the diameter of the NiO NPs (~4 nm) is chosen to be comparable to the shell thickness of Ni@NiO ones (~2 nm). The EB effect in Ni@NiO NPs is attributed to the exchange coupling between the core and the shell, with an interfacial exchange energy of ΔE~0.06 erg cm−2, thus comparable to previous reports on Ni/NiO interfaces both in thin film and NP morphologies. In contrast, the EB detected in NiO NPs is explained in a picture where uncompensated spins located on a magnetically disordered surface shell are exchange coupled to the antiferromagnetic core. In all the studied NPs, the variation of the EB field as a function of temperature is described according to a negative exponential law with a similar decay constant, yielding a vanishing EB effect aroundT~40–50 K. In addition, the onset temperature for the EB effect in both NiO and Ni@NiO NPs seems to follow a universal dependence with the NiO crystallite size.